期刊
JOURNAL OF THE ATMOSPHERIC SCIENCES
卷 78, 期 5, 页码 1389-1410出版社
AMER METEOROLOGICAL SOC
DOI: 10.1175/JAS-D-20-0117.1
关键词
Mesocyclones; Severe storms; Supercells; Tornadoes; Convective storms
资金
- NOAA [NA15OAR4590235, NA16OAR4590213, NA17NWS4680002]
- Convective Storms Group at NC State
This study examines the behavior of supercells in low-CAPE environments, showing that in these conditions, the main updrafts do not reach the theoretical equilibrium level, and vertical velocities are driven by dynamic accelerations associated with low-level mesocyclones and vortices. Low-CAPE tornado-like vortex parcels sometimes stop ascending, leading to shallower vortices.
High-shear, low-CAPE environments prevalent in the southeastern United States account for a large fraction of tornadoes and pose challenges for operational meteorologists. Yet, existing knowledge of supercell dynamics, particularly in the context of cloud-resolving modeling, is dominated by moderate- to high-CAPE environments typical of the Great Plains. This study applies high-resolution modeling to clarify the behavior of supercells in the more poorly understood low-CAPE environments, and compares them to a benchmark simulation in a higher-CAPE environment. Simulated low-CAPE supercells' main updrafts do not approach the theoretical equilibrium level; their largest vertical velocities result not from buoyancy, but from dynamic accelerations associated with low-level mesocyclones and vortices. Surprisingly, low-CAPE tornado-like vortex parcels also sometimes stop ascending near the vortex top instead of carrying large vorticity upward into the midlevel updraft, contributing to vortex shallowness. Each of these low-CAPE behaviors is attributed to dynamic perturbation pressure gradient accelerations that are maximized in low levels, which predominate when the buoyancy is small.
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