[Show abstract][Hide abstract] ABSTRACT: The James Webb Space Telescope (JWST), scheduled for launch in 2018, is the
successor to the Hubble Space Telescope (HST) but with a significantly larger
aperture (6.5 m) and advanced instrumentation focusing on infrared science
(0.6-28.0 $\mu$m ). In this paper we examine the potential for scientific
investigation of Titan using JWST, primarily with three of the four
instruments: NIRSpec, NIRCam and MIRI, noting that science with NIRISS will be
complementary. Five core scientific themes are identified: (i) surface (ii)
tropospheric clouds (iii) tropospheric gases (iv) stratospheric composition and
(v) stratospheric hazes. We discuss each theme in depth, including the
scientific purpose, capabilities and limitations of the instrument suite, and
suggested observing schemes. We pay particular attention to saturation, which
is a problem for all three instruments, but may be alleviated for NIRCam
through use of selecting small sub-arrays of the detectors - sufficient to
encompass Titan, but with significantly faster read-out times. We find that
JWST has very significant potential for advancing Titan science, with a
spectral resolution exceeding the Cassini instrument suite at near-infrared
wavelengths, and a spatial resolution exceeding HST at the same wavelengths. In
particular, JWST will be valuable for time-domain monitoring of Titan, given a
five to ten year expected lifetime for the observatory, for example monitoring
the seasonal appearance of clouds. JWST observations in the post-Cassini period
will complement those of other large facilities such as HST, ALMA, SOFIA and
next-generation ground-based telescopes (TMT, GMT, EELT).
[Show abstract][Hide abstract] ABSTRACT: We compare the nitric oxide measurements in the mesosphere and lower thermosphere (60 to 150 km) from four instruments: the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS), the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY), and the Sub-Millimetre Radiometer (SMR). We use the daily zonal mean data in that altitude range for the years 2004-2010 (ACE-FTS), 2005-2012 (MIPAS), 2008-2012 (SCIAMACHY), and 2003-2012 (SMR).
We first compare the data qualitatively with respect to the morphology, focussing on the major features, and then compare the time series directly and quantitatively. In three geographical regions, we compare the vertical density profiles on coincident measurement days. Since none of the instruments delivers continuous daily measurements in this altitude region, we carried out a multi-linear regression analysis. This regression analysis considers annual and semi-annual variability in the form of harmonic terms and inter-annual variability by responding linearly to the solar Lyman-α radiation index and the geomagnetic Kp index. This analysis helps to find similarities and differences in the individual data sets with respect to the inter-annual variations caused by geomagnetic and solar variability.
We find that the data sets are consistent and that they only disagree on minor aspects. SMR and ACE-FTS deliver the longest time series in the mesosphere, and they agree with each other remarkably well. The shorter time series from MIPAS and SCIAMACHY also agree with them where they overlap. The data agree within 30 % when the number densities are large, but they can differ by 50 to 100 % in some cases.
[Show abstract][Hide abstract] ABSTRACT: The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are? In the past ten years, we have learned how to obtain the first spectra of exoplanets using transit transmission and emission spectroscopy. With the high stability of Spitzer, Hubble, and large ground-based telescopes the spectra of bright close-in massive planets can be obtained and species like water vapour, methane, carbon monoxide and dioxide have been detected. With transit science came the first tangible remote sensing of these planetary bodies and so one can start to extrapolate from what has been learnt from Solar System probes to what one might plan to learn about their faraway siblings. As we learn more about the atmospheres, surfaces and near-surfaces of these remote bodies, we will begin to build up a clearer picture of their construction, history and suitability for life. The Exoplanet Characterisation Observatory, EChO, will be the first dedicated mission to investigate the physics and chemistry of Exoplanetary Atmospheres. By characterising spectroscopically more bodies in different environments we will take detailed planetology out of the Solar System and into the Galaxy as a whole.
[Show abstract][Hide abstract] ABSTRACT: Carbon dioxide measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument between 2002 and 2014 were analyzed to reveal the rate of increase of CO2 in the mesosphere and lower thermosphere. The CO2 data show a trend of ~5% per decade at ~80 km and below, in good agreement with the tropospheric trend observed at Mauna Loa. Above 80 km, the SABER CO2 trend is larger than in the lower atmosphere, reaching ~12% per decade at 110 km. The large relative trend in the upper atmosphere is consistent with results from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). On the other hand, the CO2 trend deduced from the Whole Atmosphere Community Climate Model (WACCM) remains close to 5% everywhere. The spatial coverage of the SABER instrument allows us to analyze the CO2 trend as a function of latitude for the first time. The trend is larger in the northern hemisphere than in the southern hemisphere mesopause above 80 km. The agreement between SABER and ACE-FTS suggests that the rate of increase of CO2 in the upper atmosphere over the past 13 years is considerably larger than can be explained by chemistry-climate models.
