Simulations of the Martian Dust Cycle with a General Circulation Model

Citation

Basu, Shabari (2006) Simulations of the Martian Dust Cycle with a General Circulation Model. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/BDB8-Z423. https://resolver.caltech.edu/CaltechETD:etd-09232005-154100

Abstract

The Martian seasonal dust cycle is examined with a General Circulation Model (GCM) that treats dust as a radiatively and dynamically interactive trace species. Dust injection is parameterized as being due to convective processes (such as dust devils) and model-resolved wind stresses. Multi-year Viking and Mars Global Surveyor mission air temperature data sets are used to quantitatively assess the quality of simulations. Varying the three free parameters for the two dust injection schemes (rate parameters for the two schemes and a threshold for wind-stress lifting), we find that northern spring and summer temperatures, which are observed to repeat very closely each year, can be reproduced by the model if the background dust haze is supplied by convective lifting. To obtain spontaneous and variable dust storms, dust injection due to high threshold and high rate stress lifting must be added. The convective scheme is found unable to generate a dust storm but is a good candidate for background dust (in agreement with imaging observations e.g., dust devils). Combining the convective scheme and high-threshold stress lifting, we obtain a "best fit" multi-year simulation, which includes simulation of both a realistic thermal state in northern spring and summer and, for the first time, the spontaneous generation of inter-annually-variable global dust storms. Our results support the idea that variable and spontaneous global dust storm behavior can emerge from a periodically forced system (the only forcing being the diurnal and seasonal cycles) when the dust injection mechanism involves an activation threshold. The general circulation model is also used to evaluate changes to the circulation and dust transport in the Martian atmosphere for simulations with a finite supply of dust on the surface. The focus is on changes to atmospheric temperatures and dust-related surface features, as these may potentially be verified by observations. In this work, the use of a finite surface dust supply increases the amount of inter-annual variability the system is capable of producing. This is due to a new set of initial conditions, in the form of available surface dust, being present at the beginning of each storm season.

Thesis Files