11th International Limb Workshop

The 11th International Limb Workshop will take place on-line from May 10 – 13, 2021.

This year’s workshop is organized by National Aeronautics and Space Administration atmospheric science teams at JPL, LaRC, and GSFC. The emphasis of the workshop continues to be remote sensing limb measurements of the Earth and other bodies, but the organizers invite presentations on all topics related to the vertical structure and composition of the atmosphere. There are no fees associated with the workshop.

Dates and deadlines
Abstract submission deadline:March 15, 2021
First program release:April 5, 2021
Workshop:May 10 – 13, 2021
Workshop: May 10 – 13, 2021 View Details
MONDAY Session 1A
13:00 UTC (+10) Introduction & Logistics
  Missions & Instruments
Chairs: Thomas von Clarmann, Glen Jaross
13:10 UTC (+15) The Changing-Atmosphere Infra-Red Tomography Explorer CAIRT – a proposal for an innovative whole-atmosphere infra-red limb imaging satellite instrument

Björn-Martin Sinnhuber [1], Michael Höpfner [1], Felix Friedl-Vallon [1], Miriam Sinnhuber [1], Gabi Stiller [1], Thomas von Clarmann [1], Peter Preusse [2], Felix Plöger [2], Martin Riese [2], Jörn Ungermann [2], Martyn Chipperfield [3], Quentin Errera (4), Bernd Funke [5], Maya Garcia Comas [5], Manuel López Puertas [5], Sophie Godin-Beekmann [6], Vincent-Henri Peuch [7], Inna Polichtchouk [7], Piera Raspollini [8], Stefanie Riel [9], Kaley Walker [10]
  1. Karlsruhe Institute of Technology, Germany
  2. Forschungszentrum Jülich, Germany
  3. University of Leeds, UK
  4. Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Belgium
  5. Instituto de Astrofísica de Andalucía (CSIC), Spain
  6. LATMOS, National Centre for Scientific Research (CNRS), France
  7. European Centre for Medium-Range Weather Forecasts (ECMWF), UK
  8. Institute of Applied Physics ‘Nello Carrara’ of the National Research Council (IFAC-CNR), Italy
  9. Airbus Space & Defence, Germany
  10. University of Toronto, Canada
To improve our knowledge of the coupling of atmospheric circulation, composition and regional climate change, and to provide the urgently needed observations of the on-going changes and processes involved, we have recently proposed the Changing-Atmosphere Infra-Red Tomography Explorer (CAIRT) to ESA as Earth Explorer 11 candidate. CAIRT will be the first limb-sounder with imaging Fourier-transform infrared technology in space. By observing simultaneously the atmosphere from the troposphere to the lower thermosphere (about 5 to 115 km altitude), CAIRT will provide global observations of temperature, ozone, water vapour, as well as key halogen and nitrogen compounds. The latter will help to better constrain coupling with the upper atmosphere, solar variability and space weather. Observation of long-lived tracers (such as N2O, CH4, SF6, CF4) will provide information on transport, mixing and circulation changes. CAIRT will deliver essentially a complete budget of stratospheric sulfur (by observations of OCS, SO2, and H2SO4-aerosols), as well as observations of ammonia and ammonium nitrate aerosols. Biomass burning and other pollution plumes, and their impact on ozone chemistry in the UTLS region, will be detected from observations of HCN, CO and a further wealth of volatile organic compounds. The potential to measure water vapour isotopologues will help to constrain water vapour and cloud processes and interactions at the Earth’s surface. The high-resolution measurements of temperature will provide the momentum flux, phase speed and direction of atmospheric gravity waves. CAIRT thus will provide comprehensive information on the driving of the large-scale circulation by different types of waves. Tomographic retrievals will provide temperature and trace gas profiles at a much higher horizontal resolution and coverage than achieved from space so far. Flying in formation with the Second Generation Meteorological Operational Satellite (MetOp-SG) will enable combined retrievals with observations by the New Generation Infrared Atmospheric Sounding Interferometer (IASI-NG) and Sentinel-5, resulting in consistent atmospheric profile information from the surface up to the lower thermosphere. Our presentation will give an overview of the proposed CAIRT mission, its objectives and synergies with other sensors.
13:25 UTC (+20) The ALTIUS mission

Didier Fussen [1], Noel Baker [1], Antonin Berthelot [1], Emmanuel Dekemper [1], Philippe Demoulin [1], Quentin Errera [1], Ghislain Franssens [1], Nina Mateshvili [1], Nuno Pereira [1], Didier Pieroux [1], Sotiris Sotiriadis [1] Adam Bourassa [2], Doug Degenstein [2], Nicholas Lloyd [2], Daniel Zawada [2]
  1. Belgian Institute for Space Aeronomy (BISA), Belgium
  2. University of Saskatchewan, Canada
ALTIUS is an original, groundbreaking mission which answers pressing questions and needs within the atmospheric remote sounding community. The project was proposed by the Belgian Institute for Space Aeronomy (BISA) and it is presently implemented as an element of the ESA Earth Watch program. The data processing algorithms will be developed in a collaboration between BISA, the University of Saskatchewan and the industry. Ozone and aerosol stratospheric profiles are the main operational objectives of the mission. The truly innovative technology being developed through ALTIUS resides in the use of a high-performance microsatellite of the PROBA class that can operate in a multi-mode approach. Starting from a well-stabilized and controlled platform attitude, a single sensor can be optimized for a combination of limb scattering measurements and solar, stellar, and planetary occultations. The combination of an imager with an accurate attitude control allows for determining the tangent altitude by relating the instrument field of view to the satellite attitude. Moreover, occultation observations can also be carried out in inertial pointing without the need for an onboard tracking mechanism. Finally, the ALTIUS instrument bridges urgent and significant gaps that exist in the availability of long-term satellite measurements which are essential to the climate research community. The latest developments of the mission will be presented.
13:45 UTC (+20) The MATS satellite mission - tomography of gravity waves in the Earth’s mesosphere

Jörg Gumbel, Linda Megner, Ole Martin Christensen, Donal P. Murtagh, Nickolay Ivchenko, and the MATS Team
  1. Stockholm University, Sweden
The Swedish MATS satellite (Mesospheric Airglow/Aerosol Tomography and Spectroscopy) is to be launched into orbit in late summer 2021. This presentation provides an update on satellite preparation, retrieval methods and scientific goals. MATS applies space-borne limb imaging in combination with tomographic and spectroscopic analysis to study gravity waves and atmospheric structures over a wide range of spatial scales. Primary measurement targets are O2 Atmospheric Band airglow in the near infrared, and sunlight scattered from noctilucent clouds in the ultraviolet. While tomography provides horizontally and vertically resolved data, spectroscopy allows retrievals of mesospheric temperature, composition, and cloud properties. Based on these dynamical tracers, MATS will produce a climatology on wave spectra during a 2-year mission. Major scientific objectives concern a characterization of gravity waves and their interactions in the mesosphere, as well as their relationship to dynamical conditions in the lower and upper atmosphere.
14:00 UTC (+15) Keystone - An Upper Atmosphere Explorer Concept for ESA EE-11

Gerber, D., Plane, J., Luebken, F.-J., Espy, P., von Savigny, C., Marsh, D., Jackson, D., Murtagh, D., Rezac, L., Ellison, B., Valavanis, A., Bowles, N.
  1. Rutherford Appleton Laboratory, UK
Keystone is a concept for a future limb sounding mission for the upper mesosphere and thermosphere. The Keystone mission - which is an evolution of the ESA Earth Explorer 10 candidate mission LOCUS - is currently competing to become ESA's 11th Earth Explorer satellite. In its present from, Keystone comprises of three instruments: A Supra-THz radiometer, an infrared radiometer, and a UVIS spectrometer. The infrared radiometer with channels at 15um (CO2), 9.6um(O3), 5.3um(NO), and 4.3um(CO2), and the UVIS spectrometer from 230nm-780nm (O, O2, O3, O+, M/Mg+, Fe/Fe+, Temperature) are a continuation of upper atmospheric measurements like MIPAS, HiRDLS or SABER, and OSIRIS, SCIAMACHY, or ICON/GOLD. Keystone thus addresses the looming gap in upper atmospheric measurements at these wavelengths. The novelty of the Keystone mission is the heterodyne Supra-THz sounder with frequencies at 770GHz(O2), 1.1THz(NO,CO), 2THz(O), 3.5THz(OH), and 4.7THz(O). The THz instrument - made possible at these very high frequencies by novel quantum cascade laser (QCL) local oscillators - will provide vertical profiles of its target species. Prime among these is the elusive atomic oxygen (O), which is the kingpin of upper atmospheric chemistry and energy balance. Atomic oxygen is the missing keystone in the interpretation of both infrared and UVIS measurements, presenting a crucial synergy between the three instruments on the Keystone mission. By resolving age old questions, like that of the quenching rate of CO2 with O, Keystone will significantly improve our understanding of the upper mesosphere and thermosphere, the least well known region of the atmosphere - arguably of the entire planet.
14:15 UTC (+15) SAGE III/ISS Mission Update and Science Milestone results and Future Plans

Marilee M. Roell, David E. Flittner, Charles A. Hill, Robert P. Damadeo, Jamie L. Nehrir, Kevin R. Leavor, Susan H. Kizer
  1. NASA Langley Research Center, USA
The Stratospheric Aerosol and Gas Experiment III on the International Space Station (SAGE III/ISS) has been collecting data on the stratosphere almost continuously for 4 years since the first light milestone was achieved on March 17, 2017. In that time, the SAGE III/ISS data products have withstood robust assessments both internal and external, using comparisons to data sets both in-situ and spaceborne, and incorporated improvements into the retrieval algorithm and the science data products themselves. With the new v5.2 release of the SAGE III/ISS science data product algorithm, improvements made to the aerosol and water vapor products have produced better correlations with both MLS and balloonsonde data. At this 4-year milestone, we will look back on the last 4 years of data collection highlighting SAGE III/ISS ozone and aerosol data from 2017-2020 in a 6-minute video highlighting the SAGE III mission. An overview of mission operations and the challenges of operating a science mission on the ISS will highlight lessons learned and the mission science objectives completed during the first three years of the mission. The future goals for the SAGE III/ISS mission, as we continue operations and science collection, will round out the presentation.
14:30 UTC (+15) BREAK
  Session 1B
  Algorithms & Error Analysis
Chairs: Robert Damadeo, Natalya Kramarova
14:45 UTC (+20) Synergy between nadir, limb scattering and solar occultation measurements for climate and chemistry studies

