{"id":11956,"date":"2024-09-16T18:02:51","date_gmt":"2024-09-16T22:02:51","guid":{"rendered":"https:\/\/zobi.alcowep.com\/bourtagshdrevxnls658739\/aura-at-20-years\/"},"modified":"2024-09-16T18:02:51","modified_gmt":"2024-09-16T22:02:51","slug":"aura-at-20-years","status":"publish","type":"post","link":"https:\/\/zobi.alcowep.com\/bourtagshdrevxnls658739\/aura-at-20-years\/","title":{"rendered":"Aura at 20 Years"},"content":{"rendered":"<h2 style=\"text-align: center;\">Aura at 20 Years<\/h2>\n<p><!-- no image --><\/p>\n<div class=\" hds-module hds-module-full wp-block-nasa-blocks-secondary-navigation\">\n<div class=\"hds-secondary-navigation-wrapper z-top width-100 padding-0\">\n<div class=\"hds-secondary-navigation width-full border-bottom-1px text-center hds-color-mode-dark hds-module hds-module-full wp-block-nasa-blocks-hdsnav\"><button type=\"button\" class=\"hds-secondary-nav-mobile-button display-flex tablet:display-flex desktop:display-none width-full flex-align-center 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margin-right-auto\">\n<figure class=\"hds-media-inner hds-cover-wrapper hds-media-ratio-fit \"><a href=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-feature-article-banner.png\" rel=\"noopener\"><img fetchpriority=\"high\" decoding=\"async\" width=\"1037\" height=\"81\" src=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-feature-article-banner.png?w=1037\" class=\"attachment-2048x2048 size-2048x2048\" alt=\"Feature Article header\" block_context=\"nasa-block\" srcset=\"https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-feature-article-banner.png 1037w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-feature-article-banner.png?resize=300,23 300w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-feature-article-banner.png?resize=768,60 768w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-feature-article-banner.png?resize=1024,80 1024w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-feature-article-banner.png?resize=400,31 400w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-feature-article-banner.png?resize=600,47 600w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-feature-article-banner.png?resize=900,70 900w\" sizes=\"(max-width: 1037px) 100vw, 1037px\" loading=\"eager\"><\/a><\/figure>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"padding-top-5 padding-bottom-3 width-full maxw-full hds-module hds-module-full wp-block-nasa-blocks-article-intro\">\n<div class=\"width-full maxw-full article-header\">\n<div class=\"margin-bottom-2 width-full maxw-full\">\n<p class=\"label carbon-60 margin-0 margin-bottom-3 padding-0\">14 min read<\/p>\n<h1 class=\"display-48 margin-bottom-2\">Aura at 20 Years<\/h1>\n<\/div>\n<\/div>\n<\/div>\n<p><strong>Introduction<\/strong><\/p>\n<p>In the 1990s and early 2000s, an international team of engineers and scientists designed an integrated observatory for atmospheric composition \u2013 a bold endeavor to provide unprecedented detail that was essential to understanding how Earth\u2019s ozone (O<sub>3<\/sub>) layer and air quality respond to changes in atmospheric composition caused by human activities and natural phenomena. This work addressed a key NASA Earth science objective. Originally referred to as Earth Observing System (EOS)\u2013CHEM (later renamed <a href=\"https:\/\/aura.gsfc.nasa.gov\/about.html\" rel=\"noopener\"><strong>Aura<\/strong><\/a>,) the mission would become the third EOS Flagship mission, joining EOS-AM 1 (Terra) launched in 1999 and EOS-PM 1 (Aqua), launched in 2002. The Aura spacecraft \u2013 see <strong>Figure 1<\/strong> \u2013 is similar in design to Terra and identical to Aqua. Aura and its four instruments were launched on July 15, 2004 from Vandenberg Air Force Base (now Space Force Base) in California \u2013 see <strong>Photo<\/strong>.<\/p>\n<div class=\"hds-media hds-module wp-block-image\">\n<div class=\"margin-left-auto margin-right-auto nasa-block-align-inline\">\n<div class=\"hds-media-wrapper margin-left-auto margin-right-auto\">\n<figure class=\"hds-media-inner hds-cover-wrapper hds-media-ratio-fit \"><a href=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-1.jpg\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" width=\"1440\" height=\"1144\" src=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-1.jpg?w=1440\" class=\"attachment-2048x2048 size-2048x2048\" alt=\"Aura 20 figure 1\" block_context=\"nasa-block\" srcset=\"https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-1.jpg 1440w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-1.jpg?resize=300,238 300w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-1.jpg?resize=768,610 768w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-1.jpg?resize=1024,814 1024w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-1.jpg?resize=400,318 400w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-1.jpg?resize=600,477 600w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-1.jpg?resize=900,715 900w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-1.jpg?resize=1200,953 1200w\" sizes=\"auto, (max-width: 1440px) 100vw, 1440px\"><\/a><\/figure><figcaption class=\"hds-caption padding-y-2\">\n<div class=\"hds-caption-text p-sm margin-0\"><strong>Figure 1<\/strong>. An artist\u2019s representation of the Aura satellite in orbit around the Earth.