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Abstract

Between November 1999 and April 2000, two major field experiments, the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment (SOLVE) and the Third European Stratospheric Experiment on Ozone (THESEO 2000), collaborated to form the largest field campaign yet mounted to study Arctic ozone loss. This international campaign involved more than 500 scientists from over 20 countries. These scientists made measurements across the high and middle latitudes of the Northern Hemisphere. The main scientific aims of SOLVE/THESEO 2000 were to study (1) the processes leading to ozone loss in the Arctic vortex and (2) the effect on ozone amounts over northern midlatitudes. The campaign included satellites, research balloons, six aircraft, ground stations, and scores of ozonesondes. Campaign activities were principally conducted in three intensive measurement phases centered on early December 1999, late January 2000, and early March 2000. Observations made during the campaign showed that temperatures were below normal in the polar lower stratosphere over the course of the 1999-2000 winter. Because of these low temperatures, extensive polar stratospheric clouds (PSC) formed across the Arctic. Large particles containing nitric acid trihydrate were observed for the first time, showing that denitrification can occur without the formation of ice particles. Heterogeneous chemical reactions on the surfaces of the PSC particles produced high levels of reactive chlorine within the polar vortex by early January. This reactive chlorine catalytically destroyed about 60% of the ozone in a layer near 20 km between late January and mid-March 2000, with good agreement being found between a number of empirical and modeling studies. The measurements made during SOLVE/THESEO 2000 have improved our understanding of key photochemical parameters and the evolution of ozone-destroying forms of chlorine.
... As a check on the loss rates indicated by the trajectory mapping approach, we again examine the integrated loss over the period of 20 January-12 March. The trajectory mapping approach results in a change of −0.5±0.2 ppmv of ozone, a result that is clearly low compared to the ozone losses for this period shown in Table 8 of Newman et al. (2002) as well as the results we found in our version of Match (−1.3±0.2 ppmv over the same period). While such comparisons are disappointing, they suggest that the uncertainties associated with TM Match may still be too small. ...
... When integrating our results for the SOLVE/THESEO 2000 campaign, we find good agreement for the accumulated ozone loss over the January to March period with other studies shown in Newman et al. (2002). Our version of Match yields an integrated ozone loss of 1.3±0.2 ...
... Newman et al. (2002) published a summary of results for integrated ozone loss during the SOLVE/THESEO 2000 campaign on the 450 K potential temperature surface. Their Ta-Same asFig. ...
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We apply the NASA Goddard Trajectory Model to data from a series of ozonesondes to derive ozone loss rates in the lower stratosphere for the AASE-2/EASOE mis- sion (January-March 1992) and for the SOLVE/THESEO 2000 mission (January-March 2000) in an approach simi- lar to Match. Ozone loss rates are computed by comparing the ozone concentrations provided by ozonesondes launched at the beginning and end of the trajectories connecting the launches. We investigate the sensitivity of the Match results to the various parameters used to reject potential matches in the original Match technique. While these filters effectively eliminate from consideration 80% of the matched sonde pairs and >99% of matched observations in our study, we con- clude that only a filter based on potential vorticity changes along the calculated back trajectories seems warranted. Our study also demonstrates that the ozone loss rates estimated in Match can vary by up to a factor of two depending upon the precise trajectory paths calculated for each trajectory. As a result, the statistical uncertainties published with previous Match results might need to be augmented by an additional systematic error. The sensitivity to the trajectory path is par- ticularly pronounced in the month of January, for which the largest ozone loss rate discrepancies between photochemical models and Match are found. For most of the two study peri- ods, our ozone loss rates agree with those previously pub- lished. Notable exceptions are found for January 1992 at 475 K and late February/early March 2000 at 450 K, both pe- riods during which we generally find smaller loss rates than the previous Match studies. Integrated ozone loss rates es- timated by Match in both of those years compare well with those found in numerous other studies and in a potential vor- ticity/potential temperature approach shown previously and in this paper. Finally, we suggest an alternate approach to Match using trajectory mapping. This approach uses infor-
... lower stratospheric ozone over the United States in summer builds on four decades of developments linking chlorine and bromine radicals to ozone loss in the polar regions (e.g., refs. [32][33][34][35][36][37][38][39][40][41][42][43], ozone depletion at midlatitudes resulting from the coupling of volcanic aerosols and temperature variability to anthropogenic chlorine and bromine (8,10,11,44), and analyses of the consequences from sulfate addition to the stratosphere from geoengineering via SRM (15)(16)(17)(18). Finally, although detailed simultaneous observations of the key catalytic free radicals, reactive intermediates, and ozone loss rates have been thoroughly investigated in the stratosphere over the Antarctic and Arctic in winter, the same is not the case for the stratosphere over the United States in summer. ...
