Near-Surface Vertical Wind Shear Observed during VORTEX-Southeast IOPs within and Near Convective Storms: Departures from Log-Law Behavior and Implications for Lower Boundary Conditions in Convective Storm Simulations

A theoretical gap exists in our knowledge of what the near-surface wind profile should look like within the cold pools and near-environments of convective storms. We are in desperate need of near-surface wind observations—and knowledge of their departures from theoretical predictions [i.e., Monin–Obukhov (M–O) similarity theory, which predicts that the mean wind in the surface layer obeys a log law]—in order to assess the credibility of our present day simulations, and to develop new formulations for the lower boundary condition in severe storms simulations. Despite the fact that M–O similarity has been used for over half a century, deviations from it are still not well understood; a priori, we would expect potentially large departures at times when surface winds are unsteady and/or being subjected to large horizontal pressure-gradient forces.

We see this as an issue of fundamental importance to advancing our understanding of storms, especially given the recent interest in the lower boundary as a possible source of horizontal vorticity for the low-level mesocyclone and tornado. This topic might seem rather esoteric in terms of operational meteorology, but we see this as an issue of fundamental importance to advancing our understanding of storms. If we are ever to have Warn-on-Forecast capabilities at high resolution, we need to improve the representation of near-surface wind profiles in numerical simulations, which requires that we obtain fundamental new knowledge in what near-surface wind profiles look like in reality.

Vertical wind profile data obtained from Doppler lidars in VORTEX-Southeast in 2016 and 2017 [the Collaborative Lower Atmospheric Mobile Profiling System (CLAMPS) and NOAA/ARL lidar] allow us to assess the departures from M–O predictions in and near convective storms. Preliminary results will be presented at the conference.