P.K. Bhartia
  1. NASA Goddard Space Flight Center, USA
15:05 UTC (+15) Training an Artificial Neural Network to Improve the Near-Real-Time Retrieval Products Derived From Observations of the Microwave Limb Sounder

Frank Werner, Nathaniel J. Livesey, Michael J. Schwartz, William J. Read, Luis V. Millan
  1. NASA Jet Propulsion Laboratory, USA
The current version of the near-real-time (NRT) algorithm for the Aura Microwave Limb Sounder (MLS) provides data products for selected species with a latency of about 2-4 hours. These products employ a simplified forward model and thus are less reliable than the standard level 2 results. In this study we present results from an improved NRT algorithm that is based on a feedforward artificial neural network, which is trained on MLS-observed brightness temperatures from different spectral bands, channels, and tangent altitudes. The neural networks are trained on more than 10 million MLS-retrieved temperature, carbon monoxide, water vapor, and ozone profiles, grouped within individual 10-degree latitude bins. Statistical analysis and examples of global data fields reveal that the new NRT approach yields significant improvements in both latency and reliability in comparison to the results obtained with the current NRT algorithm. The new NRT algorithm will be implemented in future MLS data product versions.
15:20 UTC (+15) SAGE III/ISS Rapid Data Analysis Through Dashboarding with Jupyter Notebooks

Kevin R. Leavor, David E. Flittner, Marilee M. Roell
  1. NASA Langley Research Center, USA
  2. Science Systems and Applications, Inc., USA
Spaceborne remote sensing observations of Earth’s atmosphere produce significant quantities of data over the life of each mission. In the case of the Stratospheric Aerosol and Gas Experiment III on the International Space Station (SAGE III/ISS) nearly four years of vertical profiles of atmospheric ozone, water vapor, and nitrogen dioxide concentrations as well as aerosol extinction coefficients have been released. The dichotomy of the desire for both long-term trends in the atmospheric state alongside the assessment of short-term impacts of major disruptive events such as volcanic eruptions and pyrocumulus injections requires agile tools to handle these cases in near real-time as new data are produced. The analysis landscape is further complicated by the desire to compare results between the numerous contemporary observations available for a given dataset. The SAGE III/ISS team has developed a suite of tools leveraging modern web-based frameworks allowing members to interact with a dashboard-style interface to load the data record, assess new profiles as they are generated and in ensemble, compare between species, and additionally add in measurements observed by other platforms as necessary. Leveraging a commonly packaged data format of NetCDF alongside the Python Jupyter Notebook framework, the data can be served to interested parties from an analysis server while still runnable on personal systems if required. This presentation illustrates the ecosystem developed by the SAGE III/ISS team, the applicability to measurements made by any limb-observing platform, and the benefit to transforming routine analyses into readily accessible dynamic plots. Frameworks currently exist at larger scales with projects such as GIOVANNI, and this illustration seeks to show that similar frameworks are accessible and possible within the local research environment while simultaneously unloading human processing cycles for more specialized analysis tasks.
15:35 UTC (+15) Error budget assessment for OMPS-LP ozone retrievals

Carlo Arosio [1], Alexei Rozanov [1], Natalya Kramarova [2], Chris Roth [2], John P. Burrows [2]
  1. Institute of Environmental Physics, University of Bremen, Germany
  2. NASA Goddard Space Flight Center, USA
The assessment of the uncertainty budget for single and merged satellite data sets is important, especially for validation purposes, but also for long-term trend studies. In fact, to reliably interpret discrepancies between different data sets we first need to characterize and validate the respective uncertainties in individual data sets. The aim of this study is the assessment of the error budget for OMPS-LP ozone profiles retrieved at the University of Bremen. To this end, relevant error sources shall be identified, and errors have to be propagated to level 2 (L2) data. This is done using the SCIATRAN radiative transfer model and retrieval package. In this way, an extensive error budget as a function of altitude and latitude is established. A short description of the retrieval algorithm, retrieval noise, vertical resolution and information content will be presented. In this study we focus on several sources of uncertainties. First, errors in L1 data shall be estimated and propagated into L2 data. Second, uncertainties in the ozone cross section have to be accounted for. These uncertainties are related to the cross-section measurement errors and their temperature dependence. Third, parameter errors shall be assessed. One way to propagate these uncertainties to the retrieved ozone profiles is through the usage of the gain matrix from the retrieval scheme. Additionally, we perform sensitivity studies to assess the impact of aerosol extinction, surface albedo, atmospheric background state on the retrieved ozone profiles by varying a single parameter at a time. Finally, we estimated model errors by checking the sensitivity of the retrieved profiles to polarization, Raman scattering and scattering approximations. Afterwards, the estimated errors in L2 retrievals can be propagated to the level 3 (L3) data, which are then used for trend studies. Although the random component of the uncertainty is generally not relevant for L3 data, the estimated systematic component and its variation with time has to be considered for both trend and validation studies.
15:50 UTC (+15) The IMK-IAA MIPAS version 8 data set: the current status

Gabriele P. Stiller, Thomas von Clarmann, Norbert Glatthor, Udo Grabowski, Sylvia Kellmann, Michael Kiefer, Alexandra Laeng, Andrea Linden, Bernd Funke, Maya Garcia-Comas, and Manuel Lopez-Puertas
  1. Karlsruhe Institute of Technology, Germany
MIPAS retrievals based on version 8 radiance spectra by ESA benefit from an improved nonlinearity correction in the gain calibration that accounts for detector aging and removes drifts. The most relevant features of IMK-IAA level-2 processing are: Consideration of non-local thermodynamic equilibrium effects also in temperature, ozone and water vapour retrievals; the use of version 5 results as a priori information on the along-line-of-sight structure of the atmospheric state; consideration of a background continuum up to lower mesospheric altitudes; the replacement of climatological data by de-biased model data of the actual state as temperature a priori above the highest MIPAS tangent altitude, and a refinement of the micro-window selection. The effect of these modifications of the retrieval setup will be discussed using selected examples.
16:05 UTC (+15) Systematic Comparison of Vectorial Spherical Radiative Transfer Models in Limb Scattering Geometry

Daniel Zawada, Ghislain Franssens, Robert Loughman, Antti Mikkonen, Alexei Rozanov, Claudia Emde, Adam Bourassa, Seth Dueck, Hannakaisa Lindqvist, Didier Ramon, Vladimir Rozanov, Emmanuel Dekemper, Erkki Kyrölä, John P. Burrows, Didier Fussen, and Doug Degenstein
  1. University of Saskatchewan, Canada
A comprehensive inter-comparison of seven radiative transfer models in the limb scattering geometry has been performed. Every model is capable of accounting for polarisation within a fully spherical atmosphere. Three models (GSLS, SASKTRAN-HR, and SCIATRAN) are deterministic, and four models (MYSTIC, SASKTRAN-MC, Siro, and SMART-G) are statistical using the Monte Carlo technique. A wide variety of test cases encompassing different atmospheric conditions, solar geometries, wavelengths, tangent altitudes, and Lambertian surface reflectances have been defined and executed for every model. For the majority of conditions it was found that the models agree to better than 0.2 % in the single scatter test cases and better than 1 % in the multiple scatter scalar and vector test cases, with some larger differences noted at high values of surface reflectance in multiple scatter. For the first time in limb geometry, the effect of atmospheric refraction was compared among four models that support it (GSLS, SASKTRAN-HR, SCIATRAN, and SMART-G). Differences among most models in multiple scatter with refraction enabled was less than 1 %, with larger differences observed for some models. Overall the agreement among the models with and without refraction is better than has been previously reported in both scalar and vector modes.
TUESDAY Session 2A
  Missions & Instruments
Chairs: Nathaniel Livesey, Glen Jaross
Algorithms & Error Analysis
Chairs: Christian von Savigny, David Flittner
13:00 UTC (+15) Aerosol Limb Imager: Simulations of multi-spectral, polarized limb scatter aerosol and cloud measurements

Adam Bourassa, Landon Rieger, Doug Degenstein
  1. Institute of Space and Atmospheric Studies, University of Saskatchewan, Canada
Limb scattering measurements have provided great advances in aerosol monitoring over previous decades; resolving aerosol transport, variation, and delivery into the stratosphere not possible with other techniques. While these measurements have reduced uncertainty in aerosols radiative impacts, chemical interactions and overall stratospheric loading, difficulties with cloud contamination, microphysical assumptions, and saturation in the UTLS have remained a consistent impediment. The Aerosol Limb Imager (ALI) is an instrument concept that measures 2D multispectral images of limb scattered sunlight in the 600-1500nm range, including polarization information. ALI is built around an acousto-optic tunable filter and liquid crystal rotator that allows fast wavelength selection without moving parts. Prototypes have been developed for stratospheric balloon and airplane flights. This work presents simulations of space-based ALI measurements, focusing on the improvements to limb scattering retrievals that are possible through the inclusion of longer wavelengths and polarization information, in particular cloud discrimination and particle size.
TOPAS ozone profile retrieval from TROPOMI L1B version 2 dataset

