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The Aeronomy of Ice in the Mesosphere (AIM) mission: Overview and early science results

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Abstract

The Aeronomy of Ice in the Mesosphere (AIM) mission was launched from Vandenberg Air Force Base in California at 1:26:03 PDT on April 25, 2007 becoming the first satellite mission dedicated to the study of polar mesospheric clouds. A Pegasus XL rocket launched the satellite into a near perfectly circular 600 km sun synchronous orbit. AIM carries three instruments selected because of their ability to provide key measurements needed to address the AIM goal which is to determine why these clouds form and vary. The instrument payload includes a nadir imager, a solar occultation instrument and an in-situ cosmic dust detector. Detailed descriptions of the science, instruments and observation scenario are presented. Early science results from the first northern and southern hemisphere seasons show a highly variable cloud morphology, clouds that are ten times brighter than measured by previous space-based instruments, and complex features that are reminiscent of tropospheric weather phenomena. The observations also confirm a previously theorized but never before directly observed population of small ice particles in the altitude region above the main Polar Mesospheric Cloud (PMC) layer that are widely believed to be the indirect cause of summertime radar echoes.

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... The model is described in Section 2, along with brief summaries of the satellite data from the Optical Spectrograph and InfraRed Imagining System (OSIRIS) instrument on the Odin satellite ( Llewellyn et al., 2004), the Solar Occultation for Ice Experiment (SOFIE) instrument on the Aeronomy of Ice in the Mesosphere (AIM) satellite ( Russell et al., 2009) and the Solar Backscatter Ultraviolet Radiometer (SBUV) (DeLand and Thomas, 2015), which we use to examine our modeled NLCs. In Section 3, the NLC model is described and discussed in parallel with comparisons to satellite observations. ...
... The SOFIE instrument was launched on board of the AIM spacecraft ( Russell et al., 2009). SOFIE uses the solar occultation technique to measure vertical limb path atmospheric transmission within 16 spectral bands. ...
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Ice particles in the summer mesosphere – such as those connected to noctilucent clouds and polar mesospheric summer echoes - have since their discovery contributed to the uncovering of atmospheric processes on various scales ranging from interactions on molecular levels to global scale circulation patterns. While there are numerous model studies on mesospheric ice microphysics and how the clouds relate to the background atmosphere, there are at this point few studies using comprehensive global climate models to investigate observed variability and climatology of noctilucent clouds. In this study it is explored to what extent the large-scale inter-annual characteristics of noctilucent clouds are captured in a 30-year run - extending from 1979 to 2009 - of the nudged and extended version of the Canadian Middle Atmosphere Model (CMAM30). To construct and investigate zonal mean inter-seasonal variability in noctilucent cloud occurrence frequency and ice mass density in both hemispheres, a simple cloud model is applied in which it is assumed that the ice content is solely controlled by the local temperature and water vapor volume mixing ratio. The model results are compared to satellite observations, each having an instrument-specific sensitivity when it comes to detecting noctilucent clouds. It is found that the model is able to capture the onset dates of the NLC seasons in both hemispheres as well as the hemispheric differences in NLCs, such as weaker NLCs in the SH than in the NH and differences in cloud height. We conclude that the observed cloud climatology and zonal mean variability are well captured by the model.
... Several contemporary satellite instruments have measured, or are measuring H 2 O, spanning different periods over the last two decades or so. These include the Aura Microwave Limb Sounder (MLS) from NASA, JPL ( Waters et al., 2006), the ENVISAT Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) from the European Space Agency (ESA) ( Fischer et al., 2000), the Scisat-1 Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) from the Canadian Space Agency (CSA) ( Bernath et al., 2005), and the AIM Solar Occultation for Ice Experiment (SOFIE) from NASA ( Russell et al., 2009;Gordley et al., 2009). These instruments have provided H 2 O data with prolonged, continuous temporal coverage and with extended spatial coverage. ...
... SOFIE ( Gordley et al., 2009) is one of two instruments currently operating aboard the Aeronomy of Ice in the Mesosphere (AIM) satellite (April 2007-current and 97.8 � inclination sun-synchronous at ~595-601 km altitude) dedicated to PMC studies ( Russell et al., 2009;Hervig and Gordley, 2010;McClintock et al., 2009 which are of great importance in studying chemistry and dynamics in the middle atmosphere. The latest SOFIE data version is v1.3 which is available at http://sofie.gats-inc.com/sofie/index.php. ...
... In this section, we describe some results from the PMC detection by Himawari-8/AHI, and compare those with the PMC data, v5.20 level 2 data products, obtained by AIM/ CIPS (cf. Lumpe et al., 2013;Russell III et al., 2009). UT on each day were also treated as missing data due to the same reason. ...
... As a final part of this work, we perform a validation in the detected PMC data by Himawari-8/AHI, based on a comparison with the AIM/CIPS PMC data (cf. Lumpe et al., 2013;Russell III et al., 2009). Figure 7 shows some examples in the simultaneous observations between Himawari-8/AHI and AIM/CIPS. ...
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With the objective of advancing the polar mesospheric cloud (PMC) detection capability by the Advanced Himawari Imager (AHI) onboard the Japanese geostationary‐Earth‐orbit (GEO) meteorological satellite Himawari‐8, a novel two‐step PMC detection technique applied to the Himawari‐8/AHI full‐disk images has been developed. The two‐step approach is dividing the PMC detection into stronger (the first step) and weaker (the second step) signals and enhances the detection capability while significantly decreasing the false PMC detections. The improved PMC sensitivity by Himawari‐8/AHI is comparable with the Cloud Imaging and Particle Size (CIPS) onboard the Aeronomy of Ice in the Mesosphere (AIM) satellite. With this encouraging result, PMC observations from Himawari‐8/AHI provide an additional extensive data set to the aeronomy and space science community.
... In this study we present a common volume observation of GWs over Syowa, Antarctic (69 S, 39 E) using PMC data from the Cloud Imaging and Particle Size (CIPS) experiment on the Aeronomy of Ice in the Mesosphere (AIM) satellite (Russell et al., 2009) and wind fluctuations from PMSE observations by the Program of the Antarctic Syowa (PANSY) radar (Sato et al., 2014). CIPS observes PMCs at~83 km at a horizontal resolution of 5 km, providing direct polar measurements of horizontal wavelength and propagation direction of GWs, if present. ...
... The AIM satellite was launched in April 2007 and is the first mission dedicated to the study of PMCs (Russell et al., 2009). CIPS is one of the instruments aboard AIM, and is a panoramic UV imager that consists of an array of four cameras with a combined field of view of 120 Â 80 (McClintock et al., 2009). ...
Article
Simultaneous observation of gravity waves (GWs) in the polar summer mesosphere over Syowa (69°S, 39°E) by a ground-based radar and satellite instrument are presented. On 21 January 2016, at 2.3 UT, the CIPS instrument on the AIM satellite observed Polar Mesospheric Clouds (PMCs) with GW structures over Syowa. The orientation of the wave crests suggests north-west propagation direction. A periodogram analysis indicates GWs with horizontal wavelengths of 105 ± 5 and 60 ± 5 km. Cross-spectral analysis of the PANSY radar horizontal wind components at the same time, location, and altitude indicate two dominant waves with apparent periods of 15 and 9 h, with respective horizontal wavelengths of 100 ± 5 km and 302 ± 130 km. At the PMC altitude of ∼83 km, the mean zonal component of the vertical momentum flux spectra of the observed GWs is westward and the meridional component is northward. The comparable horizontal wavelengths of the 15 h wave observed by PANSY radar and the CIPS instrument, along with the agreement between the direction of vertical flux of horizontal momentum from PANSY, the propagation direction estimated from the cross-spectral analysis, and the orientation of the wave crests from CIPS i.e. north-west propagation direction suggests that the same wave is observed by both instruments. This simultaneous observation of the same wave by CIPS and PANSY radar provide a distinctive view of both the horizontal and vertical extent of a GW in the Antarctic summer mesosphere.
... The Cloud Imaging and Particle Size (CIPS) instrument onboard the Aeronomy of Ice in the Mesosphere (AIM) satellite was launched by NASA in April 2007. AIM-CIPS can provide data of the ice water content of polar mesospheric clouds (PMC) in the full area at latitudes higher than about 70º and in the partial areas at latitudes of 58-70º from observations by the 15 satellite orbits per day (Russell et al. 2009;Thomas et al. 2019). The AIM-CIPS data are useful to study the PMC activity which is closely related to the PMSE occurrence (e.g., Rapp and Lübken 2004). ...
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Midlatitude mesosphere summer echoes (MSE) at the VHF band (VHF-MSE) were observed for 13 years (2000-2002 and 2009-2018) with a 46.5 MHz radar at Wakkanai, Japan (45.4ºN, 141.8ºE). VHF-MSE are active during June-July and appear only in the daytime mainly at altitudes of 80-88 km with a maximum occurrence at 85 km and altitude extents of 1-4 km for a duration of about half an hour or more. The VHF-MSE occurrences are positively correlated with solar activity, but not with geomagnetic activity except for very high activity. Such long-term characteristics are mostly consistent with past VHF-MSE observations at higher midlatitudes in Europe. No VHF-MSE were observed in 2002, 2014 and 2018, possible reasons for which are discussed. It is shown that cold ice particles in the upper mesosphere inducing MSE are advected from high latitudes to midlatitudes with equatorward wind. Thus, the MSE occurrences over Wakkanai are fundamentally controlled by both the solar activity and equatorward ice particle advection. One example of MSE at the HF band (HF-MSE) is presented to discuss spatial and temporal relationship between VHF-MSE and HF-MSE.
... AIM is moving in a circular, sun-synchronous orbit near 600 km altitude. AIM currently has two operating instruments, the Solar Occultation for Ice Experiment (SOFIE) ( Gordley et al., 2009) and the high-resolution UV panoramic imager CIPS. CIPS consists of four nadir-pointing wide-angle cameras with a combined FOV of 120° by 80° and operates in the UV with a spectral band centered at 265 nm with a width of 15 nm . ...
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Combining satellite observations of Polar Mesospheric Clouds are complicated due to satellite geometry and measurement technique. In this study tomographic observations from a limb viewing satellite are compared to observations from a nadir viewing satellite using a common volume approach. We present a technique that overcomes differences in scattering conditions, observation geometry, and sensitivity, and perform a thorough error characterization. The satellites show excellent agreement, which lays the basis for future insights into horizontal and vertical cloud processes.
... The AIM satellite ) was launched in 2007 into a sun-synchronous orbit near 600 km. AIM has two operating instruments, the Solar Occultation for Ice Experiment (SOFIE) and the high-resolution UV panoramic imager CIPS Russell et al., 2009) consisting of four CCD detectors with a combined field of view of 120° × 80°. The camera suite images radiance scattered from PMCs and the background atmosphere in the UV centered at 265 nm. ...
... In this study we analyze the influence of GWs on the polar summer mesosphere using PMC and mesospheric GW data from the Solar Occultation for Ice in the Mesosphere Experiment (SOFIE) instrument on the Aeronomy of Ice in the Mesosphere (AIM) satellite Russell et al., 2009). We also study the potential sources of these polar summer mesospheric GWs by analyzing the influence of both vertically and obliquely propagating GWs using data from SOFIE and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument (Russell et al., 1999) on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) spacecraft. ...
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Using an 8-year (2007-2014) data set from two different limb-viewing instruments, we evaluate the relative roles of vertically versus obliquely propagating gravity waves (GWs) as sources of GWs in the polar summer mesosphere. Obliquely propagating waves are of interest because they are presumed to be generated by the summer monsoons. In the high-latitude upper mesosphere, the correlation coefficient between the time series of ice water content (IWC) and GW amplitude is 0.48, indicating that the observed GWs enhance polar mesospheric clouds (PMCs). For vertically propagating waves, the correlation coefficient between IWC and stratospheric/lower mesospheric (20-70 km) GW amplitude at the same high latitudes becomes more negative with increasing altitude. This change in correlation from negative in the lower mesosphere to positive at PMC altitudes suggests the presence of another source of GWs. The positive correlation coefficient between the time series of IWC and GW amplitude from 0-50°N, 20-90 km shows a slanted structure suggesting oblique propagation. This slanted structure is more robust in some seasons compared to others, and this interannual variability may be due to the latitudinal gradient of the mesospheric easterly jet where steeper gradients allow for low-latitude tropospheric GWs to be refracted to the high-latitude mesosphere more efficiently. Gravity-Wave Regional or Global Ray Tracer (GROGRAT) ray tracing simulations show that more GWs propagate obliquely compared to vertically propagating waves that reach PMC altitudes. For obliquely propagating waves, GROGRAT simulations indicate that nonorographic tropospheric GWs with faster phase speed (>20 m/s) and longer horizontal wavelength (>400 km) have a higher probability of reaching the polar summer mesosphere.