Geophysical Research Letters 08/2015; 42(17). DOI:10.1002/2015GL064696 · 4.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The discovery of almost 2000 exoplanets has revealed an unexpectedly diverse
planet population. Observations to date have shown that our Solar System is
certainly not representative of the general population of planets in our Milky
Way. The key science questions that urgently need addressing are therefore:
What are exoplanets made of? Why are planets as they are? What causes the
exceptional diversity observed as compared to the Solar System?
EChO (Exoplanet Characterisation Observatory) has been designed as a
dedicated survey mission for transit and eclipse spectroscopy capable of
observing a large and diverse planet sample within its four-year mission
lifetime. EChO can target the atmospheres of super-Earths, Neptune-like, and
Jupiter-like planets, in the very hot to temperate zones (planet temperatures
of 300K-3000K) of F to M-type host stars. Over the next ten years, several new
ground- and space-based transit surveys will come on-line (e.g. NGTS, CHEOPS,
TESS, PLATO), which will specifically focus on finding bright, nearby systems.
The current rapid rate of discovery would allow the target list to be further
optimised in the years prior to EChO's launch and enable the atmospheric
characterisation of hundreds of planets. Placing the satellite at L2 provides a
cold and stable thermal environment, as well as a large field of regard to
allow efficient time-critical observation of targets randomly distributed over
the sky. A 1m class telescope is sufficiently large to achieve the necessary
spectro-photometric precision. The spectral coverage (0.5-11 micron, goal 16
micron) and SNR to be achieved by EChO, thanks to its high stability and
dedicated design, would enable a very accurate measurement of the atmospheric
composition and structure of hundreds of exoplanets.
[Show abstract][Hide abstract] ABSTRACT: We present vM21 MIPAS temperatures from the lower stratosphere to the lower thermosphere, which cover all optimized resolution measurements performed by MIPAS in the middle-atmosphere, upper-atmosphere and noctilucent-cloud modes during its lifetime, i.e., from January 2005 to April 2012. The main upgrades with respect to the previous version of MIPAS temperatures (vM11) are the update of the spectroscopic database, the use of a different climatology of atomic oxygen and carbon dioxide, and the improvement in important technical aspects of the retrieval setup (temperature gradient along the line of sight and offset regularizations, apodization accuracy). Additionally, an updated version of ESA-calibrated L1b spectra (5.02/5.06) is used. The vM21 temperatures correct the main systematic errors of the previous version because they provide on average a 1-2K warmer stratopause and middle mesosphere, and a 6-10K colder mesopause (except in high-latitude summers) and lower thermosphere. These lead to a remarkable improvement in MIPAS comparisons with ACE-FTS, MLS, OSIRIS, SABER, SOFIE and the two Rayleigh lidars at Mauna Loa and Table Mountain, which, with a few specific exceptions, typically exhibit differences smaller than 1K below 50 km and than 2K at 50-80 km in spring, autumn and winter at all latitudes, and summer at low to midlatitudes. Differences in the high-latitude summers are typically smaller than 1K below 50 km, smaller than 2K at 50-65 km and 5K at 65-80 km. Differences between MIPAS and the other instruments in the mid-mesosphere are generally negative. MIPAS mesopause is within 4K of the other instruments measurements, except in the high-latitude summers, when it is within 5-10 K, being warmer there than SABER, MLS and OSIRIS and colder than ACE-FTS and SOFIE. The agreement in the lower thermosphere is typically better than 5 K, except for high latitudes during spring and summer, when MIPAS usually exhibits larger vertical gradients.
