The annual Stratospheric Aerosol and Gas Experiment III on the International Space Station (SAGE III/ISS) Science Team Meeting was held as a hybrid event hosted at NASA Langley Research Center on October 22 and 23, with over 50 participants. Nearly 30 technical presentations were given on topics ranging from the SAGE III/ISS mission and data product status, to research findings, plans and preliminary results utilizing SAGE products, to current and future members of the international constellation for stratospheric and upper tropospheric composition observations, to data assimilation systems (past, present and future), and to ground-based correlative measurements overlapping SAGE. This was the first Science Team Meeting for the cohort of Principal Investigator-led teams selected under the 3rd ROSES call targeting SAGE-like science, with at least 4 PIs new to the Science Team. One example of data usage was given by Dr. E. Knowland (MSU/GSFC-GMAO) regarding continuing a climate record of stratospheric water vapor (SWV) after the Aura MLS mission. She highlighted results from work as a PI during the 2nd Science Team cohort that made use of the GMAO Constituent data assimilation system (CoDAS) when it was fed SAGE III/ISS SWV observations. Key findings were:

• SAGE III/ISS stratospheric water vapor (SWV) assimilation improves SWV (R ≥ 0.48) relative to Atmospheric Chemistry Experiment-Fourier Transform Spectrometer compared to chemistry only (R ≥ 0.28)
• Assimilated SAGE III/ISS SWV captures broad, subpolar features like the tropical tape recorder, but is less able to capture isolated events
• SAGE III/ISS SWV profiles can thus continue the climate data record of Aura MLS, albeit with less coverage and fine-scale fidelity

These results lend confidence that SAGE III/ISS could serve as a bridge to future SWV observations after Aura MLS.

The mission looks forward to learning of new scientific advancements at the next annual meeting in 2025.

Credits: NASA

Updated status on stratospheric aerosols using recently released public data from SAGE III/ISS

Figure 1 below shows the bulk of the stratospheric aerosol layer around 10S latitude with slightly larger amounts in the Southern Hemisphere. This spatial distribution has been similar since early 2022 following the eruption of the Hunga Tonga–Hunga Haʻapai volcano in January 2022. However, Figure 2 shows that the core of the layer was actually refreshed somewhat by the eruption of Ruang in April 2024. This variable, but somewhat consistent, enhancement of the stratospheric aerosol layer compared to the first part of the SAGE III/ISS mission (2017) has produced a less than 1% shading of the Earth’s surface. Though small, it is non-negligible when balancing the energy budget of the Earth system, especially when examining changes in greenhouse gas contributions on these time scales.

Figure 1: Latitude – altitude cross-section of SAGE III/ISS stratospheric aerosol extinction coefficient for August 2024.

Figure 2: Aerosol extinction time series for tropics during the SAGE III/ISS mission. Most notable recent events are January 2022 eruption of Hunga Tonga and April 2024 eruption of Ruang.

NASA’s internship programs offer opportunities year-round for students to undertake meaningful and challenging projects that truly make an impact on humanity. Selected students are provided with training, mentoring, and career development throughout their session with some of the best minds in the world.

With over 100 applicants to the mission’s internship program, the Stratospheric Aerosol and Gas Experiment (SAGE) III on the International Space Station (ISS) team at NASA’s Langley Research Center in Hampton, VA selected three undergraduate student interns to work on a team science and engineering project during the 10-week summer session.

Matilda Damon, Linnea Johansson, and Riley Runyon worked together on developing the SAGE III limb scattering science processing code. Experimental SAGE III measurements of atmospheric limb scattered sunlight provide an innovative way to collect atmospheric data such as stratospheric ozone and aerosol. If successfully implemented, SAGE III atmospheric observations would cover a much larger range of times and Earth locations, providing even more atmospheric data to the public.

