Martian Meteorology: Insights from the Phoenix Mission to the Martian ArcticJohn E. MooresApril 15, 2009

Talk RoadmapMars Primer, Phoenix Mission Background

The Surface Stereo Imager (SSI) DataSupra-Horizon MoviesZenith MoviesWind Telltale Mirror

Winds and Blowing Dust

Clouds and Water Ice

Trends and Conclusions

Why do we care?Understanding the behaviour of wind, water and dust at the landing site Why we see what we see locallyCompliment to LIDAR observations

Inputs to Modelling EffortsDirect observation of atmospheric parameters helps to refine the big picture of past and present climate on MarsObservations may be applicable to the terrestrial stratosphere

Pure interestAnimations of cloud help us to understand extraterrestrial weather from the human scaleMust not let terrestrial analogs overcome the data

Mars Primer4th planet from the sunSmaller than Earth

Atmospheric pressure is 6 mBar (600hPa)Main constituents are CO2 (95%) N2 (2.7%) and Ar (1.6%)Up to 100 pm of water vapor

Seasonal cycle is more extreme than the Earth due tohigh orbital eccentricity (9%)Similar axial tilt (25.4)The atmosphere condenses seasonably at the winter pole

Most water is contained in two polar caps, though much more may be buried in a deep cryosphere

The surface is blanketed by superfine dust (1.6 micron radius) which gives the planet and the sky its colour

The Phoenix MissionFirst mission to the Martian Arctic!

Hundreds of Scientists, Engineers and students came together in Tucson, AZ over the summer of 2008 to run the missionSome were present to study data, others to resolve hardware issues, but many had specific day to day operational roles

Lived on Mars Time for almost three monthsMartian day is 24hours and 39minutes

Each and every sol produced debate about where to focus the next sol's resourcesInvestigations had to fit into tight constraints of power, data volume, temperature and workloadNot every desire could be accommodated

Launch to LandingLaunched in July of 20079 month interplanetary cruise7 minutes of terror

Landed on May 25th, 2008late northern hemisphere spring (LS=76.74)Measurements were taken for 151 Sols (Martian days)

Single Lander at 68 N, 125 W Equivalent to the Mackenzie River Delta on Earth

Barry Goldstein Project ManagerGlenn Knosp Project Business ManagerCDR 50 DaysATLO 196 DaysShip 596 DaysLaunch 675 DaysEDL 971 DaysSurface Stereo ImagerMET mast(Temp/Wind)MECA: microscopy, electro-chemistry, conductivityTEGA: Thermal and EvolvedGas AnalyzerLIDARRobotic ArmIce tool, scraper bladesRA CameraThermal and Electrical conductivity probeThe Spacecraft

Major Mission FirstsPhysical Chemistry/GeologyTrenched the regolith down to sublimating ice and icy soil

ChemistryDetection of a highly oxidizing compound, a perchlorateDetection of carbonates without significant sulfates

AtmosphereFirst Mars operation of an Atmospheric LIDARDetection of virga and falling snow

The Surface Stereo Imager and the Atmospheric DatasetsMaking movies on Mars

Surface Stereo ImagerCo-I: Mark Lemmon, built at the University of Arizona

Based on the Imager for Mars PathfinderCamera head sits on 84cm extendable mastEyes set 15cm apartFOV: 13.8 degreesCross-eyed

Two 1024x1024 MER flight spare CCDsExcellent S/N at Martian Temperatures (

Atmospheric DatasetsZenith MoviesSSI Camera pointed nearly vertically, 10 frame capturesDifferential Frames to bring out contrast and movement in the atmosphereMany bispectral datasetsCaptures the direction of winds aloftCaptures spectral data to differentiate between ice and dust in the atmosphere

Supra-Horizon MoviesIdentical to Zenith Movies, except pointed just above the horizonLongest path length through the atmosphereGood for determining morphologiesCan detect atmospheric layering and wind shearAlso captures spectral data for particle differentiation

Telltale Mirror Analysis7441 images taken over the course of the mission

LIDAR and Winds AloftZenith movies can directly measure the direction of features moving aloft

LIDAR input is required to determine the height of featuresUsing the height of greatest backscatterAgrees well with the pixels around the zenith

Still leaves a great deal of errorPrecise heights may not be known (ranges only)SSI is limited in the range of speeds that are calculableSelection Biases for overlaps

Blue to Red RatiosMartian Atmosphere is coloured red by the presence of dustWell understood particle size (1.6m radius) from Viking, MPF, MER

Larger particles, such as water ice, will scatter more isotropicallyFlatter spectral profileHigher signal in the blue compared to dust

By dividing what we see at two spectral points by what we expect can derive a blue to red ratioHowever, there is a fair bit of spectral variation across the skyMust be compensated for using a radiative transfer code

Results for Blowing DustInsights from Zenith Movies and Telltale Mirror Analysis

Dust in the BackgroundDust is a constant feature of the martian atmosphere and gives the sky (and the surface) its red colour

Dust is distributed relatively evenly in the lower atmosphere

Features can be formed by density variations at different altitudesGives rise to billowy featuresOptical depth trend over the course of the mission. Courtesy of Mark Lemmon

Zenith movies of DustSome interesting zenith movies show the nature of the blowing dustSol 008Sol 009Sol 054

