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H. Wang, M. I. Richardson, A. P. Ingersoll (Caltech), R. J. Wilson (GFDL), R. W. Zurek (JPL)
The Martian dust storm provides one of the most spectacular examples of transient meteorological phenomena in the solar system. While most Martian dust lifting events are local in scale, tens to hundreds of kilometers, some are regional storms thousands of kilometers in size, and a few have been observed to initiate global dust storms that shroud the entire planet. Large dust storms represent the most dramatic component of the Martian dust cycle - one of the three main cycles determining the climate on Mars. They can generate significant perturbations of the global climate, increasing mid-level air temperatures by tens of degrees Kelvin. These storms can be categorized as major storms. Observations before Mars Global Surveyor (MGS) indicate that classical major dust storms originate in the southern hemisphere during the "dust storm season" of southern spring and summer (Ls=180-360). It was suspected that the dynamics of major dust storms involve feedback between the atmospheric circulation and radiative heating of lofted dust. However, there has been little success in providing mechanisms to explain the origin and/or transience of major storms. Recently, a new category of major dust storm has been identified, with dust lifting initially associated with northern-hemisphere fronts, and involving flushing of dust from the northern to southern hemisphere. Such "flushing" dust storms are mainly observed in mid northern fall and mid northern winter. We present a mechanism for the development of these storms, including natural explanations for diurnal, seasonal, and interannual variability of the storms. Dust flushing from the northern hemisphere requires coherence and cooperation between three major dynamical systems: baroclinic storms, thermal tides, and the Hadley circulation. Once dust is flushed into the southern hemisphere, accumulation of dust in the Hadley convergence zone will greatly increase the strength of the circulation, leading to major dust storm. These results provide not only a coherent picture of major storm development and transience, but also an example of cooperative interaction of Mars' major dynamical systems over planetary length-scales.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.