Water ice clouds have been shown to alter the thermal structure of the Martian atmosphere. Here we discuss the assimilation of total column water vapour and dust optical depth data from the Thermal Emission Spectrometer (TES) into the UK/LMD MGCM, and compare the predictions of cloud and temperature in the assimilation with observations

Lewis, S. R.

Patel, M. R.

Smith, M. D.

Steele, Liam

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsAssimilating the Martian water cycleConference or Workshop ItemHow to cite:Steele, Liam; Lewis, S. R.; Patel, M. R. and Smith, M. D. (2012). Assimilating the Martian water cycle. In:European Planetary Science Congress 2012, 23-27 Sep 2012.For guidance on citations see FAQs.c© 2012 The AuthorsVersion: Version of RecordLink(s) to article on publisher’s website:http://meetingorganizer.copernicus.org/EPSC2012/EPSC2012-321.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukAssimilating the Martian water cycleL. Steele (1), S. R. Lewis (1), M. R. Patel (1) and M. D. Smith (2).(1) Department of Physical Sciences, The Open University, UK (l.steele@open.ac.uk), (2) NASA Goddard Space FlightCenter, Greenbelt, MD, USA.AbstractWater ice clouds have been shown to alter the thermalstructure of the Martian atmosphere. Here we discussthe assimilation of total column water vapour and dustoptical depth data from the Thermal Emission Spec-trometer (TES) into the UK/LMD MGCM, and com-pare the predictions of cloud and temperature in theassimilation with observations.1. IntroductionWater ice clouds play an important role in the globaltransport of water, as well as in determining the ther-mal structure of the atmosphere, particularly over thetropics [9]. The scattering of solar radiation and theemission of infra-red radiation by clouds have localcooling effects, while the absorption of solar and infra-red radiation can lead to warming. Which of theseeffects dominates depends upon the properties of thecloud, such as height, thickness and temperature. Forexample, the cold aphelion cloud belt absorbs infra-red radiation from the surface, leading to upper atmo-sphere warming, while the warmer polar hoods emit inthe infra-red and cool the atmosphere [2].In order for the model’s prediction of clouds to beaccurate, it is vital that the atmospheric temperatureprofile and water vapour abundance is modelled cor-rectly. Data assimilation can help to constrain theseparameters, allowing a consistent, four-dimensionalmapping of the Martian atmosphere and water cycleto be obtained for the period of the observations. Theassimilated record can be used to validate independentmodel results and investigate the interaction of waterice clouds with both the water cycle and atmosphere.2. Modelling and data assimilationTo study the Martian water cycle, we use an MGCMwhich makes use of the most recent version of theLMD GCM physical schemes [1] with the UK spec-tral dynamical core and data assimilation scheme [4].The model contains a cloud microphysics scheme, ca-pable of simulating the nucleation, growth and sedi-mentation of ice particles [7]. The radiative effects ofwater-ice clouds are also included [6].The assimilation scheme used in the model was de-veloped by [3]. It is based on the Analysis Correc-tion scheme of [5], and can analsye data distributedin both time and location. The scheme has alreadybeen successfully used to assimilate TES dust opacityand temperature data into the UK/LMD MGCM [4],as well as new data being returned from Mars ClimateSounder (MCS). Here, we assimilate 3D (horizontaland time-dependent) variations in dust opacities andtotal column water vapour abundances from TES [8].The model vapour mixing ratios are vertically scaledin order for the total column value to match observa-tions.Figure 1: Zonally averaged temperature difference(vapour assimilation – free-running model) in the trop-ics, averaged over 5 sols around sol 160 (LS = 75◦)of Mars Year (MY) 25.3. Preliminary resultsFigure 1 shows the zonally-averaged temperature dif-ference between an assimilation of both dust opac-ity and total column water vapour, and a free-runningmodel. As can be seen, the assimilation has lead to anincreased warming in the middle atmosphere aroundEPSC AbstractsVol. 7 EPSC2012-PREVIEW 2012European Planetary Science Congress 2012c© Author(s) 2012EPSCEuropean Planetary Science CongressFigure 2: Global RMS error in total column watervapour (pr-µm) for sols 145-165 (LS = 68◦-77◦) ofMY 25. The red line is for the free-running model andthe blue line is for the vapour assimilation.the tropics. This is due to changes in the locationand optical thickness of water ice clouds predicted inthe assimilation compared to the free-running model.Such a warming has been shown previously by [9] whoperformed an assimilation using temperature and dustopacity data from TES. However, in this assimilation,the warming has successfully been accounted for with-out the need for temperature assimilation. Figure 2shows the global RMS error in water vapour columnfor sols 145-165 of MY 25. In general, the RMS er-ror is halved by performing the assimilation, with anaverage global RMS error of ∼3 pr-µm.Work is currently still ongoing in order to improvethe vertical scaling of the model’s water vapour profile,which should lead to further improvements in cloudprediction. Additionally, work will begin on assimi-lating water ice data from both TES and MCS.AcknowledgementsThe authors gratefully acknowledge the support of theUK Space Agency and Science and Technology Facil-ities Council.References[1] Forget, F., Hourdin, F., Fournier, R., Hourdin, C., Ta-lagrand, O., Collins, M., Lewis, S. R., Read, P. L. andHuot, J.-P.: Improved general circulation models of theMartian atmosphere from the surface to above 80 km, J.Geophys. Res., Vol. 104, 24155, 1999.[2] Haberle, R. M., Montmessin, F., Kahre, M. A.,Hollingsworth, J. L., Schaeffer, J., Wolff, M. J. and Wil-son, R. J.: Radiative Effects of Water Ice Clouds on theMartian Seasonal Water Cycle, The Fourth InternationalWorkshop on the Mars Atmosphere: Modelling and ob-servation, 8-11 February, Paris, France, 2011.[3] Lewis, S. R. and Read, P. L.: An operational data assim-ilation scheme for the Martian atmosphere, Adv. SpaceRes., Vol. 16, 9, 1995.[4] Lewis, S. R., Read, P. L., Conrath, B. J., Pearl, J. C.and Smith M. D.: Assimilation of thermal emission spec-trometer atmospheric data during the Mars Global Sur-veyor aerobraking period, Icarus, Vol. 192, 327, 2007.[5] Lorenc, A. C., Bell, R. S. and MacPherson, B.: The Me-teorological Office analysis correction data assimilationscheme, Quart. J. R. Meteor. Soc., Vol. 117, 59, 1991.[6] Madeleine, J.-. B., Forget, F. and Millour, E.: Modelingradiatively active water ice clouds: impact on the ther-mal structure and water cycle, The Fourth InternationalWorkshop on the Mars Atmosphere: Modelling and ob-servation, 8-11 February, Paris, France, 2011.[7] Montmessin, F., Forget, F., Rannou, P., Cabane, M. andHaberle, R. M.: Origin and role of water ice clouds in theMartian water cycle as inferred from a general circula-tion model, J. Geophys. Res. (Planets), Vol. 109, E10004,2004.[8] Smith, M. D.: Interannual variability in TES atmo-spheric observations of Mars during 1999-2003, Icarus,Vol. 167, 1, 2004.[9] Wilson, R. J., Lewis, S. R., Montabone, L. and Smith,M. D.: Influence of water ice clouds on Martian tropicalatmospheric temperatures, Geophys. Res. Lett, Vol. 35,L07202, 2008.

Assimilating the Martian water cycle

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Assimilating the Martian water cycle

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