Springtime mesoscale convective systems over South China: a historic radar image-based analysis of climatological features, interannual variability, and potential connections with surface aerosol

Abstract

We objectively analyzed historic radar reflectivity images and diagnosed mature mesoscale convective systems (MCSs) in South China during the spring season (March to May) of 2009 to 2019. Our goal was to understand the climatological features of mature MCSs, their interannual variations, and potential connections with surface aerosol pollution. Springtime MCSs over South China were most frequently observed in the central and east-coastal parts of Guangdong Province. The mean monthly half-hourly counts of MCSs over South China in March, April, and May were 103±83, 274±298, and 337±225, respectively, with considerable variability from year to year. Approximately 89% of springtime MCSs over South China had a linear or quasi-linear structure, with convective precipitation covering on average 34% of the total precipitating area of each individual MCS, anmied 63% of MCSs consisted of a stratiform precipitation area trailing the convective precipitation. In March, MCSs occurred most frequently mid-day; in April and May, MCSs were most frequent around midnight. From 2013 to 2019, the MCS occurrences in April were significantly lower during years with more aerosol pollution days. This finding potentially supported our previous model study’s finding that elevated anthropogenic aerosol levels may suppress April MCS occurrences in South China via aerosol-cloud-radiation interactions. Further research is required to better understand the intricate relationship between aerosol abundance and MCS activities in this region.

Potential Modulation of Aerosol on Precipitation Efficiency in Southwest China

“…The reason why the influence of aerosol on cloud precipitation capacity is more significant in spring may be that clouds and precipitation in the two study regions in summer and autumn are mainly dominated by synoptic-scale systems and the aerosol-cloud-precipitation interaction is overwhelmed, while in winter, the precipitation is very low, which does not reflect the aerosol effect. Zhang et al [76,77] found that in spring in South China, the increase of anthropogenic aerosols inhibited precipitation associated with mesoscale convective systems, mainly due to that aerosol radiative effect reducing the radiation reaching the ground, and the microphysical effect of aerosol increases the cloud-body albedo, which in turn makes the lower tropospheric atmosphere more stable. Some recent studies [78][79][80][81][82] have also indicated that absorbing aerosols and hygroscopic aerosols could make the lower troposphere atmosphere more stable through their effects on radiative and cloud processes.…”