Shedding Light on Local Martian Dust Storms with OMEGA/Mars Express

          Dust, composed of mineral micrometre-size particles, is omnipresent on Mars and has its own cycle: uplift from the surface and injection into the atmosphere, transport and formation of dust storms, and dissipation (grain sedimentation). Atmospheric dust, and thus dust storms, absorbs and diffuses incoming sunlight, strongly affecting the atmosphere by modifying its thermal structure [1] and enhancing global atmospheric circulation [2]. The intensity of these impacts depends on storm sizes, which are usually classified as local or regional storms (≥ 1.6×10⁶ km², [3]). Regional storms have been well studied (e.g., [4,5,6]) and characterised in opposition to local ones.  This work focuses on local dust storms to better understand the storm evolution mechanisms (local to regional) that are still not well constrained.

          We developed a method to detect dust storms [a] in the OMEGA IR dataset (2004-2010, Martian Years 26-30), the visible and near-IR imaging spectrometer of Mars Express (ESA). This method is based on a pixel clustering algorithm that is applied to the dust optical depth map [7] of each OMEGA observation. Then, we generate a mask that corresponds to the storm, from which we extract information, after confirming the presence of the storm, such as its size, position, local time, etc. We compiled about 440 new detections into the OMEGA/Mars Express Dust Storm Catalogue (ODSC), mainly composed of local storms (~81%).

          We identified a peak of local storms, notably in MY 27, during the northern “solstitial pause” (solar longitude, L_s~240-270°), which corresponds to a period of lower regional storm activity due to lower wave activity (e.g., [8,9]). Therefore, this decrease in regional storm detections is not due to a strong decrease in local storm formation, but to a decrease in the growth process efficiency to regional size [a]. Local storms are also very active during the “C-regional storm season” (L_s~305-330°) and widespread on Mars. We found some privileged areas: high southern latitudes (polar cap edges) and close to strong topographic gradients, as inside topographic channels (e.g., Chryse, Acidalia, Arcadia; [4]), Hellas, Valles Marineris, Olympus and Elysium Mons [a]. This suggests that topographic winds contribute to the formation of dust storms during this period. We also noticed a similar diurnal pattern between local storms detected with OMEGA (MY 26-30) and regional ones detected with EXI/EMM (MY 36, [5]).

References:
[a] Leseigneur, Y., et al. (in revision), JGR:Planets, “OMEGA/MEx Dust Storm Catalogue”.
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