<\/div>\n<div class=\"hds-credits\"><strong>Image credit:<\/strong> NASA<\/div>\n<\/figcaption><\/div>\n<\/div>\n<\/div>\n<div class=\"hds-media hds-module wp-block-image\">\n<div class=\"margin-left-auto margin-right-auto nasa-block-align-inline\">\n<div class=\"hds-media-wrapper margin-left-auto margin-right-auto\">\n<figure class=\"hds-media-inner hds-cover-wrapper hds-media-ratio-fit \"><a href=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/09\/photo.jpg\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" width=\"1440\" height=\"1801\" src=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/09\/photo.jpg?w=1440\" class=\"attachment-2048x2048 size-2048x2048\" alt=\"Aura nighttime launch photo\" block_context=\"nasa-block\" srcset=\"https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/photo.jpg 1440w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/photo.jpg?resize=240,300 240w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/photo.jpg?resize=768,961 768w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/photo.jpg?resize=819,1024 819w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/photo.jpg?resize=1228,1536 1228w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/photo.jpg?resize=320,400 320w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/photo.jpg?resize=480,600 480w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/photo.jpg?resize=720,900 720w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/photo.jpg?resize=959,1200 959w\" sizes=\"auto, (max-width: 1440px) 100vw, 1440px\"><\/a><\/figure><figcaption class=\"hds-caption padding-y-2\">\n<div class=\"hds-caption-text p-sm margin-0\"><strong>Photo<\/strong>.\u00a0 A photo of the nighttime launch of Aura on July 15, 2004.<\/div>\n<div class=\"hds-credits\"><strong>Image credit:<\/strong> NASA<\/div>\n<\/figcaption><\/div>\n<\/div>\n<\/div>\n<p>In 2014 <em>The Earth Observer<\/em> published an article called \u00a0\u201c<a href=\"https:\/\/eospso.nasa.gov\/sites\/default\/files\/eo_pdfs\/November-December_2014_color_508.pdf#page=4\" rel=\"noopener\"><strong>Aura Celebrates Ten Years in Orbit<\/strong><\/a>,\u201d [Nov\u2013Dec 2014, <strong>26<\/strong>:<strong>6<\/strong>, pp. 4\u201318] which details the history of Aura and the first decade of science resulting from its data. Therefore, the current article will focus on the science and applications enabled by Aura data in the last decade. It also examines Aura\u2019s future and the legacies of the spacecraft\u2019s instruments. Readers interested in more information on Aura and the scientific research and applications enabled by its data can visit the <a href=\"https:\/\/aura.gsfc.nasa.gov\/\" rel=\"noopener\"><strong>Aura website<\/strong><\/a>.<\/p>\n<div class=\"hds-media hds-module wp-block-image\">\n<div class=\"margin-left-auto margin-right-auto nasa-block-align-inline\">\n<div class=\"hds-media-wrapper margin-left-auto margin-right-auto\">\n<figure class=\"hds-media-inner hds-cover-wrapper hds-media-ratio-fit \"><a href=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/09\/20yearsof-aura-invite-2.png\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" width=\"1440\" height=\"997\" src=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/09\/20yearsof-aura-invite-2.png?w=1440\" class=\"attachment-2048x2048 size-2048x2048\" alt=\"aura 20 invite graphic\" block_context=\"nasa-block\" srcset=\"https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/20yearsof-aura-invite-2.png 1440w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/20yearsof-aura-invite-2.png?resize=300,208 300w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/20yearsof-aura-invite-2.png?resize=768,532 768w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/20yearsof-aura-invite-2.png?resize=1024,709 1024w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/20yearsof-aura-invite-2.png?resize=400,277 400w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/20yearsof-aura-invite-2.png?resize=600,415 600w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/20yearsof-aura-invite-2.png?resize=900,623 900w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/20yearsof-aura-invite-2.png?resize=1200,831 1200w\" sizes=\"auto, (max-width: 1440px) 100vw, 1440px\"><\/a><\/figure>\n<\/div>\n<\/div>\n<\/div>\n<p><strong>Recent Science Achievements from Aura\u2019s Instrument (in alphabetical order)<\/strong><\/p>\n<p><em>High Resolution Dynamics Limb Sounder<\/em><\/p>\n<p>The capabilities of the <a