Other
Scientific paper
Jun 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009phdt.........3e&link_type=abstract
Proquest Dissertations And Theses 2009. Section 0051, Part 0606 199 pages; [Ph.D. dissertation].United States -- Colorado: Univ
Other
Dust Storm, Mars, Radiative Transfer
Scientific paper
The purpose of this work is to study the general characteristics of Martian global dust storms, and their relation to the Martian dust cycle using infrared observations. I devised a parameter retrieval algorithm for Mars Global Surveyor Thermal Emission Spectrometer daytime data from global dust storm 2001A that extracts information about dust optical depth, effective radius, and surface temperature using Newtonian first-order sensitivity functions of the infrared spectrum in response to variations in these parameters. This algorithm is both relatively accurate and very fast, successfully retrieving parameters from 56878 spectra for global dust storm 2001A, as well as a subsequent Martian year in comparison. There are uncertainties introduced into the retrievals, especially by parameters that could not be constrained such as the optical constants of the Martian dust. Uncertainties in assumed vertical mixing of dust can lead to significant uncertainties in retrieved optical depth and dust effective radius. I discovered several aspects of the dust storm that have not previously been recognized. One of these is that the dust optical depth becomes correlated with surface pressure during the decay phase of the dust storm. Similar pressure optical depth correlations were found the following Martian year when no global dust storm occurred. Global correlation of dust optical depth and surface pressure, indicative of global dust mixing processes, also varies with the season. It is generally larger during southern hemisphere late spring and summer, and very low at all other seasons when there is no global dust storm. These pressure and optical depth data provide a tool to study atmospheric dynamics. I also found that the observed decay of optical depths at the later stages of the dust storm match, to first order, theoretical values of clearing from Stokes-Cunningham fallout of the dust. The unprecedented coverage of the retrieval of dust effective radii allowed me to discover previously unseen global trends. Zonally averaged effective radius is constant, within uncertainties, at all latitudes and seasons except at high southern latitudes around equinoxes in both Martian years, where it is larger than average. The emergence and disappearance of these larger particles correlates with observations of polar cap edge storms at those latitudes. Northern latitude observations under similar conditions yielded systematically lower average effective radii. I also discovered a previously unreported linear correlation between daytime surface temperature drop and rise in optical depth during the global dust storm. Global dust storm 2001A produced a significant optical depth and surface temperature anomaly in the dust cycle that was responsible for abating local dust storms. The observations of trends in effective radii are significantly different from trends predicted by global circulation models and need to be accounted for in future studies.
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