[Show abstract][Hide abstract] ABSTRACT: We use NO, NO2 and CO from MIPAS/ENVISAT to investigate the impact of energetic particle precipitation onto the NOx budget from the stratosphere to the lower mesosphere in the period from October 2003 to March 2004, a time of high solar and geomagnetic activity. We find that in the winter hemisphere the indirect effect of auroral electron precipitation due to downwelling of upper mesospheric/lower thermospheric air into the stratosphere prevails. Its effect exceeds even the direct impact of the very large solar proton event in October/November 2003 by nearly one order of magnitude. Correlations of NOx and CO show that the unprecedented high NOx values observed in the Northern Hemisphere lower mesosphere and upper stratosphere in late January and early February are fully consistent with transport from the upper mesosphere/lower thermosphere and subsequent mixing at lower altitudes; an additional source of NOx due to local production by precipitating electrons at altitudes below 70 km as discussed in previous publications appears unlikely. In the polar summer Southern Hemisphere, we observed an enhanced variability of NO and NO2 on days with enhanced geomagnetic activity but they seem to indicate enhanced instrument noise rather than a direct increase due to electron precipitation. A direct effect of electron precipitation onto NOx can not be ruled out, but if any, it is lower than 3 ppb in the altitude range 40-56 km and lower than 6 ppb in the altitude range 56-70 km.
[Show abstract][Hide abstract] ABSTRACT:  In this paper, observations by thermosphere, ionosphere, mesosphere energetics and dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry from 2002 to 2012 and by Envisat/Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) from 2008 to 2009 are used to study the longitudinal structure of temperature in the lower thermosphere. In order to remove the longitudinal structure induced by tides, diurnally averaged SABER temperatures are used. For MIPAS data, we use averaged temperatures between day and night. The satellite observations show that there are strong longitudinal variations in temperature in the high-latitude lower thermosphere that persist over all seasons. The peak of the diurnally averaged temperature in the lower thermosphere always occurs around the auroral zone. A clear asymmetry between the two hemispheres in the longitudinal temperature structure is observed, being more pronounced in the Southern than in the Northern Hemisphere. In both hemispheres, the longitudinal variation is dominated by the first harmonic in longitude. The total radiative cooling observed by SABER has a structure in longitude that is similar to that of temperature. Modeling simulations using the Thermosphere-Ionosphere-Electrodynamics General Circulation Model reproduce similar features of the longitudinal variations of temperature in the lower thermosphere. Comparison of two model runs with and without auroral heating confirms that auroral heating causes the observed longitudinal variations. The multiyear averaged vertical structures of temperature observed by the two satellite instruments indicate that the impact of auroral heating on the thermodynamics of the neutral atmosphere can penetrate down to about 105 km.
Journal of Geophysical Research: Space Physics 11/2013; 118(11). DOI:10.1002/2013JA019144 · 3.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) instrument on the Envisat (Environmental satellite) satellite has provided vertical profiles of the atmospheric composition on a global scale for almost ten years. The MIPAS mission is divided in two phases: the full resolution phase, from 2002 to 2004, and the optimized resolution phase, from 2005 to 2012, which is characterized by a finer vertical and horizontal sampling attained through a reduction of the spectral resolution.
While the description and characterization of the products of the ESA processor for the full resolution phase has been already described in previous papers, in this paper we focus on the performances of the latest version of the ESA (European Space Agency) processor, named ML2PP V6 (MIPAS Level 2 Prototype Processor), which has been used for reprocessing the entire mission. The ESA processor had to perform the operational near real time analysis of the observations and its products needed to be available for data assimilation. Therefore, it has been designed for fast, continuous and automated analysis of observations made in quite different atmospheric conditions and for a minimum use of external constraints in order to avoid biases in the products.
The dense vertical sampling of the measurements adopted in the second phase of the MIPAS mission resulted in sampling intervals finer than the instantaneous field of view of the instrument. Together with the choice of a retrieval grid aligned with the vertical sampling of the measurements, this made ill-conditioned the retrieval problem of the MIPAS operational processor. This problem has been handled with minimal changes to the original retrieval approach but with significant improvements nonetheless. The Levenberg-Marquardt method, already present in the retrieval scheme for its capability to provide fast convergence for nonlinear problems, is now also exploited for the reduction of the ill-conditioning of the inversion. An expression specifically designed for the regularizing Levenberg-Marquardt method has been implemented for the computation of the covariance matrices and averaging kernels of the retrieved products. The regularization of the Levenberg-Marquardt method is controlled by the convergence criteria and is deliberately kept weak. The resulting oscillations of the retrieved profile are a posteriori damped by an innovative self-adapting Tikhonov regularization. The convergence criteria and the weakness of the self-adapting regularization ensure that minimum constraints are used and the best vertical resolution obtainable from the measurements is achieved in all atmospheric conditions.
