Surface Mesovortices Formation and Maintenance in the St. Louis Metropolitan Area

Abstract

This study investigates the formation of reoccurring surface mesovortices within the Saint Louis Metropolitan Area. Prior research has shown the presence of surface mesovortices downwind from urban areas; however, the time evolution of the three-dimensional (3D) structure of these mesovortices is not well documented. Two instances of surface vortices associated with the urban heat island and affected by the terrain are investigated using the Weather Research Forecasting (WRF) model. The surface mesonet data over the Saint Louis Metropolitan area were assimilated with the WRF model to investigate the structure of these mesovortices. High-resolution simulations (i.e., 333-m grid spacing) were conducted when mesovortices were observed. Model results were then evaluated to determine the full 3D structure of the vortices and the formation of such surface vortices. The WRF simulations were able to recapture the observed surface structure of the vortices. The simulation results suggest that the interaction between the Saint Louis urban heat island (UHI), the Mississippi River, and topographic effects moderates the low-level wind field, creating the surface mesovortices.