... Therefore we calculate two different averages (median and arithmetic mean), in order to characterize a mean ice water content as a function of local time during July. In Fig. 5 we compare our IWC model results in terms of median values with measurements from the CIPS and SOFIE instruments onboard the AIM satellite for the latitude band 67-71 • N. The AIM satellite operates in a sun-synchronous orbit; hence only limited local times are available (Russell et al., 2009). For comparison with model results we take the different sensitivities of the two AIM instruments (SOFIE, CIPS) into account. ...
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The Mesospheric Ice Microphysics And tranSport model (MIMAS) is used to study local time (LT) variations of polar mesospheric clouds (PMCs) in the Northern Hemisphere during the period from 1979 to 2013. We investigate the tidal behavior of brightness, altitude, and occurrence frequency and find a good agreement between model and lidar observations. At the peak of the PMC layer the mean ice radius varies from 35 to 45 nm and the mean number density varies from 80 to 150 cm⁻³ throughout the day. We also analyze PMCs in terms of ice water content (IWC) and show that only amplitudes of local time variations in IWC are sensitive to threshold conditions, whereas phases are conserved. In particular, relative local time variations decrease with larger thresholds. Local time variations also depend on latitude. In particular, absolute local time variations increase towards the pole. Furthermore, a phase shift exists towards the pole which is independent of the threshold value. In particular, the IWC maximum moves backward in time from 08:00 LT at midlatitudes to 02:00 LT at high latitudes. The persistent features of strong local time modulations in ice parameters are caused by local time structures in background temperature and water vapor. For a single year local time variations of temperature at 69° N are in a range of ±3 K near 83 km altitude. At sublimation altitudes the water vapor variation is about ±3.5 ppmv, leading to a change in the saturation ratio by a factor of about 2 throughout the day.
... Note that several processes act on similar temporal and spatial scales, for example, nucleation, sedimentation, and horizontal transport. Furthermore, there is an impressive amount of observations of mesospheric ice clouds available from satellites, which sometimes show unexpected temporal and/or spatial variations ('voids') (see Russell III et al., 2009, for details on a more recent satellite mission dedicated to NLC science). Understanding the physics of NLC is important, for example, to interpret long term variations of ice 585 layers and their potential relationship to climate change (Thomas, 1996;von Zahn, 2003;Lübken et al., 2018). ...
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A new concept for a cluster of compact lidar systems named VAHCOLI (Vertical And Horizontal COverage by LIdars) is presented which allows to measure temperatures, winds, and aerosols in the middle atmosphere (∼10–110 km) with high temporal and vertical resolution of minutes and some tens of meters, respectively, simultaneously covering horizontal scales from few hundred meters to several hundred kilometers (four-dimensional coverage). The individual lidars (units) being used in VAHCOLI are based on a diode-pumped alexandrite laser currently designed to detect potassium (λ = 770 nm), as well as on sophisticated laser spectroscopy measuring all relevant frequencies (seeder laser, power laser, backscattered light) with high temporal resolution (2 ms) and high spectral resolution applying Doppler-free spectroscopy. The frequency of the lasers and the narrow-band filter in the receiving system are stabilized to typically 10–100 kHz which is a factor of roughly 10−5 smaller than the Doppler-broadened Rayleigh signal. Narrow-band filtering allows to measure Rayleigh and/or resonance scattering separately from the aerosol (Mie) signal, all during night and day. Lidars used for VAHCOLI are compact (volume: ∼1 m3) and are multi-purpose systems employing contemporary electronical, optical, and mechanical components. The units are designed to autonomously operate under harsh field conditions at remote locations. An error analysis with parameters of the anticipated system demonstrates that temperatures and line-of-sight winds can be measured from the lower stratosphere to the upper mesosphere with an accuracy of ±(0.1–5) K and ±(0.1–10) m/s, respectively, increasing with altitude. We demonstrate that some crucial dynamical processes in the middle atmosphere, such as gravity waves and stratified turbulence, can be covered by VAHCOLI with sufficient temporal/vertical/horizontal sampling and resolution. The four-dimensional capabilities of VAHCOLI allow to perform time-dependent analysis of the flow field, for example employing Helmholtz decomposition, and to carry out statistical tests regarding intermittency, helicity etc. First test measurements under field conditions with a prototype lidar being built for VAHCOLI were performed in January 2020. The lidar operated successfully during a six week period (night and day) without any adjustment. These observations covered a height range of ∼5–100 km and demonstrate the capability and applicability of this unit for the VAHCOLI concept.
... Examples of the first case include the Student Nitric Oxide Explorer (SNOE; Barth et al., 2003), the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) dataset on the European research satellite Envisat (Bermejo-Pantaleón et al., 2011;Bender et al., 2015) and the submillimeter radiometer (SMR) on the Swedish Odin satellite (Sheese et al., 2013;Kiviranta et al., 2018). Examples of the second case include the Solar Occultation for Ice Experiment (SOFIE; Gómez-Ramírez et al., 2013) on the Aeronomy of Ice in the Mesosphere (AIM; Russell III et al., 2009), the ACE Fourier Transform Spectrometer (ACE-FTS; Bernath et al., 2005;Bender et al., 2015) and the Halogen Occultation Experiment (HALOE) data on the NASA Upper Atmosphere Research Satellite (UARS; Russell III et al., 1993;Siskind et al., 1998). We thus deduce that, unfortunately, there is no satellite data which can directly resolve the diurnal variation of thermospheric nitric oxide. ...
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We use data from two NASA satellites, the Thermosphere Ionosphere Energetics and Dynamics (TIMED) and the Aeronomy of Ice in the Mesosphere (AIM) satellites, in conjunction with model simulations from the thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) to elucidate the key dynamical and chemical factors governing the abundance and diurnal variation of lower thermospheric nitric oxide (NO) at near-solar minimum conditions and low latitudes. This analysis was enabled by the recent orbital precession of the AIM satellite which caused the solar occultation pattern measured by the Solar Occultation for Ice Experiment (SOFIE) to migrate down to low and mid-latitudes for specific periods of time. We use a month of NO data collected in January 2017 to compare with two versions of the TIME-GCM; one is driven solely by climatological tides and analysis-derived planetary waves at the lower boundary and is free running at all other altitudes, and the other is constrained by a high-altitude analysis from the Navy Global Environmental Model (NAVGEM) up to the mesopause. We also compare SOFIE data with a NO climatology from the nitric oxide empirical model (NOEM). Both SOFIE and NOEM yield peak NO abundances of around 4×107 cm−3; however, the SOFIE profile peaks about 6–8 km lower than NOEM. We show that this difference is likely a local time effect, with SOFIE being a dawn measurement and NOEM representing late morning and/or near noon. The constrained version of TIME-GCM exhibits a low-altitude dawn peak, while the model that is forced solely at the lower boundary and free running above does not. We attribute this difference to a phase change in the semi-diurnal tide in the NAVGEM-constrained model, causing the descent of high NO mixing ratio air near dawn. This phase difference between the two models arises due to differences in the mesospheric zonal mean zonal winds. Regarding the absolute NO abundance, all versions of the TIME-GCM overestimate this. Tuning the model to yield calculated atomic oxygen in agreement with TIMED data helps but is insufficient. Furthermore, the TIME-GCM underestimates the electron density (Ne) as compared with the International Reference Ionosphere (IRI) empirical model. This suggests a potential conflict with the requirements of NO modeling and Ne modeling, since one solution typically used to increase model Ne is to increase the solar soft X-ray flux, which would, in this case, worsen the NO model–data discrepancy.
... For example, Taylor and Edwards (1991) observed several ∼ 15-20 km wavelength linear wave patterns over Hawaii in March, and Yue et al. (2009) reported capturing the mesospheric concentric waves with wavelengths in the range of ∼ 40-80 km over Colorado and a few neighboring states. The Aeronomy of Ice in the Mesosphere (AIM) satellite was launched in April 2007, becoming the first satellite mission dedicated to the study of PMCs ( Russell III et al., 2009). One of the primary research goals of the AIM mission is to explore how PMCs form and vary. ...
Article
We aim to extract a universal law that governs the gravity wave manifestation in polar mesospheric clouds (PMCs). Gravity wave morphology and the clarity level of display vary throughout the wave population manifested by the PMC albedo data. Higher clarity refers to more distinct exhibition of the features, which often correspond to larger variances and a better-organized nature. A gravity wave tracking algorithm based on the continuous Morlet wavelet transform is applied to the PMC albedo data at 83 km altitude taken by the Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) instrument to obtain a large ensemble of the gravity wave detections. The horizontal wavelengths in the range of ∼ 20-60 km are the focus of the study. It shows that the albedo (wave) power statistically increases as the background gets brighter. We re-sample the wave detections to conform to a normal distribution to examine the wave morphology and display clarity beyond the cloud brightness impact. Sample cases are selected at the two tails and the peak of the normal distribution to represent the full set of wave detections. For these cases the albedo power spectra follow exponential decay toward smaller scales. The high-albedo-power category has the most rapid decay (i.e., exponent = −3.2) and corresponds to the most distinct wave display. The wave display becomes increasingly blurrier for the medium-and low-power categories , which hold the monotonically decreasing spectral exponents of −2.9 and −2.5, respectively. The majority of waves are straight waves whose clarity levels can collapse between the different brightness levels, but in the brighter background the wave signatures seem to exhibit mildly turbulent-like behavior.
... AIM is moving in a circular, sun-synchronous orbit near 600 km altitude. AIM currently has two operating instruments, the Solar Occultation for Ice Experiment (SOFIE) ( Gordley et al., 2009) and the high-resolution UV panoramic imager CIPS. CIPS consists of four nadir-pointing wide-angle cameras with a combined FOV of 120° by 80° and operates in the UV with a spectral band centered at 265 nm with a width of 15 nm . ...
Preprint
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Two important approaches for satellite studies of Polar Mesospheric Clouds (PMC) are nadir measurements adapting phase function analysis and limb measurements adapting spectroscopic analysis. Combining both approaches enables new studies of cloud structures and microphysical processes but is complicated by differences in scattering conditions, observation geometry, and sensitivity. In this study, we compare common volume PMC observations from the nadir viewing Cloud Imaging and Particle Size instrument (CIPS) on the AIM satellite and a special set of tomographic limb observations from the Optical Spectrograph and InfraRed Imager System (OSIRIS) on the Odin satellite. While CIPS provides preeminent horizontal resolution, the OSIRIS tomographic analysis provides combined horizontal and vertical PMC information. This first direct comparison is an important step towards co-analyzing CIPS and OSIRIS data, aiming at unprecedented insights into horizontal and vertical cloud processes. We perform the first thorough error characterization of OSIRIS tomographic cloud brightness and cloud ice. We establish a consistent method for comparing cloud properties from limb tomography and nadir observations, accounting for differences in scattering conditions, resolution and sensitivity. Based on an extensive common volume, and a temporal coincidence criterion of only 5 minutes, our method enables a detailed comparison of PMC regions of varying brightness and ice content. We find that the primary OSIRIS tomography product, cloud scattering coefficient, shows very good agreement with the primary CIPS product, cloud albedo with a correlation coefficient of 0.96. However, OSIRIS systematically reports brighter clouds than CIPS and the bias between the instruments (OSIRIS – CIPS) is 3.4e−6sr−1 (±2.9e−6sr−1) on average. The OSIRIS tomography ice mass density agrees well with the CIPS ice water content, with a correlation coefficient of 0.91. However, the ice water content reported by OSIRIS is lower than CIPS, and we quantify the bias to −22gkm−2 (±14gkm−2) on average.
... Therefore we present in this section model results of ice water content (IWC) which are calculated from the integrated ice orbit, hence only limited local times are available ( Russell et al., 2009). For comparison with model data we take the different sensitivities of the two AIM instruments (SOFIE, CIPS) into account. ...