... Studies of catalytic ozone loss in the lower stratosphere at high latitudes established the network of catalytic reactions linking inorganic chlorine to the rate of ozone loss in the lower stratosphere. Simultaneous in situ aircraft observations of ClO, BrO, ClOOCl, ClONO 2 , HCl, OH, HO 2 , NO 2 , particle surface area, H 2 O, and O 3 in the transition through the boundary of the Arctic vortex (38)(39)(40)(41)(42) showed explicitly the loss of ozone as well as the distinct anticorrelation between the concentration of the rate-limiting radical ClO and the ozone concentration. It is the chlorine monoxide radical, ClO, in combination with the rate-limiting step ClO + ClO + M → ClOOCl + M in the catalytic cycle first introduced by Molina and Molina (34) and the catalytic cycle rate limited by ClO + BrO → Cl + Br + O 2 first introduced by McElroy et al. (35) that constitute the reaction mechanisms capable of removing ozone over the polar regions in winter at the observed rates (36,41,42). ...
Article
Significance Stratospheric ozone is one of the most delicate aspects of habitability on the planet. Removal of stratospheric ozone over the polar regions in winter/spring has established the vulnerability of ozone to halogen catalytic cycles. Elevated ClO concentrations engendered, in part, by heterogeneous catalytic conversion of inorganic chlorine to free radical form on ubiquitous sulfate−water aerosols, govern the rate of ozone removal. We report here observations of the frequency and depth of penetration of convectively injected water vapor into the stratosphere, triggered by severe storms that are specific to the central United States in summer, and model their effect on lower stratospheric ozone. This effect implies, with observed temperatures, increased risk of ozone loss over the Great Plains in summer.
... To address remaining questions on chemistry and transport processes in the Arctic upper tropospherelowermost stratosphere under the present load of ozone-depleting substances and state of climate variables, the POLSTRACC campaign was conducted in the Arctic winter 2015/16, several years after past intensive Arctic campaigns [e.g., SOLVE/THESEO-2000(Newman et al. 2002), EUPLEX/SOLVE-II in 2002/03, RECONCILE in 2009/10 (von Hobe et al. 2013]. By deploying the German High Altitude and Long Range Research Aircraft (HALO), POLSTRACC was designed to study the Arctic UTLMS along with its coupling with lower latitudes throughout an entire winter-spring cycle, with the following specific scientific objectives (see also Fig. 1): 1) investigate the structure, composition, and dynamics of the bottom of the polar vortex and its coupling with the upper troposphere and extravortex air masses, to quantify transport and mixing, and to identify the role of special events such as tropopause folds and polar lows; 2) study polar stratospheric clouds and highaltitude cirrus in the UTLMS in Arctic winter and spring; 3) examine the vertical redistribution of HNO 3 by PSCs and underlying processes; 4) investigate chlorine activation/deactivation in the Arctic LMS and assess the role of bromine compounds; and 5) quantify ozone loss in the LMS. ...