href=\"https:\/\/aura.gsfc.nasa.gov\/hirdls.html\" rel=\"noopener\"><strong>High Resolution Dynamics Limb Sounder<\/strong><\/a><strong> <\/strong>(HIRDLS) were compromised at launch and operations ceased in March 2008 due to an image chopper stall. Nevertheless, the HIRDLS team was able to produce a three-year dataset notable for high vertical resolution profiles of greater than 1 km (0.62 mi) for temperature and O<sub>3<\/sub> in the upper troposphere to the mesosphere. Though limited, the HIRDLS dataset demonstrated the incredible potential of the instrument for atmospheric research. So much so, that scientists are now in the study phase for a new instrument, part of the proposed <a href=\"https:\/\/www.nasa.gov\/news-release\/new-proposals-to-help-nasa-advance-knowledge-of-our-changing-climate\/\"><strong>Stratosphere Troposphere Response using Infrared Vertically-Resolved Light Explorer<\/strong><\/a> (STRIVE) mission, which would have similar capabilities as HIRDLS with advancements in spectral and spatial imaging. (STRIVE is one of four missions currently undergoing one-year concept studies, as part of NASA\u2019s Earth System Explorer Program, which was established in the <a href=\"https:\/\/www.nationalacademies.org\/our-work\/decadal-survey-for-earth-science-and-applications-from-space\" rel=\"noopener\">2017 Earth Science Decadal Survey<\/a>. Two winning proposals will be chosen in 2025 for full development and launch in 2030 or 2032.)<\/p>\n<p><em>Microwave Limb Sounder<\/em><\/p>\n<p>The <a href=\"https:\/\/aura.gsfc.nasa.gov\/mls.html\" rel=\"noopener\"><strong>Microwave Limb Sounder<\/strong><\/a> (MLS) was developed to study: 1) the evolution and recovery of the stratospheric O<sub>3<\/sub> layer; 2) the role of the stratosphere, notably stratospheric humidity, in climate feedback processes; and 3) the behavior of air pollutants in the upper troposphere. MLS measures vertical profiles from the upper troposphere at ~10 km altitude (6.2 mi) to the mesosphere at ~90 km (56 mi) of 16 trace gases, temperature, geopotential height, and cloud ice. Its unique measurement suite has made it the \u201cgo-to\u201d instrument for most data-driven studies of middle atmosphere composition over the last two decades.<\/p>\n<p>Data collection during the past decade has highlighted the ability of the stratosphere to exhibit surprising and\/or <em>envelope-redefining<\/em> behavior, (Envelope-redefining is a term that is used to refer to an event that greatly exceeded previous observed ranges of this event.) MLS observations have been crucial for the discovery and diagnoses of these extreme events. For example, in 2019, a stratospheric sudden warming over the southern polar cap in September \u2013 rare in the Antarctic \u2013 curtailed chemical processing, leading to an anomalously weak O<sub>3<\/sub> hole. As another example, prolonged hot and dry conditions in Australia during the subsequent 2019\u20132020 southern summer promoted the catastrophic \u201cAustralian New Year\u201d (ANY) fires. MLS observations showed that fire-driven <em>pyrocumulonimbus<\/em> convection lofted plumes of polluted air into the stratosphere to a degree never seen during the Aura mission.<\/p>\n<p>Apart from those individual plumes, smoke pervaded the southern lower stratosphere, leading to unprecedented perturbations in southern midlatitude lower stratospheric composition, with chlorine (Cl) shifting from its main <em>reservoir species<\/em>, hydrochloric acid (HCl), into the O<sub>3<\/sub>-destroying form, hypochlorite (ClO). Peak anomalies in chlorine species occurred in mid-2020 \u2013 months after the fires. State-of-the-art atmospheric chemistry models in which wildfire smoke has properties similar to those of sulfate (SO<sub>4<\/sub>) aerosols were unable to reproduce the observed chemical redistribution. New model simulations assuming that HCl dissolves more readily in smoke than in SO<sub>4<\/sub> particles under typical midlatitude stratospheric conditions better match the MLS observations.<\/p>\n<p>As extraordinary as these events were, their impacts on the stratosphere were spectacularly eclipsed by the impact of the January 2022 eruption of the Hunga Tonga-Hunga Ha\u2019apai\u00a0 (Hunga) volcano in the Pacific Ocean. The Hunga eruption lofted about 150 Tg of water vapor into the stratosphere \u2013 with initial injections reaching into the mesosphere. The eruption almost instantaneously increased total stratospheric water vapor by about 10%. MLS was the only sensor able to track the plume in the first weeks following the eruption. The Hunga humidity enhancement resulted in an envelope-redefining, low-temperature anomaly in the stratosphere, in turn inducing changes in stratospheric circulation. Repartitioning of southern midlatitude Cl also occurred, though to a lesser degree than following the ANY fires and in a manner broadly consistent with known chemical mechanisms. The Hunga water vapor enhancement has not substantially declined in the 2.5 years since the eruption, and studies indicate that it will likely endure for several more years.