Diurnal variation of the duration and environment for heavy rainfall during the warm season in South China

Abstract

This article aims to examine the diurnal variation of heavy rainfall (HR) for various intensities and investigate duration and environment of HR during the warm season over South China. Results show that the HR mainly occurred in the late afternoon over most regions of Guangdong Province (GD) and east of Guangxi Province (GX), as well as the nocturnal-to-morning rainfall over the mountainous regions of northwestern GX and contiguous regions among GD. It exhibited two diurnal peaks in the early morning and in the late afternoon. HR which mostly occurred during the late afternoon by 1,700-1,900 LST exhibited longer durations (3-4 hr). The enhanced southerly wind and northerly wind over the mountainous, as well as the enhancement associated with strong horizontal surface-temperature gradient due to surface heating and stronger vertical wind shear in the lower troposphere, contributed to the highfrequency occurrences of the rainfall in the late afternoon. K E Y W O R D S atmosphere, geophysical sphere, observational data analysis, physical phenomenon, rainfall, seasonal scale, surface-based observations

Nocturnal-to-morning rains during the warm season in South China: characteristics and predictability

“…To further examine the detailed evolutions of the rainfall, Figure 3 presents the distributional frequency of NMR over South China. It can be seen that for the first half of the night (2000-0000 LST), NMR events are mainly located over central-eastern GD and FJ, and it can be inferred that the NMR during this period is caused by the eastward evolution of rain belts occurring in the late afternoon (see Yu et al 2007;Jiang et al 2017;Chen et al 2018;Zhong 2020). Whereas, for the second half of the night to the next morning (0200-0800 LST), the NMR mainly occurs in the northern mountainous areas of GX, and southern coastal regions of GX and GD.…”

“…Previous studies have shown that high-frequency occurrences of torrential rain in the afternoon are mainly attributable to the regulation of convergence between the enhanced southerly winds and northerly winds over mountainous regions (Chen et al 2018;Jiang et al 2017;Luo et al 2017;Zhong 2020), as well as the effects of orographic lift (Lin, Feng, and Huang 2006;Zhong et al 2019a) and surface heating (Wu et al 2020;Zhong 2020). To examine the characteristics and environment of NMR, Figure 4 presents the average surface wind differences between −3 h (3 h before the onset hour of heavy rainfall) and the occurrence time of NMR over the north of GX and southeast coast of GD.…”

“…In the present work, hourly surface observations from more than 13,000 stations over South China during the warm season from March to September in 2015-19 are used to discuss the characteristics of NMR. These archived data have been widely used for operational forecasting at the South China Regional Meteorological Center (Lin, Feng, and Huang 2006), and in studies on diurnal variations over South China (Zhong et al 2019a;Zhong 2020). In terms of the definition of NMR, it is rainfall that takes place during the time period from 2000 LST to the next morning at 0800 LST.…”

“…South China frequently encounters extreme precipitation over its coastal regions and inland mountainous areas. In recent decades, it has been shown that the rainfall in South China exhibits an evident diurnal cycle with two peaks in the early morning and in the late afternoon (Yu et al 2007;Chen et al 2018;Jiang et al 2017;Zhong 2020). The rainfall in the early morning accounts for a large proportion of the whole day's rainfall, especially in the pre-monsoon-onset period (Jiang et al 2017).…”

“…In Zhong (2020), the duration and characteristics of heavy rainfall in the warm sector were discussed using surface observations over South China. However, the occurrence time and the distribution of the NMR were not clarified, as well as the amounts of NMR compared to daytime rainfall (DR) and the corresponding predictability in NWP models.…”