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Earth Observing System Aura
Goddard Space Flight CenterGreenbelt, Maryland 20771NP-2004-4-626-GSFC
E A R T H O B S E R V I N G S Y S T E M
To Understand and Protect Our Home PlanetN A S A E A R T H S C I E N C E E N T E R P R I S E
Earth Science Enterprise
PHOTOS OF EARTH’S ATMOSPHERE COURTESY OF EARTH SCIENCES AND IMAGE ANALYSIS LABORATORY,NASA JOHNSON SPACE CENTER. AURA SATELLITE IMAGE BY JESSE ALLEN (SSAI)
COLIN SEFTOR (RAYTHEON) AND CHRISTINA HSU (UMBC)
A Mission Dedicated to the Health of the Earth’s AtmosphereA Mission Dedicated to the Health of the Earth’s Atmosphere
HIRDLS: USA, United Kingdom
High Resolution Dynamics Limb SounderStratospheric and upper tropospheric trace gases and aerosolsmeasured by infrared limb emission
MLS: USA
Microwave Limb Sounder Stratospheric and upper tropospheric trace gases measured by microwave limb emission
OMI: Netherlands, Finland
Ozone Monitoring InstrumentTropospheric and stratospheric ozone, aerosols, air quality and surface ultraviolet radiation measured by backscatter ultraviolet and visible radiation
TES: USA
Tropospheric Emission SpectrometerTropospheric and lower stratospheric trace gases and aerosolsmeasured by nadir and limb infrared emission
A U R A I N S T R U M E N T S A Mission Dedicated to the Health of the Earth’s Atmosphere
The Earth’s Ozone Shield protects all life
Stratospheric ozone has decreased 3% globally between1980 and 2000 and thins by 50% over Antarctica in winterand spring. Depletion of the ozone layer allows more ultraviolet radiation to reach the surface. Increases inultraviolet radiation are known to have harmful effects on living things. The Montreal Protocol and its amend-ments have banned the use of ozone destroying chemicalsand the rate of ozone depletion seems to have slowed.Climate change will have an impact on how quickly ozone recovers.
The Earth’s Air Quality is fundamentalto public health and ecosystems
The atmosphere has no political boundaries; air pollutionmoves great distances across oceans and continents. Thequality of air has degraded over certain parts of the worldand has become a health issue. Severe air pollutionepisodes increase mortality.
The Earth’s Climate is affected bychanges in atmospheric composition
It is undeniable that human activity is beginning to alterthe climate. The global rise in surface temperatures sincethe 1950’s is correlated with the increase in greenhousegases. Changes in carbon dioxide, methane, nitrous oxide,ozone, cloud cover, water vapor and aerosols all contributeto climate change.
Aura is designed to answer questionsabout changes in our life-sustainingatmosphere
Aura’s four instruments will study the atmosphere’s chemistry and dynamics. Aura’s measurements will enableus to investigate questions about ozone trends, air qualitychanges and their linkage to climate change.
Aura’s measurements will provide accurate data for pre-dictive models and provide useful information for local andnational agency decision support systems.
Aura is the third in a series of large Earth observing plat-forms to be flown by the National Aeronautics and SpaceAdministration (NASA) with international contributions.Aura along with EOS Terra (launched December, 1999) andAqua (launched May, 2002) will provide an unprecedentedview of the global Earth system.
Earth’s atmosphere provides sustenance to all living things and protects life from the harsh space environment
How is theEarth changingand what are the consequencesfor life onEarth?
The Aura mission will explore the atmosphere’s natural variabilityand its responseto human activityso that we can better predictchanges in theEarth system.
The various gases in the atmosphere absorb or emit radiation at specific wavelengths dependingon their molecular structure. Aura’s instruments will measure atmospheric constituents byobserving the Earth over a large range in the electromagnetic spectrum. Measurements will bemade of solar backscatter radiation in the ultraviolet and visible regions and of thermal emission in the infrared and microwave regions.
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Ultraviolet Infrared MicrowaveVisible Submillimeter
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T he stratospheric ozone layer shields lifeon Earth from harmful solar ultraviolet(UV) radiation (wavelengths shorter than
340 nm). Research has clearly shown thatexcess exposure to UV radiation is harmful toagriculture and causes skin cancer and eyeproblems. Excess UV radiation may suppressthe human immune system.
Ozone is formed naturally in the stratospherethrough break-up of oxygen molecules (O2) bysolar UV radiation. Individual oxygen atomscan combine with O2 molecules to form ozonemolecules (O3). Ozone is destroyed when an
ozone molecule combines with an oxygen atomto form two oxygen molecules, or through catalytic cycles involving hydrogen, nitrogen,chlorine or bromine containing species. Theatmosphere maintains a natural balancebetween ozone formation and destruction.
The natural balance of chemicals in the strato-sphere has changed, particularly due to thepresence of man-made chlorofluorocarbons(CFCs). CFCs are non-reactive and accumulatein the atmosphere. They are destroyed in thehigh stratosphere where they are no longershielded from UV radiation by the ozone layer.
The stratospheric ozone layer shields us fromsolar ultraviolet radiation. Chemicals that destroyozone are formed by industrial and naturalprocesses. With the exception of volcanic injec-tion and aircraft exhaust, these chemicals arrivein the stratosphere through the tropical upwellingregion. Methane (CH4), chlorofluorocarbons(CFCs), nitrous oxide (N2O) and water are injectedinto the stratosphere through towering tropical
cumulus clouds. These compounds are brokendown by the ultraviolet radiation in the strato-sphere. Byproducts of the breakdown of thesechemicals are radicals such as NO2 and ClO thatcatalyze ozone destruction. Aerosols and cloudscan accelerate ozone loss through reactions oncloud surfaces. Thus volcanic clouds and polarstratospheric clouds can indirectly contribute toozone loss.
Destruction of CFCs yields atomic chlorine, anefficient catalyst for ozone destruction. Otherman-made gases such as nitrous oxide (N2O)and bromine compounds are broken down inthe stratosphere and also participate in ozonedestruction.
Satellite observations of the ozone layer beganin the 1970s when the possibility of ozonedepletion was just becoming an environmentalconcern. NASA’s Total Ozone MappingSpectrometer (TOMS) and StratosphericAerosol and Gas Experiment (SAGE) have provided long-term records of ozone. In 1985the British Antarctic Survey reported an unex-pectedly deep ozone depletion over Antarctica.The annual occurrence of this depletion, popu-larly known as the ozone hole, alarmed scien-tists. Specially equipped high-altitude NASAaircraft established that the ozone hole was due to man-made chlorine. TOMS and SAGEdata also showed smaller but significant ozone
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Is the stratospheric ozone layer recovering?
Ozone Facts
n In the present daystratosphere, the natu-ral balance of ozonechemistry has beenaltered by man-madechemicals, such aschlorofluorocarbons(CFCs).
n Recent data show thatozone is being depletedat a slower rate than adecade ago, but it istoo soon to tell if thistrend is a result of theinternational protocolsrestricting CFC produc-tion.
n Aura’s instruments willmeasure the totalozone column, ozoneprofiles and gasesimportant in ozonechemistry.
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Ozone Warms the Stratosphere
From the surface, temperatures decrease withaltitude. Then, in the stratosphere, tempera-tures begin to rise, because ozone absorbssolar UV energy, heating the stratosphere.Above 50 km ozone heating falls off and thetemperatures decrease again. Above 80 kmvery high energy solar radiation begins to heatthe atmosphere again.
Stratospheric Chemical Processes
Sources, Reservoirsand Radicals
Source gases – These gasesare nearly inert in the loweratmosphere, but they aresources of ozone-destroyingradicals when broken apartby ultraviolet radiation,reactions with the hydroxylradical (OH), or reactionswith excited atomic oxygen(O1D). CFCs are sources ofchlorine radicals and N2O is the source of nitrogen radicals.
Reservoirs – These gasesare less inert than sourcegases but do not destroyozone themselves. Reservoirgases are formed when radi-cals react with source gases,for example, chlorine atoms(Cl) react with methane mol-ecules (CH4) to produce thereservoir hydrochloric acid(HCl). Reservoirs are alsoformed when radicals reactwith each other, for example,OH reacts with nitrogen dioxide (NO2) to producenitric acid (HNO3).
Radicals – These are theozone destroying gases such as chlorine monoxide(ClO) and nitric oxide (NO).Radicals are freed from theirreservoir gases by photolysisand by chemical reactionsinvolving reservoir gases andother radicals.
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Thin clouds made of ice, nitric acid, and sulfuric acid mixtures form in the polar stratosphere when tem-peratures drop below -88 C (-126 F). In such polar stratospheric clouds (PSCs) active forms of chlorineare released from their reservoirs. This particular PSC appeared over Iceland at an altitude of 22 km onFebruary 4, 2003. Its beautiful colors result from refraction of sunlight by its very small ice crystals.