Article
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The Mesospheric Ice Microphysics And tranSport model (MIMAS) is used to study local time (LT) variations of polar mesospheric clouds (PMC) in the northern hemisphere during the period from 1979 to 2013. We investigate the tidal behavior of brightness, altitude and occurrence frequency and find a good agreement between model and lidar observations. Mean ice water content (IWC) values from MIMAS also match those from satellite observations. In the latitudinal band of 67.5°–70.5° N the IWC maximum throughout the day occurs at about 3 LT and the minimum around 18 LT with a ratio of maximum to minimum of 10. At the peak of the PMC layer the ice particle size varies by about 30 % while the median number density varies by a factor of 2 throughout the day. Furthermore, the absolute tidal variation of IWC generally increases towards higher latitudes and the time of maximum IWC changes from about 4 to 0 LT for latitudes from 63° N to 81° N. In the period from 1979 to 2013 we find an increase of the tidal amplitudes. The linear trend terms of diurnal and semidiurnal variations are calculated to be 3.4 and 1.4 g/km²/dec. The persistent features of strong tidal modulations are caused by tidal structures in background parameters. The temperature varies by about 2 K and water vapor by about 3 ppmv at the altitude of ice particle sublimation near 81.5 km.
... We also utilize Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) and SOFIE Russell et al., 2009) NO VMR measurements to evaluate the model representation of NO. ACE-FTS version 3.5 and SOFIE version 1.3 data have vertical resolutions in the mesosphere of 3-4 km and 2 km (Marshall et al., 2011), respectively. ...
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The energetic particle precipitation (EPP) indirect effect (IE) refers to the downward transport of reactive odd nitrogen (NOx = NO + NO2) produced by EPP (EPP-NOx) from the polar winter mesosphere and lower thermosphere to the stratosphere where it can destroy ozone. Previous studies of the EPP IE examined NOx descent averaged over the polar region, but the work presented here considers longitudinal variations. We report that the January 2009 split Arctic vortex in the stratosphere left an imprint on the distribution of NO near the mesopause, and that the magnitude of EPP-NOx descent in the upper mesosphere depends strongly on the planetary wave (PW) phase. We focus on an 11-day case study in late January immediately following the 2009 sudden stratospheric warming during which regional-scale Lagrangian coherent structures (LCSs) formed atop the strengthening mesospheric vortex. The LCSs emerged over the north Atlantic in the vicinity of the trough of a 10-day westward traveling planetary wave. Over the next week, the LCSs acted to confine NO-rich air to polar latitudes, effectively prolonging its lifetime as it descended into the top of the polar vortex. Both a whole atmosphere data assimilation model and satellite observations show that the PW trough remained coincident in space and time with the NO-rich air as both migrated westward over the Canadian Arctic. Estimates of descent rates indicate five times stronger descent inside the PW trough compared to other longitudes. This case serves to set the stage for future climatological analysis of NO transport via LCSs.
... The Solar Occultation For Ice Experiment (SOFIE) instrument on board NASA's Aeronomy of Ice in the Mesosphere (AIM) satellite was launched in April 2007 and is measuring properties of the mesosphere and lower thermosphere (J. Russell et al., 2009). SOFIE performs solar occultation measurements to retrieve temperature and vertical profiles of NO, among other chemical species . ...
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Plain Language Summary Nitric oxide (NO) is produced by energetic particle precipitation in the polar regions of the mesosphere and lower thermosphere, and its distribution rapidly increases with altitude. During winter the lifetime of NO is long enough for it to be transported by the downward atmospheric circulation in the mesosphere far from where it was produced. This makes the level of NO in the mesosphere dependent on both the local production and on transport processes. When comparing simulated NO in the model Whole Atmosphere Community Climate Model (WACCM) to observations by the satellite instrument Solar Occultation For Ice Experiment, too little NO is found in the mesosphere even when the mesospheric production is accounted for in the model. This may be related to model errors in the transport from the thermosphere. Comparing model temperatures to those observed by two different satellite instruments confirms that there are some dynamic deficiencies. The mesospheric circulation is driven by breaking gravity waves, so by changing where and how the wave energy and momentum are deposited in WACCM, the modeled circulation can be altered to improve the vertical NO distribution and the temperature profile in the polar mesosphere and lower thermosphere. The best correspondence between modeled and observed nitric oxide and temperature is found when the amplitude of the gravity waves is reduced or when the eddy diffusion is increased.
... In Page 2 of 10 Suzuki et al. Progress in Earth and Planetary Science (2022) 9:11 2007, NASA launched the Aeronomy of Ice in the Mesosphere (AIM) satellite to monitor the PMCs (Russell et al. 2009;Lumpe et al. 2013). The AIM satellite, which is still in operation, provides data regarding the temporal and spatial variations of PMCs over both polar regions. ...
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The exact occurrence frequency of noctilucent clouds (NLCs) in middle latitudes is significant information because it is thought to be sensitive to long-term atmospheric change. We conducted NLC observation from airline jets in the Northern Hemisphere during the summer 2019 to evaluate the effectiveness of NLC observation from airborne platforms. By cooperating with the Japanese airline All Nippon Airways (ANA), imaging observations of NLCs were conducted on 13 flights from Jun 8 to Jul 12. As a result of careful analysis, 8 of these 13 flights were found to successfully detect NLCs from middle latitudes (lower than 55° N) during their cruising phase. Based on the results of these test observations, it is shown that an airline jet is a powerful tool to continuously monitor the occurrence frequency of NLCs at midlatitudes which is generally difficult with a polar orbiting satellite due to sparse sampling in both temporal and spatial domain. The advantages and merits of NLC observation from jets over satellite observation from a point of view of imaging geometry are also presented.
... Polar mesospheric cloud (PMC) frequencies are derived from measurements made by the Cloud Imaging and Particle Size (CIPS) instrument (McClintock et al., 2009), which is a nadirviewing panoramic imager that measures scattered radiation at 265 nm. CIPS was launched in 2007 aboard the Aeronomy of Ice in the Mesosphere (AIM) satellite (Russell et al., 2009), and is still operational. CIPS is a nadir-viewing panoramic imager that measures scattered radiation at 265 nm. ...
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The behavior of the Earth’s middle atmosphere and ionosphere is governed by multiple processes resulting not only from downward energy transfer from the Sun and magnetosphere but also upward energy transfer from terrestrial weather. Understanding the relative importance of mechanisms beyond solar and geomagnetic activity is essential for progress in multi-day predictions of the Earth’s atmosphere-ionosphere system. The recent development of research infrastructure, particularly in Antarctica, allows the observation of new ionospheric features. Here we show for the first time that large disturbances observed in the Arctic winter polar stratosphere (20–50 km above ground and at 60–90°N) during a sudden stratospheric warming event are communicated across the globe and cause large disturbances in the summertime ionospheric plasma over Antarctica (60–90°S). Ionospheric anomalies reach ∼100% of the background level and are observed for multiple days. We suggest several possible terrestrial mechanisms that could contribute to the formation of upper atmospheric and ionospheric anomalies in the southern hemisphere.
... However, the Zodiacal Cloud Model constrained by the Planck observations Ade et al. (2014) clearly shows that the average diameter range from 0.01 µg (30 µm, JFCs) to 50 µg (400 µm, HTCs). At Earth, the flux of particles in this mass range have been observed with space-borne detectors such as the Long Duration Exposure Facility (LDEF) (Love and Brownlee 1993;Love and Allton 2006;Miao and Stark 2001;Cremonese et al. 2012), and the Cosmic Dust Experiment onboard the Aeronomy of Ice in the Mesosphere (AIM) mission (Russell et al. 2009;Poppe et al. 2011). In addition, several space missions (see Table 1) carried dedicated instruments to map the spatial and size distributions, and in some cases even the composition of interplanetary dust particles throughout the solar system. ...
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This research presents the first application of tomographic techniques for investigating gravity wave structures in Polar Mesospheric Clouds (PMCs) imaged by the Cloud Imaging and Particle Size (CIPS) instrument on the NASA AIM satellite. Albedo data comprising consecutive PMC scenes were used to tomographically reconstruct a 3D layer using the Partially Constrained Algebraic Reconstruction Technique (PCART) algorithm and a previously developed “fanning” technique [Hart et al., 2012]. For this pilot study, a large region (760 x 148 km) of the PMC layer (altitude ~83 km) was sampled with a ~2 km horizontal resolution and an intensity weighted centroid technique was developed to create novel 2D surface maps, characterizing the individual gravity waves as well as their altitude variability. Spectral analysis of seven selected wave events observed during the Northern Hemisphere 2007 PMC season exhibited dominant horizontal wavelengths of ~60-90 km, consistent with previous studies [Chandran et al., 2009; Taylor et al., 2011]. These tomographic analyses have enabled a broad range of new investigations. For example, a clear spatial anti-correlation was observed between the PMC albedo and wave-induced altitude changes; with higher-albedo structures aligning well with wave troughs, while low-intensity regions aligned with wave crests. This result appears to be consistent with current theories of PMC development in the mesopause region. This new tomographic imaging technique also provides valuable wave amplitude information enabling further mesospheric gravity wave investigations, including quantitative analysis of their hemispheric and inter-annual characteristics and variations.
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We provide an initial report on polar mesospheric cloud (PMC) observations by the Japanese Geostationary Earth Orbit (GEO) meteorological satellite Himawari-8. Heights of the observed PMCs were estimated to be 80–82km. Observed PMCs were active only during summertime in both the northern and southern polar regions. These observations are consistent with known PMC behavior. From its almost fixed location relative to the Earth, Himawari-8 is capable of continuously monitoring PMC every 10min with three visible bands: blue (0.47µm), green (0.51µm), and red (0.64µm). Thus, Himawari-8 can contribute to PMC research in the near future.
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High spatial-resolution images of Polar Mesospheric Clouds (PMC) from a camera array onboard the Aeronomy of Ice in the Mesosphere Satellite have been obtained since 2007. The Cloud Imaging and Particle Size Experiment (CIPS) detects scattered ultraviolet (UV) radiance at a variety of scattering angles, allowing the scattering phase function to be measured for every image pixel. With well-established scattering theory, the mean particle size and ice water content (IWC) are derived. In the nominal mode of operation, approximately seven scattering angles are measured per cloud pixel. However, because of a change in the orbital geometry in 2016, a new mode of operation was implemented such that one, or at most two, scattering angles per pixel are now available. Thus particle size and IWC can no longer be derived from the standard CIPS algorithm. The Albedo-Ice Regression (AIR) method was devised to overcome this obstacle. Using data from both a microphysical model and from CIPS in its normal mode, we show that the AIR method provides sufficiently accurate average IWC so that PMC IWC can be retrieved from CIPS data into the future, even when albedo is not measured at multiple scattering angles. We also show from the model that 265nm UV scattering is sensitive only to ice particle sizes greater than about 20–25nm in (effective) radius, and that the operational CIPS algorithm has an average error in retrieving IWC of −13±17%.
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We use data from two NASA satellites, the Thermosphere Ionosphere Energetics and Dynamics (TIMED) and the Aeronomy of Ice in the Mesosphere (AIM) satellites in conjunction with model simulations from the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) to elucidate the key dynamical and chemical factors governing the abundance and diurnal variation of nitric oxide (NO) at near solar minimum conditions and low latitudes. This analysis was enabled by the recent orbital precession of the AIM satellite which caused the solar occultation pattern measured by the Solar Occultation for Ice Experiment (SOFIE) to migrate down to low and mid latitudes for specific periods of time. We use a month of NO data collected in January 2017 to compare with two versions of the TIME-GCM, one driven solely by climatological tides and analysis-derived planetary waves at the lower boundary and free running at all other altitudes, while the other is constrained by a high-altitude analysis from the Navy Global Environmental Model (NAVGEM) up to the mesopause. We also compare SOFIE data with a NO climatology from the Nitric Oxide Empirical Model (NOEM). Both SOFIE and NOEM yield peak NO abundances of around 4×10⁷cm−3; however, the SOFIE profile peaks about 6–8km lower than NOEM. We show that this difference is likely a local time effect; SOFIE being a dawn measurement and NOEM representing late morning/near noon. The constrained version of TIME-GCM exhibits a low altitude dawn peak while the model that is forced solely at the lower boundary and free running above does not. We attribute this difference due to a phase change in the semi-diurnal tide in the NAVGEM-constrained model causing descent of high NO mixing ratio air near dawn. This phase difference between the two models arises due to differences in the mesospheric zonal mean zonal winds. Regarding the absolute NO abundance, all versions of the TIME-GCM overestimate this. Tuning the model to yield calculated atomic oxygen in agreement with TIMED data helps, but is insufficient. Further, the TIME-GCM underestimates the electron density [e-] as compared with the International Reference Ionosphere empirical model. This suggests a potential conflict with the requirements of NO modeling and [e-] modeling since one solution typically used to increase model [e-] is to increase the solar soft X ray flux which would, in this case, worsen the NO model/data discrepancy.
