THE EUROPEAN

MARS CLIMA TE DATABASE

for missionplanning & for scientificstudies

F. Forget,F. Hourdin, O. Talagrand and Y. Wanherdrick(LaboratoiredeMeteorologieDynamique,CNRS-UPMC,Paris,France)

S.R.Lewis, P.L. Readand F. Taylor(Atmospheric,OceanicandPlanetaryPhysics,ClarendonLaboratory, Oxford,UK)

M. Lopez-Valverdeand M. Lopez-Puertas(InstitutodeAstrofısicadeAndalucıa,Granada,Spain)

J.-P. Huot(SpaceSystemsEnvironmentandEffectsAnalysisSection,ESTEC,ESA,Noordwijk,

Netherlands)

http://www.lmd.jussieu.fr/mars.html

May 2001

Contents

1 What is the Mars Climate Database? 2

2 How do GeneralCir culation modelswork ? 3

3 How are the atmospheric dust variations and dust storms taken into ac-count ? 5

4 Ar e numerical modelsa reliablesourceof information on the Martian en-vir onment? 5

5 How is the small scalevariability of the atmosphere representedin thedatabase? 7

6 How to accessthe database? 8

7 Key References 12

1

1 What is the Mars Climate Database?

Purpose

Whenplanningspacecraftmissionsto Mars,detailedinformationaboutenvironmentalconditionson the planetis vital to reducethe chancesof missionfailure andto aidin the optimizationof the designprocess.For example,aerobrakingor aerocapturemaneuversrequiredetailedknowledgeof atmosphericdensity;whenplacinglanderson the surfaceof the planet,the wind shearcanbe a crucial factor; andextremesoftemperaturein theatmosphereandonthesurfacemustbeknown to preventelectronicandmechanicalfailures.Similarly, climatologicalstatisticsarealsoof greatvalueandinterestfor membersof thescientificcommunitywhoneedrealisticdatato studyanysubjectrelatedto theMartianatmosphereandclimate.For example,thedatabasehasbeenusedto studycloud microphysics,chemistry, geodesy, meso-scalecirculation,spacecraftdatainterpretation,etc.

Contruction

Previous so-called“engineeringmodels”(e.g. “MarsGRAM”) usedfor missionde-signwerebasedon compilationsof observationalstatisticswith simpleinterpolationschemesto provide estimatesof climatevariablesat any time andany geographicallocation. Unfortunately, the availableobservationaldataon Mars aresparseandin-completein both spaceandtime, leadingto greatuncertaintiesfor locations,times,seasonsandyearsfor whichnodatais available.

A differentapproachhasbeenusedhere.The databasehasbeenproducedfroma setof numerical simulation of Mars’sclimate and atmosphericcirculation conductedwith a GeneralCir culation Model (GCM). GCMsarewidely usedfor weatherfore-castingand climate studiesfor the Earth. The Mars GCMs have beenextensivelyvalidatedusingavailableobservationaldataandwebelievethatthey representthecur-rentbestknowledgeof thestateof theMartianatmospheregiventheobservationsandthephysicallawswhich governtheatmosphericcirculationandsurfaceconditionsontheplanet.

Contents

The MCD containssimulateddata (temperature,wind, density, pressure,radiativefluxes,etc. SeeTable1) storedon a

���������longitude–latitude grid1 from the sur-

faceup to anapproximatealtitudeof 120km(above 120km, pressureanddensitycanbeestimatedusingthedatabaseaccesssoftwares).

Theverticalcoordinatefor the3D variablesis definedas

��� � (1)

1Thegeneralcirculationmodelsusedto compilethedatabaserunwith ahigherresolutionof �� ���������� ��� � . For simplicity andto reducethesizeof thedatabase,thedatawerestoredon � � ��� � grid.