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Polar Stratospheric Clouds
Winter Polar Ozone in the Northern/Southern Hemispherelosses outside the Antarctic region. In 1987 an international agreement known as theMontreal Protocol restricted CFC production.In 1992, the Copenhagen amendments to theMontreal Protocol set a schedule to eliminateall production of CFCs.
Severe ozone depletion occurs in winter andspring over both polar regions. The polar strat-osphere becomes very cold in winter because ofthe absence of sunlight and because strongwinds isolate the polar air. Stratospheric tem-
peratures fall below –88 C. Polar stratosphericclouds (PSCs) form at these low temperatures.The reservoir gases HCl and ClONO2 react onthe surfaces of cloud particles and release chlorine.
Ground-based data have shown that CFCamounts in the troposphere are leveling off,while data from the Halogen OccultationExperiment (HALOE) on the UpperAtmosphere Research Satellite (UARS) haveshown that amounts of HCl, a chlorine reser-voir that is produced when CFCs are broken
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apart, are leveling off as well (See Global HClfigure). Recent studies have shown that therate of ozone depletion is also decreasing.
Recovery of the ozone layer may not be as sim-ple as eliminating the manufacture of CFCs.Climate change will alter ozone recoverybecause greenhouse gas increases will cause the stratosphere to cool. This cooling may temporarily slow the recovery of the ozonelayer in the polar regions, but will accelerateozone recovery at low and middle latitudes.
What will Aura do?
Aura’s instruments will observe the importantsources, radicals, and reservoir gases active inozone chemistry. Aura data will improve ourcapability to predict ozone change. Aura datawill also help untangle the roles of transportand chemistry in determining ozone trends.
UARS HALOE measurementsof stratospheric chlorine (HCl)at 55km show that internation-al controls on CFCs are work-ing. HCl amounts have leveledoff and are now decreasing.Aura’s MLS will continue theHALOE HCl record.
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Recovery predicted by model
Eruption of Pinatubo 65N - 65S
TOMS Global Ozone Compared with ModelAt both polar regions, climate and chem-istry combine to deplete ozone duringspring months. Dark blue indicates low-est ozone amounts. Arctic total ozoneamounts seen by TOMS in March 2003(above, left) were among the lowest everobserved in the northern hemisphere.
The Antarctic ozone hole of 2003(above, right) was the second largestever observed. The dark blue indicatesthe region of maximum ozone depletion.TOMS images (below) illustrate thedevelopment of the ozone hole duringthe 1980’s and 1990’s.
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Comparing models with observations allowsus to check how accurately we can predictstratospheric ozone trends. In the image tothe left, TOMS global ozone measurements(Nimbus 7, Meteor 3, Earth Probe) showthat ozone has a strong annual cycle, anddecreases following a major volcanic erup-tion. Global ozone has decreased overall byabout 3% since 1980. A model that calcu-lates annual mean ozone amounts com-pares favorably with TOMS observationsand predicts ozone layer recovery after2020. The model total ozone varies slowlydue to the 11-year solar cycle. Aura’s OMIwill continue the TOMS total ozone record.
Global HCl
When we try to pick out anything by itself, we find it is tied to everything else in the universe.
John Muir
(1838-1914)
U. S. naturalist,
explorer
Northern Hemisphere Southern Hemisphere
The Upper AtmosphereResearch SatelliteThe first comprehensive satellite measurementsof stratospheric gases, solar particle and radia-tion fluxes and upper atmosphere winds weremade by NASA’s Upper Atmosphere ResearchSatellite (UARS). UARS was deployed in 1991from the Space Shuttle Discovery and continuesto gather data from five of its 10 instruments.UARS was designed to study the chemistry anddynamics of the middle and upper stratospherewhile Aura is designed to study the lower strato-sphere and upper troposphere. Aura will continuemany of the measurements pioneered by UARS.
umpgal.gsfc.nasa.gov/uars-science.html
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and mid-western states tothe east coast of the UnitedStates, and sometimes evenfrom one continent to anoth-er. Observations and modelsshow that pollutants fromSoutheast Asia contribute topoor air quality in India.Pollutants crossing fromChina to Japan reach thewest coast of the UnitedStates. Pollutants originat-ing in the United States canreduce air quality in Europe.Precursor gases for as muchas ten percent of ozone insurface air in the UnitedStates may originate outsidethe country. We have yet toquantify the extent of inter-regional and inter-continen-tal pollution transport.
SCIAMACHY is a German, Dutch and Belgian instrument on theEuropean Space Agency Envisat satellite. SCIAMACHY is able to esti-mate the monthly average of tropospheric NO2 amounts over the UnitedStates. High levels of NO2 correspond to urban locations and specialemission sites like power plants. OMI will make similar measurementswith higher horizontal resolution and daily global coverage.
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Air Quality Facts
n Air quality is a continu-ing environmental con-cern because poor airquality impacts humanhealth and agriculturalproductivity.
n Ozone precursors arepollutant gases such ascarbon monoxide (CO),nitrogen dioxide (NO2),methane (CH4) andother hydrocarbons thatreact in the troposphereto produce ozone.Sulphur Dioxide (SO2) isa precursor for sulfateaerosol.
n Worldwide emissions ofnitrogen dioxide, carbonmonoxide, volatile hydro-carbons and aerosolshave increased consider-ably, but there is stilluncertainty in the emis-sion rates and distinc-tions between anthro-pogenic and naturalsources of these emis-sions.
n Aura measures andmaps five of the EPA’ssix “criteria pollutants,”helping to improve emis-sions inventories and todistinguish betweenanthropogenic and natu-ral sources.
A griculture and industrial activity havegrown dramatically along with thehuman population. Consequently, in
parts of the world increased emissions of pollu-tants have significantly degraded air quality.Respiratory problems and even prematuredeath due to air pollution occur in urban andsome rural areas of both the industrialized anddeveloping countries. Wide-spread burning foragricultural purposes (biomass burning) andforest fires also contribute to poor air quality,particularly in the tropics. The list of culpritsin the degradation of air quality includes tro-pospheric ozone, a toxic gas, and the chemicalsthat form ozone. These ozone precursors arenitrogen oxides, carbon monoxide, methane,and other hydrocarbons. Human activities suchas biomass burning, inefficient coal combus-tion, other industrial activities, and vehiculartraffic all produce ozone precursors.
The U.S. Environmental Protection Agency(EPA) has identified six criteria pollutants: carbon monoxide, nitrogen dioxide, sulfurdioxide, ozone, lead, and particulates (aerosols).Of these six pollutants, ozone has proved the most difficult to control. Ozone chemistryis complex making it difficult to quantify the contributions to poor local air quality.Pollutant emission inventories needed for pre-dicting air quality are uncertain by as much as50 percent. Also uncertain is the amount ofozone that enters the troposphere from thestratosphere.
For local governments struggling to meetnational air quality standards, knowing moreabout the sources and transport of air pollu-tants has become an important issue. Most pol-lution sources are local but satellite observa-tions show that winds can carry pollutants forgreat distances, for example from the western
What are the processes controlling air quality?
NASA is working with the EnvironmentalProtection Agency and the National Oceano-graphic and Atmospheric Administration to exam-ine how models will be used to forecast pollutionevents. Models use satellite data to begin a fore-cast. Satellites launched before Aura provide
Forecasting Severe Pollution Events
rough estimates of ozone and aerosols. Aura willprovide more detailed maps of pollutants such asozone and NO2 that can be combined with weath-er forecast models. These two images from theEPA AirNow website illustrate what these modelswill be able to do. The images show that the area
of unhealthy surfaceozone (red) moves fromTennessee (left panel) to eastern Pennsylvaniaand New Jersey (rightpanel) in the course ofthree days. In addition to forecasting, satellitedata and models candiscriminate betweenlocally produced pollution and pollutionthat is brought by transport. AUG 9 AUG 12
U.S. ENVIRONMENTAL PROTECTION AGENCY (EPA) AND NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION (NOAA)
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Tropospheric ozone comes from several sources.Biomass burning and industrial activity produce COand volatile organic compounds (VOCs) which areoxidized to form ozone. Nitrogen oxides (NOx) from
industrial processes, biomass burning, automobileexhaust and lightning also form troposphericozone. A small amount of tropospheric ozone alsocomes from the stratospheric ozone layer.
The Sources of Tropospheric Ozone
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Long Range Pollution Transport
The atmosphere can transport pollutants longdistances from their source. Satellite measure-ments by EOS Terra’s MOPITT instrumenthave shown carbon monoxide streams extend-ing almost 18,000 km from their source (thispage). TOMS has tracked dust and smokeevents from Northern China to the east coastof the United States (see back cover).