Nora Mettig, Mark Weber, Alexei Rozanov, Carlo Arosio, John P. Burrows
  1. IUP University Bremen, Germany
The TOPAS (Tikhonov regularized Ozone Profile retrievAl with SCIATRAN) algorithm to retrieve vertical profiles of ozone from space-borne observations in nadir viewing geometry has been developed and applied to TROPOMI L1B spectral data version 2. From the limited time period of the version 2 dataset available, spectral radiances from channel UV1 and UV2 between 270 nm and 331 nm are used for the retrieval. A re-calibration of the measured radiances is required using comparisons with simulated radiances with ozone limb profiles from collocated MLS/Aura used as input. Studies with synthetic spectra show that individual profiles in the stratosphere can be retrieved with the accuracy of about 10%. In the troposphere, the retrieval errors are larger depending on the a-priori profile used. The vertical resolution varies between 6 and 10 km above 18 km altitude and 15 - 25 km below. There are about 6 degree of freedom between 0 and 60 km. Studies with synthetic spectra show that individual profiles in the stratosphere can be retrieved with the accuracy of about 10%. In the troposphere, the retrieval errors are larger depending on the a-priori profile used. The vertical resolution varies between 6 and 10 km above 18 km altitude and 15 - 25 km below. There are about 6 degree of freedom between 0 and 60 km. The TOPAS ozone profiles retrieved from TROPOMI were validated using data from ozone sondes and stratospheric ozone lidars. Above 18 km, the comparison with sondes shows excellent agreement within less than ± 5% for all latitudes. The standard deviation of mean differences is about 10%. Below 18 km, the relative mean deviation in the tropics and northern latitudes is still quite good remaining within ± 20%. At southern latitudes larger differences of up to +40% occur between 10 and 15 km. The validation of stratospheric ozone profiles with ground-based lidar measurements also shows very good agreement. The relative mean deviation is below ± 5% in the 18 - 45 km range with a standard deviation of 10%. A pilot application for one day of TROPOMI data with a comparison to MLS and OMPS confirmed the lidar validation results. The relative mean difference between TROPOMI and MLS or OMPS is largely below ± 5% between 20 and 50 km except at very high latitudes where differences are getting larger. To improve the ozone profiles in the upper troposphere we add CrIS/SuomiNPP thermal infrared measurements in our UV retrieval. First results from combined IR and UV retrieval using collocated TROPOMI and CrIS data are presented.
13:15 UTC (+15) Spatial heterodyne observations of UTLS water vapour from a low earth orbit satellite: concept, scientific requirements, modelling and simulation

Adam Bourassa, Jeff Langille, Doug Degenstein, Landon Rieger, Jean-Pierre Blanchet, Yann Blanchard and Yi Huang
  1. University of New Brunswick, Canada
The Spatial Heterodyne Observations of Water instrument (SHOW) is a limb imaging satellite instrument concept that is being developed to provide accurate, dense, high vertical resolution measurements of water vapour in the upper troposphere and lower stratosphere. In this region, the radiative sensitivity of water vapour is most significant, and its distribution is coupled to the climate in a complex manner with potential feedbacks and strong connections to cloud and aerosol processes. However, current satellite sensors struggle to resolve smaller scale variability in this region. SHOW utilizes a field widened spatial heterodyne spectrometer operating in the limb viewing configuration to observe limb scattered sunlight in a small 3 nm spectral window centered near 1365 nm. Vertically resolved images of the limb are obtained with each frame that are inverted using non-linear optimal estimation to extract the vertical distribution of water vapour. The large throughput and high spectral resolution (0.02 nm) provided by the field widened SHS allows vertical profiles with a target vertical resolution of < 500 m to be obtained with rapid along track sampling (~50 km) from a low earth orbit satellite. This enhanced sampling will advance our understanding of the smaller scale processes that control humidity near the tropopause. The instrument is one of three instruments that have been proposed as a potential Canadian contribution to NASA’s aerosol, clouds, convection, precipitation (ACCP) mission. Synergistic observations of aerosol and cloud are obtained by the other two instruments, ALI and TICFIRE allowing for a detailed picture of aerosol, water vapour and cloud interactions. This paper presents the SHOW instrument concept and preliminary results from a detailed simulation study that is currently underway to evaluate the scientific return of the observing system, as well as synergies between the various instruments.
Hyper-parameter optimization for SCIAMACHY 2-D limb retrievals of NO in the mesosphere and lower thermosphere

Stefan Bender (1,2), Miriam Sinnhuber [3], John P. Burrows [4]
  1. Norwegian University of Science and Technology, Norway
  2. Birkeland Centre for Space Science, Norway
  3. Karlsruhe Institute for Technology, Germany
  4. University of Bremen, Germany
The SCIAMACHY retrieval of nitric oxide in the mesosphere and lower thermosphere is based on a 2-D orbit-wise setup with pre-determined smoothing parameters along altitude and latitude. These smoothing parameters are hyper-parameters of the retrieval algorithm, and they currently represent a hand-waving "best guess" estimate. Here we tune these hyper-parameters using non-linear optimization similar to the retrieval itself, thus balancing noise and resolution. Without impacting the actual retrieval algorithm too much, this estimate is carried out only for a few sample orbits, and the updated parameters serve as a new setup for future retrieval runs. Alternatively, co-fitting the smoothing parameters every orbit might improve the retrieval in all cases, given that the computing resources permit it.
13:30 UTC (+15) A novel tapered slit design to reduce stray light for the JPSS-4 OMPS Limb Sensor

Thomas Rogers, Tyler McCracken, Tevis Nichols
  1. Ball Aerospace, USA
The Ozone Mapping and Profiler Suite (OMPS), built by Ball Aerospace, contains a dedicated imaging spectrograph for measuring vertical ozone profiles called the Limb Sensor. The first Limb sensor is currently aboard the Suomi NPP spacecraft with three more units slated to fly aboard the JPSS-2, JPSS-3, and JPSS-4 spacecrafts. The Limb sensor measures the vertical distribution of ozone in the atmosphere by observing the limb of the earth from the horizon to ~120 km, across three separate scenes, from 290nm through 1000nm. The largest uncertainty in Limb-generated science is caused by stray light contamination. The JPSS-4 Limb sensor takes direct aim at reducing stray light through the use of a novel tapered slit designed to reduce low altitude signals from contaminating higher altitude channels. The new slits are designed to cut the signal from lower, brighter altitudes by a factor of ~3, while retaining SNR capabilities at the upper, dimmer altitudes. This presentation will detail design decision and predicted performance of the JPSS-4 Limb sensor with tapered slits compared to previous builds and review other design enhancements to the sensor over the course of the JPSS program.
TUNER-compliant uncertainty estimates for MIPAS data

Thomas von Clarmann, Norbert Glatthor, Udo Grabowski, Michael Kiefer, and Bernd Funke
  1. Karlsruhe Institute of Technology, Germany
MIPAS version 8 results processed at IMK in cooperation with IAA come with extensive uncertainty estimates, following the recommendations of the SPARC Activity `Towards Unified Error Reporting' (TUNER). All sizeable error components are reported separately. The aggregated error budget is divided into the total random error estimate, which shall explain the scatter of the differences with respect to independent measurements, and the total systematic error estimate, which is supposed to explain the bias with respect to independent measurements. The unclear uncertainty reporting of spectroscopic data turned out to be a major challenge.
13:45 UTC (+15) OSIRIS - Over 20 Years in Orbit

D.A. Degenstein, A.E. Bourassa, C. McLinden, C.Z. Roth, D. Zawada and N.D. Lloyd
  1. University of Saskatchewan, Canada
The Canadian Optical Spectrograph and InfraRed Imaging System (OSIRIS) hit 20 years in orbit on February 21, 2021. This is an amazing testament to the engineers and scientists from the Canadian Space Agency who fund and manage OSIRIS, Routes AstroEngineering who built OSIRIS and academic institutions around the world who proposed the concept and worked hard to make it a reality. This “two year mission” has produced results beyond anybody’s wildest dreams and this presentation will address as many highlights as time permits. With almost 20 years of high quality, vertically resolve sulphate aerosol, ozone and nitrogen dioxide profiles, OSIRIS has made substantial contributions to international initiatives like the WMO Ozone Assessment, the Intergovernmental Panel on Climate Change quadrennial report and the WCRP sponsored CMIP 6 and although OSIRIS and Odin are aging, it is anticipated that these contributions will continue for the foreseeable future.
Sensitivity of OMPS/LP ozone retrieval to assumed aerosol particle size distribution

Zhong Chen, Pawan K. Bhartia, Natalya Kramarova and Matthew DeLand
  1. NASA Goddard Space Flight Center, USA
  2. Science Systems and Applications, Inc., USA
The limb scattering technique has recently emerged as a viable low cost alternative to thermal IR and microwave instruments to measure stratospheric ozone profile at high vertical resolution. However, there are concerns about the effect of aerosols and clouds on the retrieval algorithm. The operational OMPS Limb Profiler (LP) algorithm accounts for aerosols by using an aerosol extinction profile retrieved at a single wavelength (675 nm) with a fixed aerosol particle size distribution (PSD). However, it is likely that the actual PSD varies depending upon the type of aerosols present, which can include volcanic aerosols and smoke from PyroCbs as well as dust and pollution aerosols uplifted by convective systems. In this presentation, we investigate the errors in the OMPS LP retrieved ozone profiles due to variations in the assumed aerosol PSD. We find that the LP ozone algorithm is insensitive to the assumed PSD above ~18 km, but becomes increasingly more sensitive at lower altitudes. We discuss the reasons for this result, and propose a solution.
14:00 UTC (+15) The Stratospheric Aerosol and Gas Experiment (SAGE) IV Pathfinder

Robert Damadeo, Charles Hill
  1. NASA Langley Research Center, USA
Continued observations of stratospheric constituents are critical to our understanding of the atmosphere. Many climate models rely on ingesting continuous long-term records of these constituents to properly account for Earth’s radiative balance and dynamical changes. Owing to many measurement sources over the past 40 years, we have composite data sets of stratospheric ozone, aerosol, and water vapor that continue to this day. However, despite the need to carry these observations forward, there are only limited (or even non-existent) plans to do so. Adequate continuation of long-term data records requires overlapping measurements from multiple instruments. However, most current satellite systems are well beyond their expected lifetimes and are large and expensive. A new measurement paradigm is needed to enable cost-effective, sustainable measurements of the stratosphere, particularly for ozone which is not expected to fully recover for decades. The Stratospheric Aerosol and Gas Experiment (SAGE) IV is a solar occultation imager capable of measuring ozone, aerosol, and other trace gas species with the same quality as previous SAGE instruments (including SAGE III/ISS). Taking advantage of recent technological advancements, a single sensorcraft occupies a 6U CubeSat form-factor providing an order of magnitude reduction in cost over traditional missions. SAGE IV is an example of an innovative and affordable mission that can sustain a crucial science measurement well into the future.
Altitude Registration for the Suomi NPP OMPS Limb Profiler