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POLSTRACC (Polar Stratosphere in a Changing Climate) employed the German High Altitude and Long Range research aircraft (HALO). The payload comprised an innovative combination of remote sensing and in-situ instruments. The in-situ instruments provided high-resolution observations of cirrus and polar stratospheric clouds (PSCs), a large number of reactive and long-lived trace gases, as well as temperature at the aircraft level. Information above and underneath the aircraft level was achieved by remote sensing instruments as well as dropsondes. The mission took place from 8 December 2015 to 18 March 2016 covering the extremely cold late December to early February period and the time around the major warming in the beginning of March. In 18 scientific deployments, 156 flight hours were conducted, covering latitudes from 25°N to 87°N, maximum altitudes of almost 15 km, and reaching potential temperature levels of up to 410 K.
... Stratospheric particles were sampled on board of the NASA ER-2 aircraft during the SAGE III Ozone loss and validation experiment (SOLVE), which was conducted in January-March 2000 in Kiruna (Sweden). The Multi-Sample Aerosol Newman et al. (2002). b During sampling. ...
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Eleven particle samples collected in the polar stratosphere during SOLVE (SAGE III Ozone loss and validation experiment) from January until March 2000 were characterized in detail by high-resolution transmission and scanning electron microscopy (TEM/SEM) combined with energy-dispersive X-ray microanalysis. A total of 4202 particles (TEM = 3872; SEM = 330) were analyzed from these samples, which were collected mostly inside the polar vortex in the altitude range between 17.3 and 19.9 km. Particles that were volatile in the microscope beams contained ammonium sulfates and hydrogen sulfates and dominated the samples. Some particles with diameters ranging from 20 to 830 nm were refractory in the electron beams. Carbonaceous particles containing additional elements to C and O comprised from 72 to 100 % of the refractory particles. The rest were internal mixtures of these materials with sulfates. The median number mixing ratio of the refractory particles, expressed in units of particles per milligram of air, was 1.1 (mg air)⁻¹ and varied between 0.65 and 2.3 (mg air)⁻¹. Most of the refractory carbonaceous particles are completely amorphous, a few of the particles are partly ordered with a graphene sheet separation distance of 0.37 ± 0.06 nm (mean value ± standard deviation). Carbon and oxygen are the only detected major elements with an atomic O∕C ratio of 0.11 ± 0.07. Minor elements observed include Si, S, Fe, Cr and Ni with the following atomic ratios relative to C: Si∕C: 0.010 ± 0.011; S∕C: 0.0007 ± 0.0015; Fe∕C: 0.0052 ± 0.0074; Cr∕C: 0.0012 ± 0.0017; Ni∕C: 0.0006 ± 0.0011 (all mean values ± standard deviation).High-resolution element distribution images reveal that the minor elements are distributed within the carbonaceous matrix; i.e., heterogeneous inclusions are not observed. No difference in size, nanostructure and elemental composition was found between particles collected inside and outside the polar vortex. Based on chemistry and nanostructure, aircraft exhaust, volcanic emissions and biomass burning can certainly be excluded as sources. The same is true for the less probable but globally important sources: wood burning, coal burning, diesel engines and ship emissions. Recondensed organic matter and extraterrestrial particles, potentially originating from ablation and fragmentation, remain as possible sources of the refractory carbonaceous particles studied. However, additional work is required in order to identify the sources unequivocally.
... Data from these flights have been studied extensively by Hu et al. (2002) and Fueglistaler et al. (2003). A summary of the SOLVE/THESEO 2000 campaign can be found in Newman et al. (2002). A description of the lidar system used for the measurements can be found in Browell (1989) and Browell et al. (1990). ...