<\/p>\n<p>Impacts of the Hunga humidity on polar O<sub>3<\/sub> loss have also been investigated. The timing and location of the eruption were such that the plume reached high southern latitudes only after the 2022 Antarctic winter vortex had developed. Since the strong winds at the vortex edge present a transport barrier, polar stratospheric cloud (PSC) formation and O<sub>3<\/sub> hole evolution were largely unaffected. When the vortex broke down at the end of the 2022 Antarctic winter, moist air flooded the southern polar region, increasing humidity in the region. Cold, moist conditions led to unusually early and vertically extensive PSC formation and Cl activation, but chemical processing ran to completion by mid-July, as typically occurs in southern winter. The cumulative chemical O<sub>3<\/sub> losses ended up being unremarkable throughout the lower stratosphere. The Hunga plume was also largely excluded from the 2022\u20132023 Arctic vortex. The 2023\u20132024 Arctic O<sub>3<\/sub> loss season was characterized by conditions that were dynamically disturbed and not persistently cold, and springtime O<sub>3<\/sub> was near or above average. The extraordinary stratospheric hydration from Hunga has so far had minimal impact on chemical processing and O<sub>3<\/sub> loss in the polar vortices in either hemisphere \u2013 see <strong>Figure 2<\/strong>.<\/p>\n<div class=\"hds-media hds-module wp-block-image\">\n<div class=\"margin-left-auto margin-right-auto nasa-block-align-inline\">\n<div class=\"hds-media-wrapper margin-left-auto margin-right-auto\">\n<figure class=\"hds-media-inner hds-cover-wrapper hds-media-ratio-fit \"><a href=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-2-144367.png\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" width=\"1440\" height=\"286\" src=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-2-144367.png?w=1440\" class=\"attachment-2048x2048 size-2048x2048\" alt=\"Aura 20 figure 2\" block_context=\"nasa-block\" srcset=\"https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-2-144367.png 1440w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-2-144367.png?resize=300,60 300w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-2-144367.png?resize=768,153 768w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-2-144367.png?resize=1024,203 1024w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-2-144367.png?resize=400,79 400w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-2-144367.png?resize=600,119 600w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-2-144367.png?resize=900,179 900w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/09\/figure-2-144367.png?resize=1200,238 1200w\" sizes=\"auto, (max-width: 1440px) 100vw, 1440px\"><\/a><\/figure><figcaption class=\"hds-caption padding-y-2\">\n<div class=\"hds-caption-text p-sm margin-0\"><strong>Figure 2.<\/strong> The evolution of MLS water vapor anomalies (deviations from the baseline 2005\u20132021 climatology) from January 2019 through December 2023 as a function of equivalent latitude at 700 K potential temperature in the middle stratosphere at ~27 km altitude (17 mi). Black contours mark the approximate edge of the polar vortex. The green triangle marks the time of the main Hunga eruption at latitude 20.54\u00b0S on January 15, 2022.<\/div>\n<div class=\"hds-credits\"><strong>Figure credit: <\/strong>Updated and adapted from a 2023 paper in Geophysical Research Letters<\/div>\n<\/figcaption><\/div>\n<\/div>\n<\/div>\n<p>With the end of Aura and MLS, the future for stratospheric limb sounding observations is unclear. While stratospheric O<sub>3<\/sub> and aerosol will continue to be measured on a daily, near-global basis by the Ozone Mapping and Profiler Suite (OMPS) Limb Profiler (OMPS-LP) instruments on the <a href=\"https:\/\/science.nasa.gov\/mission\/suomi-npp\/\" rel=\"noopener\"><strong>Suomi National Polar-orbiting Partnership<\/strong><\/a> (Suomi NPP) and <a href=\"https:\/\/www.nesdis.noaa.gov\/our-satellites\/currently-flying\/joint-polar-satellite-system\" rel=\"noopener\"><strong>Joint Polar Satellite System<\/strong><\/a><strong> <\/strong>(JPSS-2, -3, and -4) satellites, there are no confirmed plans for daily, near-global observations of either long-lived trace gases or halogenated species \u2013 both of which are needed to diagnose observed changes in O<sub>3<\/sub>. The only other sensor making such measurements, the Canadian <a href=\"https:\/\/www.asc-csa.gc.ca\/eng\/multimedia\/search\/image\/815\" rel=\"noopener\"><strong>Atmospheric Chemistry Experiment Fourier Transform Spectrometer<\/strong><\/a> (ACE\u2013FTS), is itself older than MLS and, as a solar occultation instrument, measures only 30 profiles-per-day, taking around a month to cover all