Leslie Moy, Glen Jaross, Natalya Kramarova, P.K. Bhartia
  1. NASA Goddard Space Flight Center, USA
  2. Science Systems and Applications, Inc., USA
One of the largest constraints to the retrieval of accurate ozone profiles from UV backscatter limb sounding sensors is altitude registration. Two methods, the Rayleigh scattering attitude sensing (RSAS) and absolute radiance residual method (ARRM), are used to determine altitude registration to the accuracy necessary for long-term ozone monitoring. The methods compare model calculations of radiances to measured radiances and are independent of onboard tracking devices. Our 2018 paper reported ARRM results of ∼ 300 to 400 m intra-orbital TH change varying seasonally ±100 m. Updates such as aerosol retreivals have been applied and show much flatter ARRM results in the northern hemisphere, and ARRM and RSAS results drifting apart after year ~2016. Our upcoming version 2.7 will include a simplified intra-orbital correction. We will summarize the altitude registration corrections made over the history of the OMPS Limb Profiles (LP).
14:15 UTC (+15) On the capability of UV-VIS limb sounders to constrain modelled stratospheric ozone and its application to the ALTIUS mission

Quentin Errera, Emmanuel Dekemper, Noel Baker, Jonas Debosscher, Philippe Demoulin, Nina Mateshvili, Didier Pieroux, Filip Vanhellemont and Didier Fussen
  1. Royal Belgian Institute for Space Aeronomy, Belgium
ALTIUS (Atmospheric Limb Tracker for the Investigation of the Upcoming Stratosphere) is the upcoming strato- spheric ozone monitoring limb sounder from ESA’s Earth Watch programme. Measuring in the ultraviolet-visible-near infrared spectral regions, ALTIUS will retrieve vertical profiles of ozone, aerosol extinction coefficients, nitrogen dioxide and other trace gases from the upper troposphere to the mesosphere. In order to maximize the geographical coverage, the instrument will observe limb- scattered solar light during daytime, solar occultation at the terminator and stellar/lunar/planetary occultations during nighttime. This paper evaluates the constraint of ALTIUS ozone profiles on modelled stratospheric ozone by the means of an Observing System Simulation Experiment (OSSE). In this effort, a reference atmosphere has been built and used to gener- ate ALTIUS ozone profiles, along with an instrument simulator. These profiles are then assimilated to provide ozone analyses. A good agreement is found between the analyses and the reference atmosphere in the stratosphere and in the extra-tropical upper troposphere. In the tropical upper troposphere, although providing a significant weight in the analyses, the assimilation of ozone profiles does not allow to completely eliminate the bias with the reference atmosphere. The weight of the different modes of observations have also been evaluated, showing that all of them are necessary to constrain ozone during polar winters where solar/stellar occultations are the most important during the polar night and limb data are the most important during the development of the ozone hole in the polar spring.
Standard Ozone Profile Product from Suomi NPP OMPS Limb Profiler

Natalya Kramarova, P.K. Bhartia, Zhong Chen, Matthew DeLand, Glen Jaross, Jungbin Mok, Leslie Moy, Philippe Xu, Clark Weaver
  1. NASA Goddard Space Flight Center, USA
The Limb Profiler (LP) sensor is a part of the Ozone Mapping and Profiler Suite (OMPS) on board of Suomi NPP satellite. LP measures limb scattered radiances in UV and VIS spectral bands from the cloud top up to 80 km enabling ozone profile retrievals with a fine vertical resolution (~1.8 km). In this presentation, we show results from a number of recent studies that used LP ozone data in various scientific applications. We will summarize what we have learned from these studies and lay out a plan for reprocessing the LP measurements with the version 2.7 algorithm planned for early 2022. The main concern that we plan to address in v2.7 is a positive drift in the LP ozone time series that is more pronounced at altitudes above 35 km and is linked to a drift in the LP altitude registration. Our team re-evaluated the LP altitude registration methods and developed adjustments, and preliminary analysis had demonstrated a significant reduction in the observed ozone drift after applying these adjustments. We will also apply corrections to LP wavelength registration in the LP Level 1 product based on coincident solar measurements. The radiometric sensitivity of LP varies with wavelength and the revised Level 1 product will also include these variations. Corrections for a drift in LP wavelength registration and instrument degradation are expected to contribute to a reduction in the observed ozone drift as well. In addition to the Level 1 changes, we will discuss several updates in the ozone retrieval algorithm and radiance simulations. We expect to see moderate improvements in the v2.7 LP ozone product, and we will show some preliminary results for v2.7 in this presentation.
14:30 UTC (+15)   A novel method of deriving time series of ozone and atmospheric vertical density from OMPS/LP data

Zhong Chen, Pawan K. Bhartia
  1. NASA Goddard Space Flight Center, USA
  2. Science Systems and Applications, Inc., USA
We present a novel method of estimating inter-annual variability and trends in ozone and atmospheric density from OMPS/LP data. Our method reverses the traditional method of retrieving ozone profile from limb measured radiances. We first retrieve trends in slant ozone and air column at each altitude separately and then combine trends from multiple altitudes to estimate trends in ozone and air density. We will compare our results with the traditional methods of processing the data and discuss pros and cons of the two methods.
14:45 UTC (+15) BREAK
  Session 2B
  Trace Gases
Chairs: Irina Petropavlovskikh, Kaley Walker
15:00 UTC (+20) Stratospheric Pyroconvective Plumes in Microwave Limb Sounder Observations

Michael Schwartz
  1. NASA Jet Propulsion Laboratory, USA
The Australian New Year’s (ANY) event was an outbreak of at least 18 pyrocumulonimbus (pyroCb) fire storms at the peak of Australia's historic 2019–2020 “Black Summer” fire season. It produced a stratospheric plume containing enhancements of combustion products, including CO, H2O, HCN, CH3CN, CH3Cl, and CH3OH, that far exceeded records successively set by the Black Saturday fires of 2009 and the Pacific Northwest Event of 2017 in 16 years of Microwave Limb Sounder observations. Solar heating of absorptive aerosol not only caused the plume to ascend into the middle stratosphere, reaching ~35 km within 70 days, but it also produced an encircling anticyclonic eddy ∼1,000 km across that served as a transport barrier, contributing to the months‐long persistent coherence of the trace‐gas anomalies. Careful analysis of constituent ratios in the various plumes requires consideration of the measurements’ contrasting spatial resolutions. There is no indication that the plume had a significant impact upon ozone chemistry in the 2020 southern polar vortex, but the longer-term impact of ANY’s injected aerosols and water vapor on Southern Hemisphere stratospheric chemistry is an area of ongoing research.
15:20 UTC (+15) Airborne infrared limb imaging measurements of biomass burning trace gases by GLORIA in the Southern Hemisphere

Sören Johansson, Michael Höpfner, Felix Friedl-Vallon, Jörn Ungermann, Gerald Wetzel, Norbert Glatthor
  1. Karlsruhe Institute of Technology, Germany
We will present trace gas distributions measured by the airborne imaging limb sounder GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere). GLORIA has been operated onboard the German HALO (High Altitude and Long Range) research aircraft above the South Atlantic and South America during the SouthTRAC campaign between September and November 2019. We show retrieval results as two-dimensional trace gas distributions derived from GLORIA observations in the UTLS (Upper Troposphere Lower Stratosphere) region above South America and the Atlantic Ocean. For this study, targeted trace gases are O3, HNO3, PAN, C2H6, and HCOOH. In a first analysis, trajectories from the HYSPLIT model are used to link measured pollution trace gas plumes to large-scale biomass burning events in central Africa, South America and Australia. In addition, we compare our GLORIA measurements with results of the CAMS (Copernicus Atmosphere Monitoring Service) reanalysis model. We show that CAMS generally is able to qualitatively reproduce measured distributions of pollutants. Quantitatively, PAN volume mixing ratios are captured quite well by the model, which however underestimates the concentrations of C2H6 and HCOOH. Furthermore, biomass burning emissions from November 2019, the beginning of the intensive Australian fire period, which are measured by GLORIA in thin filaments over South America, are not reproduced by CAMS.
15:35 UTC (+15) Estimating the impact of volcanic eruptions on the thermal structure of the mesosphere by analyzing HALOE temperature data

Sandra Wallis [1], Anne Krüger [1], Christoph Hoffmann [1], Hauke Schmidt [2], Christian von Savigny [1]
  1. University of Greifswald, Germany
  2. Max Planck Institute for Meteorology, Germany
A paper published in 1998 by She et al. [1] analyzed lidar temperature profiles and reported an episodic warming of the mesopause region that peaked in 1993 and was attributed by the authors to a delayed response to the Pinatubo eruption in 1991. They observed a considerable temperature increase with a magnitude up to 12.9 K in 100 km altitude. Our study further investigates the proposed connection between the tropical volcanic eruption of Mount Pinatubo and the temperature in the mesopause region. Therefore, temperature data from the Halogen occultation experiment (HALOE) on the Upper Atmosphere Research Satellite, starting scientific measurements four month after the eruption, was used to extract temperature variations in the middle atmosphere. Both seasonal and solar contributions were considered in order to estimate the amplitude and signature of the volcanic perturbation. The impact of a tropical volcanic eruption on the mesosphere is further investigated by simulations that use the upper-atmosphere icosahedral non-hydrostatic (UA-ICON) general circulation model. The simulations suggest a temperature increase in the extratropical summer middle atmosphere, likely related to changed gravity wave propagation conditions, that disappear by the second austral summer after the eruption. [1] C. Y. She, Steven W. Thiel, and David A. Krueger. Observed episodic warming at 86 and 100 km between 1990 and 1997: Effects of mount pinatubo eruption. Geophysical Research Letters, 25(4):497–500, 1998.
15:50 UTC (+15) Update of modeling the O and O2 photochemistry in the mesosphere using the Multiple Airglow Chemistry approach