2

Meanvariable symbol units 2-D or 3-DAtmospherictemperature t K 3-DZonal(East-West)wind u m s��� 3-DMeridional(North-South)wind v m s��� 3-DAtmosphericdensity rho kg m��� 3-DBoundarylayereddykineticenergy q2 m� s� � 3-DSurfacepressure ps Pa 2-DSurfacetemperature tsurf K 2-DLW (thermalIR) radiativeflux to surface fluxsurf lw W m� � 2-DSW (solar)radiativeflux to surface fluxsurf sw W m� � 2-DLW (thermalIR) radiativeflux to space fluxtop lw W m� � 2-DSW (solar)radiativeflux to space fluxtop sw W m� � 2-DCO� icecover co2ice kg m� � 2-DSurfaceemissivity emis none 2-D

Table1: Variablesstoredin databasemeandatafiles.

where is theatmosphericpressureand � is thesurfacepressure.Thus � is 1 at thesurfaceand0 at infinity andthe � levels follow the modelorography. Thereare32sigmalevels, with the first four level areat about5, 20, 50 and115 m whereastheupperlevel is around120km.

Fieldsareaveragedandstored12timesaday, for 12Martian“seasons”to giveacom-prehensiverepresentationof the annual and diurnal cycles. Eachseasoncovers30� in solarlongitude( "! ), andaretypically 50-70dayslong. In otherwords,ateverygrid-point,thedatabasecontains12 ”typical” days,onefor eachseason.In addition,informationonthevariabilityof thedatawithin oneseasonor within onegrid-pointarealsostoredin thedatabase.Softwaretoolsareprovidedto reconstructandsynthetizedthisvariability (section5).

2 How do GeneralCir culation modelswork ?

TheMarsClimatedatabasehasbeenconstructedbasedonoutputfrom asetof generalcirculationmodels(GCM) developedjointly at LMD andAOPP(Forgetet al., 1999).GCMsareawidely usedtool in terrestrialweatherforecasting,climateforecastingandmeteorologicalresearch.Thebasicideais thefollowing: from aninitial state(definedby temperature,pressure,wind fields,etc.),themodeluseswell known physicallaws(e.g.fluid mechanicequations,radiativetransferlaws) to computetheevolutionof thesystemtimestepsaftertimesteps.

TheGeneralCirculationModelscanbeschematicallydividedinto two parts.

# Thefirst part is anhydrodynamical codededicatedto the time andspatialin-tegrationof the equationsof hydrodynamicsto computethe large scaleatmo-sphericmotions. This part,basedon a rathergeneralformulationof theequa-tionsof fluid mechanics(primitive equationsin meteorologicaldialect)canbe

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usedwithout any changefor theotherterrestrialplanets.Two differentkind ofhydrodynamicalcodehave beendevelopedsofar: 1. finite-differencesor grid-pointsmodels(onuseatLMD) and2. spectralsolverbasedonadecompositionof thehorizontalfieldsonsphericalharmonics(onuseatAOPP).

# The secondpart of the codeconsistsof a set of physical parametrizationswhich areusedto force the generalcirculationandcomputethe detailsof thelocalclimateateverygrid point. LMD andAOPPuseacommonsetof parame-terizationswhich includes:

– Radiative transfer.This is the main sourceof atmosphericmotions(principally the latitudi-nal variationsof the absorptionof solarenergy). The effectsof gaseouscarbondioxide(absorptionandemissionof radiation)andsuspendeddust(absorption,emissionandscaterringof radiation)areincludedin themodelatsolarandthermalinfraredwavelengths.To constructthecurrentversionof the databaseandextend the top of the modelup to 120 km, a majoreffort wasput in the calculationof the radiative transferin the upperat-mospherein collaborationwith theexpertsfrom IAA in Granada.At lowpressureabove 70 km, onehave to considerthe fact that the assumptionof LocalThermodynamicEquilibrium(LTE) is notvalid andthatnon-LTEeffectsmustbe takeninto accountwhencomputingthe radiative heatingandcoolingbudgetfor theupperCO� atmosphere.

– SurfaceProcesses.The temperatureof the surfaceis computedfrom the radiative, sensibleand latentheatfluxesat the surfaceusingan 11-level modelof thermaldiffusion in the soil. Surfaceproperties,i.e. albedoandthermalinertia,arebasedon MarsGlobalSurveyor (MGS) andViking observations.Themodelalsousethe accuratetopographymapobtainedby the MOLA al-timeteraboardMGS.

– Sub-grid scaledynamics.The physicalparametrizationsmustalso includerepresentationof smallscalemotionsnot explicitly representedby thehydrodynamicalcode.Ontheonehand,this includestherepresentationof verticalexchangeof mo-mentumandenergy betweenthesurfaceandtheatmospheredueto turbu-lenceandconvection,mostly in the so-calledPlanetaryBoundaryLayer.On the otherhand,the small mountainswhich arenot representedin theGCM smoothgrid caninfluencethemodelscaleflow by (a) producingaform dragon the flow at low levels, andby (b) exciting internalgravitywaveswhich canpropagatein thevertical,break,anddeceleratetheflowfar away from themountainsthemselves.

