Mixing time scales of dustiness and some associated effects at middle atmosphere during the 2018 global dust storm

摘要

This study analyzes some characteristic features associated with the Mars year 34 (2018) global dust storm (GD18) using the retrievals of Mars Climate Sounder (MCS) and Mars Color Imager (MARCI) onboard Mars Reconnaissance Orbiter (MRO). According to the MRO MARCI's weather report and Mars daily global maps, the GD18 resulted from a large precursor dust storm in the broader Aci-dalia region at L_S ～ 186° and developed into a global scale storm at L_S ～ 194°. Dust lifting is reported to continue until L_S ～ 207° in MARCI images, and the MCS-derived column dust opacity peaks around L_S 208°. However, the middle atmospheric dust loading only peaks around L_S 211°, i.e., 3-4° L_S after the surface dust lifting maximum. High-altitude dust maximum is evident after L_S ～ 190°, a few degrees of L_S after the large precursor Acidalia dust storm. These delays probably indicate a vertical mixing timescale similar to that for a regional scale storm, indicating a common mechanism irrespective of the spatial scale of a dust storm. During GD18, the diurnal tide is strongly amplified at high altitudes, away from the tropics (especially over SH), and the vertical extent of clouds is significantly reduced. These changes are consistent with the time scale of the evolving vertical distribution of dust observed by MCS.