On July 7, 2002, MODIS on EOS-Terra andTOMS captured smoke from Canadian forestfires as the winds transported it southward (seepage 9). This pollution event was responsiblefor elevated surface ozone levels along the eastcoast. TOMS has high sensitivity to aerosolslike smoke and dust when they are elevated
above the surface layers. OMI will make simi-lar measurements with better spatial resolutionand will provide new information aboutaerosol characteristics.
What will Aura do?
The Aura instruments are designed to studytropospheric chemistry; together Aura’s instru-ments provide global monitoring of air pollu-tion on a daily basis. They measure five of thesix EPA criteria pollutants (all except lead).Aura will provide data of suitable accuracy toimprove industrial emission inventories, andalso to help distinguish between industrial andnatural sources. Because of Aura, we will beable to improve air quality forecast models.
Carbon Monoxide
Biomass burning and urban pollution plumes canbe followed using measurements of CO fromMOPITT on EOS Terra. Agricultural burning in
Two Satellite Views of Pollution Transport
MODIS July 7 ortho-rectified image shows smoke streamingsouthward from forest fires (red) in Canada.
TOMS July 7 image shows smoke streaming southward fromforest fires in Canada.
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South America and Africa produce plumes whichpropagate into the South Atlantic. The Africanplume also propagates into the Indian Ocean.Biomass. Burning in Southeast Asia produces a plume that extends across the Pacific.
The strongest arguments provenothing so long as the conclusions are not verified by experience.Experimental scienceis the queen of sciences and the goalof all speculation.
Roger Bacon
13th Century English
philosopher, scientist
Upper image shows raw RGB MODIS view of July 7, 2002smoke event. Lower image shows aerosol large mode particlefraction estimated using other MODIS data. Particles coagu-late with time, so the largest particles are seen farthest fromthe fire.
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Climate Change Facts
n Like carbon dioxide,ozone, aerosols, andwater vapor contributeto climate change.
n Gases such as carbondioxide (CO2), watervapor (H2O) and ozoneheat the troposphere bytrapping infrared radia-tion that would other-wise escape to space.Trapping infrared radia-tion is called “thegreenhouse effect” andthe gases that absorbthis radiation are called“greenhouse gases.”
n Improved knowledge ofthe sources, sinks andthe distribution ofgreenhouse gases areneeded for accurate pre-dictions of climatechange.
n Aura’s measurements ofozone, water vapor andaerosols in the tropo-sphere and lower strato-sphere will improve climate prediction.
Carbon dioxide and other gases trapinfrared radiation that would otherwiseescape to space. This phenomenon, the
greenhouse effect, makes the Earth habitable.Increased atmospheric emissions from industri-al and agricultural activities are causing cli-mate change. Industry and agriculture producetrace gases that trap infrared radiation. Theconcentrations of many of these gases haveincreased and thus have added to the green-house effect. Since the turn of the century, theglobal mean lower tropospheric temperaturehas increased by more than 0.4 C. Thisincrease has been greater than during any othercentury in the last 1000 years.
Ozone plays multiple roles in climate change,because it absorbs both ultraviolet radiation fromthe sun and infrared radiation from the Earth’ssurface. Tropospheric ozone is as important asmethane as a greenhouse gas contributor to cli-mate change. An accurate measurement of thedistribution of tropospheric ozone will improveclimate modeling and climate predictions.
Aerosols are an important but uncertain agentof climate change. Aerosols alter atmospherictemperatures by absorbing and scatteringradiation. Aerosols can either warm or coolthe troposphere. Therefore, aerosols also mod-ify clouds and affect precipitation. Sulfateaerosols can reduce cloud droplet size, makingclouds brighter so that they reflect more solarenergy. Black carbon aerosols strongly absorbsolar radiation, warming the mid-troposphereand reducing cloud formation. Poor know-ledge of the global distribution of aerosolscontributes to a large uncertainty in climateprediction.
Ozone absorbs solar radiation, warming thestratosphere. Man-made chlorofluorocarbonshave caused ozone depletion, leading to lowertemperatures. Low temperatures, in turn, leadto more persistent polar stratospheric cloudsand cause further ozone depletion in polarregions.
How is Earth’s climate changing?
Aerosols affect climate both directly by reflecting and absorbing sun-light and indirectly by modifying clouds. The TOMS aerosol index is anindicator of smoke and dust absorption. The image shows aerosolscrossing the Atlantic and Pacific oceans. Dust from the Saharadesert is carried westward toward the Americas. Asian dust and pollution travel to the Pacific Northwest.
Increasing carbon dioxide also affects the cli-mate of the upper atmosphere. Where theatmosphere is thin, increasing CO2 emitsmore radiation to space, thus cooling theenvironment. Observations show that overrecent decades, the mid to upper stratospherehas cooled by 1 to 6 C (2 to 11 F) primarilydue to increases in CO2. This cooling willproduce circulation changes in the strato-sphere that will change how trace gases aretransported.
Water vapor is the most important green-house gas. Some measurements suggest thatwater vapor is increasing in the stratosphere.This increase may be due to changes in thetransport of air between the troposphere andthe stratosphere caused by climate change, orit could be due to changes in the microphysi-cal processes within tropical clouds. Moremeasurements of upper tropospheric watervapor, trace gases and particles are needed tountangle the cause and effect relationships ofthese various agents of climate change. Wecan verify climate models of the atmosphereonly with global observations of the atmos-phere and its changes over time.
What will Aura Do?
Aura will measure greenhouse gases such asmethane, water vapor, and ozone in the uppertroposphere and lower stratosphere. Aura alsowill measure both absorbing and reflectingaerosols in the lower stratosphere and lowertroposphere, water vapor measurements insidethe high tropical clouds, and high vertical res-olution measurements of some greenhousegases in a broad swath (down to the clouds)across the tropical upwelling region. All ofthese measurements contribute key data forclimate modeling and prediction.
The chart at right distin-guishes among varioushuman and natural agentsof global climate changebetween 1750 and 2000.Greenhouse gases havebeen the most influentialagents of warming, and sul-phate aerosols have beenthe most influential agentsof cooling. Aura measure-ments will help climate mod-els by measuring stratos-pheric and troposphericozone and aerosol amounts.Aura measurements willalso help untangle climatefeedbacks by measuringupper tropospheric watervapor and cirrus clouds.
Global Climate Change
UARS MLS Upper Tropospheric Water Vapor and El Niño
Sept 1996 normal year
Earth Probe TOMS Aerosol Index
Water vapor measurements from MLS on UARS show the contrastbetween 1996 (a “normal” year) and 1997 (an “El Niño” year). In1996 the most convection and the highest mixing ratios for tropicalupper tropospheric water vapor (red) occur over Indonesia; the lowestmixing ratios for tropical upper tropospheric water vapor (blue) occurin the eastern Pacific. In 1997 the sea surface temperatures in thetropical eastern Pacific are much warmer than in 1996, and theregion of intense convection shifts eastward away from Indonesia.The situation is reversed in 1997 from 1996 with the highest mixingratios for upper tropospheric water vapor in the eastern Pacific, andvery low mixing ratios over Indonesia.
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HIRDLS Contributions toUnderstanding Air Quality
HIRDLS will measure ozone, nitric acid, andwater vapor in the upper troposphere andlower stratosphere. With these measurements,scientists will be able to estimate the amountof stratospheric air that descends into the troposphere and will allow us to separate natu-ral ozone pollution from man-made sources.
HIRDLS Contributions toUnderstanding Climate Change
HIRDLS will measure water vapor and ozone,both important greenhouse gases. The instru-ment is also able to distinguish between aerosoltypes that absorb or reflect incoming solar radia-tion. HIRDLS will be able to map high thincirrus clouds that reflect solar radiation.
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HIRDLS is an infrared limb-scanningradiometer measuring trace gases, temperature, and aerosols in the upper
troposphere, stratosphere, and mesosphere. The instrument will provide critical informa-tion on atmospheric chemistry and climate.Using vertical and horizontal limb scanningtechnology HIRDLS will provide accuratemeasurements with daily global coverage athigh vertical and horizontal resolution. TheUniversity of Colorado, the National Centerfor Atmospheric Research (NCAR), OxfordUniversity (UK) and Rutherford AppletonLaboratory (UK) designed the HIRDLS instru-ment. Lockheed Martin built and integratedthe instrument subsystems. The NationalEnvironmental Research Council funded theUnited Kingdom participation.
HIRDLS makes key contributions to each ofAura’s three science questions. A summary ofHIRDLS data products appears on page 29.
HIRDLS Contributions toUnderstanding Stratospheric Ozone
The largest ozone depletions occur in the polarwinter lower stratosphere. HIRDLS willretrieve high vertical resolution daytime andnighttime ozone profiles in this region.
HIRDLS will measure NO2, HNO3 and CFCs, gases that play a role in stratosphericozone depletion. Although international agreements have banned their production,CFCs are long-lived and will remain in thestratosphere for several more decades. By measuring profiles of the long-lived gases at1.2 km vertical resolution, from the upper tro-posphere into the stratosphere, HIRDLS willmake it possible to quantify the transport ofair from the troposphere into the stratosphere.
