Eddy evolution during large dust storms

Abstract

The evolution of eddy kinetic energy during the development of large regional dust storms on Mars is investigated using the Mars Analysis Correction Data Assimilation (MACDA) reanalysis product and the dust storm data derived from Mars Global Surveyor Mars Daily Global Maps. Transient eddies in MACDA are decomposed into different components according to their eddy periods: $P\leq1$ sol, $1<P\leq8$ sols, $8<P\leq60$ sols. This paper primarily focuses on the Mars year 24 pre-solstice "A" storm that starts with many episodes of frontal/flushing dust storms from the northern hemisphere and attains its maximum global mean opacity after dust expansion in the southern hemisphere. During the development of this storm, the dominant eddies in terms of eddy kinetic energy progress from the $1<P\leq8$ sol eddies in the northern mid/high latitudes to the $P\leq1$ sol eddies (dominated by thermal tides) in the southern mid latitudes, and the $8<P\leq60$ sol eddies show a prominent peak with the increased global-mean dust opacity. The peaks of the $1<P\leq8$ sol eddies are found to best correlate with the average area of textured frontal/flushing dust storms within 40$^\circ$N $-$ 60$^\circ$N. The region where the $1<P\leq8$ sol eddies increase the most corresponds to the main flushing channel. The eddy kinetic energy of the $P\leq1$ eddies, dominated by $P$ = 1 and its harmonics, increases with the global mean dust opacity both before and after the winter solstice in Mars year 24. The $8<P\leq60$ sol eddies briefly spike during large, regional dust storms but remain weak if dust storm sequences do not lead to a major dust storm. Zonal wavenumber analysis of eddy kinetic energy shows that the peaks of the $1<P\leq8$ eddies often result from combinations of zonal wavenumbers 1 to 3, while the $P\leq1$ eddies and $8<P\leq60$ sol eddies are each dominated by zonal wavenumber 1.