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: A scheme for introducing mountain wave-induced temperature perturbations in a microphysical polar stratospheric cloud (PSC) model has been developed. A data set of temperature fluctuations attributable to mountain waves as computed by the Mountain Wave Forecast Model (MWFM-2) has been used for the study. The PSC model has variable microphysics, enabling different nucleation mechanisms for nitric acid trihydrate, NAT, to be employed. In particular, the difference between the formation of NAT and ice particles in a scenario where NAT formation is not dependent on preexisting ice particles, allowing NAT to form at temperatures above the ice frost point, T(sub ice), and a scenario where NAT nucleation is dependent on preexisting ice particles, is examined. The performance of the microphysical model in the different microphysical scenarios and a number of temperature scenarios with and without the influence of mountain waves is tested through comparisons with lidar measurements of PSCs made from the NASA DC-8 on 23 and 25 January during the SOLVE/THESEO 2000 campaign in the 1999-2000 winter and the effect of mountain waves on local PSC production is evaluated in the different microphysical scenarios. Mountain waves are seen to have a pronounced effect on the amount of ice particles formed in the simulations. Quantitative comparisons of the amount of solids seen in the observations and the amount of solids produced in the simulations show the best correspondence when NAT formation is allowed to take place at temperatures above T(sub ice). Mountain wave-induced temperature fluctuations are introduced in vortex-covering model runs, extending the full 1999-2000 winter season, and the effect of mountain waves on large-scale PSC production is estimated in the different microphysical scenarios. Regardless of the choice of microphysics, the inclusion of mountain waves increases the amount of NAT particles by as much as 10%.
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During winter 2015/2016, the Arctic stratosphere was characterized by extraordinarily low temperatures in connection with a very strong polar vortex and with the occurrence of extensive polar stratospheric clouds. From mid-December 2015 until mid-March 2016, the German research aircraft HALO (High Altitude and Long-Range Research Aircraft) was deployed to probe the lowermost stratosphere in the Arctic region within the POLSTRACC (Polar Stratosphere in a Changing Climate) mission. More than 20 flights have been conducted out of Kiruna, Sweden, and Oberpfaffenhofen, Germany, covering the whole winter period. Besides total reactive nitrogen (NOy), observations of nitrous oxide, nitric acid, ozone, and water were used for this study. Total reactive nitrogen and its partitioning between the gas and particle phases are key parameters for understanding processes controlling the ozone budget in the polar winter stratosphere. The vertical redistribution of total reactive nitrogen was evaluated by using tracer–tracer correlations (NOy–N2O and NOy–O3). The trace gases are well correlated as long as the NOy distribution is controlled by its gas-phase production from N2O. Deviations of the observed NOy from this correlation indicate the influence of heterogeneous processes. In early winter no such deviations have been observed. In January, however, air masses with extensive nitrification were encountered at altitudes between 12 and 15 km. The excess NOy amounted to about 6 ppb. During several flights, along with gas-phase nitrification, indications for extensive occurrence of nitric acid containing particles at flight altitude were found. These observations support the assumption of sedimentation and subsequent evaporation of nitric acid-containing particles, leading to redistribution of total reactive nitrogen at lower altitudes. Remnants of nitrified air masses have been observed until mid-March. Between the end of February and mid-March, denitrified air masses have also been observed in connection with high potential temperatures. This indicates the downward transport of air masses that have been denitrified during the earlier winter phase. Using tracer–tracer correlations, missing total reactive nitrogen was estimated to amount to 6 ppb. Further, indications of transport and mixing of these processed air masses outside the vortex have been found, contributing to the chemical budget of the winter lowermost stratosphere. Observations within POLSTRACC, at the bottom of the vortex, reflect heterogeneous processes from the overlying Arctic winter stratosphere. The comparison of the observations with CLaMS model simulations confirm and complete the picture arising from the present measurements. The simulations confirm that the ensemble of all observations is representative of the vortex-wide vertical NOy redistribution.
Chapter
Polar ozone depletion is a major environmental issue, for the alterations induced on the chemical-physical equilibrium of the stratosphere and their impact on planetary climate and ecosystem.
Chapter
The Arctic atmosphere is coupled to lower latitudes, both as a receptor for global pollution and as a driver for the global climate system. Arctic atmospheric composition is variable and changing, making measurements of trace gas concentrations essential for understanding atmospheric processes.
