The thermal structure, dust loading, and meridional transport in the Martian atmosphere during late southern summer

Details The thermal structure, dust loading, and meridional transport in the Martian atmosphere during late southern summer The thermal structure, dust loading, and meridional transport in the Martian atmosphere during late southern summer

Sep 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt.........1s&link_type=abstract

Ph.D. Thesis California Inst. of Tech., Pasadena.

Computer Science

Mars Atmosphere, Meridional Flow, Radiative Heat Transfer, Temperature Distribution, Zonal Flow (Meteorology), Dust, Emission Spectra, Iris Satellites, Solar Heating, Thermal Emission

Scientific paper

The thermal structure, dust loading, and meridional transport in the Martian atmosphere are investigated using thermal emission spectra recorded by the Mariner 9 infrared interferometer spectrometer (IRIS). The analysis is restricted to a subset of the IRIS data consisting of approximately 2400 spectra spanning Ls = 343 - 348 deg, corresponding to late southern summer on Mars. Simultaneous retrieval of the vertical distribution of both atmospheric temperature and dust optical depth is accomplished through an iterative procedure which is performed on each spectrum. Although atmospheric temperatures decrease from equator to pole at lower altitudes, both dayside and nightside temperatures above about 0.1 mbar (approximately 40 km) are warmer over the winter (north) polar region than over the equator or the summer (south) polar region. Zonal-mean zonal winds are derived from the atmospheric temperatures assuming gradient wind balance and zero surface zonal wind. Both hemispheres have intense mid-latitude westerly jets (with velocities of 80-90 m/s near 50 km); in the southern tropics the winds are strongly easterly (with velocities of 100 m/s near 50 km). A comprehensive radiative transfer model is used to compute solar heating and thermal cooling rates from the retrieved IRIS temperature and dust distributions. There are large net heating rates (up to 8 K/day) in the equatorial region and large net cooling rates (up to 20 K/day) in the polar regions. These net heating rates are used in a diagnostic stream function model which solves for the meridional and vertical components of the diabatic circulation simultaneously. The results show a vigorous two-cell circulation, with rising motion over the equatorial region (approximately 1.5 cm/s), poleward flow in both hemispheres (approximately 2 m/s), sinking motion over both polar regions (1-2 cm/s), and return flow in the lowest atmospheric levels. The meridional transport time scale is approximately 13 days. Water vapor desorbed from the low-latitude regolith during late northern winter/early northern spring may be transported upward by the ascending branch of this circulation, where it may be advected back to the polar regions by the high-altitude meridional winds. This process could provide a high-altitude source of water vapor for the formation and maintenance of the north polar hood.

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