– CO � condensation.a specificparametrizationhasbeendevelopedfor Marsto accountfor thecondensationof the CO� atmospherein the polar region during the po-lar night seasons.CO� cancondensedirectly on the surfaceor up in the

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atmosphere.In that last case,the CO� ice particlesformedin the atmo-spherecanaffect theinfraredemissivity of thesystemassuggestedby theoabservations.

3 How are the atmosphericdust variations and dust stormstaken into account?

Themajorfactorwhichgovernsthevariability in theMartianatmosphereis theamountanddistributionof suspendeddust.Someyearsmayhavelow or moderatedustloadingthroughouttheyear, whileothersmayhaveregionalor globalduststormswhichengulftheplanet.

Becauseof this variability, and sinceeven for a given year the detailsof the dustdistribution andopticalpropertiescanbeuncertain,multi-annualmodelintegrationswerecarriedout for the databaseassumingvarious“dust scenarios”,i.e. prescribingvariousamountof airbornedustin thesimulatedatmosphere.

Fivedustscenarioshave beenused:

# A first scenario,namedMars Global Surveyor Dust Scenariobasedon recentspacecraftobservations,which shouldbe usedfor mostaplications. It is ourcurrent“best guess”thoughtto representthe moderatelydustyplanetMars asobservedby MarsGlobalSurveyor.

# Two additional annualscenarioswhich are provided to bracketthe possibleglobalconditionsonMars(Figure1) outsideglobalduststorms.

– The“Viking Lander” DustScenario: arelatively dustyyearmadeby gen-eralizingtheViking Landerdustopacityobservationsto theentireplanet,but with thelargeduststormsremoved.

– TheLowDustScenario: a veryclearyear(visibleopticaldepth $ �&%�')( ).# Two additionalduststormscenarioswhich areprovidedonly duringtheperiod

duringwhich suchglobaleventsareknown to occur(southernspringandsum-mer):

– DustStormScenario( $ �&* ) : a moderateglobalduststorm

– DustStormScenario( $ � � ) : A severeglobalduststorm

Furtherdetailson thedustscenariocanbefoundin Lewis etal. (2001b).

4 Ar e numerical modelsa reliable sourceof information onthe Martian envir onment?

Oneparticularstrengthof usingaGCM to compilesuchadatabaseis thatit providesaphysicallyconsistentestimateof theenvironmentalconditionsonMarsfor seasonsand

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Figure1: A typical temperatureprofileobservedbyradio-occultation(thick solid line,february1998, "! �1*32�( � , (�(�'42 � S-( �3� � E, local time : 4:30) compared to tempera-ture profilespredictedby the databaseat the sametime and location. Profilesfromthe “MGS” scenarioare usually very closeto the MGS observations,whereasthe“Viking” and“low dust” scenariosyield warmerandcoldertemperaturesprofilesinthe lower atmosphere, respectively. MGSdatacourtesyof D. Hinson,Stanford Uni-versity.

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dustloadingswhich arenot coveredby theobservations.But is theclimatedatabaseconsistentwith theavailableobservations?

First,severalkey parameters(pressure,dustscenario)of theGeneralCirculationmod-els have beentunedto matchthe observations. For instance,the GCM doesa verygoodjob in reproducingtheseasonalpressurevariationsrecordedby Viking Lander1and2 becausethe total atmospheremassandpolar capsalbedowerechosenfor thispurpose.On this basis,we areextremelyconfidentin the ability of the databasetopredictthesurfacepressureelsewhereon theplanet,somethingonly aGCM cando !

Second,the MCD hasbeenvalidatedagainstmostof the availableobservations. Inmostcases,it is found that the modelis ableto predictthe observationswith a verygoodaccuracy. Figures1, 2, 3, 4 and5 show suchcomparisonfor recentobservationsfrom theMarsGlobalSurveyor andMarsPathfindermission.Furthercomparisonscanbefind in Lewisetal. (1999)andin Forgetetal. (2001b).Thisvalidationprocesseshasalsoshownthatsomeproblemsremainin somelocationsandseasons.For instance,theGCMsdonot simulatethelargetemperatureinversionswhich aresometimeobservedin thetropicsin summer; polarnightprofilesseemsto beslightly colderin realitythanin thedatabaseduringsouthernwinter ; thereis nopermanentsouthernCO� ice polarcapsin thedatabase...

