A 10-yr Rainfall and Cloud-to-Ground Lightning Climatology over Coastal and Inland Regions of Guangdong, China during the Pre-Summer Rainy Season

Abstract

A comparative analysis of the spatiotemporal distribution characteristics of rainfall and lightning in coastal and inland areas of Guangdong Province of China during the pre-summer rainy season (PSRS) from 2008 to 2017 reveals distinct patterns. In the inland target region (ITR), rainfall is concentrated in the central and eastern mountainous areas. It exhibits a bimodal diurnal variation, with peaks in the afternoon and morning. The afternoon peak becomes more pronounced during the post-monsoon-onset period because of the increased rainfall frequency. Similarly, in the coastal target region (CTR), rainfall concentrates around mountainous peripheries. However, CTR’s rainfall is weaker than ITR’s during the pre-monsoon-onset period, primarily associated with the lower-level moisture outflow in CTR, but it strengthens significantly during the post-monsoon-onset period owing to enhanced moisture inflow. CTR’s diurnal rainfall variation transitions from bimodal to a single broad peak during the post-monsoon-onset period, influenced by changes in both rainfall frequency and intensity. In contrast to rainfall, the spatiotemporal distribution of lightning centers remains relatively stable during the PSRS. The strongest center is located over ITR’s plains west of the rainfall center, with a secondary center in the western plains of CTR. Lightning activity significantly increases during the post-monsoon-onset period, particularly in ITR, primarily because of the increased lightning hours. The diurnal lightning flash density and lightning hours show a single afternoon peak in the two target regions, and the timing of the peak in ITR is approximately two hours later than in CTR. Composite circulation analysis indicates that during early morning, the lower atmosphere is nearly neutral in stratification. The advected warm, moist, unstable airflow, combined with topography, favors convection initiation. In the afternoon, solar radiation increases thermal instability, further enhancing the convection frequency and intensity. Improved moisture and thermal conditions contribute to an increase in rainfall and lightning during the post-monsoon-onset period. Moreover, the occurrence of lightning is found to be closely linked to the most unstable convective available potential energy, low-level vertical wind shear, and updraft intensity.