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We present the chain of mechanisms linking free radical catalytic loss of stratospheric ozone, specifically over the central United States in summer, to increased climate forcing by CO2 and CH4 from fossil fuel use. This case directly engages detailed knowledge, emerging from in situ aircraft observations over the polar regions in winter, defining the temperature and water vapor dependence of the kinetics of heterogeneous catalytic conversion of inorganic chlorine (HCl and ClONO2) to free radical form (ClO). Analysis is placed in the context of irreversible changes to specific subsystems of the climate, most notably coupled feedbacks that link rapid changes in the Arctic with the discovery that convective storms over the central US in summer both suppress temperatures and inject water vapor deep into the stratosphere. This places the lower stratosphere over the US in summer within the same photochemical catalytic domain as the lower stratosphere of the Arctic in winter engaging the risk of amplifying the rate limiting step in the ClO dimer catalytic mechanism by some six orders of magnitude. This transitions the catalytic loss rate of ozone in lower stratosphere over the United States in summer from HOx radical control to ClOx radical control, increasing the overall ozone loss rate by some two orders of magnitude over that of the unperturbed state. Thus we address, through a combination of observations and modeling, the mechanistic foundation defining why stratospheric ozone, vulnerable to increased climate forcing, is one of the most delicate aspects of habitability on the planet.
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Eleven particle samples collected in the polar stratosphere during SOLVE (SAGE III Ozone loss and validation experiment) from January until March 2000 were characterized in detail by high-resolution transmission and scanning electron microscopy (TEM/SEM) combined with energy-dispersive X-ray microanalysis. A total number of 4175 particles (TEM = 3845; SEM = 330) was analyzed from these samples which were collected mostly inside the polar vortex in the altitude range between 17.3 and 19.9 km. By particle volume, all samples are dominated by volatile particles (ammonium sulfates/hydrogen sulfates). By number, approximately 28–82 % of the particles are refractory carbonaceous with sizes between 20–830 nm. Internal mixtures of refractory carbonaceous and volatile particles comprise up to 16 %, individual volatile particles about 9 to 72 %. Most of the refractory carbonaceous particles are completely amorphous, a few of the particles are partly ordered with a graphene sheet separation distance of 0.37 ± 0.06 nm (mean value ± standard deviation). Carbon and oxygen are the only detected major elements with an atomic O / C ratio of 0.11 ± 0.07. Minor elements observed include Si, S, Fe, Cr and Ni with the following atomic ratios relative to C: Si / C: 0.010 ± 0.011; S / C: 0.0007 ± 0.0015; Fe / C: 0.0052 ± 0.0074; Cr / C: 0.0012 ± 0.0017; Ni / C: 0.0006 ± 0.0011 (all mean values ± standard deviation). High resolution element distribution images reveal that the minor elements are distributed within the carbonaceous matrix, i.e., heterogeneous inclusions are not observed. No difference in size, nanostructure and elemental composition was found between particles collected inside and outside the polar vortex. Based on chemistry and nanostructure, aircraft exhaust, volcanic emissions and biomass burning can certainly be excluded as source. The same is true for the less probable, but globally important sources: wood burning, coal burning, diesel engines and ship emissions. Rocket exhaust and carbonaceous material from interplanetary dust particles remain as possible sources of the refractory carbonaceous particles studied. However, additional work is required in order to identify the sources unequivocally.
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[1] We compared the version 5 Microwave Limb Sounder (MLS), version 3 Polar Ozone and Aerosol Measurement III (POAM III), version 6.0 Stratospheric Aerosol and Gas Experiment II (SAGE II), and NASA ER-2 aircraft measurements made in the Northern Hemisphere in January-February 2000 during the SAGE III Ozone Loss and Validation Experiment (SOLVE). This study addresses one of the key scientific objectives of the SOLVE campaign, namely, to validate multiplatform satellite measurements made in the polar stratosphere during winter. This intercomparison was performed by using a traditional correlative analysis (TCA) and a trajectory hunting technique (THT). TCA compares profiles colocated within a chosen spatial-temporal vicinity. Launching backward and forward trajectories from the points of measurement, the THT identifies air parcels sampled at least twice within a prescribed match criterion during the course of 5 days. We found that the ozone measurements made by these four instruments agree most of the time within +/-10% in the stratosphere up to 1400 K (similar to35 km). The water vapor measurements from POAM III and the ER-2 Harvard Lyman alpha hygrometer and Jet Propulsion Laboratory laser hygrometer agree to within +/-0.5 ppmv (or about +/-10%) in the lower stratosphere above 380 K. The MLS and ER-2 ClO measurements agree within their error bars for the TCA. The MLS and ER-2 nitric acid measurements near 17- to 20-km altitude agree within their uncertainties most of the time with a hint of a positive offset by MLS according to the TCA. We also applied the Atmospheric and Environmental Research, Inc. box model constrained by the ER-2 measurements for analysis of the ClO and HNO3 measurements using the THT. We found that: (1) the model values of ClO are smaller by about 0.3-0.4 (0.2) ppbv below (above) 400 K than those by MLS and (2) the HNO3 comparison shows a positive offset of MLS values by similar to1 and 1-2 ppbv below 400 K and near 450 K, respectively. Our study shows that, with some limitations (like HNO3 comparison under polar stratospheric cloud conditions), the THT is a more powerful tool for validation studies than the TCA, making conclusions of the comparison statistically more robust.