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We make an initial report on polar mesospheric clouds (PMCs) observed by Himawari-8, the Japanese Geostationary-Earth-Orbit (GEO) meteorological satellite. Heights of the observed PMCs were estimated to be 80–82 km. The PMCs were active only during summertime in both the northern and southern polar regions. These results are concrete evidences of PMCs. PMC observations by Himawari-8 can provide continuous PMC monitoring at every 10 minutes with 3 visible bands from its almost fixed location relative to the Earth, and it would enhance PMC research in the near future.
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The altitude- and latitude-dependent responses of neutral temperature in the lower thermosphere to the 2013 St. Patrick's Day geomagnetic storm have been studied using neutral temperature measurements from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the TIMED satellite and the Solar Occultation For Ice Experiment (SOFIE) instrument onboard the AIM satellite. Both SABER and SOFIE observations revealed that both temperature increase (having peaks of ~15-25 K) and decrease (having peak of ~15 K), which were associated with the storm, occurred in the two hemispheres. The magnitudes of temperature variations changed with latitude, altitude, and the phase of the storm. The peaks of the temperature increase occurred 0.5-1.5 days later than the peak of the AE index, depending on latitude and height. Global circulation changes initiated due to heating and ion drag in the auroral region are likely responsible for the temperature increases or decreases in the lower thermosphere.
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Observations from satellites and a ground-based station are combined to construct a global data set for investigating the tertiary ozone maximum in the winter mesosphere for the period August 2004 to June 2017. These give a comprehensive picture of this ozone maximum in latitude, pressure, and time. The location of the tertiary ozone maximum shifts in latitude and pressure with the evolving season; the ozone peak occurs at lower latitude and higher pressure around the winter solstice. Highest average nighttime ozone concentrations and greatest degree of interannual variability are seen in late winter in the Northern Hemisphere (NH). The hemispheric differences and interannual variability in nighttime ozone are related to variations of temperature, H2O, and OH associated with dynamical activity. Elevated stratopause events in the NH winter are associated with transport of air that is depleted in H2O and enhanced in OH; photochemistry then leads to downward displacement of the altitude of maximum ozone and enhancement in the ozone amount. Transport by planetary waves in the NH extends the region of high ozone further from the pole and leads to longitudinal variations. The analysis shows that while the tertiary ozone maximum responds to a particular radiative situation as shown in previous studies, it is also the result of very dry air found in the winter polar mesosphere.
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The composition of meteoric smoke particles in the mesosphere is constrained using measurements from the Solar Occultation For Ice Experiment (SOFIE) in conjunction with models. Comparing the multiwavelength observations with models suggests smoke compositions of magnetite, wüstite, magnesiowüstite, or iron-rich olivine. Smoke compositions of pure pyroxene, hematite, iron-poor olivine, magnesium silicate, and silica are excluded, although this may be because these materials have weak signatures at the SOFIE wavelengths. Information concerning smoke composition allows the SOFIE extinction measurements to be converted to smoke volume density. Comparing the observed volume density with model results for varying meteoric influx (MI) provides constraints on the ablated fraction of incoming meteoric material. The results indicate a global ablated MI of 3.3 ± 1.9 t d−1, which represents only iron, magnesium, and possibly silica, given the smoke compositions indicated here. Considering the optics and iron content of individual smoke compositions gives an ablated Fe influx of 1.8 ± 0.9 t d−1. Finally, the global total meteoric influx (ablated plus surviving) is estimated to be 30 ± 18 t d−1, when considering the present results and a recent description of the speciation of meteoric material.
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Data from the Cloud Imaging and Particle Size experiment on the Aeronomy of Ice in the Mesosphere (AIM) satellite are employed to study the impact of small-scale gravity wave (GW) on albedo, ice water content (IWC), and particle radius (PR) of polar mesospheric clouds. Overall, 23,987 eligible GW events, with a horizontal wavelength of 20-150 km are eventually extracted from Cloud Imaging and Particle Size level 2 orbit albedo maps during 2007-2011. The overall statistical results show that when small-scale GWs travel horizontally in polar mesospheric clouds, they can amplify the albedo and IWC by a rate of 10.0-22.6%, while reducing the PR by as much as -7.01%. Owing to the strong temporal and spatial dependences, the albedo and IWC variations are larger on an average during the core of the season, while they decrease during the initial and final periods of the season. The obvious zonal asymmetries are also found. The albedo variations show a positive linear relation with the GW amplitudes in albedo, as opposed to a negative linear relation with GW horizontal wavelengths. In most of the GW events, the periodic variation in the trend of albedo exhibits an anticorrelation with that of PR. Combining previous research studies with our results, we deduce that the rapid change in particle concentration and the upward movement of water vapor by GWs may be very important aspects for explaining the influence mechanism.
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Recent advances in data processing from the Cloud Imaging and Particle Size (CIPS) instrument on the NASA Aeronomy of Ice in the Mesosphere satellite allow observation of bright mesospheric clouds at mid‐latitudes (<60°). When adjusted for the evolving local time (LT) of the CIPS observations during its mission we find that the frequencies of these bright clouds in the northern hemisphere show no trend from 2007 to 2021 and no dependence on the solar cycle, although the interannual variability is extreme. Rather we investigate the possible link with propellant exhaust from orbital vehicles, typically launched at lower latitudes. By filtering the launch record equatorward of 60°N using only those launches between 23 and 10 LT, we find a strong correlation with the observed mid‐latitude mesospheric cloud frequency variability between 56° and 60°N. Meridional winds at 92 km from a meteorological analysis system reveal that these morning launches occurred at the time of maximum northward transport. Based upon this combination of high correlation between the cloud frequency and the launch record plus favorable transport conditions, it is likely that space traffic has a strong influence on the interannual variability of these bright mesospheric clouds.
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High spatial resolution images of polar mesospheric clouds (PMCs) from a camera array on board the Aeronomy of Ice in the Mesosphere (AIM) satellite have been obtained since 2007. The Cloud Imaging and Particle Size Experiment (CIPS) detects scattered ultraviolet (UV) radiance at a variety of scattering angles, allowing the scattering phase function to be measured for every image pixel. With well-established scattering theory, the mean particle size and ice water content (IWC) are derived. In the nominal mode of operation, approximately seven scattering angles are measured per cloud pixel. However, because of a change in the orbital geometry in 2016, a new mode of operation was implemented such that one scattering angle, or at most two, per pixel are now available. Thus particle size and IWC can no longer be derived from the standard CIPS algorithm. The Albedo-Ice Regression (AIR) method was devised to overcome this obstacle. Using data from both a microphysical model and from CIPS in its normal mode, we show that the AIR method provides sufficiently accurate average IWC so that PMC IWC can be retrieved from CIPS data into the future, even when albedo is not measured at multiple scattering angles. We also show from the model that 265 nm UV scattering is sensitive only to ice particle sizes greater than about 20–25 nm in (effective) radius and that the operational CIPS algorithm has an average error in retrieving IWC of -13±17 %.
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Polar mesospheric clouds (PMCs) occur in the summer near 82 -85km altitude due to seasonal changes of temperature and humidity. However, water vapor and associated PMCs have also been observed associated with rocket exhaust. The effects of this rocket exhaust on the temperature of the upper mesosphere are not well understood. To investigate these effects, 220 kg of pure water was explosively released at 85 km as part of the Super Soaker sounding rocket experiment on the night of January 25-26, 2018 at Poker Flat Research Range (65°N, 147°W). A cloud formed within 18 s and was measured by a ground-based Rayleigh lidar. The peak altitude of the cloud appeared to descend from 92 to 78 km over 3 min. Temperatures leading up to the release were between 197 and 232 K, about 50 K above the summertime water frost point when PMCs typically occur. The apparent motion of the cloud is interpreted in terms of the expansion of the explosive release. Analysis using a water vapor radiative cooling code coupled to a microphysical model indicates that the cloud formed due to the combined effects of rapid radiative cooling (∼25 K) by meter-scale filaments of nearly pure water vapor (∼1 ppv) and an increase in the frost point temperature (from 150 to 200 K) due to the high concentration of water vapor. These results indicate that water exhaust not only acts as a reservoir for mesospheric cloud production but also actively cools the mesosphere to induce cloud formation.
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The total areas and other related characteristics of polar mesospheric clouds of the Southern Hemisphere are determined on the basis of the processing of images obtained from the AIM satellite mission. Daily images have been analyzed from 2007 to 2008 to 2019–2020 austral summer seasons. The set of the analyzed data allowed us to study the features of seasonal and inter-seasonal changes in the development of polar mesospheric clouds (PMCs). Long-term temporal changes in such parameters as the maximum and integral areas of the cloud field, the date of the first appearance and disappearance of PMCs, as well as their season durations have been considered in detail. The conclusion about the non-random nature of changes in these characteristics in some seasons is substantiated. It is possible that the PMC evolution is influenced by fluctuations in weather and climatic conditions in the Antarctic region. This assumption is supported by both the relationship between the intensity of mesospheric clouds development in the Southern Hemisphere and variations in seasonal mean (in the context of the clouds existence) temperatures in Antarctica as well as between the stable similarity in seasonal changes in temperature and PMC field areas.
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The exact occurrence frequency of noctilucent clouds (NLCs) in middle latitudes is significant information because it is thought to be sensitive to long-term atmospheric change. We conducted NLC observation from airline jets in the Northern Hemisphere during the summer 2019 to evaluate the effectiveness of NLC observation from airborne platforms. By cooperating with the Japanese airline All Nippon Airways (ANA), imaging observations of NLCs were conducted on 13 flights from Jun 8 to Jul 12. As a result of careful analysis, 8 of these 13 flights were found to successfully detect NLCs from middle latitudes (lower than 55°N) during their cruising phase. Based on the results of these test observations, it is shown that an airline jet is a powerful tool to continuously monitor the occurrence frequency of NLCs at midlatitudes which is generally difficult with a polar orbiting satellite due to sparse sampling in both temporal and spatial domain. The advantages and merits of NLC observation from jets over satellite observation from a point of view of imaging geometry is also presented.
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Measurements from the Solar Occultation For Ice Experiment (SOFIE) in both hemispheres are used to characterize meteoric smoke in the mesosphere and to estimate the meteoric flux into Earth's atmosphere. New smoke extinction retrievals from sunrise measurements in the Northern Hemisphere (NH) are presented, which complement the previously reported sunset observations in the Southern Hemisphere (SH). The sunrise observations are in good agreement with simulations from the Whole Atmosphere Community Climate Model (WACCM), for both the seasonal and height dependence of smoke in the mesosphere. The SOFIE-WACCM comparisons assumed that smoke in the mesosphere exists purely as Fe-rich olivine. This is justified because olivine is detected optically by SOFIE, meteoric ablation is predicted to inject similar quantities of the most abundant elements (Fe, Mg, and Si) into the mesosphere, and olivine is anticipated by theory and laboratory experiments. In addition, the ablated meteoric influx (AMI) and total meteoric influx determined from SOFIE assuming Fe-rich olivine is in agreement with a recent and independent investigation based on models and observations. SOFIE observations from 2007 to 2021 indicate a global AMI of 7.3 ± 2.2 metric tons per day (t d−1), which corresponds to a total influx (ablated plus surviving material) of 24.7 ± 7.3 t d−1. Finally, the results indicate stronger descent in the NH polar winter mesosphere than in the SH winter. This hemispheric asymmetry at polar latitudes is indicated by smoke and water vapor results from both SOFIE and WACCM.
