Lewis, S.R.

Montabone, L.

Read, P.L.

Rogberg, P.

Yamazaki, Y.H.

English

Open Research Online (OU)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsClimatology on Mars: interannual variability of meanfieldsConference or Workshop ItemHow to cite:Rogberg, P.; Read, P.L.; Lewis, S.R.; Montabone, L. and Yamazaki, Y.H. (2006). Climatology on Mars:interannual variability of mean fields. In: Second Workshop on Mars atmosphere modelling and observations, 27 Feb- 3 Mar 2006, Granada, Spain.For guidance on citations see FAQs.c© [not recorded]Version: [not recorded]Link(s) to article on publisher’s website:http://adsabs.harvard.edu/cgi-bin/nph-bib query?bibcode=2006mamo.conf..162R&amp;db key=AST&amp;data type=HTML&amp;format=&amp;high=44aa7ebb1d26986Copyright 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.ukCLIMATOLOGY ON MARS: INTERANNUAL VARIABILITY OF MEAN FIELDS.P. Rogberg, Dept of Physics, University of Oxford, UK (p.rogberg1@physics.ox.ac.uk), P. L. Read, Dept of Physics,University of Oxford, UK, S. R. Lewis, Dept. of Physics & Astronomy, CEPSAR, The Open University, UK, L.Montabone, Dept. of Physics › AOPP, University of Oxford, Oxford, UK › now at Laboratoire de M ·et·eorologieDynamique du CNRS, Paris, France, Y.H. Yamazaki, Dept of Physics, University of Oxford, UK.IntroductionIn this abstract we present results based on measure-ments extracted from a data- assimilation set that spansa continuous period over more than three years. We haveconcentrated here on an analysis of geopotential, station-ary wave and vorticity fields over two periods, centeredaround perihelion respectively aphelion. The motivationto study these field lies in their generic connection to thelarge scale circulation and its stability. In particular thevorticity field carries information about the presence e.g.of inertial stability. The data set has been created by acombination of the observed data by the Thermal Emis-sion Spectrometer on the Mars Global Surveyor withmodel data generated by the Oxford-MGCM, describedin more detail in [4] and [5].Geopotential height Ls = 600- 900 at 100 Pa-180 -120 -60 0 60 120 180Longitude (deg)-60-3003060Latitude (deg) 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30  (km)Stationary eddy Ls = 600- 900 at 100 Pa-180 -120 -60 0 60 120 180Longitude (deg)-60-3003060Latitude (deg) -6000 -4000 -2000 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 2000 4000 6000  (m)Figure 1: The geopotential height field and its fluctuations at100 Pa around aphelion during MY25, both fields are timeaveraged over 30 Sols. Observe that the colorbar are slightlydifferent between the two mean fields, while being constantfor the fluctuationsAssimilation with the Oxford MGCMThe model was run with a horizontal resolution equal toa triangular spectral truncation at wave number   , withnon-linear terms evaluated on a  	grid. While 25 -levels were are used to resolve the vertical resolutionwhich cover the atmosphere up to  km height withthree sponge layers above to damp vertical propagatingwaves.The data cover at present the period   (Sol ) MY24 to ﬀﬁ (Solﬂﬀ) MY27. The obser-vational data consists primarily of vertical temperatureprofiles below   km and maps of total column dustopacity. The data, stored in netcdf-format, is dividedinto seasonal units, i.e. each data file spans  Sols withdata sampled at two-hour intervals. There are eight datafields in each data file : ﬃ! -distribution, surface tem-perature and pressure, atmospheric temperature, zonaland meridional winds, wind variance and the total opti-cal dust.Geopotential height Ls = 2400- 2700 at 100 Pa-180 -120 -60 0 60 120 180Longitude (deg)-60-3003060Latitude (deg) 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29  (km)Stationary eddy Ls = 2400- 2700 at 100 Pa-180 -120 -60 0 60 120 180Longitude (deg)-60-3003060Latitude (deg) -6000 -4000 -2000 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 2000 4000 6000  (m)Figure 2: The same fields as for fig. 1 but at perihelionREFERENCESStationary eddy Ls = 600- 900 at 100 Pa-180 -120 -60 0 60 120 180Longitude (deg)-60-3003060Latitude (deg) -6000 -4000 -2000 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 2000 4000 6000  (m)Stationary eddy Ls = 600- 900 at 50 Pa-180 -120 -60 0 