martian meteorology: insights from the phoenix mission to the martian arctic
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Martian Meteorology: Insights from the Phoenix Mission to the Martian Arctic. John E. Moores April 15, 2009. Talk Roadmap. Mars Primer, Phoenix Mission Background The Surface Stereo Imager (SSI) Data Supra-Horizon Movies Zenith Movies Wind Telltale Mirror Winds and Blowing Dust - PowerPoint PPT PresentationTRANSCRIPT
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Martian Meteorology: Insights from the Phoenix Mission to the Martian ArcticJohn E. MooresApril 15, 2009
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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
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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
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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
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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
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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
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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
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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
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The Surface Stereo Imager and the Atmospheric DatasetsMaking movies on Mars
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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 (
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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
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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
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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
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Results for Blowing DustInsights from Zenith Movies and Telltale Mirror Analysis
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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
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Zenith movies of DustSome interesting zenith movies show the nature of the blowing dustSol 008Sol 009Sol 054
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Wind DirectionsThe direction of the winds aloft and at the surface appear to be correlated
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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
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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
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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
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Results for Water Ice Cloud
Insights from Zenith and Supra-Horizon Movies
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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
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Supra Horizon Cloud MorphologiesHigher level regular clouds are common features in the supra-horizon moviesSol 78
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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
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Supra Horizon Cloud MorphologiesThey have also been seen to form and sublimate from locally available water vapourSol 112
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Supra Horizon Cloud MorphologiesMorphologically distinct, streaky clouds are seen at night during the middle of the missionSol 84
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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
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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
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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
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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
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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
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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
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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
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Trends and Conclusions
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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
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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
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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
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Thank-you!
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