High Resolution Dynamics Limb Sounder
HIRDLS
HIRDLS Co-Principal
Investigators Dr.John Gille (left), andDr. John Barnett(right) hold a modelof the Aura space-craft. Gille andBarnett have ledthe developmentand application ofIR limb sounding.Gille and Barnett
and their team are responsible for the instrument calibration, develop-ment of the algorithms, monitoring instrument performance and dataprocessing. Dr. Gille is a senior researcher at the National Center forAtmospheric Research and a professor at the University of Colorado. Dr. Barnett is a Lecturer in atmospheric physics at Oxford University.
HIRDLS InstrumentCharacteristics
n HIRDLS is an advanced,scanning 21-channelinfrared radiometerobserving the 6-17micron thermal emis-sion of the Earth’slimb.
n Infrared instruments,without HIRDLS hori-zontal scanning capa-bility, have flown onprevious NASA atmos-pheric research satel-lites such as Nimbus 7and UARS.
n HIRDLS looks backwardand scans both verti-cally and horizontallyacross the satellitetrack. Very precisegyroscopes provideinstrument pointinginformation. To detectthe weak infrared radia-tion from the Earth’slimb, HIRDLS detectorshave to be kept at tem-peratures below liquidnitrogen. An advancedcryogenic refrigeratorwill keep the detectorscool.
HIRDLS spatial coverage hasbeen simulatedusing an atmos-pheric chemistrymodel. TheHIRDLS instru-ment team “flew”the spacecraftthrough the model to test theretrieval algorithmand demonstratethe ability ofHIRDLS to maptrace ozone.Colors representozone abundanceat 16 km altitude.
HIRDLS high vertical resolution measurementshave been demonstrated using model data. The solid line is the “true” profile taken from a model. The radiance that HIRDLS wouldobserve is computed from this profile. The redhorizontal lines show the ozone mixing ratiomeasurement and error retrieved with theHIRDLS algorithm.
Ozone Profile Simulated HIRDLS Ozone Measurements
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The need for high horizontal resolution measurements of the stratosphere is illustrated above. Using a model,the long-lived trace gas N2O is transported by observedwinds. The transport processes produce filamentarystructures that are predicted but have never beenobserved globally. HIRDLS high horizontal resolutionmeasurements will be able to observe these structureswhich are signatures of transport.
Simulated HIRDLS Sampling
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MLS is a limb scanning emissionmicrowave radiometer. MLS measuresradiation in the GHz and THz fre-
quency ranges (millimeter and submillimeterwavelengths). Aura’s MLS is a major techno-logical advance over the MLS flown on UARS.MLS will measure important ozone-destroyingchemical species in the upper troposphere andstratosphere. In addition, MLS has a uniqueability to measure trace gases in the presence ofice clouds and volcanic aerosols. NASA’s JetPropulsion Laboratory (JPL) developed, built,tested, and will operate MLS.
MLS contributes to each of Aura’s three sciencequestions. A summary of MLS data productsappears on page 29.
MLS Contributions to Understanding Stratospheric Ozone
Aura’s MLS will continue the ClO and HClmeasurements made by UARS. These measure-ments will inform us about the rate at whichstratospheric chlorine is destroying ozone. MLSwill also provide the first global measurementsof the stratospheric hydroxyl (OH) andhydroperoxy (HO2) radicals that are part of thehydrogen catalytic cycle for ozone destruction.In addition, MLS will measure brominemonoxide (BrO), a powerful ozone-destroyingradical. BrO has both natural and man-madesources.
Microwave Limb Sounder
MLS
MLS Instrument Characteristics
n MLS is an advancedmicrowave radiometerthat will measuremicrowave emissionfrom the Earth’s limb infive broad spectralbands. These bands arecentered at 118 GHz,190 GHz, 240 GHz, 640GHz, and 2.5 THz.
n MLS will measure tracegases at lower altitudesand with better preci-sion and accuracy thanits predecessor on UARS.MLS will obtain tracegas profiles with a verti-cal resolution of 3 km.
n MLS pioneers the useof planar diodes andmonolithic-millimeterwave integrated cir-cuits to make theinstrument more reli-able and resilient tolaunch vibration. MLSlooks outward from thefront of the spacecraft.
MLS measurements of ClO and HCl will beespecially important in the polar regions. TheHCl measurements tell scientists how stablechlorine reservoirs are converted to the ozonedestroying radical, ClO. Since the Arctic strat-osphere may now be at a threshold for moresevere ozone loss, Aura’s MLS data will beespecially important.
MLS Contributions to Understanding Air Quality
MLS measures carbon monoxide (CO) andozone in the upper troposphere. CO is animportant trace gas that can indicate theexchange of air between the stratosphere andtroposphere. CO is also a tropospheric ozoneprecursor and its appearance in the upper tro-posphere can indicate strong vertical transportfrom pollution events.
MLS Contributions to Understanding Climate Change
MLS’s measurements of upper troposphericwater vapor, ice content, and temperature will be used to evaluate models and thusreduce the uncertainty in climate forcing.MLS also measures greenhouse gases such asozone and N2O in the upper troposphere.
A U R A 1514 A U R A
Joe Waters of the NASA’s Jet PropulsionLaboratory is Principal Investigator for
Aura MLS, as he was for UARS MLS. Dr.Waters has led the development and application of microwave limb sounding sincestarting it in 1974. His team at NASA’s JPL,along with the MLS team at the University of Edinburgh (UK) led by Professor RobertHarwood, is responsible for development ofthe algorithms that generate MLS data prod-ucts, monitoring instrument performance,data processing, validation, and analyses.
UARS MLS has made unprecedentedmeasurements of water vapor in thelower stratosphere and upper tropo-sphere. The tropical measurementsindicate the year-to-year percentagevariation in water vapor as a differencefrom the mean value at each level.The upper tropospheric measurementis possible because MLS can makemeasurements in the presence of thinclouds that block infrared measure-ments. Air ascends slowly into thestratosphere (above 16 km) carryingthe water vapor signal from the tropi-cal tropopause upward.
UARS MLS simultaneously mapped key chemicalconstituents nitric acid, chlorine monoxide, andozone over the winter polar regions in bothNorthern (upper) and Southern (lower)Hemispheres where the greatest ozone lossoccurs. Aura MLS will map these and otherchemicals with better coverage and larger alti-
tude range than UARS MLS. Together withHIRDLS, Aura MLS will measure an array ofsource, radical and reservoir gases in the activeregion of the polar stratosphere to give a com-plete picture of the ozone depletion process andpredicted recovery. MLS will also make globalmeasurements of BrO, OH and HO2.
Earth’s Lower Stratosphere in 1996 Northern and Southern Winters
MLS Measurements of Water Vapor
16 km
26 km
6 km
MICHELLE SANTEE, IN WATERS, ET AL. “THE UARS AND EOS MICROWAVE LIMB SOUNDER (MLS) EXPERIMENTS,” J. ATMOSPHERIC SCIENCES,VOL. 56, PP 194-218, 15 JAN 1999.
WILLIAM READ, “DEHYDRATION IN THE TROPICALTROPOPAUSE LAYER: IMPLICATIONS FROM UARS MLS,” J.GEOPHYS. RES., VOL. 109, NO. D6,DOI:10.1029/2003_JD004056, 2004.”
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tion from MLS and HIRDLS to produce mapsof tropospheric ozone and nitrogen dioxide.OMI will also measure the tropospheric ozoneprecursor formaldehyde. Scientists will useOMI measurements of ozone and cloud coverto derive the amount of ultraviolet radiation(UV) reaching the Earth’s surface. TheNational Weather Service will use OMI data toforecast high UV index days for public healthawareness.
OMI Contributions to UnderstandingClimate Change
OMI tracks dust, smoke and industrial aerosolsin the troposphere. OMI’s UV measurementsallow scientists to distinguish reflecting andabsorbing aerosols and thus OMI measure-ments will help improve climate models.
16 A U R A
OMI is a nadir viewing spectrometerthat measures solar reflected andbackscattered light in a selected range
of the ultraviolet and visible spectrum. Theinstrument’s 2600 km viewing swath is per-pendicular to the orbit track, providing com-plete daily coverage of the sunlit portion of theatmosphere. OMI is Aura’s primary instrumentfor tracking global ozone change and will con-tinue the high quality column ozone recordbegun in 1970 by Nimbus-4 BUV. BecauseOMI has a broader wavelength range and bet-ter spectral resolution, OMI will also measurecolumn amounts of trace gases important toozone chemistry and air quality. OMI will mapaerosols and estimate ultraviolet radiationreaching the Earth’s surface. OMI’s horizontalresolution is about four times greater thanTOMS.