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A new concept for a cluster of compact lidar systems named VAHCOLI (Vertical And Horizontal COverage by LIdars) is presented, which allows for the measurement of temperatures, winds, and aerosols in the middle atmosphere (∼ 10–110 km) with high temporal and vertical resolution of minutes and some tens of meters, respectively, simultaneously covering horizontal scales from a few hundred meters to several hundred kilometers (“four-dimensional coverage”). The individual lidars (“units”) being used in VAHCOLI are based on a diode-pumped alexandrite laser, which is currently designed to detect potassium (λ=770 nm), and on sophisticated laser spectroscopy measuring all relevant frequencies (seeder laser, power laser, backscattered light) with high temporal resolution (2 ms) and high spectral resolution applying Doppler-free spectroscopy. The frequency of the lasers and the narrowband filter in the receiving system are stabilized to typically 10–100 kHz, which is a factor of roughly 10−5 smaller than the Doppler-broadened Rayleigh signal. Narrowband filtering allows for the measurement of Rayleigh and/or resonance scattering separately from the aerosol (Mie) signal during both night and day. Lidars used for VAHCOLI are compact (volume: ∼ 1 m3) and multi-purpose systems which employ contemporary electronic, optical, and mechanical components. The units are designed to autonomously operate under harsh field conditions in remote locations. An error analysis with parameters of the anticipated system demonstrates that temperatures and line-of-sight winds can be measured from the lower stratosphere to the upper mesosphere with an accuracy of ±(0.1–5) K and ±(0.1–10) m s−1, respectively, increasing with altitude. We demonstrate that some crucial dynamical processes in the middle atmosphere, such as gravity waves and stratified turbulence, can be covered by VAHCOLI with sufficient temporal, vertical, and horizontal sampling and resolution. The four-dimensional capabilities of VAHCOLI allow for the performance of time-dependent analysis of the flow field, for example by employing Helmholtz decomposition, and for carrying out statistical tests regarding, for example, intermittency and helicity. The first test measurements under field conditions with a prototype lidar were performed in January 2020. The lidar operated successfully during a 6-week period (night and day) without any adjustment. The observations covered a height range of ∼ 5–100 km and demonstrated the capability and applicability of this unit for the VAHCOLI concept.
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We report on a Polar Mesospheric Cloud (PMC) front structure observed on July 2, 2007 over Greenland. This structure appears to be localized solitary wave, with a sharp boundary that separates a cloud and cloud-free region. Near-coincident temperature measurements indicate a 20 K temperature difference between these two regions that likely contributed to the sharp PMC front boundary. Gravity wave temperature amplitude and buoyancy frequency show that large amplitude GWs and the formation of a stable atmospheric layer between two unstable regions supported the formation of a pronounced mesospheric temperature inversion that destroyed PMCs. Given the absence of an inversion layer close to the location of PMC front, it is not clear if a similar thermal duct but with colder temperatures supported the formation of a single wave resulting in the formation of the observed PMC front. The buoyancy frequency structure with stable and unstable regions also indicates mesospheric wave propagation, and is present in both the cloud and cloud-free regions. We identify a tropospheric low-pressure area and a frontal system as potential sources of these mesospheric GWs. Ray-tracing simulations indicate that GWs from these sources propagated to the mesosphere and may have contributed to the observed PMC variability.
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The Wind spacecraft, launched on November 1, 1994, is a critical element in NASA's Heliophysics System Observatory (HSO) -- a fleet of spacecraft created to understand the dynamics of the sun-Earth system. The combination of its longevity (>25 years in service), its diverse complement of instrumentation, and high resolution and accurate measurements has led to it becoming the "standard candle" of solar wind measurements. Wind has over 55 selectable public data products with over ~1100 total data variables (including OMNI data products) on SPDF/CDAWeb alone. These data have led to paradigm shifting results in studies of statistical solar wind trends, magnetic reconnection, large-scale solar wind structures, kinetic physics, electromagnetic turbulence, the Van Allen radiation belts, coronal mass ejection topology, interplanetary and interstellar dust, the lunar wake, solar radio bursts, solar energetic particles, and extreme astrophysical phenomena such as gamma-ray bursts. This review introduces the mission and instrument suites then discusses examples of the contributions by Wind to these scientific topics that emphasize its importance to both the fields of heliophysics and astrophysics.
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The particle size distribution of Polar Mesospheric Clouds (PMC) is closely related to the fundamental processes of cloud formation and evolution. Still, despite substantial observational efforts, specific details about the particle size distribution have remained obscure. In this study, we aim at deriving more constraints on PMC size distributions by combining optical measurements from two satellite instruments observing a common PMC volume. We use a special set of 2D tomographic limb observations from the Optical Spectrograph and Infrared Imager System (OSIRIS) on the Odin satellite from 2010 to 2011 in the latitude range 78° N to 80° N and compare these to simultaneous PMC observations from the nadir-viewing Cloud Imaging and Particle Size (CIPS) instrument on the AIM satellite. A key goal is to find the assumption on the mathematical shape of the particle size distribution that should be applied to a vertically resolving limb-viewing instrument to reach consistent size results compared to the column-integrated ice distribution as seen by a nadir-viewing instrument. Our results demonstrate that viewing geometry and sampling volume of each instrument must be carefully considered and that the same size distribution assumption cannot simultaneously describe a column-integrated and a local height-resolved size distribution. In particular, applying the standard Gaussian assumption, used by many earlier PMC studies, to both limb and nadir observation leads to an overestimate of particle sizes seen by OSIRIS by about 10 nm as compared to CIPS. We show that the agreement can be improved if a Log-normal assumption with a broad distribution width around σ = 1.42 is adopted for OSIRIS. A reason for this broad distribution best describing the OSIRIS observations we suggest the large retrieval volume of the limb measurement. Gravity waves and other small-scale processes can cause horizontal variations and a co-existence of a wide range of particle populations in the sampling volume. Horizontal integration then leads to apparently much broader size distributions than encountered in a small horizontal sampling volume.
Preprint
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The Wind spacecraft, launched on November 1, 1994, is a critical element in NASA’s Heliophysics System Observatory (HSO) – a fleet of spacecraft created to understand the dynamics of the sun-Earth system. The combination of its longevity (>25 years in service), its diverse complement of instrumentation, and high resolution and accurate measurements has led to it becoming the “standard candle” of solar wind measurements. Wind has over 55 selectable public data products with over ∼1100 total data variables (including OMNI data products) on SPDF/CDAWeb alone. These data have led to paradigm shifting results in studies of statistical solar wind trends, magnetic reconnection, large- scale solar wind structures, kinetic physics, electromagnetic turbulence, the Van Allen radiation belts, coronal mass ejection topology, interplanetary and interstellar dust, the lunar wake, solar radio bursts, solar energetic particles, and extreme astrophysical phe- nomena such as gamma-ray bursts. This review introduces the mission and instrument suites then discusses examples of the contributions by Wind to these scientific topics that emphasize its importance to both the fields of heliophysics and astrophysics.
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Abstract NRLMSIS® 2.0 is an empirical atmospheric model that extends from the ground to the exobase and describes the average observed behavior of temperature, eight species densities, and mass density via a parametric analytic formulation. The model inputs are location, day of year, time of day, solar activity, and geomagnetic activity. NRLMSIS 2.0 is a major, reformulated upgrade of the previous version, NRLMSISE‐00. The model now couples thermospheric species densities to the entire column, via an effective mass profile that transitions each species from the fully mixed region below ~70 km altitude to the diffusively separated region above ~200 km. Other changes include the extension of atomic oxygen down to 50 km and the use of geopotential height as the internal vertical coordinate. We assimilated extensive new lower and middle atmosphere temperature, O, and H data, along with global average thermospheric mass density derived from satellite orbits, and we validated the model against independent samples of these data. In the mesosphere and below, residual biases and standard deviations are considerably lower than NRLMSISE‐00. The new model is warmer in the upper troposphere and cooler in the stratosphere and mesosphere. In the thermosphere, N2 and O densities are lower in NRLMSIS 2.0; otherwise, the NRLMSISE‐00 thermosphere is largely retained. Future advances in thermospheric specification will likely require new in situ mass spectrometer measurements, new techniques for species density measurement between 100 and 200 km, and the reconciliation of systematic biases among thermospheric temperature and composition data sets, including biases attributable to long‐term changes.
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The refined Cloud Imaging and Particle-Size (CIPS) cloud wind tracking algorithm is elaborated and the wind product is assessed against the Navy Operational Global Atmospheric Prediction System - Advanced Level Physics and High Altitude (NOGAPS-ALPHA) winds and the horizontal wind model (HWM14) climatological winds. Multiple searching frame sizes are adopted to generate the preliminary wind sets which are then merged and further edited based on the clustering of the similar wind directions (±20°). The mean values of the clusters within the sampling grids of 1.5 ° × 1.5 ° or 4.5 ° × 4.5 ° are taken as the final wind product. At the coincidences the CIPS and NOGAPS winds show a moderate degree of deterministic consistency. We have further shown that on the orbit-to-orbit basis when the NOGAPS modeled ice and CIPS measured ice correlate better, the wind agreement is also better. The difference in the two wind sets is most likely attributed to the NOGAPS temperature being deviated from the true temperature that will affect the geostrophic component of the winds and also to the fact that the CIPS winds are often ageostrophic and are cascaded into smaller scales. The CIPS zonal (westward) winds are decreased and then reversed in early June and late August whereas in the core of the season they are stronger. This overall variation pattern is shared by both NOGAPS and HWM14 zonal winds. Both NOGAPS and HWM14 zonal winds exhibit ∼8–10 m/s difference between cases using all local times (LTs) and the CIPS LT range 13–23 h due to the dominant diurnal migrating tides, and this may partially interpret the weaker CIPS zonal winds. The meridional (equatorward) winds do not follow any established intra-seasonal variation pattern but rather the variability is susceptible to the sampling longitudes/latitudes.
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Permanently polarized Polyvinylidene Fluoride (PVDF) films have been used on a variety of spacecraft as in situ dust detectors to measure the size and spatial distributions of micron and sub-micron dust particles. The detectors produce a short electric pulse when impacted by a hypervelocity dust particle. The pulse amplitude depends on the mass and relative speed of the dust grain. This relationship has been studied both empirically and numerically to better understand the film’s principle of operation, as well as the effects of film thickness, film temperature, and particle penetration depth. However, little work has been done to constrain the effects of varying particle density and incidence angle despite the frequent occurrence of such configurations in most space-based applications. We present calibrations of non-penetrating impacts on 28 μm thick films at varying incidence angles ranging from 0° to 75° for iron and aluminum particles in the mass and speed range of 10⁻¹² ≤ m ≤ 10⁻⁸ g and 0.5 ≤ v ≤ 7 km/s, respectively. The study was carried out at the 3 MV dust accelerator laboratory at the University of Colorado at Boulder. The results show that PVDF signals are largely independent of particle density and incidence angle up to 75° for non-penetrating impacts.
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Noctilucent clouds (NLC) – also known as polar mesospheric clouds (PMC) – occur at mid and high latitudes during the summer months in each hemisphere and are with altitudes of about 83 km the highest clouds in the terrestrial atmosphere. NLC are an optically thin phenomenon. They are known to consist of H2O ice particles with radii of less than about 100 nm. The first reported sightings of NLC occurred in 1885, two years after the eruption of the volcano Krakatoa in 1883. They exhibit spatial and temporal variability over a large range of scales and react very sensitively to variations in ambient conditions. This high sensitivity makes them highly relevant observables for the investigation of a wide variety of different atmospheric processes including dynamical effects, solar-terrestrial interactions and long-term changes of the Earth’s middle atmosphere. The role of NLC as indicators of long-term changes in the mesopause region in particular has been a topic of intensive debate.
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The Utah State University Advanced Mesospheric Temperature Mapper was deployed at the Amundsen‐Scott South Pole Station in 2010 to measure OH temperature at ~87 km as part of an international network to study the mesospheric dynamics over Antarctica. During the austral winter of 2014, an unusually large amplitude ~28‐day oscillation in mesospheric temperature was observed for ~100 days from the South Pole Station. This study investigates the characteristics and global structure of this exceptional planetary‐scale wave event utilizing ground‐based mesospheric OH temperature measurements from two Antarctic stations (South Pole and Rothera) together with satellite temperature measurements from the Microwave Limb Sounder on the Aura satellite and the Solar Occultation For Ice Experiment on the Aeronomy of Ice in the Mesosphere satellite. Our analyses have revealed that this large oscillation is a wintertime, high‐latitude phenomenon, exhibiting a coherent zonal wave #1 structure below 80‐km altitude. At higher altitudes, the wave was confined in longitude between 180°E and 360°E. The amplitude of this oscillation reached ~15 K at 85 km, and it was observed to grow with altitude as it extended from the stratosphere into the lower thermosphere in the Southern Hemisphere. The satellite data further established the existence of this oscillation in the Northern Hemisphere during the boreal wintertime. The main characteristics and global structure of this event as observed in temperature are consistent with the predicted 28‐day Rossby Wave (1,4) mode.