Olexandr Lednyts'kyy, Christian von Savigny
  1. Institute of Physics, University of Greifswald, Germany
Time series of atomic oxygen (O(3P)) concentration ([O(3P)]) and Volume Emission Rate (VER) retrieved using spectral nightglow oxygen green line emissions measured with the instrument SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) aboard the satellite Envisat are provided to the scientific community, see https://physik.uni-greifswald.de/pl/ag-von-savigny/projects/dfg-projekt-mesoxy/ Two modified established photochemical models used to retrieve the [O(3P)] time series, see Lednyts'kyy et al., AMT, 8 (2015), were also used to calculate [O(3P)] profiles using green line emissions measured in situ during ETON (Energy Transfer in the Oxygen Nightglow) and WAVE2004 (WAVes in airglow structures Experiment, 2004) campaigns. [O(3P)] profiles, calculated and measured in situ ones, agree with each other, see Lednyts'kyy et al., JASTP, 194 (2019) and Lednyts'kyy and von Savigny, ACP, 20 (2020). The [O(3P)] time series retrieved using both modified established models are in focus also because they were used to estimate the O(3P) sensitivity to the ~11-year and ~27-day solar cycles, see Lednyts'kyy et al., JASTP, 162 (2017). Sensitivity values to the ~27-day solar forcing were estimated for the first time, and sensitivity values estimated to the ~11-year solar forcing agree with simulations carried out using the reference models HAMMONIA (Hamburg Model of Neutral and Ionized Atmosphere) and WACCM (Whole Atmosphere Community Climate Model). The Multiple Airglow Chemistry model developed to represent the oxygen photochemistry and the oxygen nightglow in the mesopause region is also discussed in this talk using [O(3P)] profiles calculated for the ETON, WAVE2004 and another two rocket campaigns, see Lednyts'kyy et al., JASTP, 194 (2019) and Lednyts'kyy and von Savigny, ACP, 20 (2020).
16:05 UTC (+15) Gravity Wave-Forced Clouds Observed by OMPS Limb Profiler

Matthew DeLand, Nick Gorkavyi
  1. Science Systems and Applications, Inc., USA
The OMPS Limb Profiler instrument on the Suomi NPP satellite is very successful at detecting polar stratospheric clouds (PSCs) and polar mesospheric clouds (PMCs). Seasonal behavior of these clouds observed by OMPS LP is very consistent with other published results for both PSCs (compared to CALIPSO) and PMCs (compared to AIM CIPS). The OMPS LP data set also identifies these clouds at less-expected locations and times, particularly near the southern tip of South America and the Antarctic Peninsula. While this result suggests orographically forced gravity waves as a possible source mechanism for the clouds, LP measurements are also susceptible to transient signals caused by charged particles in the South Atlantic Anomaly (SAA) that could cause a “false positive” detection. We can evaluate the probability of valid cloud detections in such situations by examining multiple additional criteria, such as the local temperature near the cloud as indicated by MERRA-2 FPIT assimilation temperature profiles, and simultaneous PMC detection algorithm results using a second wavelength. Results from these approaches will be presented.
16:20 UTC (+15) Comparison of sodium concentration profiles and column densities in the MLT region obtained from OSIRIS nightglow measurements with results from SCIAMACHY and GOMOS measurements

Julia Koch [1], Adam Bourassa [2], Nick Lloyd [2], Chris Roth [2], Christian von Savigny [1]
  1. Institute of Physics, University of Greifswald, Germany
  2. University of Saskatchewan, Canada
Metal layers in the upper mesosphere and lower Thermosphere are known to be an indicator for changes in this altitude region as well as a means to estimate meteoric intake in the earths’ atmosphere. In both cases the knowledge of exact sodium concentrations is a key-factor for further research. In order to contribute to this research we report on sodium concentration profiles and column densities obtained from Odin/Osiris nightglow measurements and compare them to Envisat/SCIAMACHY sodium concentration profiles and column densities and Envisat/GOMOS sodium column densities. The nightglow is a result of sodium reacting with ozone and using those measurements together with ozone concentration profiles from SABER/TIMED we obtain sodium profiles. The major challenge of this work is the differing temporal and spatial coverage of both, the data sets needed to obtain sodium profiles from OSIRIS measurements as well as the data sets used for comparison. And even though SCIAMACHY yields slightly larger values, we can still show that the LER and VER profiles from Osiris and SCIAMACHY agree very well. But as a result of the different coverage and a high sensitivity of the retrieved sodium to fluctuations of ozone concentrations, SCIAMACHY yields higher and Gomos lower sodium column densities than the OSIRIS measurements
  Trace Gases
Chairs: Doug Degenstein, Natalya Kramarova
13:00 UTC (+15) GEOS-SCREAM: Stratospheric Composition Reanalysis with Aura MLS

Krzysztof Wargan, Brad Weir, Gloria L. Manney, Stephen E. Cohn
  1. NASA Goddard Space Flight Center, USA
  2. Science Systems and Applications, Inc., USA
Chemical composition reanalyses use the data assimilation methodology to propagate observations of atmospheric constituents in time and space to produce global three-dimensional maps of these species at high spatial and temporal resolutions. So far, these reanalyses have focused mainly on the troposphere and air quality applications with one notable exception of the Belgian BRAM2 stratospheric product. In this presentation, we will introduce another stratospheric reanalysis produced at NASA’s Global Modeling and Assimilation Office. Named GEOS Stratospheric Composition Reanalysis with Aura MLS (GEOS-SCREAM), it assimilates ozone, water vapor, hydrogen chloride, nitric acid, and nitrous oxide profiles from the Microwave Limb Sounder (MLS) on the EOS Aura satellite at 50-km horizontal resolution and covers the period between late 2004 and 2020 with output generated at a three-hourly frequency. We will demonstrate that the assimilated constituents agree very well with MLS observations as well as with independent data from the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer, the Gimballed Limb Observer for Radiance Imaging of the Atmosphere instrument and with the BRAM2 reanalysis. We will show the main results of a study of the 2019 ozone hole that was done using this product and discuss other potential applications of GEOS-SCREAM. This work underscores the critical importance of continuing measurements of stratospheric composition at high vertical resolution and global coverage such as provided by satellite-borne limb sensors.
13:15 UTC (+15) Tropospheric ozone daily and hourly synoptic maps derived from EPIC and assimilated MLS ozone measurements

J. R. Ziemke, N. A. Kramarova, L. K. Huang, J. R. Herman, P. K. Bhartia
  1. GESTAR / NASA Goddard Space Flight Center, USA
Daily and hourly maps of tropospheric ozone residual (TOR) are derived by differencing MERRA-2 assimilated Microwave Limb Sounder (MLS) stratospheric column ozone (SCO) from Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) v3 total ozone. The EPIC/MLS TOR maps are measured every 1-2 hours averaging 10-22 maps per day. The TOR measurements provide a unique high temporal resolution data set for science applications as well as a useful evaluation tool for TOR derived from geostationary satellite sensors, such as current GEMS and upcoming TEMPO and Sentinel-4.
13:30 UTC (+15) The first global climatology of BrONO2: MIPAS observations in comparison to atmospheric modelling

Michael Höpfner [1], Oliver Kirner [2], Gerald Wetzel [1], Björn-Martin Sinnhuber [1], Florian Haenel [1], Johannes Orphal [1], Roland Ruhnke [1], Gabriele Stiller [1], Thomas von Clarmann [1]
  1. Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research, Germany
  2. Karlsruhe Institute of Technology, Steinbuch Centre for Computing, Germany
The first detection of BrONO2 in the atmosphere had been achieved by analysis of infrared limb-emission spectra from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on the Envisat satellite. On availability of improved infrared cross-sections, this was followed by the analysis of the behaviour of BrONO2 during sunrise and sunset through MIPAS balloon observations. Here we present the first observational dataset of vertically resolved global stratospheric BrONO2 distributions from July 2002 until April 2012 in comparison to EMAC atmospheric model results. The space-borne measurements are based on averaged MIPAS/Envisat infrared limb-emission spectra from the recently available MIPAS version 8 level 1b-dataset. The derived altitude profiles of BrONO2 volume mixing ratios are zonal latitude and 3-daily means, respectively for day- and night-time observations. The vertical resolution ranges from 3 to 8 km between 15 and 35 km altitude with estimated uncertainties of around 2–4 pptv. All leading modes of spatial and temporal variability of stratospheric BrONO2 in the observations are well replicated by the simulations. Three major areas of inconsistency between measurements and model results are observed: (1) a model underestimation of enhanced BrONO2 in the polar winter stratosphere above about 30 km, (2) lower observational than modelled values globally in the lower stratosphere (up to 25 km) most obvious during night, and (3) lower modelled values at low latitudes between 27 and 32 km during daytime conditions. (1) is explained by the model missing enhanced NOx produced in the mesosphere and lower thermosphere and subsided at high latitudes in winter. (2) could only be reproduced by an enhanced loss of BrONO2 through hydrolysis at stratospheric aerosol particles in the lower stratosphere, requiring, however, surface area densities hardly compatible with observations. The enhanced daytime signal in the observations (3) could only barely be matched in the model runs by drastically decreasing the loss-rate through reaction with O(3P). The observations have been used to independently derive the total stratospheric bromine content relative to years of stratospheric entry between 1997 and 2007. With an average value of 21.2+-1.4 pptv of Bry at mid-latitudes where the modelled adjustment from BrONO2 to Bry is lowest, the MIPAS data lie well within the estimation from previous observations of BrO.
13:45 UTC (+15) Ozone trends on different geophysically based coordinate systems

L. Millan, G. Manney, M. Santee, N. Livesey
  1. NASA Jet Propulsion Laboratory, USA
Ozone trend estimates have shown large uncertainties in the upper troposphere/lower stratosphere (UTLS) region due to the high degree of spatial and temporal variability. This variability is in part caused by competing transport, chemical, and mixing processes near the tropopause, variations in the tropopause location, as well as the position of the subtropical and polar jets.Using Microwave Limb Sounder and Atmospheric Chemistry Experiment Fourier Transform Spectrometer data, we will study the impact of using different geophysically based coordinates systems upon uncertainties in UTLS ozone trend estimates. In principle, different coordinate systems should help us isolate different sources of variability. The coordinate systems to be used include potential temperature, tropopause coordinate systems, and jet coordinate systems (horizontal and vertical). This research is being performed as part of the OCTAV-UTLS (Observed Composition Trends and Variability in the UTLS) initiative which is part of the SPARC (Stratosphere-troposphere Processes And their Role in Climate) community. 2021 All rights reserved.
14:00 UTC (+15) Evaluating the SAGE III/ISS version 5.2 water vapor retrieval in the presence of aerosol loading