The Netherlands Agency for Aerospace Pro-grams (NIVR) and the Finnish MeteorologicalInstitute (FMI) contributed the OMI instru-ment to the Aura mission. The Netherlandscompanies, Dutch Space and TNO-TPD,together with Finnish companies, Patria, VTTand SSF, built the instrument.
OMI’s contributes to each of Aura’s three science questions. A summary of OMI dataproducts appears on page 29.
OMI Contributions to UnderstandingStratospheric Ozone
OMI will continue the 34-year satellite ozonerecord of SBUV and TOMS, mapping globalozone change. OMI data will supportCongressionally mandated and internationalozone assessments. Using its broad wavelengthrange and spectral resolution, OMI scientistswill be able to resolve the differences amongsatellite and ground based ozone measure-ments. OMI will also measure the atmosphericcolumn of radicals such as nitrogen dioxide(NO2) and chlorine dioxide (OClO).
OMI Contributions to UnderstandingAir Quality
Tropospheric ozone, nitrogen dioxide, sulfurdioxide, and aerosols are four of the U. S.Environmental Protection Agency’s six criteriapollutants. OMI will map troposphericcolumns of sulfur dioxide and aerosols. OMImeasurements will be combined with informa-
Ozone Monitoring Instrument
OMI
A U R A 17
This monthly average map wasmade by subtracting the stratos-pheric ozone column from TOMScolumn ozone. The stratosphericcolumn is calculated using UARSMLS measurements. Higher qualitytropospheric ozone maps on adaily basis will be produced fromOMI and HIRDLS data.
OMI will collect data on aerosol optical thickness in the ultravioletwith eight times better spatial resolution than TOMS instruments.Optical thickness in the ultraviolet tells scientists whether theaerosols absorb or reflect radiation; this information is necessaryfor climate studies. The figure shows aerosol measurements(monthly average, August 1997) by ATSR-2 at an OMI resolutionof 13 x 24 km.
OMI InstrumentCharacteristics
n OMI is an advancedhyperspectral imagingspectrometer with a114º field of view. Itsnadir spatial resolutionranges from 13 x 24km to 24 x 48 km.OMI’s swaths almosttouch at the equator soOMI is able to produce global mapseach day.
n OMI contains two spec-trometers; the firstmeasures the UV in thewavelength range of270-365 nm, while theother spectrometermeasures the visible inthe range of 365 to 500nm. Both spectrometershave a bandpass ofabout 0.5 nm with spec-tral sampling rangingfrom 0.15 to 0.3nm/pixel, depending on wavelength.
n OMI uses a CCD solidstate detector array toprovide extended spec-tral coverage for eachpixel across the meas-urement swath.
OMI PrincipalInvestigator Pieternel
Levelt is a research scientist at the RoyalNetherlands Meteoro-logical Institute (KNMI).Co-Principal Investigatorsare Ernest Hilsenrath,from NASA GoddardSpace Flight Center(GSFC), and GilbertLeppelmeier, from the
Finnish Meteorological Institute. Pawan Bhartia leadsthe US science team. Bhartia and Hilsenrath have ledthe development and application of UV backscattertechniques for measuring trace gases. These scientistsand their teams have overseen OMI instrument develop-ment and are responsible for calibration, developingalgorithms, monitoring instrument performance, dataprocessing, analysis and validation.
KNMI (Royal NetherlandsMeteorological Institute) forecast-ed the unusual splitting of theAntarctic ozone hole inSeptember 2002. This six-dayforecast for column ozone onSeptember 25, 2002 used datafrom the European SpaceAgency’s Global Ozone MonitoringExperiment (GOME) with the windfields obtained from a dataassimilation system. Subsequentsatellite data verified the predic-tion. KNMI, NASA and NOAA willuse similar assimilation tech-niques with OMI data to makeregular forecasts of the amountand distribution of total columnozone. OMI will deliver data threehours after observation.
[DU]
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TES Contributions to Understanding Climate Change
TES will measure tropospheric water vapor,methane, ozone and aerosols, all of which arerelevant to climate change. Additional gasesimportant to climate change can be retrievedfrom the TES spectra.
T ES is an imaging Fourier TransformSpectrometer observing the thermalemission of the Earth’s surface and
atmosphere, night and day. TES will measuretropospheric ozone and of other gases impor-tant to tropospheric pollution. Satellite tropos-pheric chemical observations are difficult tomake due to the presence of clouds. To over-come this problem TES was designed toobserve both downward (in the nadir) and hor-izontally (across the limb). This observationcapability provides measurements of the entirelower atmosphere, from the surface to thestratosphere. NASA’s JPL developed, built,tested, and will operate TES.
The TES primary objective is to measure tracegases associated with air quality. A summary of TES data products appears on page 29.
TES Contributions to UnderstandingStratospheric Ozone
TES limb measurements extend from theEarth’s surface to the middle stratosphere, andthe TES spectral range overlaps the spectralrange of HIRDLS. As a result, TES’s high resolution spectra will allow scientists to make measurements of some additional stratospheric constituents as well as improveHIRDLS measurements of species common to both instruments.
TES Contributions to UnderstandingAir Quality
TES will measure the distribution of gases inthe troposphere. TES will provide simultane-ous measurements of tropospheric ozone andkey gases involved in tropospheric ozonechemistry, such as HNO3 and CO. TES datawill be used to improve regional ozone pollu-tion models.
18 A U R A A U R A 19
Reinhard Beer of the NASA’s JetPropulsion Laboratory serves as the
Principal Investigator for TES. Beer is a pioneer in the development and applica-tion of Fourier Transform technology forremote sensing. Beer and his team areresponsible for developing the atmosphericconstituent retrieval algorithms, monitoringinstrument performance, calibration, dataprocessing and analysis.
With its pointing capabilityand smal pixel size (5 x 8km) TES can detectchanges in ozone levels inlarge urban locations suchas Los Angeles. Theorange and red areas rep-resent regions of unhealthyozone levels. The orangearea indicates ozone levelsgreater than 80 parts perbillion by volume (ppbv)and the red area indicateslevels greater than 125ppbv.
80-e03.7 >80-e05.1 <
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Harvard University’sGEOS-CHEM modeldemonstrates that TESwill observe the majorfeatures in troposphericozone on a single day.The top panel showsthe GEOS-CHEM simu-lated ozone field at681 hPa (about 3.1km). The white areasare mountainousregions where the sur-face pressure is below681 hPa. The ‘+’ signson the bottom panelindicate Aura’s flightpath and the locationsof TES nadir measure-ments. White areas arefound on the flight pathwhere clouds obscurethe entire TES footprint.The map in the lowerpanel is constructedfrom the simulated val-ues at the ‘+’ loca-tions. The simulatedmap reproduces manyof the features found inthe original model field.
Ground Level Ozone
TES Simulated DataTES Instrument Characteristics
n TES is a high-resolutioninfrared-imagingFourier TransformSpectrometer withspectral coverage of3.2 to 15.4 µm at aspectral resolution of0.025 cm-1. The instru-ment can provide infor-mation on essentiallyalmost all radiativelyactive gases in theEarth’s lower atmos-phere.
n TES makes both limband nadir observations.In the limb mode, TEShas a height resolutionof 2.3 km, with cover-age from 0 to 34 km. Inthe nadir mode, TES hasa spatial resolution of5.3 x 8.5 km. Theinstrument can bepointed to any targetwithin 45 degrees ofthe local vertical.
n In order to detect theinfrared radiation fromthe Earth’s atmos-phere, TES’s detectorshave to be kept at verycold temperatures. Anadvanced cryogenicrefrigerator keeps thedetectors cool.
Tropospheric Emission Spectrometer
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of Aura’s four instruments. TES provides abackup for HIRDLS. MLS and HIRDLS bothmeasure nitric acid and MLS measures HCland chlorine monoxide (ClO), two gases thatare transformed by the chemical processesinvolving aerosols.
Air Quality
Measuring tropospheric ozone and its precursorgases is a major goal for Aura. Aura’s instru-ments provide two methods of tracking ozonepollution. First, TES measures tropospheric
ozone directly. The second estimate of the totaltropospheric ozone amount can be obtained bysubtracting HIRDLS stratospheric ozone meas-urements from OMI’s total column ozonemeasurements. A similar procedure can beused to estimate the tropospheric amount ofNO2, an important ozone precursor.
In the clear upper troposphere, Aura instru-ments provide overlapping measurements ofCO (MLS, TES), H2O (MLS, TES, HIRDLS),
The Aura instruments were selected andthe satellite was designed to maximizescience impact. The four Aura instru-
ments have different fields of view and comple-mentary capabilities. The instruments allobserve the same air mass within about 13minutes, a short enough time so the chemicaland dynamical changes between observationsare small.
Stratospheric Ozone
Understanding stratospheric ozone changeinvolves measurements of both the ozone pro-file and the total column amount, as well asthe chemicals responsible for ozone change.