Nevertheless,theagreementbetweenthedatabaseandtheobservationsshouldbegoodenoughfor mostapplications,andwebelievethatthedatabaseis thebesttool availablefor mostpurpose.

5 How is the small scalevariability of the atmosphererepre-sentedin the database?

Meanfieldsarestoredin the databaseoncea season.Although the mainvariability,which is due to the diurnal cycle, is capturedby storing the fields 12 times a day,theremaystill besignificantvariationaboutthemeandueto, for example,motionsofbaroclinicweathersystems.

# Large scalevariability in the databaseis representedusinga novel approachbasedona techniquethatis widely usedin meteorologicaldataanalysisaswellas in othersubjectareas,usingEmpirical OrthogonalFunctions(EOFs). Let576983:

bethedatabasemeanverticalprofileof ameteorologicalvariable.Weaddaseriesof functionsto themeanverticalprofile,

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�C9DEC 6983: (2)

wherethe functions D�C areeigenvectorsof the covariancematrix of the mod-elled profiles(the EOFs)and �C arethe amplitudesof the functions(the Prin-cipal Components).The D C form anoptimal linear basissuchthat thevariancecapturedis high evenwhenthe truncationlimit is low. In orderto retaincross-correlationsin altitudebetweendifferentvariableswecombineall thevariables

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Figure2: Exampleof verygoodfits to theobservationsthat canbeobtainedwith thedatabaseMGSscenarioat variousseasons.Theblack solid linesshowtemperatureprofilesmeasuredby radio-occultation with Mars Global Surveyor. Thered dashedlinesare theMCD predictionsat thesamelocationsand times.Themodelis usuallyableto simulateaccuratelythevariationsof thetemperatureprofilesdueto changeindustloadingandinsolation.

togetherandform a setof multivariatefunctions. In practicethe series(2) istruncatedto 6 EOFswhich,onaverage,capturearound80-90%of thevariance.

# A small scalevariability model, simulatingperturbationsof density, tempera-tureandwind dueto theupwardpropagationof smallscalegravity waveshavebeenincludedin thedatabasesystem.Themodelis basedontheparametrizationschemeusedthenumericalmodelsthatsimulatedthedatain thedatabase.

Furtherdetailson thevariability modelscanbefoundin Lewis etal. (1999,2001b)

6 How to accessthe database?

For moderateuse: the World Wide Website.

For anyonehaving accessto internet,A World Wide Web sitehasbeendevelopedatLMD (http://www.lmd.jussieu.fr/mars.html). In aditionto a completedocumention,this interactivesiteoffer a directandconvenientaccessto thedatain avariety of graphicalandnumericalformats. However, the variability modelsarenotavailableon theweb-site.

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Figure4: A comparisonof theMars Pathfindersurfacemeasurementswith theMCD.Thesmall squaresshowthe Mars Pathfindermeasurementsand the solid line is themeanof the observationstakenover the first 30 daysof the mission. Thelargecir-clesconnectedby dashedlines showthe MCD predictionsinterpolatedto the MarsPathfinderlocation. Redlines: MGS“dust scenario” (the low dust scenariogivesverysimilar results).Greenline: Viking scenario.Top pannel: Thepressurediurnalcycle: theMGSscenarioappearsto underestimatethetotal amplitudeof thesurfacepressure tide, whereasthe Viking dustscenarioappearsto givea betterfit. Middlepanel: thetemperatureat thetopof the1 mmeteorologicalmast(about1.27mabovethe surface). The dotted lines are the MCD surfacetemperature (top line at mid-day)andtheMCD lowestatmosphericlevel (5 m) temperature(bottomline). Bottompanel: Thewind directionaxis, indicatedby thecompasspoint fromwhich the windis blowingfrom( % � is a northerly).Thegeneral senseof rotationis determinedby thepassageof thediurnal thermaltide; thedetails,such asthesmall rotationtoward aneasterlyneardawnbefore thesubsequentrotationto a westerly, are a consequenceofthelocal topography. 10

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Figure5: A comparisonof thedensitymeasuredin-situ (reddots)by theMars GlobalSurveyor accelerometerduring aerobraking around125 km during northernwinter(Keatinget al., 1998)with the densitiespredictedat about the samelocation by theMars ClimateDatabase(MGSscenario). The absolutevalueof the densityis wellpredictedin spiteof theextremesensitivityof densityto theentireatmospherebelow. Inaddition,theMCD predictslongitudinal variationscomprisingwave-likewavenumber1 and2 structureswhich are quitesimilar to theobservations.