Michael Heitz, David Flittner, Robert Damadeo
  1. NASA Langley Research Center, USA
The Stratospheric Aerosol and Gas Experiment operating on the International Space Station (SAGE III/ISS) is an occultation instrument that retrieves aerosol extinction and ozone, water vapor, and other trace gas concentrations. Water vapor in the stratosphere plays a role in ozone depletion and global temperature regulation making it an important species to monitor. The SAGE III/ISS instrument provides high quality, vertically resolved profiles of water vapor throughout the stratosphere and upper troposphere. In previous versions of SAGE water vapor products, a dry bias was noted in comparison to other satellite retrievals in the presence of elevated aerosol optical depth. Several updates for the version 5.2 water vapor algorithm will be presented and compared with previous versions of the data and other satellite products during different periods of aerosol loading.
14:15 UTC (+15) Investigation and amelioration of long-term instrumental drifts in water vapor and other 190-GHz measurements from the Aura Microwave Limb Sounder (MLS)

Nathaniel J. Livesey [1], William G. Read [1], Lucien Froidevaux [1], Alyn Lambert [1], Michelle L. Santee [1], Michael J. Schwartz [1], Luis F. Millan [1], Robert F. Jarnot [1], Paul A. Wagner [1], Dale F. Hurst [2], Kaley A. Walker [3], Patrick E. Sheese [3], Gerald E. Nedoluha [4]
  1. NASA Jet Propulsion Laboratory, USA
  2. Cooperative Institute for Research in Environmental Sciences, University of Colorado, USA, and NOAA Global Monitoring Laboratory, USA
  3. University of Toronto, Canada
  4. Remote Sensing Division, Naval Research Laboratory, USA
The Microwave Limb Sounder (MLS), launched on NASA's Aura spacecraft in 2004, measures vertical profiles of the abundance of key atmospheric species from the upper troposphere to the mesosphere with daily near-global coverage. We review the first 15 years of the record of H2O and N2O measurements from the MLS 190-GHz subsystem (along with other 190-GHz information) with a focus on their long-term stability, largely based on comparisons with measurements from other sensors. These comparisons generally show signs of an increasing drift in the MLS "version 4" H2O observations starting around 2010 and ranging between +2% and +11%/decade, depending on the pressure level considered and the source of correlative H2O information. In contrast, the MLS version 4 N2O product is shown to be generally decreasing over the same period (when an increase in stratospheric N2O is expected, reflecting a secular increase in tropospheric emissions), with a more pronounced drift in the lower stratosphere than seen in H2O. Detailed investigations of the behavior of the MLS 190-GHz subsystem reveal a drift in the "sideband fraction" (the relative sensitivity of the 190-GHz receiver to the two different parts of the microwave spectrum it observes). Our studies indicate that sideband fraction drift accounts for much of the observed changes in the MLS H2O product and some portion of the changes seen in N2O. The 190-GHz sideband fraction drift has been corrected in the new "version 5", MLS algorithms, used to reprocess the 16-year (to date) MLS record. Studies of regional and seasonal-to-annual changes in MLS v4 H2O and N2O will not be affected by the drift. However, in light of the drift scientists are advised to avoid interpreting multi-year changes in the MLS version 4 H2O and N2O products, and instead use the new version 5 data for such research, in consultation with the MLS team. Importantly, this drift does not affect any of the MLS observations made in other spectral regions such as O3, HCl, CO, ClO, or temperature.
14:30 UTC (+15) ANCISTRUS: What's new?

Thomas von Clarmann, Udo Grabowski, Gabriele P. Stiller, Beatriz M. Monge-Sanz, Norbert Glatthor, Sylvia Kellmann
  1. Karlsruhe Institute of Technology, Germany
The inverse method `Analysis of the Circulation of the Atmosphere using Spectroscopic measurements (ANCISTRUS)' infers stratospheric circulation by inverting the continuity equation, as it was presented at the Limb Workshop in Greifswald in 2018. Since then, the method has been thoroughly validated. Model recovery tests have proven the general robustness of the method and allowed to test the effect of the regularization strength. Jack-knife tests were performed to assess the relevance of the different trace gas fields used to feed the inverted continuity equation. A climatology of stratospheric circulation based on MIPAS trace gas distributions will be presented.
14:45 UTC (+15) BREAK
  Session 3B
Chairs: Adam Bourassa, David Flittner
15:00 UTC (+15) Limb scattered aerosol measurements in the UTLS

Landon Rieger, Adam Bourassa, Doug Degenstein
  1. University of Saskatchewan, Canada
The upper troposphere and lower stratosphere often contains a large fraction of the total stratospheric aerosol, particularly after events such as forest fires and volcanic eruptions; playing an important role not only in direct forcing, but cloud interactions as well. However, these lower altitudes are more difficult to measure for limb scattering instruments due to the large contribution from Rayleigh scattering and reduced sensitivity to aerosols. The makeup is also more complex, with aerosols containing organics, black carbon and ash that is difficult to account for in the retrieval process. These problems are further exacerbated by the near ubiquitous presence of clouds, whose signals can be difficult to distinguish from the aerosols under investigation. Together, these complexities make the UTLS a difficult region, but also one of important scientific consequence. This work explores the aerosol extinction uncertainty of limb measurements in the UTLS through comparisons of multiple limb scattering aerosol datasets, and other platforms less sensitive to retrieval assumptions. The updated OSIRIS version 7 product that uses a multi-wavelength approach to reduce dependence on particle size assumptions is compared with coincident OMPS, CALIPSO and SAGE measurements during background conditions as well as volcanic and wildfire enhanced scenarios.
15:15 UTC (+15) Comparing stratospheric aerosol particle size distributions: measurement vs. measurement & measurement vs. model results

Christian von Savigny [1], Christoph Hoffmann [1], Ulrike Niemeier [2], Felix Wrana [1]
  1. University of Greifswald, Germany
  2. Max Planck Institute for Meteorology, Germany
Stratospheric sulfate aerosols play an important role for the physics and chemistry of the atmosphere. Despite the fundamental importance of the particle size distribution (PSD) of these aerosols, the particle sizes published in different studies cover a fairly wide range – even under volcanically quiescent stratospheric conditions – and the comparison of measured and modelled particle size distributions is not straightforward. This contribution covers two parts. In the first part we investigate a potential reason for systematic differences in PSD parameter retrievals from different optical techniques, i.e., lidar backscatter and solar occultation measurements. The key point of the results is that erroneous a priori assumptions on the PSD will lead to systematic errors in the retrieved PSD parameters that are different for different observation geometries. This is related to different sensitivities of these measurement techniques to specific parts of the aerosol particle population. In particular, stratospheric aerosol size retrievals based on solar occultation observations may yield systematically larger particle size estimates compared to, e.g., lidar backscatter measurements. Observed aerosol concentration - on the other hand - may be systematically smaller in retrievals based on occultation measurements compared to lidar measurements. In the second part we compare modelled stratospheric aerosol particle size information with observations. Such a comparison is not straightforward, because of the limited sensitivity of optical measurements to the smallest particles of the particle population. We compare the evolution of the stratospheric aerosol PSD modelled with the MAECHAM5-HAM model for a Pinatubo-like eruption with particle size information and color ratios obtained from SAGE II solar occultation measurements. The aerosol PSD in MAECHAM5-HAM is treated using a multi-modal aerosol microphysical model with four different modes. We discuss issues related to the comparison of measured and modelled particle size information and propose an approach to perform this comparison in an objective way.
15:30 UTC (+15) Stratospheric aerosol size distributions and extinction coefficients from SCIAMACHY limb observations and their comparison to balloon-borne measurements and ECHAM5-HAM simulations

Christine Pohl, Alexei Rozanov, Elizaveta Malinina-Rieger, Terry Deshler, Ulrike Niemeier, Claudia Timmreck, John P. Burrows
  1. University of Bremen, Institute of Environmental Physics, Germany
Stratospheric aerosols alter the radiative budget of the Earth affecting the global temperature and interact with stratospheric trace gases leading to ozone depletion. Thus, the vertical and spatial distribution of stratospheric aerosols is crucial for the initialization of climate models, investigation of geoengineering, validation of aerosol micro-physical models, and improvement of trace gas retrievals. We present an optimal estimation method to retrieve the stratospheric aerosol particle size distribution parameters (mode radius and distribution width, number density) or the extinction coefficient on a global scale from limb observations of SCIAMACHY (Scanning Imaging Absorption spectroMeter for Atmospheric ChartograpHY) operated aboard Envisat between 2002 and 2012. Retrieved particle size distribution profiles are compared with in-situ balloon-borne measurements from Laramie, Wyoming. Both data-sets agree below 25 km but differences increases with higher altitudes. A better consistency is obtained if the number density is retrieved in addition to the mode radius and distribution width. The stratospheric plume evolution after the eruption of Sarychev in the Kuril Islands, Russia, in June 2009 is investigated and compared to simulations from the aerosol-climate modelling system ECHAM5-HAM. Differences can be attributed to uncertainties in the simulated vertical aerosol transport.
15:45 UTC (+15) Satellite observations of volcanic eruptions leading to smaller average stratospheric aerosol sizes

Felix Wrana, Christian von Savigny, Larry W. Thomason
  1. University of Greifswald, Germany
We present surprising results of our stratospheric aerosol size retrieval which is using the SAGE III/ISS solar occultation measurements, that started in 2017. Due to the broad wavelength spectrum covered by the instrument a robust and simultaneous retrieval of the median radius and mode width of monomodal lognormal size distributions is possible. Other quantities like the number density can be calculated based on the results. We focus on three small to mid-intensity volcanic eruptions that were observed by SAGE III/ISS and that reached and perturbed the stratospheric aerosol layer: The Ambae eruptions (15.3°S) in spring of 2018 and the Raikoke (48.3°N) and Ulawun (5.05°S) eruptions, both in June 2019. While the Raikoke eruption led to an increase in the median radius of the stratospheric aerosols, which was to be expected and is in line with previous observations, the Ambae and Ulawun eruption had the opposite effect. After both eruptions the average aerosol size decreased, with lower median radii and narrower size distributions, while the number density increased strongly. The observation that volcanic eruptions may lead to smaller average stratospheric aerosol sizes, as also recently discussed by Thomason et al. (2021), is a novel one and should be of great interest to the modeling as well as remote sensing community. We will present the temporal and spatial evolution of the stratospheric perturbations and discuss what may distinguish those three eruptions from each other. References: Thomason, L. W., Kovilakam, M., Schmidt, A., von Savigny, C., Knepp, T., Rieger, L (2021). Evidence for the predictability of changes in the stratospheric aerosol size following volcanic eruptions of diverse magnitudes using space-based instruments. Atmospheric Chemistry and Physics, 21(2), 1143-1158. doi: 10.5194/acp-21-1143-2021
16:00 UTC (+15) OMPS LP V2.0 aerosol extinction profile data records