All of Aura’s instruments make ozone profilemeasurements. HIRDLS profiles have thehighest vertical resolution and extend fromcloud tops to the upper stratosphere. MLSmeasurements have lower vertical resolutionthan HIRDLS, but MLS can measure ozone inthe presence of aerosols and upper tropospheric
ice clouds. TES limb ozone measurementsoverlap the measurements from HIRDLS andMLS up to the middle stratosphere. OMI canalso make broad ozone profile measurementsusing a modified SBUV technique.
To establish the scientific basis for ozonechange, scientists must measure the global dis-tribution of the source, reservoir, and radicalchemicals in the nitrogen, chlorine, and hydro-gen families. Together, the Aura instrumentsfill this requirement. For example, HIRDLSmeasures the halocarbons (chlorine sourcegases) and chlorine nitrate (one of the majorchlorine reservoir gases), while MLS measuresthe radical chlorine monoxide and hydrogenchloride (the other major chlorine reservoir).
Stratospheric aerosols influence ozone concen-trations through chemical processes that trans-form ozone-destroying gases. HIRDLS meas-ures stratospheric aerosols with the best hori-zontal coverage and highest vertical resolution
20 A U R A
Mission Synergy: Maximizing Science Results
A U R A 21
Mission Synergy
n Aura measures a fullrange of gases active in ozone chemistry.
n Aura measures five ofthe six EPA criterion air pollutants.
n Aura measures uppertroposphere ozone andwater vapor, both impor-tant contributors to climate change.
continues on page 22
Fields of view for Aura’sinstruments appear in differ-ent colors: HIRDLS in yellow,OMI in blue, MLS in green,and TES in red. HIRDLS looksbackward through the limband scans the atmosphere’svertical profiles across thesatellite track. MLS looks forward through the limb andscans the atmosphere verticalprofiles along the satellitetrack. OMI looks downwardand has a cross track swathof 2600 km. TES looks bothin the nadir and limb and also has off nadir pointingcapability.
Each of Aura’s four instruments provides uniqueand complementary capabilities to enable dailyglobal observations of Earth's atmospheric ozonelayer, air quality, and climate. The chart (above)summarizes the specific atmospheric physicalproperties and chemical constituents measuredby each instrument. OMI also measures UVB flux
and cloud top height and coverage. The altituderange for measurement appears as the verticalscale. In several cases instrument measurementsoverlap, which provides independent perspectivesand cross calibration. These measurements willresult in the most comprehensive set of atmos-pheric composition ever measured from space.
Aura Atmospheric Measurements
HIRDLS: High Resolution Dynamics Limb Sounder
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HNO3 (MLS, TES, HIRDLS). Carbon monox-ide (CO) is an ozone precursor and HNO3 is areservoir gas for NO2. The combination of TES nadir measurements and MLS limb measurements through clouds will provideimportant new information on the distributionof CO and H2O.
An emerging problem in air quality is theincreasing amount of aerosols in the air webreathe. OMI measures aerosols, and distin-guishes between smoke, mineral dust, andother aerosols. Both TES and HIRDLS meas-ure aerosol characteristics in the upper tropo-sphere to help understand how aerosols aretransported.
Climate Change
Atmospheric chemistry and climate are inti-mately connected. Ozone, water vapor, and
N2O take part in tropospheric chemicalprocesses and are also greenhouse gases.Changes in these and other greenhouse gasescan upset the atmosphere’s heat balance andalter climate. Measurements of these gases,their sources and sinks are essential if we are tounderstand how the climate is changing as aresult of human activity. All of the Aurainstruments provide information on tropos-pheric ozone.
Clouds and aerosols are also important contrib-utors to climate change. HIRDLS and MLSwill measure cirrus clouds. OMI will measureaerosol distributions and cloud distributionsand their heights.
By 2006, Aura will be a member of aconstellation of satellites flying in formation. This formation is referred
to as the “A-Train.” Flying with Aura in theA-Train are Aqua, CloudSat, CALIPSO, andOCO. The French space agency, CentreNational d’Etudes Spatiales (CNES), plans tosend a sixth satellite, PARASOL, to join theA-Train. All six satellites will cross the equatorwithin a few minutes of one another near 1:30p.m. local time and again in the early morn-ing, about 1:30 a.m.
While each satellite has an independent sciencemission, these complementary satellite obser-vations will enable scientists to obtain moreinformation than they could using the observa-tions of a single mission.
The A-Train formation allows us to focus onnew science questions. For example:
n What are the aerosol types and how doobservations match global emission andtransport models?
Data from Aura’s OMI will provide informa-tion on the global distribution of absorbing
aerosols. Aerosol height information obtainedby CALIPSO can be combined with data onaerosol size distribution and composition fromPARASOL and Aqua’s MODIS.
n What is the role of polar stratosphericclouds in ozone loss in the Antarctic vortex?
Aura’s MLS and HIRDLS will provide cloudheight and temperature data, and ozone, nitricacid and chlorine monoxide concentrations.CALIPSO measures precise polar stratosphericcloud height and cloud type.
n What is the vertical distribution of cloudwater and ice in upper troposphericcloud systems?
Aura’s MLS will provide water vapor measure-ments in the presence of clouds while CloudSatwill measure cloud height. PARASOL willprovide particle type information while Aqua’sMODIS will give particle size information.
Aura and the A-Train
The satellites of the A-Train.
Simulated Tropospheric Ozone
Atmospheric scientists derive troposphericozone amounts by combining measurementsfrom different satellites, such as subtractingstratospheric amounts from NASA’s UARSMLS or NOAA’s SBUV/2 instruments fromTOMS column amounts. These show how tro-pospheric ozone is transported across conti-nents and oceans. Aura will provide moreaccurate tropospheric ozone by subtractingthe HIRDLS stratospheric profiles from OMIcolumn amounts as simulated in this figure.The high spatial resolution of these two instru-ments will provide data necessary to quantifychemical and dynamic processes controllingtropospheric ozone.
Completing the Picture of Stratospheric Chemistry
Chemical and transport processes have led to changes in the stratosphericozone layer, and scientists need measurements of many different chemicalspecies to puzzle out the causes for these observed changes. Measurementsof ozone-destroying radicals such as ClO, NO2, BrO and OH and reservoir gasessuch as N2O5, ClONO2 and HNO3 help solve the chemical part of the puzzle.Measurements of long-lived gases such as N2O and CH4 tell scientists aboutthe puzzling effects of transport. Ozone and some other constituents are meas-ured by all the instruments; some constituents like hydrochloric acid are meas-ured by only one. New Aura measurements, such as OH, will help us completethe picture. The new measurements are shown as detached pieces.
Satellite Constellation
Aura will fly in a carefully-designed constellation of sixEarth-observing satellitesthat gather concurrent sci-ence data in a virtual plat-form. Constellation flyingincreases mission capabilitywhile it lowers total missionrisk and mission cost.
Aura contributes to the collective science mission,particularly with regard toquestions about the role ofpolar stratospheric clouds in polar ozone loss, and thevertical distribution of waterand ice in cloud systems.
0 Tropospheric Ozone (DU) 100
If the air isaltered ever soslightly, the stateof the psychic spirit will bealtered perceptibly.
Maimonides,12th Century
philosopher
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The Aura spacecraft providesthe essential services foroperating the four scientific
instruments over the life of themission. The spacecraft, based onthe EOS Common Spacecraftdesign, was built by NorthropGrumman Space Technology andadapted for the Aura instrumentpayload.
Building a complex spacecraftrequires an engineering teamwith a diverse set of technicalskills. The team has to translatethe scientific requirements of themission into the technicalrequirements for the spacecraft toassure that when the subsystemsand instruments are broughttogether to form the observatory(spacecraft plus instruments), theyfunction as one cohesive system.
The spacecraft is made up of thefollowing subsystems: commandand data handling; communica-tions; electrical power; electricaldistribution; guidance, naviga-tion and control; propulsion,software and thermal control. Each subsystemrequires designers, engineers, analysts andtechnicians with specialized training. A teamof integration and test specialists assembles theobservatory and tests it as a system, simulatingthe launch and on-orbit environments as close-ly as possible. For example, the spacecraft isexposed to vibrations similar to what it wouldexperience during launch. As the observatorycomes together, the flight operations teamlearns and practices how to operate the obser-vatory well before launch.
The Aura observatory will be launched on aDelta II 7920 rocket from Vandenberg AirForce Base in California into a near polar, sun-synchronous orbit of 438 mi (705 km), with aperiod of approximately 100 minutes and a1:45 PM equator crossing time. The spacecraftrepeats its ground track every 16 days.