Currently, the SAGE III instrument uses solar and lunar occultation to capture these data products for the public. Such measurements only occur when the orbiting ISS experiences a sunrise, sunset, moonrise, or moonset. SAGE observes the light from the Sun or the Moon that passes through the atmosphere during both rise and set events to measure gases and particles in that region of the atmosphere. Occultation is a measurement of transmitted light, not scattered light. Adding limb scattering products to the SAGE inventory would add considerable value.

The intern team worked on coding a software Multiplicative Extended Kalman Filter (MEKF) that provides SAGE with an absolute attitude reference during limb scattering measurements. By combining solar edge detection with attitude rate data from the Disturbance Monitoring Package (DMP) subsystem aboard the SAGE III payload, the MEKF-derived attitude will supply high-accuracy telescope pointing information, which is important for ensuring the accuracy of the limb scattering atmospheric retrievals. The DMP is a three-axis ring laser gyroscope that the students used for attitude dead reckoning. Pointing error slowly accumulates as an angle random walk while dead reckoning in the absence of an occasional absolute attitude correction. Their filter will work to reduce the effects of this random walk between absolute measurements. To show how the filter impacts the attitude estimation, they also compared DMP dead reckoning directly with the filter results. To accomplish this, they relied heavily on quaternion mathematics. Quaternions are hypercomplex 4-D numbers that can represent rotations in 3-D space and are used for more than just aerospace applications. Your phone likely uses quaternion math to determine whether you’re holding it in portrait or landscape mode!

In addition to their limb scatter remote sensing project, the interns attended weekly SAGE III science and mission operations team meetings, weekly mentor check-ins, and several presentations on other missions, projects, and facilities at Langley. They particularly enjoyed learning about the history of NASA Langley’s Gantry.

Matilda Damon is a rising sophomore at Brown University studying astrophysics, engineering, and planetary science. At Brown, she rows for the Varsity Women’s Crew team, which helped prepare her for productive teamwork during her internship at NASA. She flies planes and studies astronomy in her free time at Brown.

“Knowing that code we wrote will help produce the gold standard of atmospheric data for the world is incredibly exciting. I am grateful to my mentors and peers for the opportunity to contribute to the SAGE III mission and for all the wisdom they imparted to me. Our mentors not only taught us coding, math, and science relevant to the mission, but also life skills such as collaboration, coding resource management, overcoming setbacks, and critical thinking,” said Damon.

Linnea Johansson is a rising junior at Washington and Jefferson College studying physics and mathematics. At school, she is a member of the varsity soccer team. She is also a leader of the Special Olympics Club and the Society for Physics Students. In her free time, she enjoys being outside and reading.

“This has been an incredible experience to help contribute to SAGE III. Working alongside my mentors has been rewarding and has taught me many valuable skills such as coding, version control, and working in a professional environment. I have also enjoyed the bonds that I have formed with the other interns,” said Johansson.

Riley Runyon is a rising junior at Washington and Jefferson College majoring in physics and mathematics. He is the leader of his school’s Climbing and Outdoors Club. He spends his free time running and playing his guitar.

“I loved every second of it. My mentors and coworkers are the coolest, most eclectic bunch of people I’ve ever had the privilege of knowing. Because of them and the work they assigned to me, I feel like I’ve learned how to think and work like an engineer and a scientist—systematically, precisely, and cautiously,” said Runyon.

The innovation, hard work, and dedication of the SAGE III summer internship team will continue to support and benefit the Langley mission team for the foreseeable future.

To apply for the next session of NASA internships, please visit intern.nasa.gov.

NASA Langley’s Richard Eckman and Robert Damadeo were elected to the prestigious International Ozone Commission (IO3C) at this year’s Quadrennial Ozone Symposium, held in Boulder, Colorado, from July 15-19, 2024. Membership in the IO3C is highly selective, limited to about 30 leading scientists globally, and is determined through a peer election process. Members serve four-year terms with the possibility of renewal, contributing to the global study and analysis of atmospheric processes related to ozone.