latitudes. Similarly, no other sensor is set to provide daily, near-global measurements of stratospheric water vapor until the launch of the Canadian <a href=\"https:\/\/www.asc-csa.gc.ca\/eng\/satellites\/hawc\/\" rel=\"noopener\"><strong>High-altitude Aerosols, Water vapour and Clouds<\/strong><\/a><strong> <\/strong>(HAWC) mission in the early 2030s. Some potential new mission concepts are under consideration by both NASA and ESA, but they are subject to competition. Even if both instruments are ultimately selected, gaps in the records of many species measured by MLS are inevitable. The MLS PI is leading an effort to develop new technologies that would allow an instrument that could restart MLS measurements to be built in a far smaller mass\/power footprint (e.g., 60\u00a0kg, 90\u00a0W vs. 500\u00a0kg, 500\u00a0W for Aura MLS), and technologies exist for yet-smaller MLS-like instruments that could assume the legacy of the highly impactful MLS record at low cost in future decades.<\/p>\n<p><em>Ozone Monitoring Instrument<\/em><\/p>\n<p>The <a href=\"https:\/\/aura.gsfc.nasa.gov\/omi.html\" rel=\"noopener\"><strong>Ozone Monitoring Instrument<\/strong><\/a> (OMI) continues the <a href=\"https:\/\/eospso.nasa.gov\/missions\/total-ozone-mapping-spectrometer-earth-probe\" rel=\"noopener\"><strong>Total Ozone Mapping Spectrometer<\/strong><\/a><strong> <\/strong>(TOMS) record for total O<sub>3<\/sub> and other atmospheric parameters related to O<sub>3<\/sub> chemistry and climate. It employs hyperspectral imaging in a push-broom mode to observe solar backscatter radiation in the visible and ultraviolet.<\/p>\n<p>OMI is a Dutch\u2013Finnish contribution to the Aura mission, and its remarkable stability and revolutionary two-dimensional (2D) detector (spatial in one dimension and spectral in the other) has produced a two-decade record of science- and trend-quality datasets of atmospheric column observations. OMI continues the long-term record of total column O<sub>3<\/sub> measurements begun in 1979, and its observations of nitrogen dioxide (NO<sub>2<\/sub>), sulfur dioxide (SO<sub>2<\/sub>), formaldehyde (CH<sub>2<\/sub>O), and absorbing aerosols provided exceptional spatial resolution for study of anthropogenic and natural trends and variations of these pollutants around the world. Its radiometric and spectral stability has made it a valuable contributor for solar spectral irradiance measurements to complement dedicated solar instruments on other satellites. The many achievements made possible with OMI are documented in a <a href=\"https:\/\/doi.org\/10.5194\/acp-18-5699-2018\" rel=\"noopener\"><strong>review article<\/strong><\/a>.<\/p>\n<p>OMI\u2019s multidecade data records have revolutionized the ability to monitor <a href=\"https:\/\/airquality.gsfc.nasa.gov\/\" rel=\"noopener\"><strong>air quality changes around the world<\/strong><\/a>, even at the sub-urban level. In particular, <a href=\"https:\/\/airquality.gsfc.nasa.gov\/no2\" rel=\"noopener\"><strong>OMI NO<sub>2<\/sub><\/strong><\/a> data have been transformative. Recently, these data were used to <a href=\"https:\/\/airquality.gsfc.nasa.gov\/news\" rel=\"noopener\"><strong>track changes in air pollution associated with efforts to control the spread of SARS-CoV-2<\/strong><\/a>. OMI\u2019s long, stable data record allowed for changes in pollution levels in 2020 \u2013 at the height of global lockdowns \u2013 to be put into historical perspective, especially within the envelope of typical year-to-year variations associated with meteorological variability. Many research studies assessed the impact of the pandemic lockdowns on air pollution, supporting novel uses of OMI data for socioeconomic-related research. For example, OMI NO<sub>2<\/sub> data were shown to serve as an environmental indicator to evaluate the effectiveness of lockdown measures and as a significant predictor for the deceleration of COVID-19 spread. OMI NO<sub>2<\/sub> data were also used as a proxy for the economic impact of the pandemic as NO<sub>2<\/sub> is emitted during fossil fuel combustion, which is another proxy for economic activity since most global economies are driven by fossil fuels \u2013 see <strong>Animation<\/strong>.<\/p>\n<div class=\"width-full maxw-full margin-left-auto margin-right-auto hds-media-align-inline hds-module wp-block-nasa-blocks-video\">\n<div class=\"hds-cover-wrapper width-full maxw-full flex-column\">\n<div class=\"hds-video-container width-full embed-container\"><video title=\"aura20-animation\" class=\"video-js video-player vjs-fluid width-full\" data-setup='{\"controls\":true,\"preload\":\"auto\",\"plugins\":{\"mux\":{\"debug\":false,\"data\":{\"env_key\":\"91nns8oppqdfqc44lgo4b1gni\",\"player_name\":\"www.nasa.gov Player\",\"video_name\":\"aura20-animation\"}}}}' preload=\"none\"><source src=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/09\/aura20-animation.mp4\" type=\"video\/mp4\"><p class=\"vjs-no-js\">To view this video please enable JavaScript, and consider upgrading to a web browser that<br \/>\n\t\t\t\t\t<a href=\"https:\/\/videojs.com\/html5-video-support\/\" target=\"_blank\" rel=\"noopener\">supports HTML5 video<\/a><\/p>\n<p><\/source><\/video><\/div>\n<\/div>\n<div class=\"hds-media-caption hds-caption padding-y-2\">\n<div class=\"hds-caption-text p-sm margin-0\">\n<div><strong>Animation.