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.

Spatiotemporal Characteristics and Associated Synoptic Patterns of Extremely Persistent Heavy Rainfall in Southern China

“…There were clear differences in the diurnal cycles of EPHR and SHR, which may be related to the triggering and maintenance mechanisms of the two processes. In addition, the diurnal variation of EPHR is consistent with convection initiation, namely the convection occurrence (Bai et al, 2020), which is mainly triggered from midnight to early morning, and it is similar to the long-duration rainfall events (G. Chen et al, 2009) and coastal rainfall events (G. J. Li et al, 2019) studied previously, peaking in the early morning.…”

“…The distribution of the EPHR on the coast is similar to the hotspots of convection initiation (CI) discovered by Bai et al. (2020).…”

“…There were clear differences in the diurnal cycles of EPHR and SHR, which may be related to the triggering and maintenance mechanisms of the two processes. In addition, the diurnal variation of EPHR is consistent with convection initiation, namely the convection occurrence (Bai et al., 2020), which is mainly triggered from midnight to early morning, and it is similar to the long‐duration rainfall events (G. Chen et al., 2009) and coastal rainfall events (G. Chen et al., 2018; J. Li et al., 2019) studied previously, peaking in the early morning. Strong convection in the afternoon occurs frequently but has a short‐duration, and the occurrence and maintenance of EPHR at night may be related to land and sea breezes (X. Chen et al., 2016), low‐level jets accelerating at night (H. Chen et al., 2010; Du & Chen, 2019; Liu et al., 2020; Yu et al., 2009), the contribution of the coupling of LLJ and mesoscale outflow boundary (Luo & Chen, 2015), and inertial oscillations of nongeostrophic winds in the boundary layer (Xue et al., 2018; Y. Zhang et al., 2019).…”

“…In addition, there was a wide area of high accumulated precipitation in Guangxi Province, which could be divided into two centers in the middle and north, with precipitation levels in the north being greater. The distribution of the EPHR on the coast is similar to the hotspots of convection initiation (CI) discovered by Bai et al (2020).…”

A large-eddy simulation study of deep-convection initiation through the collision of two sea-breeze fronts

“…Deep convection frequently occurs over Leizhou Peninsula (Bai et al, 2020), which is the southernmost part of mainland China. A deep-convection case on 25 September 2018 was chosen for this study.…”