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

Abstract

The characteristics of nocturnal-to-morning rainfall (NMR) during the warm season in South China are examined using hourly surface observations from 2015–2019. Results show that strong NMR is mainly located in coastal regions and mountainous areas. NMR mainly occurs during 0200–0800 LST. The distribution of NMR can be divided into two types. The first pattern is a coastal type where NMR is mainly located at windward sites, such as southern coastal mountain areas in Guangdong (GD) and in Guangxi (GX). The second type is an inland type where NMR is mainly located at windward sites, such as the northern mountainous areas in GX and the Pearl River Delta regions in GD. The strong convergence between the northerly wind over the mountainous regions and southerly wind, as well as the strong downhill winds strengthened by the narrow pipe effect over the valleys in mountainous areas, together contribute to the high frequency of inland NMR. The strong southeasterly onshore wind and the cyclonic circulations strengthened by the northeasterly wind over the northern mountainous areas contribute to the high frequency of coastal NMR. Though the GRAPES (Global/Regional Assimilation and Prediction System) model can capture the intensity and distribution of large-scale NMR, it exhibits low predictability of small-scale NMR, especially that in the warm sector.

Keywords

• south china
• warm season
• nocturnal-to-morning rainfall
• grapes