The Aura Spacecraft
Spacecraft Subsystems
n Structure—Graphiteepoxy composite overhoneycomb core
n Electrical Power— Thedeployable flat-panelsolar array with over20,000 silicon solarcells provides 4800watts of power in sunlight and charges a24-cell nickel-hydrogenbattery for the nightphase of the orbit
n Command and DataHandling System—Storesover 100 gigabits of sci-entific data on-board
n Communications—X-band (high data rate)for science data, S-band(low data rate) for com-mand and telemetry, viapolar ground stations
n Guidance, Navigationand Control—Stellar-inertial, and momentumwheel-based attitudecontrols
n Propulsion—System offour one-pound thrusthydrazine monopropel-lant rockets
n Software—The satellitesystems are managedby a flight computerthat is responsible forthe health and safety ofall the instrument sub-systems
Right, Spacecraft descending into thermal vacuum test chamber, October 2003.
Spacecraft assembly
Spacecraft delivery
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Validation is the process by which scien-tists show that their space-based meas-urements have their expected accuracy.
Validation of Aura measurements involvesmaking similar atmospheric measurementsfrom airplanes, balloons or ground-based sites.Scientists compare Aura data with calibratedmeasurements collected as the satellite passesoverhead.
Ground-based radiometers and spectrometersmake column measurements similar to those fly-ing on Aura. Lidars measure temperature andsome trace gas constituent profiles. Aircraft suchas the DC-8 (medium altitude) and the ER-2(high altitude) carry airborne spectrometers,radiometers, and air samplers to measure upperatmospheric constituents.
The Aura validation program capitalizes on routine sources of data such as the ozonesondenetwork and the Network for Detection ofStratospheric Change (NDSC). Balloon-borneinstruments will measure profiles of stratosphericconstituents up to 25 miles (40 km). Smallerballoons will carry water vapor instruments inthe tropics to validate Aura’s measurements ofthis important gas. Aircraft flights provide tropospheric profiles of ozone, carbon monoxide,and nitrogen species. Aircraft lidars will measureprofiles of ozone and temperature for long distances along the satellite track. Scientists will also compare profiles of stratospheric constituents from Aura with those from othersatellites, including the NASA UARS, the ESAEnvisat, and the Canadian SCISAT, and use dataassimilation techniques to identify systematicdifferences among the data sets.
The Aura project has adopted a strategy toincrease the scientific return from the valida-tion program. Some of the validation activitieswill be embedded within focused science cam-paigns. These campaigns have been selected toobtain data needed to unravel complex sciencequestions that are linked to the three mainAura science goals. Scientists will use the satel-lite data to understand the overall chemicaland meteorological environment during thecampaigns. Aircraft measurements will be usedto both validate Aura data and address the science by making additional measurements.
This strategy emphasizes the strengths of both data sets. Campaign instruments makeconstituent measurements that are more com-plete than can be obtained from satellites.Campaign data are obtained for much smallerspatial scales and with high temporal resolu-tion compared to satellite data. Aircraft mis-sions take place a few times each year at mostand are limited to a small portion of the globe,while the Aura instruments will make globalobservations throughout the year. The Aura
Aura Validation
26 A U R A A U R A 27
instruments will provide datasets that will tellscientists whether or not the campaign obser-vations are truly representative of the atmos-phere’s chemistry.
Aura’s focus on the upper troposphere andlower stratosphere (UT/LS) presents challenges
for validation, because the UT/LS exhibitsmuch more spatial and temporal variability(weather) than the middle and upper strato-sphere. The Aura validation program includesan instrument development program and fieldcampaigns between October 2004 andAutumn 2007.
High altitude aircraft will make in situ measurements of stratospher-ic and tropospheric constituents. Above, the Proteus, and below, theNASA ER-2 have been frequently used in satellite validation.
High altitude balloonmeasurements will provide trace gas profilesfor Aura validation.
Instruments on board the NASA DC-8 willmeasure tropospheric and lower stratospherictrace gases.
Unpiloted aerial vehi-cles (UAVs), such asNASA’s Altair shownabove, will be usedin Aura validation tomake measurementsalong the satellitetrack. Aura is pioneering the use of UAVs for validation.
Ground-based measurements from sites likethe one pictured above at Barrow, Alaska, willprovide a long time series of constituentmeasurements for validation.
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A U R A M I S S I O N
28 A U R A
T he EOS Aura ground system has twoequally important functions: to operatethe Aura satellite, and to process, archive
and distribute the Aura data. NASA’s EOSData and Information System (EOSDIS) sup-ports both of these.
Operating the Aura Satellite
Mission operations are based at the NASAGoddard Space Flight Center in Greenbelt,Maryland. The Flight Operations Team at theEOS Operations Center (EOC) will commandand control the Aura spacecraft and instru-ments, monitor their health and safety andperform mission planning and scheduling.Instrument teams at NASA’s JPL, Universityof Colorado and KNMI, Holland are responsi-ble for day-to-day planning, scheduling, andmonitoring of their instruments through the
EOC. The data collected by the Aura instru-ments will be recorded onboard the spacecraftand relayed to ground stations in Alaska andNorway when the satellite passes overhead.
Data Processing, Archive andDistribution
The data will be transmitted from the groundstations to the EOS Data and OperationsSystem (EDOS). From there the data forHIRDLS, MLS and OMI will be sent to theGoddard Distributed Active Archive Center(DAAC); data for TES will be sent to theLangley Research Center (LaRC) DAAC. EachScience Investigator-led Processing System(SIPS) will receive the data from the DAAC for further processing. The SIPS will producescientific data such as profiles and columnamounts of ozone and other important atmos-pheric species. Each instrument team willmonitor the data products to ensure that theyare of high quality. The data products willthen be sent back to the DAACs where theywill be archived. The DAACs are responsiblefor distribution of data to scientists all over the world.
Getting the data
Researchers, government agencies and educators will have unrestricted access to the Aura data via the EOS data gateway(eos.nasa.gov/imswelcome). Data seekers can search for and order data from any of theEOS DAACs.
The EOS Aura Ground System
A U R A 29
Aura Instruments and Data Products
ACRONYM NAME CONSTITUENT INSTRUMENT DESCRIPTION
HIRDLS High Resolution Profiles of T, O3, H2O, Limb IR filter radiometerDynamics Limb CH4, N2O, NO2, HNO3, from 6.2 to 17.76 µmSounder N2O5, CF3Cl, CF2Cl2, 1.2 km vertical resolution
ClONO2, aerosol up to 80 kmcomposition
MLS Microwave Limb Profiles of T, H2O, O3, ClO, Microwave limb sounder Sounder BrO, HCl, OH, HO2, HNO3, from 118 GHz to 2.5 THz,
HCN, N2O, CO, cloud ice with 1.5-3 km vertical HOCI, CH3CN resolution
OMI Ozone Monitoring Column O3, aerosols, Hyperspectral nadir Instrument NO2, SO2, BrO, OClO, HCHO, imager, 114º FOV,
UV-B, cloud top pressure, 270-500 nm, 13x24 km O3 profiles footprint for ozone and
aerosols
TES Tropospheric Profiles of T, O3, NO2, CO, Limb (to 34 km) and Emission HNO3, CH4, H2O nadir IR Fourier transform Spectrometer spectrometer 3.2-15.4µm
Nadir footprint 5.3x8.5km, limb 2.3 km
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GYA U R A M I S S I O N
Man and Nature must workhand in hand. The throwing out of balance of the resources of nature, throws out of balance the lives of men.
F. D. Roosevelt, 1935, President of the United States
30 A U R A
NASA missions to study the Earth and other planets continue to inspirethe next generation of explorers.
Aura’s three areas of science investigation—stratospheric ozone, climate change, and airquality—are issues of everyday concern. Aura investigators have partnered with theSmithsonian Institution, the AmericanChemical Society, and the GLOBE Programto reach multiple audiences.
Hundreds of thousands of visitors to theSmithsonian Institution’s National Museum ofNatural History will have the opportunity toexperience a new permanent exhibit based onAura science, The Atmosphere: Change Is Inthe Air. The new exhibit resides in the Forcesof Change exhibit hall, where connectionsamong land, oceans and atmosphere areexplored. Interactive displays immerse visitorsin the early history, evolution, and structure ofthe atmosphere. Northrop Grumman SpaceTechnology has contributed a one-eighth scalemodel of the Aura satellite to the exhibit, andthe Smithsonian’s Department of Educationhas developed learning activities for studentgroup visits. In association with the exhibit,the Smithsonian Press will publish a book byNobel Prize Winner, Sherwood Rowland,Atmosphere.
By the time the Aura satellite achieves orbit,every high school chemistry teacher in theUnited States will have received four specialissues of the high school magazine, ChemMatters, devoted to Aura mission science,mathematics, engineering, and technology.The American Chemical Society (ACS) andNASA collaborated in the production of thesemagazines. The first issue (2001) introducesstudents to the Aura mission itself; the secondissue (2002) portrays the professional and per-sonal lives of the people who make Aura possi-ble; the third issue (2003) explores atmospher-
ic chemistry and transport; and the fourthissue (2005) will focus on Aura results. In asso-ciation with the National Chemistry Weektheme The Earth’s Atmosphere and Beyond! ACSand NASA have also collaborated to conductworkshops for teachers at all of the regionalNational Science Teachers Association meet-ings from 2002 to 2004.