Article
The Microwave Limb Sounder (MLS) experiments obtain measurements of atmospheric composition, temperature, and pressure by observations of millimeter- and submillimeter-wavelength thermal emission as the instrument field of view is scanned through the atmospheric limb. Features of the measurement technique include the ability to measure many atmospheric gases as well as temperature and pressure, to obtain measurements even in the presence of dense aerosol and cirrus, and to provide near-global coverage on a daily basis at all times of day and night from an orbiting platform. The composition measurements are relatively insensitive to uncertainties in atmospheric temperature. An accurate spectroscopic database is available, and the instrument calibration is also very accurate and stable. The first MLS experiment in space, launched on the (NASA) Upper Atmosphere Research Satellite (UARS) in September 1991, was designed primarily to measure stratospheric profiles of ClO, O3, H2O, and atmospheric pressure as a vertical reference. Global measurement of ClO, the predominant radical in chlorine destruction of ozone, was an especially important objective of UARS MLS. All objectives of UARS MLS have been accomplished and additional geophysical products beyond those for which the experiment was designed have been obtained, including measurement of upper-tropospheric water vapor, which is important for climate change studies. A follow-on MLS experiment is being developed for NASA's Earth Observing System (EOS) and is scheduled to be launched on the EOS CHEMISTRY platform in late 2002. EOS MLS is designed for many stratospheric measurements, including HOx radicals, which could not be measured by UARS because adequate technology was not available, and better and more extensive upper-tropospheric and lower-stratospheric measurements.
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A form of potential vorticity is described that has conservation properties similar to those of Ertel's potential vorticity (EPV) but removes the exponential variation with height displayed by EPV. This form is thus more suitable for inspecting vertical cross sections of potential vorticity and for use (with potential temperature) as a quasi-conserved coordinate in the analysis of chemical constituent data.
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We present simultaneous in situ observations of OH, HO2, ClONO2, HCl, and particle surface area inside a polar stratospheric cloud undergoing rapid heterogeneous processing. A steady-state analysis constrained by in situ observations is used to show that concentrations of OH calculated during a processing event are extremely sensitive to the assumptions regarding aerosol composition and reactivity. This analysis shows that large perturbations in the abundance of OH are consistent with the heterogeneous production of HOCl via ClONO2 + H2O → HOCl + HNO3 and removal via HOCl + HCl → Cl2 + H2O in a polar stratospheric cloud. If the cloud is composed of supercooled ternary solution (STS) aerosols and solid nitric acid trihydrate (NAT) particles, comparison with observations of OH show that modifications to surface reactivity to account for high HNO3 content in STS aerosols and low HCl coverage on NAT particles are appropriate. These results indicate that with the low HCl levels in this encounter and in a processed polar vortex in general, reactions on STS aerosols dominate the total heterogeneous processing rate. As a consequence, the formation of NAT does not lead to significantly faster reprocessing rates when HCl concentrations are low and STS aerosols are present. Model calculations that include these modifications to uptake coefficients for STS and NAT will lead to significantly slower reprocessing and faster recovery rates of chlorine in the springtime Arctic polar vortex.
