Spatial distribution of lightning and possible effects of urban heat island effect over Beijing Metropolitan Region

Abstract:

The Spatial distribution of lightning over Beijing Metropolitan Region (BMR) were analyzed based on the data from the Dynamical–microphysical–electrical Processes in Severe Thunderstorms and Lightning Hazards (STORM973) comprehensive field observations of thunderstorms during the warm season from 2014 to 2018. The flash density maximums were found in the central urban area and downstream area of Beijing Metropolitan Region. In addition, the flash rate associated with super thunderstorms can reach hundreds of flashes per minute in the central city regions. The super (5% of the total), strong (35%), and weak (60%) thunderstorms contributed about 37%, 56%, and 7% to the total flashes in the BMR, respectively. Most of the severe thunderstorm cases were intensified over the urban area (southeastern plain of the BMR) even though they initiated in different mountainous locations, indicating a possible substantial urban island effect on the evolution and intensification of severe thunderstorms. The urban heat island effect of the BMR substantially alters the heat and moisture fluxes in the urban areas compared with the neighboring rural areas. The aerosol loading from the urban area also affects the microphysical processes of the thunderclouds. The synergy of thermodynamic and microphysical processes may substantially modify the thunderstorm evolution in the urban area when thunderstorms spread from the northwest mountainous area to the urban area, increase the effectiveness of charge separation and electrification processes, and enhance lightning activity over the urban area, accordingly.