Abstract

Orographic effects on tornadic supercell development, propagation, and structure are investigated using Cloud Model 1 (CM1) with idealized bell-shaped mountains of various heights and a homogeneous fluid flow with a single sounding. It is found that blocking effects are dominative compared to the terrain-induced environmental heterogeneity downwind of the mountain. The orographic effect shifts the storm track towards the left of storm motion, particularly on the lee side of the mountain, when compared to the storm track in the control simulation with no mountain. The terrain blocking effect also enhances the supercells inflow, which was increased more than one hour before the storm approached the terrain peak. The enhanced inflow allows the central region of the storm to exhibit clouds with a greater density of hydrometeors than the control. Moreover, the enhanced inflow increases the areal extent of the supercells precipitation, which, in turn enhances the cold pool outflow serving to enhance the storm’s updraft until becoming strong enough to undercut and weaken the storm considerably. Another aspect of the orographic effects is that downslope winds produce or enhance low-level vertical vorticity directly under the updraft when the storm approaches the mountain peak.

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