The Aura team supports the GLOBE Program(Global Learning and Observations to Benefitthe Environment) to involve young researchersin atmospheric chemistry. More than 13,000kindergarten through 12th grade schools in100 countries participate in the GLOBE pro-gram. Aura supported the development of inex-pensive instruments to measure UV radiation,surface ozone, and aerosols. GLOBE developsprotocols for students to follow when makingmeasurements and reporting their data. Schoolsin the Netherlands are particularly active inAura science observations through a partnershipbetween GLOBE Netherlands and KNMI, theOMI PI institute. About 20 Dutch schools planto become part of the data validation programfor Aura.
The Aura team has published six articles aboutatmospheric science on Earth Observatory,NASA’s award-winning website, earthobserva-tory.nasa.gov. The articles include “UltravioletRadiation: How It Affects Life on Earth”;“Highways of a Global Traveler”; and“Watching Our Ozone Weather”. About300,000 individuals visit this website eachmonth, and 36,000 subscribe to a weeklyupdate. More articles, including one on scien-tist-teacher-student partnerships, are underdevelopment.
For current information on education opportu-nities, visit the Aura website at:
eos-aura.gsfc.nasa.gov
Aura Education and Public Outreach
A U R A 31
Website Addresses
n See National Museum of Natural History online at: www.nmnh.si.edu/
n See Chem Matters online at: www.acs.org/education/curriculum/chemmatt.html
n See the GLOBE Program online at: www.globe.gov/fsl/welcome/welcomeobject.pl
n For current information on education opportunities, visit the Aurawebsite at: eos-aura.gsfc.nasa.gov
A U R A M I S S I O N
Students and teachers in Czechoslovakia investigate surfaceozone amounts through GLOBE, an international science andeducation program. Trainers from the U.S. pose with them andtheir teacher.
GLOBE studentsmeasure injury to
plant leaves forozone air quality
studies.
A GLOBE teacher and students learn how to measure aerosols with a hand-held sun photometer.
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Goddard Project OfficeR. Pickering, J. Bolek, C. Dent, M. Domen, M. Fontaine, G. Jackson, J. Lohr, J. Loiacono, S. Manning,
K. McIntyre, A. Razzaghi
NASA HQ Program OfficeP. DeCola, D. Anderson , J. Gleason, M. Kurylo, M. Tanner
Project Science Office M. Schoeberl, A. Douglass, and E. Hilsenrath
Science Teams
HIRDLSU. S. A. Team: L. Avallone, B. Boville, G. Brasseur, M. Coffey, T. Eden, D. Edwards , D. Kinneson, A. Lambert,
C. Leovy, B. Nardi , C. Randall, W. Randel , B. Toon
U. K. Team: D. Andrews, R. Harwood, M. McIntyre, H. Muller, C. Mutlow, A. O’Neill, J. Pyle, C. Rodgers,F. Taylor, G. Vaughan, R. Wells, J. Whitney, E. Williamson
MLS U. S. A. Team: R. E. Cofield, L. Froidevaux, R. Jarnot, N. Livesey, G. Manney, H. Pickett, W. Read, M. Santee,
P. Siegel, J. Waters, D. Wu
U. K. Team: M. J. Filipiak, R. Harwood, H. Pumphrey
OMIDutch team: B. van den Oord, J. Claas, M. Dobber, M. Kroon, P. Veefkind, S. van Broekhoven,
J. van den Bovenkamp, E. Brinksma, J. de Haan, R. Dirksen, R. Noordhoek, R. Voors
Finnish Team: G. Leppelmeier, A. Mälkki, E. Kyrö, A. Tanskanen
U. S. A. Team: P. Bhartia, R. Cebula, K. Chance, D. Cunnold, J. Fishman, A. Fleig, L. Flynn, J. Gleason,D. Heath E. Hilsenrath, J. Joiner, A. Krueger, R. McPeters, G. Mount, S. Sander,I. Stajner, O. Torres,C. Trepte
International team: I. Isaksen, D. Hauglustaine, U. Platt, P. Simon, I. Aben, F. Denterer, H. Kelder, P. Stammes,D. Swart, G. de Leeuw, F. Boersma, R. van Oss
TESU. S. A. Team: S. Clough, M. Gunson, D. Jacob, J. Logan, F. Murcray, D. Rider, C. Rinsland, , S. Sander,
H. Worden
U. K. Team: C. Rodgers, F. Taylor
Brochure Team Authors: Ernest Hilsenrath, Mark R. Schoeberl, and Anne Douglass (NASA GSFC)
Project Coordinator: Stephanie Stockman (SSAI)
Designer: Ellen Baker Smyth, Elle Designs
Contributing Writer/Editor: Jeannie Allen (SSAI)
Acknowledgements
A U R A M I S S I O N
A U R A c332 A U R A
BrO Bromine monoxideCF2Cl2 DichlorodifluoromethaneCFCl3 TrichlorofluoromethaneCH3CN Methyl cyanideCH4 MethaneCl ChlorineClO Chlorine monoxide
ClONO2 Chlorine nitrateCO Carbon monoxideCO2 Carbon dioxideH20 WaterHCl Hydrogen chlorideHCHO FormaldehydeHCN Hydrogen Cyanide
HNO3 Nitric acidHO2 Hydroperoxy radicalHOCl Hypochlorous acidN2O Nitrous oxideN2O5 Dinitrogen pentoxideNO Nitric oxideNO2 Nitrogen dioxide
NOx Nitrogen oxideO2 OxygenO3 OzoneOClO Chlorine dioxideOH HydroxylSO2 Sulfur dioxide
Chemicals
ACS American Chemical SocietyASTER Advanced Spaceborne Thermal Emission and Reflection RadiometerASTR Along Track Scanning RadiometerBUV Backscatter Ultraviolet InstrumentCALIPSO Cloud-Aerosol Lidar and Infrared Pathfinder SatelliteCCD Charge Coupled DeviceCFC ChlorofluorocarbonCNES Centre National d'Etudes SpatialesDAAC Distributed Active Archive CenterDFRC Dryden Flight Research CenterDU Dobson UnitEOC EOS Operations CenterEOS Earth Observing SystemEOSDIS Earth Observing System Data and Information SystemEPA Environmental Protection AgencyESA European Space AgencyGISS Goddard Institute for Space StudiesGLOBE Global Learning and Observations to Benefit the EnvironmentGOME Global Ozone Monitoring ExperimentGSFC Goddard Space Flight CenterHALOE Halogen Occultation Experiment, instrument on UARS satellite HIRDLS High Resolution Dynamics Limb Sounder (One of the four Aura
instruments) JPL Jet Propulsion LaboratoryKNMI Royal Dutch Meteorological InstituteMLS Microwave Limb Sounder (One of the four Aura instruments) MODIS Moderate-resolution Imaging Spectroradiometer MOPITT Measurements of Pollution in the Troposphere
NASA National Aeronautics and Space AdministrationNCAR National Center for Atmospheric ResearchNDSC Network for the Detection of Stratospheric ChangeNGST Northrop Grumman Space TechnologyNimbus 7 NASA satellite, operated from 1978-1994 carrying a
TOMS instrumentNimbus-4 NASA satellite,operated from 1970-1980 carrying the BUV instrumentNOAA National Oceanic and Atmospheric AdministrationOCO Orbiting Carbon ObservatoryOMI Ozone Monitoring Instrument (One of the four Aura instruments) OMPS Ozone Mapping Profiler Suite PARASOL Polarization and Anisotropy of Réflectances for Atmospheric Sciences
coupled with Observations from a Lidarppbv Parts per billion volumeSAGE Stratospheric Aerosol and Gas Experiment SBUV Solar Backscatter Ultraviolet SCIAMACHY Scanning Imaging Absorption Spectrometer for
Atmospheric CartographySIPS Science Investigator Processing SystemsSSAI Science Systems & Applications, Inc.TES Tropospheric Emission Spectrometer (One of the four Aura
instruments) TOMS Total Ozone Mapping SpectrometerUARS Upper Atmosphere Research SatelliteUK United KingdomUMBC University of Maryland Baltimore CountyUV UltravioletVOC Volatile Organic Compound
Acronyms
This brochure is
dedicated to
the memory of
Professor James Reed
Holton (1938-2004),
an inspirational
atmospheric scientist
and a member of the
UARS and Aura
Science Teams.
Jim Holton made
countless
contributions
to atmospheric science
and enriched the lives
of his students and
colleagues.
JES
SE A
LLEN
(S
SAI)