The IO3C plays a crucial role in organizing studies of ozone worldwide, including ground-based and satellite measurement programs to better understand atmospheric composition and ozone dynamics. The study of ozone, Earth’s sunscreen, is important because of the large role it plays in protecting the Earth from harmful levels of ultraviolet solar radiation, as well as its role as a greenhouse gas in Earth’s climate system.

Eckman started his career in atmospheric science research almost 40 years ago as a grad student at the University of Colorado. In 1988, he joined the NASA Langley Atmospheric Sciences Division and was involved in atmospheric modeling and data analysis. Over the last 15 years, Eckman has been managing the Atmospheric Composition Modeling and Analysis Program (ACMAP) at NASA Headquarters, as well as serving as the Program Scientist for the Earth science instruments on the Deep Space Climate Observatory (DSCOVR) and the Stratospheric Aerosol and Gas Experiment (SAGE) III on the International Space Station.

“I am honored to be recognized by the IO3C and elected as a member of the commission. It’s been a dream career, and the IO3C recognition is like icing on the cake,” said Eckman.

Damadeo currently serves as a Co-Principal Investigator for the SAGE IV project, and the Lead Algorithm Scientist for the SAGE III on ISS mission.

Not only has Damadeo worked on past, present and future SAGE missions, but he continues to do extensive research on long-term trends in stratospheric ozone. In particular, he has been a part of the LOTUS (Long-term Ozone Trends and Uncertainties in the Stratosphere) effort since its inception in 2016 and is currently the leader. LOTUS is an APARC (Atmospheric Processes And their Role in Climate) sponsored effort whose primary goal is to foster collaboration within the scientific community to provide vital contributions to the World Meteorological Organization (WMO) Ozone Assessment in an organized and cohesive way. Work performed under LOTUS has been responsible for a significant amount of content featured in the 2018 and 2022 Assessments.

“I am honored to be elected to the IO3C by my peers and colleagues,” said Damadeo.

To learn more about the IO3C, please visit https://www.io3c.org.  

The 3rd cohort of SAGE III/ISS Science Team selections have been made from proposals submitted to the NASA ROSES 2023 A.30 solicitation. Total funding of the 10 investigations selected is approximately $4.8 million, over a period of three years, to begin by mid-year 2024. The range of topics touch all the current occultation science products with a majority emphasizing stratospheric aerosols, including 4 related to smoke in the stratosphere. Several proposals point to the unique position of the SAGE III/ISS mission to carry forward the record of stratospheric water vapor from heritage missions to future, yet unnamed, ventures. Many projects will combine SAGE III/ISS data with other datasets to examine questions spanning time scales outside the growing 7-year mission record.

The Principal Investigators are:

Sean Davis (NOAA Earth System Research Laboratory)
Lars Kalnajs (University of Colorado at Boulder)
Cheng-Hsuan Lu (State University of New York at Albany)
Luis Millan Valle (Jet Propulsion Laboratory)
Mahesh Varma Mundakkara Kovilakam (ADNET Systems, Inc./NASA Langley Research Center)
Brian Soden (University of Miami, Key Biscayne)
Pamela Wales (Goddard Space Flight Center)
Hsiang-Jui (Ray) Wang (Georgia Institute of Technology)
Jun Wang (University of Iowa, Iowa City)
Jianglong Zhang (University of North Dakota)
In addition, Professor Jun Wang has been selected as the Science Team Leader.

Further details on the selections can be found here.
The SAGE III/ISS mission looks forward to advancements and new insights to be gained by the new Science Team.

Stratospheric aerosol plays an important role in chemistry and climate. Space-based observations of their optical properties have been key elements of the study of the effects of major volcanic and extreme fire events. To aid users of SAGE III/ISS Level 2 aerosol data, the mission is releasing a Level 2 aerosol auxiliary product that identifies cloud-free observations using the method of Kovilakam et al. 2023 (https://doi.org/10.5194/amt-16-2709-2023). The algorithm is similar to that developed for the Global Space-based Stratospheric Aerosol Climatology (GloSSAC), in which SAGE III/ISS data plays a crucial role alongside other space-based measurements (asdc.larc.nasa.gov/project/GloSSAC). The new Level 2 aerosol auxiliary product is released at the same cadence as the L2 solar products. For general ease of use, the results are grouped into monthly netcdf file.