<\/strong> OMI data show changes in average levels of NO<sub>2<\/sub> from March 20 to May 20 for each year from 2015 to 2023 over the northeast U.S. Levels in 2020 were ~30% \u00a0lower relative to previous years because of efforts to slow the spread of COVID-19. OMI data indicate similar reductions in NO<sub>2<\/sub> in cities across the globe in early 2020 and a gradual recovery in pollutant emissions in late 2020 into 2023. Additional images for other world cities and regions are available through the NASA <a href=\"https:\/\/svs.gsfc.nasa.gov\/\" rel=\"noopener\">Science Visualization Studio<\/a> website and the <a href=\"https:\/\/airquality.gsfc.nasa.gov\/\" rel=\"noopener\">Air Quality Observations from Space website<\/a>.<\/div>\n<\/div>\n<div class=\"hds-credits\">\n<div><strong>Animation<\/strong> <strong>credit: <\/strong><a href=\"https:\/\/svs.gsfc.nasa.gov\/\" rel=\"noopener\">NASA Science Visualization Studio<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n<p>OMI\u2019s datasets are being continued by successor 2D detector array instruments, such as the previously mentioned Copernicus Sentinel-5P TROPOMI mission, the Republic of Korea\u2019s <a href=\"https:\/\/sdghelpdesk.unescap.org\/technical-assistance\/best-practices\/geostationary-environment-monitoring-spectrometer-gems-republic\" rel=\"noopener\"><strong>Geostationary Environment Monitoring Spectrometer<\/strong><strong> <\/strong>(<\/a>GEMS), and NASA\u2019s <a href=\"https:\/\/tempo.si.edu\/overview.html\" rel=\"noopener\"><strong>Tropospheric Emissions: Monitoring of Pollution<\/strong><\/a> (TEMPO). All of these missions have enhanced spatial resolution relative to OMI, but have benefited from the innovative retrieval algorithms pioneered by OMI\u2019s retrieval teams.<\/p>\n<p><em>Tropospheric Emission Spectrometer<\/em><\/p>\n<p>The <a href=\"https:\/\/aura.gsfc.nasa.gov\/tes.html\" rel=\"noopener\"><strong>Tropospheric Emission Spectrometer<\/strong><\/a> (TES) provided vertically-resolved distributions of a number of tropospheric constituents, e.g., O<sub>3<\/sub>, methane (CH<sub>4<\/sub>), and various volatile organic compounds. The instrument was decommissioned in 2018 due to signs of aging associated with a failing Interferometer Control System motor encoder bearing. Nevertheless, TES measurements led to a number of key results regarding changes in atmospheric composition that were published over the past 10 years.<\/p>\n<p>Measurements from TES, OMI, and MLS showed that transport of O<sub>3<\/sub> and its precursors from East Asia offset about 43% of the decline expected in O<sub>3<\/sub> over the western U.S., based on emission reductions observed there over the period 2005\u20132010. TES <a href=\"https:\/\/tes.jpl.nasa.gov\/tes\/science\/highlights\/revealing-air-quality-over-megacities\/\" rel=\"noopener\"><strong>megacity measurements<\/strong><\/a> revealed that the frequency of high-O<sub>3<\/sub> days is particularly pronounced in South Asian megacities, which typically lack ground-based pollution monitoring networks. TES water vapor and semi-heavy water measurements indicated that water transpired from Amazonian vegetation becomes a significant moisture source for the atmosphere, during the transition from dry to wet season. The increasing water vapor provides the fuel needed to start the next rainy season. Measurements of CH<sub>4<\/sub> from TES and carbon monoxide (CO) from <a href=\"https:\/\/www2.acom.ucar.edu\/mopitt\" rel=\"noopener\"><strong>Measurements of Pollution in the Troposphere<\/strong><\/a><strong> <\/strong>(MOPITT) on Terra showed that CH<sub>4<\/sub> emissions from fires declined at twice the rate expected from changes in burned area from 2004\u20132014. This finding helped to balance the CH<sub>4<\/sub> budget for this period, because it offset some of the large increases in fossil fuel and wetland emissions. Through direct measurement of the O<sub>3<\/sub> greenhouse gas effect, TES instantaneous radiative kernels revealed the impact of hydrological controls on the O<sub>3<\/sub> radiative forcing and were used to show substantial radiative bias in <a href=\"https:\/\/www.ipcc.ch\/\" rel=\"noopener\"><strong>Intergovernmental Panel on Climate Change<\/strong><\/a> (IPCC) chemistry\u2013climate models. The TES team pioneered the retrieval of a number of species, such as peroxyacetyl nitrate, carbonyl sulfide, and ethylene.