Random and systematic errors, as well as vertical and horizontal resolution are compared in the two phases of the mission for all products, namely: temperature, H2O, O3, HNO3, CH4, N2O, NO2, CFC-11, CFC-12, N2O5 and ClONO2. The use in the two phases of the mission of different optimized sets of spectral intervals ensures that, despite the different spectral resolutions, comparable performances are obtained in the whole MIPAS mission in terms of random and systematic errors, while the vertical resolution and the horizontal resolution are significantly better in the case of the optimized resolution measurements.
[Show abstract][Hide abstract] ABSTRACT: Observations of Titan atmosphere made with the VIMS instrument on board
the Cassini satellite show a strong limb emission around 3.3 μm at
high atmospheric altitudes (above 700 km). This emission exhibits the
spectral signatures of the strong CH4 bands. A detailed analysis of the
spectra reveals an additional strong emission centered at 3.28 μm and
peaking at about 950 km. Here we present an analysis of this residual
spectra and show that it attributed to emission from heavy aromatic
[Show abstract][Hide abstract] ABSTRACT: The recent 23-30 January and 7-11 March 2012 solar proton event (SPE)
periods were substantial and caused significant impacts on the middle
atmosphere. These were the two largest SPE periods of solar cycle 24 so
far. The highly energetic solar protons produced considerable ionization
of the neutral atmosphere as well as HOx (H, OH,
HO2) and NOx (N, NO, NO2). We compute a
NOx production of 1.9 and 2.1 Gigamoles due to these SPE
periods in January and March 2012, respectively, which places these SPE
periods among the 12 largest in the past 50 yr. Aura Microwave Limb
Sounder (MLS) observations of the peroxy radical, HO2, show
significant enhancements of > 0.9 ppbv in the northern polar
mesosphere as a result of these SPE periods. Both MLS measurements and
Goddard Space Flight Center (GSFC) two-dimensional (2-D) model
predictions indicated middle mesospheric ozone decreases of > 20% for
several days in the northern polar region with maximum depletions >
60% over 1-2 days as a result of the HOx produced in both the
January and March 2012 SPE periods. The SCISAT-1 Atmospheric Chemistry
Experiment Fourier Transform Spectrometer (ACE) and the Envisat
Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)
instruments measured NO and NO2 (~ NOx), which
indicated enhancements of over 20 ppbv in most of the northern polar
mesosphere for several days as a result of these SPE periods. The GSFC
2-D model was used to predict the medium-term (~ months) influence and
showed that the polar middle atmosphere ozone was most affected by these
solar events in the Southern Hemisphere due to the increased downward
motion in the fall and early winter. The downward transport moved the
SPE-produced NOy to lower altitudes and led to predicted
modest destruction of ozone (5-9%) in the upper stratosphere days to
weeks after the March 2012 event. Total ozone reductions were predicted
to be a maximum of 1% in 2012 due to these SPEs.
[Show abstract][Hide abstract] ABSTRACT: The wavelength range probed by SOIR allows a detailed chemical inventory
of the Venus atmosphere at the terminator in the upper mesosphere and
lower thermosphere (70 to 170 km) with an emphasis on vertical
distribution of the gases. In particular, measurements of CO2 density
vertical profiles have been routinely performed. From these density
measurements, kinetic temperature profiles are derived using the
hydrostatic equilibrium. A permanent cold layer is observed at the
mesopause (± 120 km).
A different and independent method is developed here, making use of the
information obtained from the rotational structure of the CO2 bands to
derive rotational temperature profiles. The rotational temperature
profiles are compared to the hydrostatic temperature profiles, and they
confirm the presence of the cold layer at the mesopause.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we analyze the strong unidentified emission near 3.28 μm in Titan’s upper daytime atmosphere recently discovered by Dinelli et al.We have studied it by using the NASA Ames PAH IR Spectroscopic Database. The polycyclic aromatic hydrocarbons (PAHs), after absorbing UV solar radiation, are able to emit strongly near 3.3 μm. By using current models for the redistribution of the absorbed UV energy, we have explained the observed spectral feature and have derived the vertical distribution of PAH abundances in Titan’s upper atmosphere. PAHs have been found to be present in large concentrations, about (2–3) × 104 particles cm−3. The identified PAHs have 9–96 carbons, with a concentration-weighted average of 34 carbons. The mean mass is ∼430 u; the mean area is about 0.53 nm2; they are formed by 10–11 rings on average, and about one-third of them contain nitrogen atoms. Recently, benzene together with light aromatic species as well as small concentrations of heavy positive and negative ions have been detected in Titan’s upper atmosphere. We suggest that the large concentrations of PAHs found here are the neutral counterpart of those positive and negative ions, which hence supports the theory that the origin of Titan main haze layer is located in the upper atmosphere.
