Fine-Scale Spatiotemporal Characteristics of Warm-Season Severe Convection in 2021 Revealed from X-Band Phased-Array Radar Network Observations in Xiamen, China

In September 2020, a pioneering observational network of three X-band phased-array radars (XPARs) was established in Xiamen, a subtropical coastal and densely populated city in southeastern China. Statistically, this study demonstrated that the XPAR network outperforms single S-band radar in revealing the warm-season convective storms in Xiamen in a fine-scale manner. The findings revealed that convective activity in Xiamen is most frequent in the central and northern mountainous regions, with lower frequency observed in the southern coastal areas. The diurnal pattern of convection occurrence exhibited a unimodal distribution, with a peak in the afternoon. The frequent occurrence of convective storms correlates well in both time and space with the active terrain uplift that occurs when the prevailing winds encounter mountainous areas. Notably, September stands apart with a bimodal diurnal pattern, featuring a prominent afternoon peak and a significant secondary peak before midnight. Further examination of dense rain gauge data in Xiamen indicates that high-frequency areas of short-duration heavy rainfall largely coincide with regions of active convective storms, except for a unique rainfall hotspot in southern Xiamen, where moderate convection frequency is accompanied by substantial rainfall. This anomalous rainfall, predominantly nocturnal, appears less influenced by terrain uplift and exhibits higher precipitation efficiency than daytime rainfall. These preliminary findings offer insights into the characteristics of convection occurrence in Xiamen's subtropical coastal environment and hold promise for enhancing the accuracy of convection and precipitation forecasts in similar environments.