<\/p>\n<p>The spirit of TES lives on through the NASA <a href=\"https:\/\/tes.jpl.nasa.gov\/tropess\/\" rel=\"noopener\"><strong>TRopospheric Ozone and its Precursors from Earth System Sounding<\/strong><\/a><strong> <\/strong>(TROPESS) project, which generates data products of O<sub>3<\/sub> and other atmospheric constituents by processing data from multiple satellites through a common retrieval algorithm and ground data system. TROPESS builds upon the success of TES and is considered a bridge to allow the development of a continuous record of O<sub>3<\/sub> and other trace gas species as a follow-on to TES.<\/p>\n<p><strong>Future of Aura<\/strong><\/p>\n<p>In April 2023, Aura\u2019s mission operations team performed the last series of maneuvers to maintain its position in the <a href=\"https:\/\/atrain.nasa.gov\/\" rel=\"noopener\"><strong>A-Train constellation<\/strong><\/a> of satellites. Since then, Aura has begun <a href=\"https:\/\/aura.gsfc.nasa.gov\/Potential_Evolution_of_Aura.html\" rel=\"noopener\">drifting<\/a>. As of July 2024, Aura has descended ~5 km (3 mi) in altitude from ~700 km (435 mi) and its equator crossing time has increased by ~9 min from ~1:44 PM local time. This amount of drift is small, and the Aura MLS and OMI retrieval teams are ensuring the science- and trend-quality of the datasets.<\/p>\n<p>As Aura continues to drift, the amount of sunlight reaching its solar panels will slowly decrease and will no longer be able to generate sufficient power to operate the spacecraft and instruments by mid-2026. At this point, the amount of local time drift will still be relatively small \u2013 less than one hour \u2013 so the retrieval teams will be able to ensure quality for most data products until this time.<\/p>\n<p>In the remaining years, Aura\u2019s aging but remarkably stable instruments will continue to add to the unprecedented two decades of science- and trend-quality data of numerous key tropospheric and stratospheric constituents. Aura data will be key for monitoring the evolution of the Hunga volcanic plume and understanding its continued impact on the chemistry and dynamics of the stratosphere. Observations from MLS and OMI will also be used to evaluate data from new and upcoming instruments (e.g., ESA\u2019s <a href=\"https:\/\/www.esa.int\/Applications\/Observing_the_Earth\/Altius\" rel=\"noopener\"><strong>Atmospheric Limb Tracker for Investigation of Upcoming Stratosphere<\/strong><\/a><strong> <\/strong>(Altius); NASA\u2019s TEMPO, <a href=\"https:\/\/pace.gsfc.nasa.gov\/\" rel=\"noopener\"><strong>Plankton, Aerosol, Cloud, ocean Ecosystem<\/strong><\/a> (PACE), and <a href=\"https:\/\/eospso.nasa.gov\/missions\/total-and-spectral-solar-irradiance-sensor-2\" rel=\"noopener\"><strong>Total and Spectral Solar Irradiance Sensor-2<\/strong><\/a> (TSIS-2) missions, or at least used to help minimize the gaps between data collections.<\/p>\n<p><strong>Aura\u2019s Scientific Legacy<\/strong><\/p>\n<p>The Aura mission has been nothing short of transformative for atmospheric research and applied sciences. The multidecade, stable datasets have furthered process-based understanding of the chemistry and dynamics of atmospheric trace gases, especially those critical for understanding the causes of trends and variations in <a href=\"https:\/\/ozonewatch.gsfc.nasa.gov\/\" rel=\"noopener\"><strong>Earth\u2019s protective ozone layer<\/strong><\/a>. \u00a0<\/p>\n<p>The two decades that Aura has flown have been marked by profound atmospheric changes and numerous serendipitous events, both natural and man-made. The data from Aura\u2019s instruments have given scientists and applied scientists an unparalleled view \u2013 including at the sub-urban scale \u2013 of air pollution around the world, clearly showing the influence of rapid industrialization, environmental regulations designed to improve air quality, seasonal agricultural burning, catastrophic wildfires, and even a global pandemic, on the air we breathe. The Aura observational record spans the period that includes the decline of O<sub>3<\/sub>-destroying substances, and Aura data illustrate the beginnings of the recovery of the Antarctic O<sub>3<\/sub> hole, a result of unparalleled international cooperation to reduce these substances.<\/p>\n<p>Aura\u2019s datasets have given a generation of scientists the most comprehensive global view to date of critical gases in Earth\u2019s atmosphere and the chemical and dynamic processes that shape their concentrations. Many, but not all, of these datasets are being\/will be continued by successor instruments that have benefited from the novel technologies incorporated into the design of Aura\u2019s instruments as well as the innovative retrieval algorithms pioneered by Aura\u2019s retrieval teams.