The Astrophysical Journal 06/2013; 770:132. DOI:10.1088/0004-637X/770/2/132 · 5.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT:  Ozone profiles in the upper mesosphere (70–100 km) retrieved from nine instruments are compared. Ozone from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument is used as the basis of comparison. Other measurements are from the Halogen Occultation Experiment, the High Resolution Doppler Imager, the Michelson Interferometer for Passive Atmospheric Sounding, the Global Ozone Monitoring by Occultation of Stars, the Atmospheric Chemistry Experiment—Fourier Transform Spectrometer, the Solar Occultation For Ice Experiment, the Optical Spectrograph and InfraRed Imaging System, and the Superconducting Submillimeter-Wave Limb-Emission Sounder. Comparisons of each data set with SABER using coincident profiles indicate agreement in the basic vertical profile of ozone but also some systematic differences in daytime ozone. Ozone from the SABER 9.6 μm channel is higher than the other measurements over the altitude range 60–80 km by 20–50%. Nighttime comparisons indicate better relative agreement (<10% difference). Taking all the data, not limited to coincidences, shows the global and seasonal distributions of ozone in the upper mesosphere from each instrument. The average maximum in ozone mixing ratio is around 90–92 km during daytime and 95 km at night. There is a maximum in ozone density at night (∼90 km) and during some hours of the day. The latitude structure of ozone has appreciable variations with season, particularly in the tropical upper mesosphere. The basic latitude-altitude structure of ozone depends on local time, even when the analysis is restricted to day-only observations.
Journal of Geophysical Research Atmospheres 06/2013; DOI:10.1002/jgrd.50445 · 3.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: During the solar proton events (SPE) on 23-30 January and 7-15 March
2012, the Michelson Interferometer for Passive Atmospheric Sounding
(MIPAS) on Envisat monitored atmospheric temperature and composition
with global coverage. In the Northern Hemisphere, the January SPE
started at the end of a polar stratospheric warming period. The SPE
effect is superimposed by large-scale subsidence of mesospheric
NOx-rich air, which partly masks direct chemical SPE effects.
SPE-induced NOx increases by 5, 20, 50, and 100 ppbv at
altitudes of 50, 57, 60, and 70 km, respectively, are observed during
the January SPE and those by 2, 5, 10, 20, 30, and 35 ppbv at altitudes
of 47, 50, 53, 60, 63, and 66 km, respectively, during the March SPE.
SPE-related ozone loss is clearly observed in the mesosphere,
particularly in the tertiary ozone maximum. A sudden short-term
HNO4 increase immediately after the January SPE hints at
SPE-triggered HOx chemistry. In the Southern Hemisphere, a
large NOx response is observed (increases by 2, 5, 10, 20,
and 30 ppbv at 52, 56, 59, 63, and 70 km in January and by 2, 5, 10, 20,
30, and 35 ppbv at 47, 50, 53, 60, 63, and 66 km in March), while the
effect on other species seems much less pronounced than in the Northern
Hemisphere. SPE-related destruction of mesospheric ozone in the Southern
Hemisphere was much more pronounced after the March SPE than the January
SPE but in both cases, ozone recovered within about a day.
Geophysical Research Letters 05/2013; 40(10):2339-2343. DOI:10.1002/grl.50119 · 4.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have analyzed limb daytime observations of Titan's upper atmosphere at 3.3 μm, acquired by the visual-infrared mapping spectrometer (VIMS) on Cassini. They were previously studied by García-Comas et al. (2011) to derive CH4 densities. Here, we report an unidentified emission peaking around 3.28 μm, hidden under the methane R branch. This emission is very strong, with intensity comparable to the CH4 bands located in the same spectral region. It presents a maximum at about 950 km and extends from 600 km up to 1250 km. It is definitely pumped by solar radiation since it vanishes at night. Our analysis shows that neither methane nor the major hydrocarbon compounds already discovered in Titan's upper atmosphere are responsible for it. We have discarded many other potential candidates and suggest that the unidentified emission might be caused by aromatic compounds.
Geophysical Research Letters 04/2013; 40(8):1489. DOI:10.1002/grl.50332 · 4.20 Impact Factor