For intensiveor precisework : the CD-ROMs

TheMCD is availablefor distributionon a coupleof CD-ROMs thatcanbeobtainedfrom LMD. In its currentversionThedataaredistributedin portablebinaryformats,suchasthe DataRetrieval andStorage(DRS) library developedfor the Programfor(Terrestrial)ClimateModelDiagnosisandIntercomparisonto facilitatethetransferofdatabetweendifferentplatforms(Lewis etal., 2001a).

Bearingin mindthepotentiallydiverserangeof usersof theMCD, includingengineersinvolved in thedesignof spacecraftmissions,scientistsspecializingin GCM studieswho arefamiliar with manipulatingsimilar datasetsandscientistsfrom otherareaswho mayrequireinformationon environmentalconditionson Mars,thedatamaybeaccessedby severalmethods:

# If you know FORTRAN, thebestway to retrieve environmentaldatafrom theMarsclimatedatabaseis to usethesubroutine modeof thesoftwaresuppliedwith the MarsClimateDatabase.In practice,oneonly hasto call a mainsub-routinenamedatmemcd from within any programwrittenin FORTRAN to getenvironmentaldataatany givenlocationsandtimes.A simpleexampleof suchaprogram(test emcd), whichcanbeeasilymodified,is provided.Thismodewasdeveloppedwith a particularattentionto trajectorysimulationapplication,but It shouldalsobeusedfor otherpurpose.A programmer’s guideis available(Forgetetal. 2001a).

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# An interface,MCDGM, issuppliedwith theMarsClimateDatabase.TheMCDGMinterfaceperformsin a very similar way to MarsGRAM version3.5. It is in-tendedto makethedatabaseaseasyto useaspossiblefor thosewith prior ex-perienceof MarsGRAMaswell asproviding possibleaccessfor all usersto thecompletedatabase,It canberun in interactiveor batchmode.

# It is possibleto accessthedatabasedirectly from within any program,written inFORTRAN or C, by usingtheDRS library .

# Control files, instructionsand examplescriptsareprovided for accessingthedatabaseusingGrADS. GrADS is a freely availablepackagefor access,ma-nipulation and display of earthsciencedatawhich runs on many computingplatforms.

7 KeyReferences

(availableon theweb-site: http://www.lmd.jussieu.fr/mars.html)

Technicaldocumentation

Forget,F., C. HourtolleandLewis, S.R.(2001a)MarsClimateDatabaseatmemcdsubroutineprgrammer’s guide.

Forget,F., Y. WanherdrickandLewis, S.R.(2001b)Validationof the Mars GeneralCircula-tion modelandClimateDatabasewith new spacecraftobservations. EuropeanSpaceAgencyTechnicalReport.

Lewis, S.R.,Collins, M. andForget, F. (2001a)Mars ClimateDatabasev3.0: UserManual,EuropeanSpaceAgency TechnicalReport.

Lewis, S.R.,Collins,M. andForget,F. (2001b)MarsClimateDatabasev3.0: DetailedDesignDocument,EuropeanSpaceAgency TechnicalReport.

Scientificarticles

Forget, F., Hourdin, F., Fournier, R., Hourdin, C., Talagrand,O., Collins, M., Lewis, S.R.,Read,P.L. andHuot, J.-P. (1999)“Improvedgeneralcirculationmodelsof theMartianatmo-spherefrom thesurfaceto above 80km,” J.Geophys.Res.,104,24,155–24,176.

Lewis, S.R.,Collins, M., Read,P.L., Forget, F., Hourdin,F., Fournier, R., Hourdin, C., Ta-lagrand,O. andHuot, J.-P. (1999) “A ClimateDatabasefor Mars,” J. Geophys.Res.,104,24,177–24,194.

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