Orographic Effects on Supercell: Development, Structure, Intensity, and Tracking

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. Terrain blocking effects shifted the storm towards the north (to the left of storm motion), particularly on the lee side of the mountain, when compared to the track in the case with no mountain. The terrain blocking effects also enhanced the supercells inflow, which was increased more than one hour before the storm approached the terrain peak. This allowed the central region of the storm to exhibit clouds with a greater density of hydrometeors than the control. Moreover, the enhanced inflow increased the areal extent of the supercells precipitation, which, in turn enhanced 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 down slope winds produced or enhanced low-level vertical vorticity directly under the updraft when the storm approached the mountain peak. In addition to these findings we have developed a method to declare if a simulated supercell thunderstorm is tornadic.