Information about these new data products can be found at the following ASDC link: https://asdc.larc.nasa.gov/project/SAGE III-ISS

These data products are available from the ASDC via the following options:

Earthdata Search

Direct Data Download

OPeNDAP

Time series of globally averaged Stratospheric Aerosol Optical Depth (SAOD) for 1020 nm. Credits: NASA/SSAI

On September 12 & 13, 2023, the Stratospheric Aerosol and Gas Experiment III on the International Space Station (SAGE III/ISS) held its sixth annual science team meeting. This year it was hosted by ROSES science team PI Dr. Hsiang Jui (Ray) Wang of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology in Atlanta, GA. The meeting was organized by the science team leader, Prof. Jun Wang (U. Iowa), Ray Wang, David Flittner, and Richard Eckman. This hybrid meeting was the first SAGE III/ISS STM held outside of LaRC. The facilities were top-notch, allowing science discussions both in-person and online.

The mission team briefed the science team on payload health, operations, data product status and plans for the future, data evaluation using correlative measurements, and the new ‘Quicklook’ data image portal. In short, with successful passage of the ESD review of operating missions, SAGE data products can be expected to be produced with the same quality/quantity for the remainder of this decade.

Research results concerning SAGE science were presented from various science team PIs, Co-Is and collaborators. Topics included: stratospheric aerosol sizes determined from SAGE data or combined with other sensors, especially after the Hunga Tonga – Hunga Ha’apai (HTHH) eruption; the progression of the HTHH injected water vapor; the key roles of SAGE data products in continuing important stratospheric databases beyond the certain end of the NASA Aura satellite and the Microwave Limb Sounder.

Figure 1 below is an example shown by M.C. McKee (LaRC) of SAGE ozone profile comparisons with surface-launched ozone-sondes from Observatory Haute-Provence (OHP). On average SAGE and OHP are within +/-5% from 17 to 32 km. Above 32 km the sonde results drift-off because of pump inefficiencies noted in presentations by Co-Is Drs. Anne Thompson (GSFC) and Ryan Stauffer (GSFC), who also showed the pump efficiencies can vary from sonde to sonde. This highlights the need for continual comparisons of the ground-based network with a stable ozone profile measurement technique like SAGE occultations. Figure 2 is SAGE ozone compared with other space-based instruments.

The mission looks forward to the next annual meeting, by which the results of the current AO for the third cycle of the ROSES SAGE III/ISS Science Team will be known.

Along with the recent release of the Stratospheric Aerosol and Gas Experiment (SAGE) III / International Space Station (ISS) v5.3 data, the mission is debuting a portal on the SAGE website for public viewing level 2 solar data products: SAGE III/ISS Level 2 Quicklook Browse Images (nasa.gov). The new tool provides a quick and easy view into the publicly released data.

Primarily, the vertically resolved data are segregated by time progressing from the entire length of the mission to-date to monthly zonal means, to weekly curtains and culminating in daily groupings of individual profiles. The monthly zonal means combine both sunrise and sunset events, while all other images are grouped by the rising or setting of the sun as seen from the ISS. For all but a few days a year, the type of solar events are the same at the ground/atmosphere as they are from the ISS.

“The team designed the portal to display our data in images covering timescales including days, weeks, and months to tailor the experience for users wanting to deep dive into specific events or to get a broader overview of how SAGE III has observed changes in our atmosphere,” said SAGE III Lead Data Scientist Kevin Leavor.

There are two streams of data to view: publicly released (original data is available at the Atmospheric Science Data Center) and expedited pre-release results. The main difference between the two streams is the latency, which in turn is driven by the availability of ancillary meteorological inputs.