Wind DirectionsThe direction of the winds aloft and at the surface appear to be correlated

Wind SpeedsEven with LIDAR difficult to get wind speed aloft

Tried correlating the wind speed withTime of DaySol of MissionAltitude

Altitude only relationship showing a reasonable correlationNot unexpectedSaturated region highlighted2 populations, dust and cloud

Telltale MirrorDiurnal Trend in Dust loading is also seen in the fractional coverage of the telltale mirrorBest explanation is the turning wind cleaning the mirror daily and re-depositing finesIrradiation effects should be seen at 12:00 or 15:00Mirror accumulates dust in wind shadows

Closer look at the patternsSol 029 hecto-telltale 100 frames captured near the turn-around time show increased variability after 13:00 LTSTMission-long trends with the diurnal effect removed show little variability

Thus the Diurnal trend DominatesMore consistent with wind scour then quiescent settling

Results for Water Ice Cloud

Insights from Zenith and Supra-Horizon Movies

Water Ice in the Martian AtmospherePhoenix was first to observe martian snowfall, but putative water ice clouds have been seen beforeDiurnal cloud patterns on the larger volcanosFormation of a polar hoodCloud inferred from TIR and direct sensing with MOLA

The water ice clouds are largely absent for the first 79 sols of the missionSupra-Horizon movies show some possible very thin clouds as early as the 60sCirrus Clouds photographed by Opportunity rover at Endurance Crater

Supra Horizon Cloud MorphologiesHigher level regular clouds are common features in the supra-horizon moviesSol 78

Supra Horizon Cloud MorphologiesStarting on sol 94, optically thick, fluffier, more cumulus-like clouds are evident

These clouds have pronounced blue to red ratiosSol 94

Supra Horizon Cloud MorphologiesThey have also been seen to form and sublimate from locally available water vapourSol 112

Supra Horizon Cloud MorphologiesMorphologically distinct, streaky clouds are seen at night during the middle of the missionSol 84

Supra Horizon Cloud MorphologiesThe cloud-forms get increasingly complex, optically thick and appear to move faster across the sky as the mission progresses

But some days remain relatively drySol 132Sol 148

Zenith movies of Water IceZenith movies also show water ice cloudNon-ideal viewing geometryCan still get blue to red ratios out of the dataSol 101Sol 141

Seasonal TrendQuantitative: Blue to Red Ratios confirm more water ice later in the missionTime-Varying Component has bigger increase then mean frame

Variability: Late in the mission there continue to be days when the BRR is low

Also the dust remains a significant atmospheric componentBRRs from Supra-Horizon Movies plot lower then for Zenith Movies

Diurnal TrendA strong diurnal trend is also visibleA peak in cloudiness is observed around mid-dayVariable cloudiness in the early morning? (Selection bias effect)

The formation of cloud is inhibited in the early afternoon and eveningSublimation?Out of Water Vapor?Boundary Layer decoupling? (formation of an intermediate stable layer)

The trend is also seen in the last 20 sols of the missionSome days have strong cloud at middayOn some days cloud is absent

Extension to the first 50 solsThe Signal to Background ratio corresponds to the BRR of the Time Variable ComponentCan use the Signal to Background ratio to get an idea of cloudiness early in the missionA possible minimum is observed near sol 50 with water ice ramping up starting near sol 80

VirgaLIDAR has seen evidence of fall streaks at night, characteristic of Virga

The SSI has also observed this behaviour on several occasions during the day in Supra-Horizon moviesSol 126Sol 80

Observed Wind ShearRecall: Winds aloft match well with winds at the surfaceCorrespondence is good early in the mission when dusty conditions dominateLater in the mission many features pass by too rapidly to observe

However, several supra-horizon movies show two layers moving at different rates and in different directionsCould locally-driven winds be interacting with larger-scale flows?Sol 096

Trends and Conclusions

Summary of ObservationsObserved a diurnally rotating wind aloft matching with the wind telltale

Low-fidelity data for wind speed aloft shows no evidence for higher wind speeds aloft

Dustiness of the wind telltale mirror shows a diurnal pattern consistent with wind deposition and scour instead of settling

Variation in morphologies of cloud indicate an active hydrological cycle

Clouds have high BRRs, likely made of relatively large particles

BRRs have a diurnal trend peaking around 10:00 to 12:00 LTST

BRRs and Time-Varying Signal Strength are correlated and have a minimum near sol 50

BRRs increase from sol 50 to sol 150 but show significant day to day variability

Virga and differential motion of cloud layers have been observed

Significance of TrendsStrongly expressed diurnal cycle in wind, dust movement and atmospheric water iceSuggests the water and temperature cycles are dominated by local effects instead of transportConsistent with water and much of the dust being confined to the PBL (LIDAR) and consistent surface air temperatures

Strongly expressed seasonal increase in atmospheric water iceProgressively colder atmospheric temperatures later in the summer allow for more expression of cloud even with declining water vapor

Exceptions to the Rule

Some significant variability exists in the seasonal datasetVery dry days can be seen late in the summer when cloud is increasing Wind shear and multiple movements at different heights appear to be present occasionallyArgues for not insignificant regional transport of water ice/vapor

Thank-you!

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