<\/p>\n<div class=\"hds-media hds-module wp-block-image\">\n<div class=\"margin-left-auto margin-right-auto nasa-block-align-inline\">\n<div class=\"hds-media-wrapper margin-left-auto margin-right-auto\">\n<figure class=\"hds-media-inner hds-cover-wrapper hds-media-ratio-fit \"><a href=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" width=\"1037\" height=\"24\" src=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png?w=1037\" class=\"attachment-2048x2048 size-2048x2048\" alt=\"Black Separator Line\" block_context=\"nasa-block\" srcset=\"https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png 1037w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png?resize=300,7 300w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png?resize=768,18 768w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png?resize=1024,24 1024w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png?resize=400,9 400w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png?resize=600,14 600w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png?resize=900,21 900w\" sizes=\"auto, (max-width: 1037px) 100vw, 1037px\"><\/a><\/figure>\n<\/div>\n<\/div>\n<\/div>\n<p><strong>Acknowledgements<\/strong><br \/>The author wishes to acknowledge the decades of hard work of the many hundreds of people who have contributed to the success of the international Aura mission. There are too many to acknowledge here and I\u2019m sure that many names from the early days are lost to time. I would like to offer special thanks to those scientists who, back in the 1980s, first dreamed of the mission that would become Aura.<\/p>\n<div class=\"hds-media hds-module wp-block-image\">\n<div class=\"margin-left-auto margin-right-auto nasa-block-align-inline\">\n<div class=\"hds-media-wrapper margin-left-auto margin-right-auto\">\n<figure class=\"hds-media-inner hds-cover-wrapper hds-media-ratio-fit \"><a href=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" width=\"1037\" height=\"24\" src=\"https:\/\/science.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png?w=1037\" class=\"attachment-2048x2048 size-2048x2048\" alt=\"Black Separator Line\" block_context=\"nasa-block\" srcset=\"https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png 1037w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png?resize=300,7 300w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png?resize=768,18 768w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png?resize=1024,24 1024w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png?resize=400,9 400w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png?resize=600,14 600w, https:\/\/smd-cms.nasa.gov\/wp-content\/uploads\/2024\/05\/eo-blackseparator-line.png?resize=900,21 900w\" sizes=\"auto, (max-width: 1037px) 100vw, 1037px\"><\/a><\/figure>\n<\/div>\n<\/div>\n<\/div>\n<p><strong><em><strong><em>Bryan Duncan<\/em><\/strong><\/em><br \/><em>NASA\u2019s Goddard Space Flight Center (GSFC)<\/em><\/strong><br \/><a href=\"mailto:bryan.n.duncan@nasa.gov\"><strong><em>bryan.n.duncan@nasa.gov<\/em><\/strong><\/a><\/p>\n<div class=\"nasa-gb-align-full width-full maxw-full padding-x-3 padding-y-0 nasa_template_article_a hds-module hds-module-full wp-block-nasa-blocks-credits-and-details\">\n<section class=\"padding-x-0 padding-top-5 padding-bottom-2 desktop:padding-top-7 desktop:padding-bottom-9\">\n<div class=\"grid-row grid-container maxw-widescreen padding-0\">\n<div class=\"grid-col-12 desktop:grid-col-2 padding-right-4 margin-bottom-5 desktop:margin-bottom-0\">\n<div class=\"padding-top-3 border-top-1px border-color-carbon-black\">\n<div class=\"margin-bottom-2\">\n<h2 class=\"heading-14\">Share<\/h2>\n<\/div>\n<div class=\"padding-bottom-2\">\n<ul class=\"social-icons social-icons-round\">\n<li class=\"social-icon social-icon-x\">\n\t\t\t\t\t\t\t<a href=\"https:\/\/x.com\/intent\/tweet?via=NASA&#038;text=Aura%20at%2020%20Years&#038;url=https%3A%2F%2Fscience.nasa.gov%2Fscience-research%2Fearth-science%2Faura-at-20-years%2F\" aria-label=\"Share on X.\"><br \/>\n\t\t\t\t\t\t\t\t<svg width=\"1200\" 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class=\"heading-14\">Related Terms<\/h2>\n<\/div>\n<ul class=\"article-tags\">\n<li class=\"article-tag\"><a href=\"https:\/\/science.nasa.gov\/earth-science\/\" rel=\"noopener\">Earth Science<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n<\/div>\n<p class=\"wpematico_credit\"><small>Powered by <a href=\"http:\/\/www.wpematico.com\" target=\"_blank\" rel=\"noopener\">WPeMatico<\/a><\/small><\/p>\n<p><a href=\"https:\/\/science.nasa.gov\/science-research\/earth-science\/aura-at-20-years\/\" target=\"_blank\" rel=\"noopener\">Get The Details&#8230;<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Introduction In the 1990s and early 2000s, an international team of engineers and scientists designed an integrated observatory for atmospheric composition \u2013 a bold endeavor to provide unprecedented detail that was essential to understanding how Earth\u2019s ozone (O3) layer and air quality respond to changes in atmospheric composition caused by human activities and natural phenomena. 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