SAGE III takes measurements across the globe using a technique called occultation, which involves looking at the light from the Sun or Moon as it passes through Earth’s atmosphere at the edge, or limb, of the planet. Every time the sun, or moon, rises and sets, SAGE uses the light that passes through the atmosphere to measure gases and particles in that region of the atmosphere.

The ISS provides a unique vantage point from which to take these measurements. The coverage from the ISS occurs over 30 times per day, taking about a month to cover the Southern Hemisphere, tropics, and Northern Hemisphere.

The figures below highlight some of the views available for the released solar data products. Figure 1, from the latitude band of Hunga Tonga – Hunga Ha’apai (HTHH), illustrates the initial appearance of the HTHH aerosol layer and its descent driven mainly by gravitational settling. Figures 2 and 3 are monthly zonal averages for the monthly data update in April 2023. The HTHH aerosol layer is mainly within the Southern Hemisphere, but has also spread to the Northern Hemisphere. The HTHH water layer has been distributed globally, more equally than the aerosol layer.

“We provide all of our species including gases, aerosols, and derived aerosol extinction ratios to leverage SAGE III’s strengths for our users, and visualize that information at a glance,” said Leavor. “Zonal regions are highlighted in our Mission Overviews to emphasize atmospheric events that have occurred over the entire coverage extent of the mission.”

This great addition to the mission website represents many hours of development by the SAGE III/ISS web and visualization teams.

“The SAGE III/ISS team hopes that this website is a tool for users to easily engage with science data produced by our mission. We are proud of our data product and what we’ve been able to do with it, and we want to share that with everyone,” said Leavor.

Figure 1: Mission summary 1021 nm aerosol-to-molecular extinction ratio for latitude band 10S to 20S that is available from the Quicklook portal. Several perturbations from episodic terrestrial events, notably the Jan. 2022 eruption of Hunga Tonga – Hunga Ha’apai. The ratio of how much the aerosol particles scatter light compared to the molecules in the air (like nitrogen and oxygen) is what scientists call the aerosol-to-molecular extinction ratio. This ratio can vary depending on the type and amount of particles present in the air, and it can be used to estimate the concentration of particles in the atmosphere, which is important for understanding air quality and climate change.

Figure 2: April 2023 aerosol-to-molecular extinction ratio for 1021 nm.

Figure 3: Water vapor mixing ratio for April 2023. Water vapor mixing ratio is a way to measure the amount of moisture or humidity present in the air. It is defined as the mass of water vapor present in a unit of dry air.

The newest version of SAGE III/ISS science data products are now publicly available at the NASA Atmospheric Science Data Center (ASDC). This new version (v5.3) replaces the previous version (5.2) and is the version for forward processing, but prior versions will still be available from ASDC. Several improvements are realized in v5.3. The most notable changes for the solar products are adjustments to the automated Quality Assurance (auto-QA) filtering of events and corrections for mechanical disturbances. An important upgrade for all products was choosing a slightly different representation of the ancillary meteorological fields available from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). 

For v5.3, the auto-QA has been adjusted to recover events around the Hunga Tonga eruption that were withheld by auto-QA in v5.2. These events were being filtered out by a step in the auto-QA where Chappuis ozone products “AO3” and “MLR” were compared and flagged if they differ around the ozone maximum greater than a certain threshold. These 64 events were reviewed, deemed to be releasable, the auto-QA threshold was disabled, and the events are available in v5.3. 