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An analysis of the Atmospheric Chemistry Experiment (ACE) infrared Fourier transform spectrometer (FTS) spectra for signatures of Polar Mesospheric Clouds (PMCs) has been carried out by looking for the O-H vibrational mode at ≈ 3240 cm−1. PMCs are thought to be indicators of climate change in the mesosphere and have been found to be increasing in recent years. Additionally, there are a number of open questions about the microphysics of the clouds, and their physical properties such as temperature, density, and particle shape and size. ACE has access to the entire infrared spectrum, potentially providing more accurate retrievals of these parameters. Using the T-matrix scattering code, we have made fits to the 3 micron ACE-FTS spectra. The ACE data set yielded 1762 unique occultations; after accounting for false positives, 955 occultations were left. We assumed oblate spheroids with a fixed effective radius of 40 nm and a nominal cloud size of 200 km, and obtained reasonable distributions for temperature, axial ratio and particle density. We expect that the methods presented here will allow a new routine ACE PMC data product to be developed.
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Two important approaches for satellite studies of polar mesospheric clouds (PMCs) are nadir measurements adapting phase function analysis and limb measurements adapting spectroscopic analysis. Combining both approaches enables new studies of cloud structures and microphysical processes but is complicated by differences in scattering conditions, observation geometry and sensitivity. In this study, we compare common volume PMC observations from the nadir-viewing Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of Ice in the Mesosphere (AIM) satellite and a special set of tomographic limb observations from the Optical Spectrograph and InfraRed Imager System (OSIRIS) on the Odin satellite performed over 18 d for the years 2010 and 2011 and the latitude range 78 to 80∘ N. While CIPS provides preeminent horizontal resolution, the OSIRIS tomographic analysis provides combined horizontal and vertical PMC information. This first direct comparison is an important step towards co-analysing CIPS and OSIRIS data, aiming at unprecedented insights into horizontal and vertical cloud processes. Important scientific questions on how the PMC life cycle is affected by changes in humidity and temperature due to atmospheric gravity waves, planetary waves and tides can be addressed by combining PMC observations in multiple dimensions. Two- and three-dimensional cloud structures simultaneously observed by CIPS and tomographic OSIRIS provide a useful tool for studies of cloud growth and sublimation. Moreover, the combined CIPS/tomographic OSIRIS dataset can be used for studies of even more fundamental character, such as the question of the assumption of the PMC particle size distribution. We perform the first thorough error characterization of OSIRIS tomographic cloud brightness and cloud ice water content (IWC). We establish a consistent method for comparing cloud properties from limb tomography and nadir observations, accounting for differences in scattering conditions, resolution and sensitivity. Based on an extensive common volume and a temporal coincidence criterion of only 5 min, our method enables a detailed comparison of PMC regions of varying brightness and IWC. However, since the dataset is limited to 18 d of observations this study does not include a comparison of cloud frequency. The cloud properties of the OSIRIS tomographic dataset are vertically resolved, while the cloud properties of the CIPS dataset is vertically integrated. To make these different quantities comparable, the OSIRIS tomographic cloud properties cloud scattering coefficient and ice mass density (IMD) have been integrated over the vertical extent of the cloud to form cloud albedo and IWC of the same quantity as CIPS cloud products. We find that the OSIRIS albedo (obtained from the vertical integration of the primary OSIRIS tomography product, cloud scattering coefficient) shows very good agreement with the primary CIPS product, cloud albedo, with a correlation coefficient of 0.96. However, OSIRIS systematically reports brighter clouds than CIPS and the bias between the instruments (OSIRIS – CIPS) is 3.4×10-6 sr−1 (±2.9×10-6 sr−1) on average. The OSIRIS tomography IWC (obtained from the vertical integration of IMD) agrees well with the CIPS IWC, with a correlation coefficient of 0.91. However, the IWC reported by OSIRIS is lower than CIPS, and we quantify the bias to −22 g km−2 (±14 g km−2) on average.
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A recent Eos article [von Zahn, 2003] has challenged the notion that Noctilucent Clouds may be a “miner's canary” of global change [Thomas, 1996]. We first note our terminology: we use the generic term Mesospheric Clouds (MC) to denote this phenomenon encompassing both the terms Polar Mesospheric Clouds (PMC) and Noctilucent Clouds (NLC). In this article, we address his specific criticisms on a point-by-point basis. We critically address his assertion that available data sets derived from satellite measurements of cloud radiance are too short for assessing long-term trends. We argue that his inference of large and irregular natural variability of MC is based on statistically-unreliable data from the older literature. We show from published space-based data that substantial interdecadal trends are present in MC brightness. We point out that MC heights (which have apparently remained constant) are not necessarily sensitive indicators of changes of MC properties. Finally we address the question of attribution, raised by von Zahn. We argue that the space observations are readily explained by well-documented water vapor variability.
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[1] Polar Mesospheric Clouds (PMCs) were observed by a limb-scanning ultraviolet spectrometer on the Student Nitric Oxide Explorer (SNOE). Radiance profiles at 215 and 237 nm are analyzed to determine the presence of clouds. Once detected, the altitude and brightness of a cloud relative to the background atmosphere is determined. SNOE observations provide the frequency of occurrence of PMC as a function of location and time for the years 1998 through 2003. The observations show at high latitudes a general rise in frequency of occurrence beginning approximately 3 weeks before summer solstice in both hemispheres and lasting for approximately 1 week. These rises are followed by approximately 60 days of relatively high but variable occurrence frequencies. The declines in frequency of occurrence at the ends of the seasons are generally slower and more structured then the beginning of the seasons. One of the major results from the SNOE observations is that significantly more PMCs are observed in the Northern Hemisphere than in the south, leading us to conclude that the southern polar mesosphere must be on average less saturated than the northern polar mesosphere. The SNOE observations also suggest that the frequency of occurrence of PMCs is strongly modulated by local dynamical influences. The SNOE results are in general agreement with results from the Solar Mesosphere Explorer which observed PMC with similar instrumentation in the years 1981 through 1986.
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[1] Since 1994, Rayleigh lidar measurements of the Arctic middle atmosphere have been conducted at the Sondrestrom research facility near Kangerlussuaq, Greenland (67.0N,50.9W). The summer lidar observations typically cover the late June through August period. From these observations, 220 hours of noctilucent clouds (NLCs) have been detected by the lidar spanning 16 hours of local time. Organizing the cloud characteristics irrespective of local time reveals the most common cloud height as 82.5 km, the most common full-width-half-maximum (FWHM) as 0.7 km, and the most common peak volume backscatter coefficient as 20.0 × 10−11 m−1sr−1. The FWHM is noticeably thinner than determined by other lidar observations of NLCs in Norway and the South Pole. We found the mean backscatter strength to increase and the FWHM to decrease with decreasing cloud height. In addition, the cloud slopes with time are greater for the thicker weaker clouds at higher altitudes than the thinner stronger clouds at lower altitudes. Gravity-wave signatures are routinely observed in the cloud detections. Upon estimating stratospheric wave activity in the data, we observed stronger cloud backscatter during low gravity-wave activity and weak cloud backscatter during high gravity-wave activity. To help support these results, simulations from a microphysical cloud model were performed under summer mesospheric conditions with and without gravity-wave activity. Upon including short-period (∼2–3 hours) gravity-wave activity, the model simulation reproduced the behavior observed in the ensemble cloud properties by producing a broader altitude distribution, weaker backscatter strength, and thinner clouds.
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Micrometeorites that ablate in the lower thermosphere and upper mesosphere are thought to recondense into nanometer-sized smoke particles and then coagulate into larger dust particles. Previous studies with one-dimensional models have determined that the meteoric dust size distribution is sensitive to the background vertical velocity and have speculated on the importance of the mesospheric meridional circulation to the dust spatial distribution. We conduct the first three-dimensional simulations of meteoric dust using a general circulation model with sectional microphysics to study the distribution and characteristics of meteoric dust in the mesosphere and upper stratosphere. We find that the mesospheric meridional circulation causes a strong seasonal pattern in meteoric dust concentration in which the summer pole is depleted and the winter pole is enhanced. This summer pole depletion of dust particles results in fewer dust condensation nuclei (CN) than has traditionally been assumed in numerical simulations of polar mesospheric clouds (PMCs). However, the total number of dust particles present is still sufficient to account for PMCs if smaller particles can nucleate to form ice than is conventionally assumed. During winter, dust is quickly transported down to the stratosphere in the polar vortex where it may participate in the nucleation of sulfate aerosols, the formation of the polar CN layer, and the formation of polar stratospheric clouds (PSCs). These predictions of the seasonal variation and resulting large gradients in dust concentration should assist the planning of future campaigns to measure meteoric dust.
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Polar mesospheric clouds (PMCs) have been measured in the infrared for the first time by the Halogen Occultation Experiment (HALOE). PMC extinctions retrieved from measurements at eight wavelengths show remarkable agreement with model spectra based on ice particle extinction. The infrared spectrum of ice has a unique signature, and the HALOE-model agreement thus provides the first physical confirmation that water ice is the primary component of PMCs. PMC particle effective radii were estimated from the HALOE extinctions based on a first order fit of model extinctions.
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We discuss spectrally resolved measurements of the light scattering by mesospheric ice particles from lidars and satellite-borne instruments in order to test whether Gaussian particle size distributions predicted by microphysical models are consistent with these observations. This study shows that none of the considered data sets is consistent with this assumption as long as spherical particles are assumed whose scattering properties may be described by Mie scattering theory. In addition, lognormal size distributions fail to explain data sets obtained from the SME and SNOE satellite, again assuming spherical particles described by the Mie theory. However, considering needle- or plate-like spheroid-shaped particles with Gaussian size distributions, we find that particles with axial ratios of ~0.2 and/or 5.0 allow us to find a consistent set of ice particle distribution parameters. This parameter set can simultaneously explain all considered observations and is in good agreement with microphysical model results. On the basis of these findings we suggest that nonspherical particle scattering theory be considered for the precise analysis of optical soundings of mesospheric ice particles.
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Layers in the summer mesosphere are studied using an ice model which applies background conditions from a new model called LIMA (Leibniz Institute Middle Atmosphere Model). LIMA covers the height range 0–150 km with high resolution. At low altitudes LIMA assimilates ECMWF ERA 40 data which introduces variability in the upper atmosphere. LIMA adequately represents the conditions in the mesosphere/lower thermosphere. Ice formation is interactively coupled to background water vapour which leads to ‘freeze drying’. Model ice layers vary in time and space and occasionally appear at mid latitudes. The geographical distribution of ice clouds generally agrees with observations. For example, the mean noctilucent cloud height at 69°N is 83.8 km (observations: 83.3 km). The occurrence rates of (polar) mesosphere summer echoes from the model also agree with measurements. At high latitudes ice layers sometimes disappear (‘ice holes’). From time to time wind fluctuations redistribute water vapor but in general freeze drying overwhelms.
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Lidar observations of polar mesospheric clouds (PMC) were made at Rothera, Antarctica, from December 2002 to March 2005. Overall, 128 hours of PMC were detected among the 459 hours of observations, giving a mean occurrence frequency of 27.9%. The mean PMC centroid altitude is 84.12 ± 0.12 km, the mean PMC total backscatter coefficient is 2.34 ± 0.11 × 10−6 sr−1, and the mean layer RMS width is 0.93 ± 0.03 km. The distribution of PMC centroid altitudes over all observations is symmetric (nearly Gaussian), with the most probable altitude (∼84 km) near the center of the distribution. The distribution of PMC brightness is non-Gaussian and is dominated by weak PMC. The observed PMC altitudes at Rothera support the earlier lidar findings that Southern Hemispheric PMC are on average 1 km higher than corresponding Northern Hemispheric PMC, and higher PMC occur at higher latitudes. Significant interannual and diurnal variations are observed in PMC centroid altitude and brightness. Mean PMC altitude varies more than 1 km from one year to another. In addition, 24-hour, 12-hour, and 8-hour oscillations are clearly shown in PMC centroid altitude and brightness. The altitude distribution of PMC brightness peaks at a nearly constant altitude of 84 km, with weaker PMC found on either side of this altitude. The mean PMC altitudes averaged in brightness bins are anticorrelated with the PMC brightness, where weaker PMC occur at higher altitude and the PMC altitudes are proportional to the logarithm of the PMC brightness.
