DPS 2001 meeting, November 2001
Session 27. Mars Atmosphere I: Circulation
Oral, Chairs: J. Hollingsworth, A. Toigo, Thursday, November 29, 2001, 10:30am-12:30pm, Regency E

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[27.05] The effects of atmospheric dust on the sublimation of CO2 on Mars

B. Bonev, P.B. James, J.E. Bjorkman (University of Toledo), M.J. Wolff (Space Science Institute)

Dust storm activity has been proposed to be a primary factor controlling the interannual variability in the regression of the Martian polar caps. The effects of atmospheric dust on the sublimation of surface CO2 include both a reduction of the direct solar heating as well as an opposing increase in the back-warming of the surface by IR thermal dust emission. The net effect depends sensitively on the dust properties, surface albedo, and solar zenith angle. Consequently, quantitative modeling of the radiative transfer in a dusty atmosphere is necessary to understand how atmospheric dust changes the CO2 sublimation rate. In this work, we employ a ``full spectrum" Monte Carlo radiative transfer model (Bjorkman, J.E., and Wood, K. 2001, ApJ, 554, 615) that was adapted to model a planetary atmosphere. We have used dust properties (opacity, albedo, and scattering phase function) appropriate for Martian dust, and we have also modified the lower surface boundary condition to account for the wavelength-dependent absorption and reflection by CO2 ice. Finally, we account for sublimation by an appropriate modification to the energy balance that determines the planetary surface temperature. We present calculations of the sublimation rate as a function of dust optical depth, surface albedo, and solar zenith angle. Ultimately, the purpose of such calculations is to improve the understanding of interannual variability in the CO2 seasonal cycles on Mars.

The present research is especially timely because a global dust storm, similar to that in 1977, was observed on Mars earlier this year. Comparison of MOC data for this year with those for the previous, non-dusty year will provide a very good opportunity to investigate the effects of an early dust storm on the south polar cap's regression.

This research was supported by a grant from the Mars Data Analysis Program.

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