Investigating the impact of atmospheric stability on thunderstorm outflow winds and turbulence

Abstract

Abstract.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 ) 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 10 in 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.

On wind turbine loads during the evening transition period

“…The extent of turbulence in the wind fields can affect the strength of air cushions when downbursts touch down and form impinging jets near the ground. The interaction with ambient turbulence also affects the strength and development rate of associated outburst winds . The relationships between stability change and turbine‐scale flow field variables (ie, Section ) is expected to be of interest when the impact of downburst winds on turbine loads is to be estimated.…”