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Meteoric material entering Earth's atmosphere ablates in the mesosphere and is then expected to recondense into tiny so-called "smoke particles." These particles are thought to be of great importance for middle atmosphere phenomena like noctilucent clouds, polar mesospheric summer echoes, metal layers, and heterogeneous chemistry. Commonly used one-dimensional (1-D) meteoric smoke profiles refer to average global conditions and yield of the order of a thousand nanometer sized particles per cubic centimeter at the mesopause, independent of latitude and time of year. Using the first two-dimensional model of both coagulation and transport of meteoric material we here show that such profiles are too simplistic, and that the distribution of smoke particles indeed is dependent on both latitude and season. The reason is that the atmospheric circulation, which cannot be properly handled by 1-D models, efficiently transports the particles to the winter hemisphere and down into the polar vortex. Using the assumptions commonly used in 1-D studies results in number densities of nanometer sized particles of around 4000/cc at the winter pole, while very few particles remain at the Arctic summer mesopause. If smoke particles are the only nucleation kernel for ice in the mesosphere this would imply that there could only be of the order of 100 or less ice particles per cc at the Arctic summer mesopause. This is much less than the ice number densities expected for the formation of ice phenomena (noctilucent clouds and polar mesospheric summer echoes) that commonly occur in this region. However, we find that especially the uncertainty of the amount of material that is deposited in Earth's atmosphere imposes a large error bar on this number, which may allow for number densities up to 1000/cc near the polar summer mesopause.
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We report the discovery of a layer of enhanced water vapor in the Arctic summer mesosphere that was made utilizing two new techniques for remotely determining water vapor abundances. The first utilizes Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI) OH measurements as a proxy for water vapor. The second is a re-analysis of Halogen Occultation Experiment (HALOE) water vapor data with a technique to simultaneously determine polar mesospheric cloud (PMC) ice particle extinction along with the water vapor abundance. These results reveal a narrow layer of enhanced water vapor centered between 82-84 km altitude and coincident with PMCs, that exhibits water vapor mixing ratios of 10-15 ppmv. This indicates that a higher degree of supersaturation is present in the PMC region, and that PMCs are thus more efficient at sequestering total water (both ice particles and vapor) within the layer, than previously believed.
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1] The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on the SciSat satellite measured nearly 30 spectra of polar mesospheric clouds (PMCs) between 65° and 70°N from July 5 to 14, 2004. The ACE-FTS measurements are augmented by UV observations made at the same latitude and time period by the Optical Spectrograph and Infrared Imager System (OSIRIS) on the Odin satellite. Our analysis of these measurements shows that PMC particles are composed of nonspherical ice crystals with mean (equivalent spherical) particle radii of 59 ± 5 nm. Citation: Eremenko, (2005), Shape and composition of PMC particles derived from satellite remote sensing measurements, Geophys. Res. Lett., 32, L16S06, doi:10.1029/ 2005GL023013.
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The Student Dust Counter (SDC) experiment of the New Horizons Mission is an impact dust detector to map the spatial and size distribution of dust along the trajectory of the spacecraft across the solar system. The sensors are thin, permanently polarized polyvinylidene fluoride (PVDF) plastic films that generate an electrical signal when dust particles penetrate their surface. SDC is capable of detecting particles with masses m>10−12 g, and it has a total sensitive surface area of about 0.1 m2, pointing most of the time close to the ram direction of the spacecraft. SDC is part of the Education and Public Outreach (EPO) effort of this mission. The instrument was designed, built, tested, integrated, and now is operated by students.
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The Cassini-Huygens Cosmic Dust Analyzer (CDA) is intended to provide direct observations of dust grains with masses between 10-19 and 10-9 kg in interplanetary space and in the jovian and satumian systems, to investigate their physical, chemical and dynamical properties as functions of the distances to the Sun, to Jupiter and to Saturn and its satellites and rings, to study their interaction with the saturnian rings, satellites and magnetosphere. Chemical composition of interplanetary meteoroids will be compared with asteroidal and cometary dust, as well as with Saturn dust, ejecta from rings and satellites. Ring and satellites phenomena which might be effects of meteoroid impacts will be compared with the interplanetary dust environment. Electrical charges of particulate matter in the magnetosphere and its consequences will be studied, e.g. the effects of the ambient plasma and the magnetic field on the trajectories of dust particles as well as fragmentation of particles due to electrostatic disruption. The investigation will be performed with an instrument that measures the mass, composition, electric charge, speed, and flight direction of individual dust particles. It is a highly reliable and versatile instrument with a mass sensitivity 106 times higher than that of the Pioneer 10 and 11 dust detectors which measured dust in the saturnian system. The Cosmic Dust Analyzer has significant inheritance from former space instrumentation developed for the VEGA, Giotto, Galileo, and Ulysses missions. It will reliably measure impacts from as low as 1 impact per month up to 104 impacts per second. The instrument weighs 17 kg and consumes 12 W, the integrated time-of-flight mass spectrometer has a mass resolution of up to 50. The nominal data transmission rate is 524 bits/s and varies between 50 and 4192 bps.
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The Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of the Ice in the Mesosphere (AIM) spacecraft is a 4-camera nadir pointed imager with a bandpass centered at 265 nm and a field of view of 120°×80°. CIPS observes polar mesospheric clouds (PMCs) against the sunlit Rayleigh-scattered background. At individual polar locations approximately 5 km×5 km in area, CIPS observes the same volume of air seven times over a range of scattering angles from about 35° to 150°. These multi-angle observations allow the identification and extraction of the PMC scattered radiance from the Rayleigh-scattered background. We utilize the fact that the former has a highly asymmetric phase function about 90° scattering angle, while the latter has a phase function that is symmetric. The retrieved PMC phase function can then be interpreted to obtain PMC particle size distributions. We describe a technique for identification of PMCs in the CIPS observations through the separation of the Rayleigh and PMC radiances. PMC phase function results are shown for the first season of CIPS observations. Assuming the particles are oblate spheroids with an axial ratio of 2, and a Gaussian distribution of width 14 nm, we find the phase functions are consistent with mean radii between 50 and 60 nm. These results are similar to those discussed by Hervig et al. [2009. Interpretation of SOFIE PMC measurements: cloud identification and derivation of mass density, particle shape, and particle size. J. Atmos. Sol. Terr. Phys., in review.] in this issue from the Solar Occultation for Ice Experiment (SOFIE) which also flies on the AIM satellite.
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The Cloud Imaging and Particle Size Experiment (CIPS) is one of three instruments aboard the Aeronomy of Ice in the Mesosphere spacecraft. CIPS provides panoramic ultraviolet images of the atmosphere over a wide range of scattering angles in order to determine the presence of polar mesospheric clouds, measure their spatial morphology, and constrain the parameters of cloud particle size distribution. The AIM science objectives motivate the CIPS measurement approach and drive the instrument requirements and design, leading to a configuration of four wide-angle cameras arrayed in a ‘+’ arrangement that covers a 120° (along orbit track)×80° (across orbit track) field of view. CIPS began routine operations on May 24, 4 weeks after AIM was launched. It measures scattered radiances from PMCs near 83 km altitude to derive cloud morphology and particle size information by recording multiple exposures of individual clouds to derive PMC scattering phase functions and detect nadir horizontal spatial scales to approximately 3 km. This paper describes the instrument design, its prelaunch characterization and calibration, and flight operations. Flight observations and calibration activities confirm performance inferred during ground test, verifying that CIPS exceeds its measurement requirements and goals. These results are illustrated with example flight images that demonstrate the instrument measurement performance.
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Measurements of dust particles in comet Halley's coma from Vega spacecraft made with instruments using a new principle of dust detection and having a high time resolution over a large range of dust fluxes and masses are reported. The dust coma, whether quiescent (as seen by Vega 2) or containing a major jet structure, (as seen by Vega 1) displays large, short-term variations throughout which are at times quasi-periodic. The integral mass spectra increase in intensity to the lowest masses measured, and the flux levels lie approximately in the ranges estimated previously from ground-based observations. The coma is highly dynamical on all spatial and temporal scales, suggesting a complex structure of localized regions of dust emission from the nucleus.
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MaCWAVE ( M ountain a nd C onvective W aves A scending VE rtically) was a highly coordinated rocket, ground-based, and satellite program designed to address gravity wave forcing of the mesosphere and lower thermosphere (MLT). The MaCWAVE program was conducted at the Norwegian Andøya Rocket Range (ARR, 69.3° N) in July 2002, and continued at the Swedish Rocket Range (Esrange, 67.9° N) during January 2003. Correlative instrumentation included the ALOMAR MF and MST radars and RMR and Na lidars, Esrange MST and meteor radars and RMR lidar, radiosondes, and TIMED ( T hermosphere I onosphere M esosphere E nergetics and D ynamics) satellite measurements of thermal structures. The data have been used to define both the mean fields and the wave field structures and turbulence generation leading to forcing of the large-scale flow. In summer, launch sequences coupled with ground-based measurements at ARR addressed the forcing of the summer mesopause environment by anticipated convective and shear generated gravity waves. These motions were measured with two 12-h rocket sequences, each involving one Terrier-Orion payload accompanied by a mix of MET rockets, all at ARR in Norway. The MET rockets were used to define the temperature and wind structure of the stratosphere and mesosphere. The Terrier-Orions were designed to measure small-scale plasma fluctuations and turbulence that might be induced by wave breaking in the mesosphere. For the summer series, three European MIDAS ( Mi ddle Atmosphere D ynamics a nd S tructure) rockets were also launched from ARR in coordination with the MaCWAVE payloads. These were designed to measure plasma and neutral turbulence within the MLT. The summer program exhibited a number of indications of significant departures of the mean wind and temperature structures from ``normal" polar summer conditions, including an unusually warm mesopause and a slowing of the formation of polar mesospheric summer echoes (PMSE) and noctilucent clouds (NLC). This was suggested to be due to enhanced planetary wave activity in the Southern Hemisphere and a surprising degree of inter-hemispheric coupling. The winter program was designed to study the upward propagation and penetration of mountain waves from northern Scandinavia into the MLT at a site favored for such penetration. As the major response was expected to be downstream (east) of Norway, these motions were measured with similar rocket sequences to those used in the summer campaign, but this time at Esrange. However, a major polar stratospheric warming just prior to the rocket launch window induced small or reversed stratospheric zonal winds, which prevented mountain wave penetration into the mesosphere. Instead, mountain waves encountered critical levels at lower altitudes and the observed wave structure in the mesosphere originated from other sources. For example, a large-amplitude semidiurnal tide was observed in the mesosphere on 28 and 29 January, and appears to have contributed to significant instability and small-scale structures at higher altitudes. The resulting energy deposition was found to be competitive with summertime values. Hence, our MaCWAVE measurements as a whole are the first to characterize influences in the MLT region of planetary wave activity and related stratospheric warmings during both winter and summer.
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Polar mesosphere summer echoes (PMSE) are very strong radar echoes primarily studied in the VHF wavelength range from altitudes close to the polar summer mesopause. Radar waves are scattered at irregularities in the radar refractive index which at mesopause altitudes is solely determined by the electron number density. For efficient scatter, the electron number density must reveal structures at the radar half wavelength (Bragg condition; ~3 m for typical VHF radars). The question how such small scale electron number density structures are created in the mesopause region has been a longstanding open scientific question for almost 30 years. This paper reviews experimental and theoretical milestones on the way to an advanced understanding of PMSE. Based on new experimental results from in situ observations with sounding rockets, ground based observations with radars and lidars, numerical simulations with microphysical models of the life cycle of mesospheric aerosol particles, and theoretical considerations regarding the diffusivity of electrons in the ice loaded complex plasma of the mesopause region, a consistent explanation for the generation of these radar echoes has been developed. The main idea is that mesospheric neutral air turbulence in combination with a significantly reduced electron diffusivity due to the presence of heavy charged ice aerosol particles (radii ~5–50 nm) leads to the creation of structures at spatial scales significantly smaller than the inner scale of the turbulent velocity field itself. Importantly, owing to their very low diffusivity, the plasma structures acquire a very long lifetime, i.e. 10 min to hours in the presence of particles with radii between 10 and 50 nm. This leads to a temporal decoupling of active neutral air turbulence and the existence of small scale plasma structures and PMSE and thus readily explains observations proving the absence of neutral air turbulence at PMSE altitudes. With this explanation at hand, it becomes clear that PMSE are a suitable tool to permanently monitor the thermal and dynamical structure of the mesopause region allowing insights into important atmospheric key parameters like temperatures, winds, gravity wave parameters, turbulence, solar cycle effects, and long term changes.