Article
The microwave limb sounder (MLS) on the Upper Atmosphere Research Satellite (UARS) is the first satellite experiment using limb sounding techniques at microwave frequencies. Primary measurement objectives are stratospheric ClO, O3, H2O, temperature, and pressure. Measurements are of thermal emission: all are performed simultaneously and continuously and are not degraded by ice clouds or volcanic aerosols. The instrument has a 1.6-m mechanically scanning antenna system and contains heterodyne radiometers in spectral bands centered near 63, 183, and 205 GHz. The radiometers operate at ambient temperature and use Schottky-diode mixers with local oscillators derived from phase-locked Gunn oscillators. Frequency tripling by varactor multipliers generates the 183- and 205-GHz local oscillators, and quasi-optical techniques inject these into the mixers. Six 15-channel filter banks spectrally resolve stratospheric thermal emission lines and produce an output spectrum every 2 s. Thermal stability is sufficient for “total power” measurements which do not require fast chopping. Radiometric calibration, consisting of measurements of cold space and an internal target, is performed every 65-s limb scan. Instrument in-orbit performance has been excellent, and all objectives are being met.
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The combined SAGE III Ozone Loss and Validation Experiment and Third European Stratospheric Experiment on Ozone 2000 (SOLVE/THESEO 2000) campaign during winter 1999/2000 sought, in part, to quantify ozone loss within the Arctic polar vortex using a variety of aircraft-, balloon-, ground-, and space-based instrument platforms. The Midcourse Space Experiment/Ultraviolet and Visible Imagers and Spectrographic Imagers (MSX/UVISI) suite of instruments performed 31 stellar occultation observations from 23 January through 4 March 2000 in and near the Arctic polar vortex. Using a newly developed combined extinctive-refractive algorithm, ozone mixing ratio profiles, along with profiles of total density, pressure, and temperature, were retrieved. Retrieved temperature and ozone profiles are shown to agree well with other measurements. Diabatic trajectory calculations are used to remove the effects of subsidence within the vortex, allowing photochemical ozone loss to be inferred from these occultation measurements. A maximum ozone loss of about 1 ppmv is found at 400-500 K (˜16-21 km) during the 41-day period for which occultation data are available, in agreement with several other ozone loss analyses of the campaign. This corresponds to an average daily loss rate of ˜0.024 ppmv/day. The combined extinctive-refractive stellar occultation technique is demonstrated to accurately measure stratospheric ozone loss during polar winter.
Article
Simulations of the development of the chemical composition of the Arctic stratosphere for spring 2000 are made with the Chemical Lagrangian Model of the Stratosphere (CLaMS). The simulations are performed for the entire Northern Hemisphere on four isentropic levels (400-475 K). The initialization in early February is based on observations made from satellite, balloon and ER-2 aircraft platforms. Tracer-tracer correlations from balloon-borne cryosampler (Triple) and ER-2 measurements, as well as tracer-PV correlations, are used to derive a comprehensive hemispherical initialization of all relevant chemical trace species. Since significant denitrification has been observed on the ER-2 flights, a parameterization of the denitrification is derived from NOy and N2O observations on board the ER-2 aircraft and the temperature history of the air masses under consideration. Over the simulation period from 10 February to 20 March, a chemical ozone depletion of up to 60% was derived for 425-450 K potential temperature. Maximum vortex-averaged chemical ozone loss rates of 50 ppb d-1 or 4 ppb per sunlight hour were simulated in early March 2000 at the 425 and 450 K potential temperature levels. We show comparisons between the measurements and the simulations for the location of the ER-2 flight paths in late February and March and the location of the Triple balloon flight. The simulated tracer mixing ratios are in good agreement with the measurements. It was not possible to reproduce the exact details of the inorganic chlorine compounds. The simulation agrees with ClOx observations on the Triple balloon flight but overestimates for the ER-2 flights. The simulated ozone depletion agrees with estimates from other observations in the 425 and 450 K levels, but is underestimated on the 475 K level.