Abstract
<p class="1Body">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.</p>
Highlights
Despite decades of observations and numerical simulations of supercell thunderstorms and tornados, our understanding of how orography affects tornadic supercell thunderstorms (SCs) has been limited mainly to case studies of tornadic supercells that occurred over various terrain (e.g. Bluestein 2000, Homar 2003, LaPenta et al 2005, Bosart et al 2006, Schneider 2009)
Cloud Model 1 (CM1) uses the Gal-Chen and Somerville (1975) terrain-following coordinates to map the model levels to the terrain while the model top is at constant height, and the governing equations are adapted from those described by Wicker and Skamarock (2002)
In the following we focus on the investigation of orographic effects on supercell thunderstorm; structure and development, intensity, and track
Summary
Despite decades of observations and numerical simulations of supercell thunderstorms and tornados, our understanding of how orography affects tornadic supercell thunderstorms (SCs) has been limited mainly to case studies of tornadic supercells that occurred over various terrain (e.g. Bluestein 2000, Homar 2003, LaPenta et al 2005, Bosart et al 2006, Schneider 2009). Homar et al (2003) investigated tornadoes that occurred over complex terrain in eastern Spain on 28 AUG 1999 They used the 5th generation of the Pennsylvania State University - National Center for Atmospheric Research Mesoscale Model (MM5.v3, Dudhia, 1993; Grell et al 1995) to perform a triple nested simulation varying the resolution of the reference terrain and they found that during this tornadic event terrain was essential in modifying the environment to produce super cellular convection. Markowski and Dotzek (2011) advanced our understanding of how supercells are affected by terrain induced environmental modifications, there are several factors that were not considered in their study such as mountain height variation and its impact supercell track, intensity, structure and development.
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