60 120 180Longitude (deg)-60-3003060Latitude (deg) -6000 -4000 -2000 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 2000 4000 6000  (m)Stationary eddy Ls = 600- 900 at 10 Pa-180 -120 -60 0 60 120 180Longitude (deg)-60-3003060Latitude (deg) -6000 -4000 -2000 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 2000 4000 6000  (m)Stationary eddy Ls = 600- 900 at 2 Pa-180 -120 -60 0 60 120 180Longitude (deg)-60-3003060Latitude (deg) -6000 -4000 -2000 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 2000 4000 6000  (m)Figure 3: The figure shows fluctuations in the geopotentialheight field at 100, 50, 10 and 2 Pa around aphelion duringMY26ClimatologyWe consider two climatological aspects in this abstract,interannual variability and hemispheric asymmetry andtheir impact on mean fields during the periods for MY25-26 (MY24 is covered only by the later interval) "$#&%'(ﬀ)+*-,() and " # %/.0 (ﬀ)1* .2 () . The first period, apheil-ion, coincide with NH summer, while the second, peri-helion, occur during the NH winter. Processes affectingglobal circulation and dust lifting are significantly dif-ferent during these periods. Whereas the period aroundaphelion is associated with weak atmospheric activityall over Mars, in contrast NH winter exhibits strongerglobal circulation and often very intense dust lifting. In-deed almost all major observed dust storms in the pasthave been observed during this season of the year[1].Indication of hemispheric asymmetries in stationarywave patterns during NH winter were found in a modelstudy by Hollingsworth and Barnes ([3]). Where theyfound that the dominating eddies in the NH were typ-ically of zonal wave number 2, while SH eddies weremore commonly of wave number 1. The latter werealso found to be significant larger in amplitude. Similartrends are clearly apparent in the assimilated record, asevident in Fig. 1 and 2, which shows maps of meangeopotential height at 100 Pa (corresponding to an alti-tude of around 20 km) togther with its associated station-ary eddy fields around aphelion and perihelion. The SHeddies in particular are found to be dominated by 34%65 ,though only over a restricted range of longitude. Bothmean and eddie fields display the seasonal impact withthe change of geopotential gradient and latitude bandwith eddies. Furthermore, the planetary orbit makesthe geopotential gradient steeper during NH winter aswell as increase the eddy amplitude, which is reflectedin stronger zonal flow. Fig. 3 display the change ofthe stationary eddy field with height during one timeperiod, where both wavelength and amplitude increasesup to around 10 Pa ( 740(km). Further aspects of thestationary wave and vorticity fields will be discussed inthe presentation.Inertial instability typically manifests itself in theEarth’s atmosphere in association with patches of anoma-lous potential vorticity[2]. The evolution of the insta-bility in the Earth’s stratosphere has shown a correlationwith interannual variability of Rossby wave breaking[2].Such instabilities have not been extensively studied inthe Martian atmosphere so far, however. In this presen-tation we will present diagnostics indicating the clima-tology of inertial instability on Mars as a function ofseason.References[1] B.A. Cantor, et al, ’Martian dust storms: 1999Mars Orbiter Camera observations’, J. Geop. Res., 106,REFERENCES(E10) 23653 (2001)[2] J.A. Knox and V.L. Harvey, ’Global climatology ofinertial instability and Rossby wave breaking in thestratosphere’, J. Geop. Res., 110, D06108 (2005)[3] J.L. Hollingsworth and J.R. Barnes, ’Forced Station-ary Planetary Waves in Mars’s winter Atmosphere’,J. Atmos. Sci.,53, 428 (1996)[4] S.R. Lewis, et al, ’Assimilation of Thermal Emis-sion Spectrometer atmospheric data during the MarsGlobal Surveyor aerobraking period’, Submitted toIcarus[5] S.R. Lewis, et al, ’Data assimilation for Mars: Anoverview of results from the Mars Global Surveyorperiod, proposals for future plans and requirementsfor open access to assimilation output’, This issue.

Climatology on Mars: interannual variability of mean fields

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Climatology on Mars: interannual variability of mean fields

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