Interannual Variability of Mars Global Dust Storms: an Example of Self-Organized Criticality?

Details Interannual Variability of Mars Global Dust Storms: an Example of Self-Organized Criticality? Interannual Variability of Mars Global Dust Storms: an Example of Self-Organized Criticality?

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p31b0993p&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #P31B-0993

Physics

5409 Atmospheres: Structure And Dynamics, 5415 Erosion And Weathering, 5470 Surface Materials And Properties, 6225 Mars, 3220 Nonlinear Dynamics

Scientific paper

Previous simulations of Martian global dust storms with a simple low-order model showed the desired interannual variability of storms if one of the model parameters - the threshold wind speed for starting saltation and lifting dust from the surface - was finely tuned. In this paper we show that the fine-tuning of this parameter could be the result of negative feedback in which processes associated with global dust storms raise the threshold and small-scale processes like dust devils, which are active in years between the storms, lower the threshold. The mechanisms responsible for the increase and decrease in the threshold wind speed could be the removal of sand grains and exposure of non-erodible elements, and gradual re-introduction of sand by small-scale processes and mantling of the non-erodible elements, respectively. We show how the atmosphere/dust system could organize itself to stay close to the critical state, so that global dust storms occur some years but not every year. According to our model, if the climate changed and the peak winds increased, the saltation threshold wind speed would increase so that global dust storms would continue to occur irregularly. The same thing would happen if the peak winds decreased. In both cases the system would continue to exhibit interannual variability. This takes away the mystery of why the system is so finely tuned: It tunes itself. Regardless of the initial conditions, the winds redistribute the sand grains in surface reservoirs until the threshold wind speed is close to the critical value. This explanation of the interannual variability of the global dust storms is not unique and we have only demonstrated this mechanism in the context of a low order model of the circulation. Our aim is not to resolve all the issues related to the interannual variability of global dust storms on Mars entirely, but to stimulate further thinking and follow-on GCM studies.

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