Impact of Urbanization on Mesoscale Convective Systems: Insights From a Radar Wind Profiler Mesonet, Theoretical Analyses, and Model Simulations

Abstract

The role of planetary boundary layer (PBL) in the urban effect on mesoscale convective systems (MCSs) remains highly uncertain. The high-density Mesonet of radar wind profilers (RWPs) in Beijing, along with geostationary satellite data from Fengyun-2, were used to investigate the MCS evolution and potential impact of urbanization. An MCS as observed by satellite tends to weaken over urban and downstream areas under strong precipitating conditions as opposed to an invigorated MCS over urban and downstream areas under weak precipitating conditions. The pattern of low-level convergence and high-level divergence from RWP Mesonet dominates the PBL of all MCS events under strong precipitating conditions, as compared with fluctuating vertical structures of convergence under weak precipitating conditions. Under strong precipitating conditions, turbulent friction weakens MCS activity over the Beijing urban area. Under weak precipitating conditions, thermal effect dominated over urban areas, favoring the formation of surface-level convergence and invigorating MCSs. Using the large-eddy simulation, we further investigated the influence of turbulent structural characteristics on the development of MCS. For the strong (weak) precipitating case, turbulence dissipation (buoyancy) dominated the turbulent kinetic energy over urban areas, explaining well the characteristics of MCSs propagating over these areas. Overall, the theoretical analysis and model simulation results confirm the observed impact of urbanization on MCSs. Besides the above scientific findings, our study highlights the importance of the RWP Mesonet in studying the urban effect on MCSs.