Modeling of Martian atmospheric phenomena and atmosphere ...

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to guide and validate the models. The basic work has considered parameterization methods forthe physical processes in the Martian atmosphere (e.g., turbulence, radiative transfer, soil heattransfer, cloud and fog physics). The applied work has consisted of studies of mesoscale andplanetary boundary layer (PBL) phenomena driven by atmosphere-surface interactions.FMI’s space research has since mid-1980s had a substantial involvement in Mars missions withspecial emphasis on atmospheric investigations. FMI has previously participated in, e.g., theMars 96, Mars Polar Lander, NetLander and Beagle 2 missions; currently the FMI team isworking on, e.g., the MetNet surface meteorological network concept as well as on the Phoenixand Mars Science Laboratory missions. FMI also represents Finland in the International MarsExploration Working Group. The modeling activities and the mission involvements togetherform a strong and comprehensive Mars atmospheric research effort.2. PROCESS STUDIES, PHYSICAL PARAMETERIZATIONS AND THE COLUMNMODELWe have studied the fundamental physical processes of the Martian atmosphere and have developedparameterizations for them. A radiative transfer study for the dustless case (Savijärvi,1991b) showed that the effect of H 2 O in Mars is generally small. It has so far been left out ofMars General Circulation Models (MGCMs), but should be included in the next generation.A column model including a mixing length closure for turbulence and simple radiation schemesfor the effects of CO 2 , H 2 O and dust gave a fairly good simulation for the two Viking Lander(VL) sites (Savijärvi, 1991a). The diurnal cycle of H 2 O was studied more closely in Savijärvi(1995) with a refined scheme for the thermal diffusion in the soil. Also the preliminaryMPF observations were fairly well simulated (Savijärvi, 1999). With the MPF wind speed datafinally available and with a radiation scheme tuned and validated against line-by-line (LBL)calculations, the match was even better (Savijärvi et al., 2004; Määttänen and Savijärvi, 2004).The shortwave (SW) LBL comparison (Savijärvi et al., 2005) included a general improvementsuggested for the so-called delta-two-stream SW radiation schemes. The improvement reducedthe systematic error of these methods by more than 50 %. It can be applied in Earth GCMschemes as well. The improved method was then used to study the “anti-greenhouse” effectof the Martian dust on its climate as the function of dust amount and dust optics. A Marsintercomparison of radiation codes is now an ongoing worldwide project lead by UH and FMI.In this project, all the main Mars GCM codes are being compared against the first-principlesLBL results in fixed reference conditions.Presently the temperature profiles from the thermal emission spectrometers (mini-TES) onboardthe Mars Exploration Rovers (MER) are being studied by the group, and compared with modelcalculations. These profiles appear to indicate strong daytime convection above the radiativelyheated surface layer, as predicted by the column model.224
3. THE 2-D MESOSCALE MODELThe 2-D Mars Mesoscale Circulation Model (MMCM) is in a way an extension of of the 1-Dcolumn model, as the 2-D model adds a horizontal dimension representing a “slice” of the atmosphere.The limited spatial dimensionality brings with it inherent limitations — the area understudy and simulation has to exhibit only moderate or small variations in the most significantvariables in the direction perpendicular to the computational grid.The 2-D MMCM is based on a terrestrial research model. The Mars version was created alreadyin the early 1990s. It has subsequently been developed further and used to study primarily socalledsurface-induced circulation phenomena, such as slope winds (Savijärvi and Siili, 1993),circulations driven by horizontal thermal contrasts caused by variations in surface propertiessuch as albedo, thermal inertia (Siili, 1996), ice (CO 2 and/or H 2 O) cover (Siili et al., 1997)as well as combinations thereof. In the recent years phenomena in the Martian polar regionshave been of primary interest. Consequently H 2 O condensation, sublimation and transport (horizontaladvection, vertical diffusion) processes have been incorporated into the model, the approachis essentially as described by Savijärvi (1995).Since atmospheric modelling is sensitive to initial conditions, ensemble or statistical type approacheshave been investigated for and even introduced to terrestrial models to some degree.In these approaches a forecast is arrived at by running a set of simulations with varied initial orboundary conditions and analysing the set of results using statistical methods. The robustnessof these approaches is mitigated by the high computational cost. Due to its reasonable computationalcost the we have used our 2-D model in a pilot study of Mars ensemble simulations.4. THE MARS LIMITED AREA MODELThe Mars Limited Area Model (MLAM) is a spatially fully 3-D MMCM and is based on thedynamical core of the widely (also by FMI) used operational weather forecast model HIRLAM(HIgh Resolution Limited Area Model), v. 5.0.0. As with the 1-D and 2-D models earlier,planetary constants and parameterizations (the “physics”) appropriate for Mars have replacedthe terrestrial values and schemes. A limited area model needs also realistic initial and boundaryconditions; they were taken initially from the European Mars Climate Database and currentlysimulation results of the Oxford University’s MGCM are used. Results from other MGCMscould also be used in the future. Our model system is hence the first European 3-D MMCM.The MLAM results have been tested and compared against the 1-D and 2-D and other 3-DMMCM model results as well as VL, MPF and most recently MER Mini-TES observations.VL1 and MPF diurnal temperature cycles and wind fields are reproduced very well. An exampleof the results is shown in Figure 1. The 3-D nature of the model has also enabled more realisticsimulations of Hellas impact basin summertime circulations. We are also planning MER simulationsusing data of the Mars Global Surveyor/Thermal Emission Spectrometer instrumentassimilated with the Oxford MGCM as initial and boundary conditions for the MLAM.225
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