Convection Initiation in Monsoon Coastal Areas (South China)

Abstract

Monsoon coasts are characterized by active convection, but the features of associated convection initiation (CI) are not well understood. An analysis of kilometer-resolution radar observations in South China reveals a distinct dependence of CI on monsoon activity, land-sea contrast, and coastal orography. The CI occurrence becomes highly active after the monsoon onset and extends northward in summer. Several CI hotspots appear on tropical islands, peninsulas, and windward slopes of coastal mountains. Daytime CI occurrences are concentrated on land within 100 km of the coastline. The nocturnal CI maxima are located on coastlines and in the offshore areas with adjacent mountains. CI shows an offshore propagation after midnight prior to rainfall, probably due to the convergence of land breezes or downslope winds with diurnally enhanced onshore monsoon flows. The improved understanding of CI may provide additional benefit for forecasting severe weather because CI foretells the development of full-fledged deep convection.