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On the night of August 9-10, 1991, two rocket payloads were launched into simultaneously occurring noctilucent clouds (NLC) and polar mesospheric summer echoes (PMSE) above Esrange, a third rocket payload was launched into a NLC where a PMSE was detected 5 minutes later above Esrange, in Sweden as part of the NLC-91 campaign. An aim of this experiment was to compare the vertical structures and locations of the NLC and PMSE events. To this end, in-situ optical photometers and particle impact sensors were used to measure the altitude and vertical structure of the NLC layer, while the Cornell University portable radar interferometer (CUPRI) was used to probe the PMSE. Although this comparison is complicated by the horizontal separations between the in-situ measurements and the radar volume, and low electron densities which reduced the overall radar reflectivity, we conclude that the PMSE layer in the CUPRI radar volume remained above the NLC layer detected by the in-situ instruments by 300 to 2000 m throughout the experiment. We interpret this result as supporting the view that PMSE are more likely to result from the presence of aerosols smaller than the ones optically detectable as NLCs.
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Results are presented on eight years of satellite observations of the polar mesospheric clouds (PMCs) by the SBUV spectral radiometer, showing that PMCs occur in the summertime polar cap regions of both hemispheres and that they exhibit year-to-year variability. It was also found that the increase in the PMC occurrence frequency was inversely correlated with solar activity. Two kinds of hemispherical asymmetries could be identified: (1) PMCs in the Northern Hemisphere were significantly brighter than in the Southern Hemisphere, in accordance with previous results derived from SME data; and (2) the solar cycle response in the south is more pronounced than in the north. The paper also describes the cloud detection algorithm.
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The possiblity is investigated that a substantial change has occurred in middle-atmospheric water vapor as a result of the increase in atmospheric methane over the past century and a half. It is shown from modeling of mesospheric ice-particle formation that noctilucent cloud brightness should be a sensitive indicator of the water content at the high-latitude summertime mesopause. From an examination of the historical record of noctilucent cloud occurrence, it is found that such clouds are absent from the record before 1885, a finding which is consistent with the hypothesis proposed in this paper.
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[1] We infer from the observed occurrence frequency of polar mesosphere summer echoes and from the three-dimensional (3-D) modeling of conditions in the high-latitude mesopause region that a persistent layer of icy particles exists in midsummer at all latitudes poleward of about 60°N at and a few kilometers below the mesopause. All of these icy particles are transported equatorward by the climatological mean winds. At the same time, many of the larger icy particles possess a high enough sedimentation velocity to induce a net downward transport of water vapor. Both types of particle motions cause the mesopause region to become substantially dryer than without these transports of icy particles. We follow the interactions between water vapor and icy particles by means of a 3-D dynamical and chemical model, which includes a module for the formation, growth, and sublimation of icy particles. For midsummer conditions and poleward of 67°N latitude, the model predicts (1) a strongly dehydrated region, typically above 84 km, in which the water vapor mixing ratio can fall below 0.2 ppmv and (2) atmospheric regions with enhanced water vapor abundance near both the lower and the equatorward borders of the icy particle layer.
Article
We have used a two-dimensional numerical model of mesospheric cloud formation to simulate the effects of internal gravity waves on the formation and appearance of ice clouds at the mesopause. We have used gravity wave parameters (amplitude, wavelength, period, etc.) consistent with measurements of gravity waves in the high-latitude mesosphere, including observations of band and billow structures in noctilucent clouds (NLCs). We have investigated both the dynamical effects due to wave-induced winds and the microphysical effects due to wave-induced temperature perturbations. We find that the structures observed in NLC from the ground are predominantly caused by dynamical processes. Since the time required for ice crystal growth at the mesopause is much longer than the observed wave periods and ice crystal sublimation is much more rapid than deposition growth, the primary effect of wave-induced temperature perturbations is to decrease the albedo of the clouds. The fact that gravity waves with periods less than a few hours are ubiquitous near the high-latitude, summertime mesopause imposes an additional constraint on the formation of visible NLC. We find that the mean mesopause temperature must be about 5 K colder for NLC to form when gravity waves are present than when they are not present. Long-period (>10 hours) waves may temporarily enhance the brightness of existing NLC but will not induce the formation of NLC.
Article
In the last 10 years a total of 89 falling spheres (FS) have been launched at high latitudes (˜70°N) in the summer season between late April and late September. From this experimental technique, densities and temperatures in the mesosphere and upper stratosphere (˜95-35 km) are deduced which represent nearly the entire data set regarding the thermal structure in the high-latitude summer mesosphere where optical methods have problems to give reliable results because of the large solar photon background. Some of the launches took place at times in the season where no measurements have been performed before. The seasonal variation of the mean temperatures and densities derived from the FS measurements deviates significantly from the latest empirical models, in particular, in the upper mesosphere during summer. For example, at the summer mesopause (88 km) the FS temperatures are lower by more than 10 K compared to CIRA-1986 in the time period from the beginning of June until the end of August. The thermal structure in the upper mesosphere is rather persistent throughout the core summer months and changes rapidly in the winter-summer transition at mid-May, and vice versa at mid-August. For example, at typical noctilucent cloud altitudes (82 km) the mean temperature is in the range 153±3 K from the beginning of June until mid-August but changes by, typically, 5-10 K per week before and after this period. A comparison of the FS temperatures with the occurrence probability of noctilucent clouds and polar mesosphere summer echoes suggests that the thermal structure is the main controlling factor for these layers, whereas other ingredients required to form aerosol particles, such as water vapor or condensation nuclei, are of secondary importance.
Article
A recent Eos article [von Zahn, 2003] has challenged the notion that Noctilucent Clouds may be a ``miner's canary'' of global change [Thomas, 1996]. We first note our terminology: we use the generic term Mesospheric Clouds (MC) to denote this phenomenon encompassing both the terms Polar Mesospheric Clouds (PMC) and Noctilucent Clouds (NLC). In this article, we address his specific criticisms on a point-by-point basis. We critically address his assertion that available data sets derived from satellite measurements of cloud radiance are too short for assessing long-term trends. We argue that his inference of large and irregular natural variability of MC is based on statistically-unreliable data from the older literature. We show from published space-based data that substantial interdecadal trends are present in MC brightness. We point out that MC heights (which have apparently remained constant) are not necessarily sensitive indicators of changes of MC properties. Finally we address the question of attribution, raised by von Zahn. We argue that the space observations are readily explained by well-documented water vapor variability.
Article
Noctilucent clouds appear during the summertime at high latitudes near the top of the mesosphere. In this review, the observational facts about them, obtained from ground level, by rocket sounding and from orbiting spacecraft, are reviewed. The data are not sufficiently clear and unambiguous to permit dogmatic assertion about the origin and nature of the clouds. They seem to be ice particles nucleated at very low pressures and temperatures by either meteoric smoke or by atmospheric ions. Wavepatterns in the clouds may well result from quite close relations between the troposphere and the mesosphere. The very existence of the clouds leads to difficulties in explaining why there is so much water vapour at this great height in the atmosphere. To try to predict the microscopic behaviour of the cloud particles leads one into assessment of the relative importance of radiometer effects, radiation balance, Brownian movement, electric polarization and the influence of Coulomb attraction on the growth of large clustered ions. Finally, a list is given of published sources of observational data.
Article
During the NLC-93 rocket campaign at Esrange, Sweden, the vertical structure of a noctilucent cloud layer has been investigated in situ. As in earlier rocket flights, combinations of scattered light detectors and electrostatic impact probes have been applied. While the photometric measurement provides the total downward radiance scattered from the cloud particles, the impact probe yields local information about the particle properties. The responses of both techniques scale differently with the particle size. This feature is utilized to derive information about the height dependence of the particle population. The analysis of three NLC passages indicates little vertical variation of the population throughout most of the layer. The lower part of the cloud is characterized by an increase in particle size and a decrease in particle density towards the cloud base. This is to be expected for an NLC brightness peak caused by large particles sedimenting out of the cloud. Implications for the dynamical structure of the cloud are discussed.
Article
Noctilucent clouds (NLC) occur close to 83 km altitude during summer at polar, high, and mid-latitudes. They are frequently visible to Earth-bound observers, provided the observers are on the night side of Earth and the clouds are still illuminated by the Sun. Under these conditions, NLC can become a quite impressive sight. NLC owe their existence to the extremely low temperatures (well below 150 K) which prevail during summer over a wide latitude band in the 82- to 90-km altitude region. For a major review of NLC science, the reader is referred to Gadsden and Schröder [1989].
Article
During the night of August 5/6, 1989 for the first time a noctilucent cloud (NLC) was detected and measured by a lidar instrument. The NLC developed at about 22:20 UT, reached its maximum backscatter cross-section at 23:05 UT and became unobservable at around 00:10 UT. During this period, the NLC exhibited the following properties: (1) its altitude ranged between 83.4 and 82.2 km; (2) its full width at half-maximum ranged between 1.4 and 0.3 km; (3) the ratio of measured backscatter intensity from the NLC to the calculated Rayleigh signal from 82.6 km reached 450; (4) its volume backscatter cross section maximized at 6.5 x 10 to the -9th/m/sr.
Article
Previous studies have suggested that there should be secular trends in polar mesospheric cloud (PMC) occurrence frequency and brightness on decadal timescales and that those trends would be strongest at the lowest latitudes of the PMC existence region. We have analyzed the 27-year PMC data set created from Solar Backscatter Ultraviolet (SBUV, SBUV/2) satellite instruments for long-term variations in albedo using three latitude bands (50°-64°, 64°-74°, 74°-82°). The improved version 3 data set includes revisions to the PMC detection algorithm to produce more consistent results in all measurement conditions. A detailed error analysis yields an approximate uncertainty of 1-2% for seasonally averaged 252-nm albedo values. Adjustments for local time variations in PMC brightness between different satellite data sets were derived to ensure accurate trend calculations. Multiple linear regression fits show that albedo variations are anticorrelated with solar activity in all latitude bands, with a stronger response at high latitudes. The albedo increase from solar maximum to solar minimum ranges from +2% at 50°-64°S to +17% at 74°-82°N. Secular trends in albedo are positive, with long-term changes over 27 years ranging from +12% to +20% depending on hemisphere and latitude. The derived long-term trend in PMC albedo at 50°-64° is smaller than that of higher latitudes. This result contradicts previous suggestions that PMC brightness changes might be most rapid at low latitudes. The albedo response to solar variations is larger in the Northern Hemisphere, while long-term trends are approximately the same in both hemispheres.
Article
An analysis was performed of data on nine summer seasons (1981-1985) collected by the SME satellite to study large-scale geographical and temporal variability of polar mesospheric clouds (PMC). It was found that the PMC season begins at high latitude, and, within 10 to 20 days, propagates to the lowest latitude where PMC exist; this occurs at about 20 to 40 days before summer solstice. It was also found that both PMC and mesopause temperatures reach their extrema about 20 days after solstice, supporting the ice particle hypothesis of PMC. There was no indication of any influence of the location of the auroral oval on the spatial distribution of PMC.
Article
Triggered by recent experimental evidence showing that some parts of the Cho et al. [1992] theory describing electron diffusion in the vicinity of charged aerosol particles cannot be correct, we reconsider the process of electron diffusion under the conditions of the polar summer mesopause region. The key idea is that perturbations in the distribution of charged aerosol particles created for example by neutral air turbulence almost immediately lead to (anticorrelated) perturbations in the electron number density due to simple charge neutrality and zero net current arguments. We obtain analytical solutions of the coupled diffusion equations for electrons, charged aerosol particles, and positive ions subject to the initial condition of anticorrelated perturbations in the charged aerosol and electron distribution. The main signatures of these solutions are in line with available in situ evidence of small-scale plasma structures in the vicinity of polar mesosphere summer echoes (PMSE), i.e., electron perturbations are anticorrelated to both perturbations in the distributions of negatively charged aerosol particles and positive ions. The lifetime of these perturbations is proportional to the square of the aerosol particle radius such that the presence of particles with radii larger than ~10 nm allows for the existence of electron number density perturbations up to several hours after the initial creation mechanism has stopped. These results are almost independent of the ratio between the aerosol charge number density and the number density of free electrons. These electron perturbations potentially give rise to a radar reflectivity comparable to values observed with 50 MHz VHF radars. Our model results can readily explain why in situ measurements of neutral air turbulence have repeatedly shown active turbulence only in the upper part of the PMSE layer whereas turbulence was basically absent in the lower part. Furthermore, our model concept qualitatively yields the correct altitude profile of the mean PMSE occurrence frequency based on the measured altitude profile of the turbulence occurrence frequency.