Ghassan Taha, Robert Loughman
  1. USRA / NASA Goddard Space Flight Center, USA
In this presentation, we will discuss the newly released Version 2.0 OMPS multi-wavelength aerosol extinction coefficient retrieval algorithm. The algorithm now produces aerosol extinction profiles at 510, 600, 674, 745, 869, and 997 nm wavelengths. The OMPS LP Version 2.0 data products are compared to the SAGE III/ISS, OSIRIS and CALIPSO missions and shown to be of good quality and suitable for scientific studies. The comparison shows significant improvements in the OMPS LP retrieval performance in the Southern Hemisphere and at lower altitudes. In particular, the extinction coefficients at 745, 869 and 997 nm are shown to be the most accurate, with relative accuracies and precisions close to 10% and 15% respectively, while the 675 nm relative accuracy and precision are on the order of 20%. The 510 nm extinction coefficient is shown to have limited accuracy in SH and is only recommended for use between 20 - 24 km, and only in the Northern Hemisphere. We will also present analysis of the OMPS LP aerosol extinction profile nine years global climatology, showing the impact of several volcanic eruptions and pyroCb events and their global distribution and transport in the upper troposphere and stratosphere.
16:15 UTC (+20) Stratospheric Sulfur and its Role in CLimate (SSiRC) - A SPARC activity

Stefanie Kremser, Larry W. Thomason
  1. Bodeker Scientific, New Zealand
SSiRC is an established SPARC (Stratosphere-Troposphere Processes and their role in Climate) activity, with SPARC being a core project within the World Climate Research Program (WCRP). SSiRC aims to foster collaboration across observational and modelling groups to better understand the stratospheric aerosol layer and the drivers for its observed variations. SSiRC’s primary focus is on the processes that form the stratospheric aerosol layer and, in particular, those related to volcanic injections of sulfur bearing aerosol and aerosol precursors like sulfur dioxide. Aerosol in the stratosphere form a generally optically thin veil with a well-known impact on climate and atmospheric chemistry. Large aperiodic volcanic eruptions, like that of Mt. Pinatubo in 1991, can change the stratospheric aerosol loading by factors of 100 or more effectively instantaneously. Following such events, stratospheric aerosol cool the planet as a whole and can create potentially devastating changes to regional weather patterns. In the modern era, large volcanic events can temporarily slow the pace of anthropogenic global warming. Since 2000, variability of aerosol in the stratosphere has primarily been dominated by a steady drumbeat of small to moderate eruptions. However, the frequency of injections of smoke from wildfires has become more common and events like the Canadian wildfires of 2017 and the colossal Australia fires of 2019/2020 injected smoke as levels comparable to moderate volcanic events. The degree to which these events are a “new normal” or simply exceptions is among the issues that SSiRC seeks to address. Thus, beyond sulfur, SSiRC seeks to understand the role of non-sulfur aerosol in the overall morphology of stratospheric aerosol and their subsequent impact on climate. These diverse aerosols include smoke, volcanic ash, meteoritic dust, and organic aerosols. In this presentation we will present an overview of the current SSiRC’s science questions and its activities that help illuminate those questions. Among these activities are understanding the sulfur burden and long-term aerosol variability including the construction of climatologies and the recovery of historical data sets.
Chairs: Ghassan Taha, Rob Damadeo
Trace Gases
Chairs: Gabriele Stiller, Natalya Kramarova
13:00 UTC (+15) OMPS LP Aerosol Algorithm Development

Robert Loughman, Ghassan Taha, Pete Colarco, Tong Zhu, the OMPS Limb Science Team
  1. Hampton University, USA
This presentation focuses on recent and ongoing work to develop NASA’s OMPS LP aerosol extinction coefficient retrieval algorithm, building on the recently-released Version 2 (V2) dataset. The V2 algorithm produces aerosol extinction retrievals at several wavelengths from 500 – 1000 nm. Updates made to the algorithm's limb scattering radiative transfer and retrieval models will be discussed and evaluated.
OSIRIS Ozone version 7

Chris Z. Roth, Daniel J. Zawada, Adam E. Bourassa, Douglas A. Degenstein
  1. Institute of Space and Atmospheric Studies, University of Saskatchewan, Canada
We present the newest version of the OSIRIS ozone dataset, the retrieval algorithm changes, and improvements to the forward model since the version 5 dataset.
13:15 UTC (+15) GOMOS aerosol products for the Copernicus Climate Change Service: an update

Christine Bingen, Charles Robert, Filip Vanhellemont, Nina Mateshvili
  1. Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Belgium
The stratospheric aerosol extinction derived from GOMOS using the AerGOM algorithm is one of the aerosol products delivered to the Copernicus Climate Change Service (C3S). AerGOM, the retrieval algorithm optimized for aerosol products, is still the object of improvements, and last developments integrates the results of a large investigation of the AerGOM performance for trace gas retrieval. Taking into account the lessons learned from these investigations, the retrieval strategy of the Level 2 GOMOS extinction was adapted for use in the GOMOS product delivered to C3S. In this communication, we present the latest version of the Level 2 AerGOM retrieval, with a full validation against contemporaneous satellite experiments, and present the updated version of the corresponding Level 3 C3S product.
OMPS Limb profiler verification with NOAA Umkehr and ozonesonde time series

Irina Petropavlovskikh, Koji Miyagawa, Jeannette Wild, Natalya Kramarova, Eric Beach, Lawrence Flynn
  1. NOAA Global Monitoring Laboratory and CU/CIRES, USA
The 1987 Montreal Protocol and its amendments regulate ozone-depleting substance production. The WMO/UNEP Ozone assessment (2018) confirmed stratospheric ozone recovery. However, some differences in trends derived from multiple combined satellite records were found. Some of these combined records use OMPS limb profiler information and the others use nadir profiler retrievals. Since the OMPS LP and NP records began in 2012 they weigh significantly in the 20-years long ozone recovery period. It is thus important to make sure that these records are stable and do not influence the trends of combined satellite records. We present comparisons between OMPS LP, OMPS NP, and ground-based Umkehr and ozonesonde records from three NOAA stations.
13:30 UTC (+15) Retrieval of stratospheric aerosol extinction profiles from SCIAMACHY solar occultation measurements with an Optimal Estimation approach – preliminary results

Christoph G. Hoffmann [1], Alexei Rozanov [2], Felix Wrana [1], Christian von Savigny [1], John P. Burrows [2]
  1. Institute of Physics, University of Greifswald, Germany
  2. Institute of Environmental Physics, University of Bremen, Germany
Stratospheric aerosols are an important aspect of climate research as they significantly influence the radiative transfer by scattering and absorption and are a precursor of polar stratospheric clouds. Although stratospheric aerosols are globally observed by satellites since the 1970s, their coverage by observations can still be improved. Therefore, also retrieving aerosol parameters from past missions is still of interest. The Scanning Imaging Absorption spectrometer for Atmospheric CHartographY (SCIAMACHY) on Envisat measured the spectral signature of stratospheric aerosols (among that of many other species) from 2002 to 2012 in limb and occultation geometry. The aerosol data from the limb measurements have been retrieved and published in a number of publications. In contrast, the occultation measurements remained unpublished until they were recently presented by Noël et al., 2020, who used an onion peeling approach for the retrieval. We are also working on the retrieval of this solar occultation dataset, but use an Optimal Estimation approach in contrast to Noël et al., 2020. Since retrieval results from remote sensing measurements always depend on a number of assumptions, it is of scientific value to evaluate the same dataset with a different numerical technique in order to at least check the robustness of the results and maybe improve the reliability. One major difference between the approaches is, e.g., that the forward model SCIATRAN is run online in each retrieval iteration with updated aerosol properties by our approach. Our retrieval development is work in progress and we will present some preliminary results to discuss them with the community. The final data set will contain aerosol extinction profiles between about 15 and 30 km altitude for different wavelength ranges between about 380nm and 1500nm. The dataset will cover a latitude range of about 50°N to 70°N and the whole Envisat period from 2002 to 2012. References: Noël, S., Bramstedt, K., Rozanov, A., Malinina, E., Bovensmann, H., & Burrows, J. P. (2020). Stratospheric aerosol extinction profiles from SCIAMACHY solar occultation. Atmospheric Measurement Techniques, 13(10), 5643–5666. https://doi.org/10.5194/amt-13-5643-2020
Comparison of SAGE III/ISS NO2 measurements with ground-based observations from Lauder, NZ

David Flittner [1], Kimberlee Dube [2], Richard Querel [3]
  1. NASA Langley Research Center, USA
  2. Institute of Space and Atmospheric Studies, University of Saskatchewan, Canada
  3. National Institute of Water & Atmospheric Research Ltd, New Zealand
Nitrogen dioxide (NO2) has a key role in the ozone cycle of the stratosphere, making it an important piece of the puzzle regarding recovery of the ozone layer. The Stratospheric Aerosol and Gas Experiment III (SAGE III) installed onboard the International Space Station (ISS) makes routine measurements of the vertical distribution of NO2 concentration since June 2017 using the stable occultation technique. Here we make stratospheric NO2 comparisons between SAGE III/ISS measurements and ground-based observations from Lauder, NZ, which stretches back to 1980 and overlaps multiple forerunners of SAGE III/ISS. Although both data sets are acquired at sunrise/sunset, additional analysis is done to convert these different measurements to a common quantity for assessing the performance of the relatively young SAGE III/ISS NO2 record against this respected long-term record.
13:45 UTC (+15) Can smoke and sulfuric acid aerosol be distinguished in the SAGE III/ISS data?

