Behavior of dust in the Martian atmosphere

[摘要] Two aspects of the dust cycle on Mars are examined: the seasonal variation of dust aerosolsin the atmosphere as observed by spacecraft and dust lifting by high wind stress at the southpole during late spring employing a specially developed mesoscale atmospheric model. Reanalysisof Viking mission optical depth measurements shows that the visible to infraredratio of total extinction opacity varies with season, and is due to seasonally varying waterice haze. The Martian atmosphere is clearer of dust, especially during northern spring andsummer, than previously thought. Water ice hazes can provide roughly 50% of the totalvisible opacity in these seasons, and that they represent only 1-5% of the total water column.Next, the conversion for use on Mars of a terrestrial mesoscale atmospheric model(the Mars MM5) is presented and described. Validation of the Mars MM5 is conductedby comparison with a general circulation model on scales of a few hundred kilometers andwith Martian surface landers (Viking Lander 1, Viking Lander 2, and Mars Pathfinder)on scales of a few kilometers, and in both cases there is good agreement in the meteorologicalvariables of temperature, pressure, and wind. Tides are found to be at least asimportant as slopes in generating the diurnal cycle of winds at the lander sites, in contrastto previous one-dimensional studies. Finally, assuming that dust injection is related to themovement of sand-sized grains or aggregates, the Mars MM5 predicts wind stresses of sufficientstrength to initiate movement of sand-sized particles, and hence dust lifting, duringlate southern spring in the south polar region. It is found that the direct cap edge thermalcontrast provides the primary drive for high surface wind stresses at the cap edge at this seasonwhile sublimation flow is not found to be particularly important. Comparison betweensimulations, in which dust is injected when wind stresses are high and those with inactivedust injection, show no signs of consistent feedback due to dust clouds on the surface wind stress fields during the late spring season examined here.

[发布机构] University:California Institute of Technology;Department:Geological and Planetary Sciences

[关键词] Planetary Science and Mechanical Engineering