Investigating the impact of atmospheric stability on thunderstorm outflow winds and turbulence
Downburst events initialized at various hours during the evening transition (ET) period are simulated to determine the effects of ambient stability on the outflow of downburst winds. The simulations are performed using a pseudo-spectral large eddy simulation model at high resolution to capture b...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-04-01
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| Series: | Wind Energy Science |
| Online Access: | https://www.wind-energ-sci.net/3/203/2018/wes-3-203-2018.pdf |
| Summary: | Downburst events initialized at various hours during the evening transition
(ET) period are simulated to determine the effects of ambient stability on
the outflow of downburst winds. The simulations are performed using a
pseudo-spectral large eddy simulation model at high resolution to capture
both the large-scale flow and turbulence characteristics of downburst winds.
First, a simulation of the ET is performed to generate realistic initial and
boundary conditions for the subsequent downburst simulations. At each hour in
the ET, an ensemble of downburst simulations is initialized separately from
the ET simulation in which an elevated cooling source within the model domain
generates negatively buoyant air to mimic downburst formation.<br><br>
The simulations show that while the stability regime changes, the ensemble
mean of the peak wind speed remains fairly constant (between
35 and 38 m s<sup>−1</sup>) and occurs at the lowest model level for each
simulation. However, there is a slight increase in intensity and decrease in
the spread of the maximum outflow winds as stability increases as well as an
increase in the duration over which these strongest winds persist. This appears
to be due to the enhanced maintenance of the ring vortex that results from
the low-level temperature inversion, increased ambient shear, and a lack of
turbulence within the stable cases. Coherent turbulent kinetic energy and
wavelet spectral analysis generally show increased energy in the convective
cases and that energy increases across all scales as the downburst passes. |
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| ISSN: | 2366-7443 2366-7451 |