T.N. Knepp, M. Kovilakam, L. Thomason, D. Flittner, R. Damadeo, K. Leavor
  1. NASA Langley Research Center, USA
Located on the Kuril archipelago (48.3 N, 153.3 E), the Raikoke volcano began injecting sul-fur dioxide and ash directly into the stratosphere (13-17 km) when it erupted on 22-June 2019with a volcanic explosivity index of 4. Coincident with this eruption were two major wildfires thatinjected smoke into the stratosphere: one in Siberia the other in Alberta, Canada. The volcanicash was quickly removed from the stratosphere, and the sulfur dioxide oxidized to produce sulfu-ric acid aerosol, which mixed with the wildfire smoke as the two circumnavigated the globe. Ofparticular interest is a cloud that broke off from the main Raikoke plume and moved south whilecontinuing to be lofted to higher altitudes. It was suggested that this rogue cloud contained smokefrom these wildfires, so we asked the question: Can the SAGE III/ISS extinction coefficient spectrabe used to discriminate between smoke and sulfuric acid aerosol? Herein we present preliminaryresults of our efforts to identify smoke and sulfuric acid aerosol using these extinction spectra. Wetest this method on four case-study events: 2018 Ambae eruption, 2019 Ulawun eruption, 2017Canadian pyroCb, 2020 Australian pyroCb. This method is then applied to the Raikoke eruptionto identify the presence of smoke and/or sulfuric acid aerosol.
Climatological studies using the Atmospheric Chemistry Experiment data set

Kaley A. Walker [1], Laura Saunders [1], Niall J. Ryan [1], Paul Jeffery [1], David Plummer [2], Patrick E. Sheese [1], Christopher Sioris [3]
  1. Department of Physics, University of Toronto, Canada
  2. Climate Research Division, Environment and Climate Change Canada, Canada
  3. Environment and Climate Change Canada, Canada
The Canadian-led Atmospheric Chemistry Experiment (ACE) mission completed its seventeenth year in orbit on board the SCISAT satellite in 2020. The long lifetime of ACE has provided a valuable time series of composition measurements that contribute to our understanding of ozone recovery, climate change and pollutant emissions. The two instruments on board SCISAT use infrared and UV-visible spectroscopy to make their solar occultation measurements. The ACE Fourier Transform Spectrometer (ACE-FTS) is an infrared FTS operating between 750 and 4400 cm-1 and the ACE-MAESTRO (Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) is a dual UV-visible-NIR spectrophotometer which was designed to extend the ACE wavelength coverage to the 280-1030 nm spectral region. This paper will describe current studies being undertaken using upper tropospheric and stratospheric climatologies derived from ACE measurements and from sampling the specified dynamics version of the Canadian Middle Atmosphere Model (CMAM39) to match the measurement climatologies. This work focuses on total inorganic chlorine, Cly, in the stratosphere and on ozone and water vapour in the UTLS.
14:00 UTC (+15) Deriving the Unimodal Lognormal Stratospheric Particle Size Distribution from OMPS-LP Observations for an Event Associated with the Canadian Boreal Fires in 2017 and Validating the Derived Angstrom exponent with SAGE Measurements

Ernest Nyaku, Omar Torres, P.K. Bhartia, Matthew DeLand
  1. NASA Goddard Space Flight Center, USA
  2. Science Systems and Applications, Inc., USA
Pyrocumulonimbus (pyroCb) clouds of mesoscale size in August of 2017 associated with wildfires in British Columbia injected large amounts of carbonaceous aerosols into the upper troposphere that reached the stratosphere in a few days. The presence of these aerosols in the Northern Hemisphere stratosphere were highlighted in the Ozone Mapping and Profiler Suite Limb Profiler (OMPS -LP) aerosol extinction retrievals. In this study, the 510nm residuals of an event from the OMPS -LP in late August 2017, are used to derive the mode width (sigma) of the unimodal lognormal particle size distribution (PSD). The derived PSD is used to compute the angstrom exponent (AE) which is then validated with the SAGE measured AE. An investigation to determine the variability of PSD with time is then done by considering how the PSD changed from August 2017 to March 2018. Further validations are performed by comparing the OMPS -LP extinction coefficients at 745nm with that of SAGE.
Stratospheric Aerosol and Gas Experiment III on the International Space Station (SAGE III/ISS) Validation of the Latest Version 5.2 Data Products

S. Kizer [1,2], M. Roell [2], D. Flittner [2], R.Damadeo [2], C. Roller [1,2], D. Hurst [3,4], E. Hall [3,4], A. Jordan [3,4], P. Cullis [3,4], B. Johnson [4], R. Querel [5]
  1. Science Systems and Applications, Inc., USA
  2. NASA Langley Research Center, USA
  3. Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, USA
  4. NOAA Earth System Research Laboratory (ESRL), Global Monitoring Division (GMD), USA
  5. National Institute of Water and Atmospheric Research (NIWA), New Zealand
The Stratospheric Aerosol and Gas Experiment III (SAGE III) instrument installed on the International Space Station (ISS) has completed over three and a half years of data collection and production of science data products. The SAGE III/ISS is a solar and lunar occultation instrument that scans the light from the Sun and Moon through the limb of the Earth’s atmosphere to produce vertical profiles of aerosol, ozone, water vapor, and other trace gases. It continues the legacy of previous SAGE instruments dating back to the 1970s to provide data continuity of stratospheric constituents critical for assessing trends in the ozone layer. This presentation shows the improvements to the SAGE water vapor product with the release of the newest data version. It also focuses on validation by comparing SAGE III/ISS v5.2 ozone and water vapor vertical profiles with those of in situ and satellite data.
14:15 UTC (+15) Stratospheric Aerosol Mass from the British Columbia 2017 and Australia 2020 pryroCb's

Omar Torres, Hiren Jethva, Ghassan Taha, Ernest Nyaku
  1. NASA Goddard Space Flight Center, USA
We use OMPS LP 997 nm extinction measurements, to estimate the aerosol mass associated with the two pyro-cumulonimbus events that injected unprecendented amounts of carbonaceous aerosols in the stratosphere over the last four years. We monitor the aerosol mass increase and decay over a year after each event. A comparative analysis results will be presented.
Assessment of the quality of ACE-FTS stratospheric ozone data

Patrick E. Sheese, Kaley A. Walker, Chris D. Boone, Adam E. Bourassa, Doug A. Degenstein, Lucien Froidevaux, C. Thomas McElroy, Donal Murtagh, James M. Russell III, Jason Zou
  1. University of Toronto, Canada
For the past 17 years, the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) instrument on the Canadian SCISAT satellite has been measuring profiles of atmospheric ozone. Currently, there are two operational versions of the level 2 ozone data—versions 3.6 and 4.1. This study will show how both products compare with correlative data from other limb-sounding satellite instruments, namely MAESTRO, MLS, OSIRIS, SABER, and SMR. In general, v3.6, with respect to the other instruments, exhibits a smaller positive bias (~2-4%) in the middle stratosphere than v4.1 (~2-9%). However, both data sets are biased due to field-of-view modelling errors, and when the data sets are corrected for this bias, the average overall v3.6 bias in the middle stratosphere is within ±4% and v4.1 exhibits a positive bias on the order of 0-5%. The bias exhibited in the v4.1 data tends to be stable to within ±1% per decade, whereas the v3.6 product tends to exhibit a significant negative trend on the order of 1-3% per decade.
14:30 UTC (+15) Detecting tropospheric aerosols in tropical regions using measurements from Suomi-NPP/OMPS Limb-Nadir and CALIPSO/CALIOP sensors

Wesley Combs, Omar Torres, Pawan Bhartia, Matthew Deland, Hiren Jethva, Ernest Nyaku
  1. NASA Goddard Space Flight Center, USA
The Ozone Mapping and Profiling Suite (OMPS) was launched aboard the Suomi-NPP satellite in 2011, and hosts three separate instruments: the limb profiler, nadir mapper, and nadir profiler. The Limb Profiler is designed to retrieve vertical profiles of ozone and aerosols, while the Nadir Mapper produces 36 cross-track measurements of total column ozone and aerosols. Historically, the Limb Profiler has been used to detect ozone and aerosols in the stratosphere and above. Here, we propose a method of combining data from both the limb and nadir instruments aboard OMPS to detect tropospheric aerosols such as smoke and dust at altitudes as low as 3 kilometers. We utilize the Nadir Mapper’s UV Aerosol Index as a method of both screening and confirmation in the analysis of vertical profiles from the Limb Profiler to find these aerosols and separate them from water and ice clouds. We apply this method to several case studies, where the Limb Profiler demonstrates unambiguous detection of low-altitude aerosols in the tropical region, and compare these observations to lidar products from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite. We find good agreement between the two sensors in detecting both low-altitude tropospheric aerosols and clouds. Our analysis, perhaps for the first time, has shown the potentials of using the OMPS Limb Profiler in detecting tropospheric aerosols in conjunction with Nadir Mapper and CALIOP lidar observations.
15 years of Odin-OSIRIS OH (3-1) nightglow

Anqi Li, Donal Murtagh, Chris Roth, Adam Bourassa, Ole Martin Christensen, Kristell Pérot, Doug Degenstein
  1. Chalmers University of Technology, Sweden
The infrared imager (IRI) of Odin-OSIRIS has been routinely measuring the 1.53 μm OH (3-1) emission since 2001, but processing of this complete dataset has not been done until recently. We will present an overview of the variations in the nighttime OH airglow manifested in this new OH dataset in terms of zonal mean volume emission rate profiles for at least 15 years of data. Thanks to Odin’s near-polar-orbit, an excellent coverage over the high latitudes is provided.
14:45 UTC (+15) BREAK
  Session 4B
15:00 UTC (+30) Conclusions / Discussion
Chairs: Nathaniel Livesey, David Flittner
David Flittner NASA / Langley Research Center
Glen Jaross NASA / Goddard Space Flight Center
Natalya Kramarova NASA / Goddard Space Flight Center
Nathaniel Livesey NASA / Jet Propulsion Laboratory


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