The nature of the occultation technique used by the SAGE series of instruments requires accurate and precise pointing knowledge. On a spacecraft with a relatively benign mechanical vibration environment, like SAGE II experienced on the Earth Radiation Budget Satellite, the developed methodology performs superbly, allowing the retrieval of precise ozone profiles from SAGE II observations. However, operating on the ISS poses challenges, as it is frequently visited by vehicles, performs maneuvers, and experiences other mechanical disturbances that affect the pointing of the instrument during measurements. A Disturbance Monitoring Package (DMP) comprised of a miniature inertial measurement unit built by Honeywell Aerospace that measures rotation in inertial space using ring laser gyroscopes oriented about three orthogonal axes is used to improve the pointing knowledge. With v5.3, data from the DMP have been incorporated into the science processing algorithm to correct pointing errors caused by these mechanical disturbances. The DMP correction has been determined to improve pointing accuracy in general and is applied to all observations unless DMP data are unavailable, and a DMP usage flag notifies users. DMP flags are included in the product files to indicate disturbances where pointing errors prior to correction exceeded mission requirements. Based on DMP data, major disturbances occur less than 10% of the time and are now corrected in v5.3. The DMP corrections are only applied to the solar products and are not implemented for lunar products at this time. Figure 1 illustrates the improvement in the uncertainty of the transmission (Level 1b) when the DMP corrections are utilized. 

For both lunar and solar products v5.3 processing uses 72-layer MERRA-2 data as opposed to the 42 level MERRA-2 data used in previous versions. Generally, this extends the MERRA-2 data to higher altitudes and has finer vertical resolution in the lower stratosphere and a better fit for SAGE observations. This change to the meteorological data created no significant differences below the mesosphere. 

Collectively the modifications in v5.3 result in a much more consistent SAGE dataset. Figure 2 depicts the tropical time series of aerosol extinction coefficient using v5.3 with annotations of volcanic eruptions and extreme wildfires punctuating the record.

Figure 1: Event by event statistics representing improvements in computed atmospheric transmission. Top panel: DMP computed deviations in the direction of the elevation scan mirror (arc-s) for 68th and 90th percentiles. Middle-panel: Derived transmission root mean square error without using DMP elevation deviations for a representative tangent altitude. Bottom-panel: Derived transmission root mean square error with using DMP elevation deviations to correct the pointing, producing a more consistent data set. Slide 10 of Hill et al. (2022).

Figure 2: Version 5.3 tropical aerosol extinction coefficient. SAGE III/ISS vertically resolved aerosol extinction coefficient for the tropics over the current mission duration. Brighter colors denote larger extinction values. Also plotted as circles are the daily average tropopause altitudes showing the invisible boundary between the troposphere below and the stratosphere above. Significant volcanic eruptions and extreme wildfires that have made a resulting mark on the stratosphere are annotated.

Data Access Methods:

Direct Data Download

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For questions regarding data usage, please ask us on the Earthdata Forum.

Related URLS: https://asdc.larc.nasa.gov/project/SAGE III-ISS

A Research Opportunities in Space and Earth Sciences (ROSES) call was put out on NASA’s Solicitation and Proposal Integrated Review and Evaluation System (NSPIRES) seeking proposals for members of the SAGE III/ISS Science Team. NASA’s goal of understanding the composition of Earth’s atmosphere and changes that are taking place is furthered by this research opportunity that allows additional studies to take place using data from instruments such as SAGE III/ISS.

Proposals are sought in six topical areas that appear below. The first five areas are presented in no particular priority order, while the sixth topic, independent validation, is deemed of somewhat lower priority. While NASA is soliciting proposals in all of the areas, it is not committing to funding proposals in each of these areas.

• Assessing Long-term Changes in Atmospheric Composition
• Aerosol and Cloud Studies
• Data Analysis and Modeling Efforts Using SAGE Data Sets
• Multi-sensor Data Product Development
• Limb Scatter Retrieval Algorithm Development or Adaptation
• Independent Validation

In addition to proposals for SAGE III/ISS Science Team membership, there is also the opportunity to propose for the position as Team Leader for the SAGE III/ISS Science Team.

Notices of intent are requested by September 21, 2023, and proposals are due November 3, 2023.

Learn more here: https://nspires.nasaprs.com/external/viewrepositorydocument/cmdocumentid=918580/solicitationId=%7b50D0255E-DD1D-A11D-D153-C508DE3BDE52%7d/viewSolicitationDocument=1/A.30%20SAGEIII.pdf

Questions concerning the SAGE III/ISS Science Team may be directed to Richard Eckman, who may be reached at richard.s.eckman@nasa.gov.