Effects of the Low-level Wind Profile on Outflow Position and Near-surface Vertical Vorticity in Simulated Supercell Thunderstorms

Effects of the Low-level Wind Profile on Outflow Position and Near-surface Vertical Vorticity in... AbstractSupercell thunderstorms are simulated using an idealized numerical model to analyze the effects of modifications to the environmental low-level wind profile on near-surface rotation. Specifically, the orientation, magnitude, and depth of the low-level vertical wind shear are modified in several suites of experiments and compared to control simulations with no vertical wind shear in the prescribed layer.The overall morphology of the simulated supercells is highly sensitive to even shallow changes in the low-level wind profile. Moreover, maximum near-surface vertical vorticity varies as the low-level wind profile is modified. The results suggest this is principally a consequence of the degree to which favorable dynamic forcing of negatively buoyant outow is superimposed upon the near-surface circulation maximum. Simulations with easterly shear and weaker storm-relative winds over the depth of the gust front promote forward-surging outow and smaller separation between the near-surface circulation maximum and mesocyclone aloft compared with other hodograph shapes. This promotes near-surface vertical vorticity intensification in these simulations. Similar trends in near-surface vertical vorticity as a function of low-level shear orientation are observed for varying shear layer depths and bulk shear magnitudes over the shear layer. The degree to which specific hodograph shapes promote strong near-surface rotation may vary with different deep-layer wind profiles or thermodynamic environments from those simulated here; however, this study concludes that favorable positioning of the near-surface circulation maximum and mesocyclone aloft are a necessary condition for supercell tornadogenesis and this positioning may be modulated by the low-level wind profile. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of the Atmospheric Sciences American Meteorological Society

Effects of the Low-level Wind Profile on Outflow Position and Near-surface Vertical Vorticity in Simulated Supercell Thunderstorms

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0469
D.O.I.
10.1175/JAS-D-17-0174.1
Publisher site
See Article on Publisher Site

Abstract

AbstractSupercell thunderstorms are simulated using an idealized numerical model to analyze the effects of modifications to the environmental low-level wind profile on near-surface rotation. Specifically, the orientation, magnitude, and depth of the low-level vertical wind shear are modified in several suites of experiments and compared to control simulations with no vertical wind shear in the prescribed layer.The overall morphology of the simulated supercells is highly sensitive to even shallow changes in the low-level wind profile. Moreover, maximum near-surface vertical vorticity varies as the low-level wind profile is modified. The results suggest this is principally a consequence of the degree to which favorable dynamic forcing of negatively buoyant outow is superimposed upon the near-surface circulation maximum. Simulations with easterly shear and weaker storm-relative winds over the depth of the gust front promote forward-surging outow and smaller separation between the near-surface circulation maximum and mesocyclone aloft compared with other hodograph shapes. This promotes near-surface vertical vorticity intensification in these simulations. Similar trends in near-surface vertical vorticity as a function of low-level shear orientation are observed for varying shear layer depths and bulk shear magnitudes over the shear layer. The degree to which specific hodograph shapes promote strong near-surface rotation may vary with different deep-layer wind profiles or thermodynamic environments from those simulated here; however, this study concludes that favorable positioning of the near-surface circulation maximum and mesocyclone aloft are a necessary condition for supercell tornadogenesis and this positioning may be modulated by the low-level wind profile.

Journal

Journal of the Atmospheric SciencesAmerican Meteorological Society

Published: Dec 14, 2017

References

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