Principal Modes of Diurnal Cycle of Rainfall over South China during the Pre-summer Rainy Season

Abstract

The principal modes of diurnal cycle of rainfall (DCR) over South China during the pre-summer rainy season are examined using 23-year satellite observations and reanalysis data. Three distinctly different DCR modes are identified via empirical orthogonal function analysis, i.e., the early-afternoon precipitation (EAP) mode, the late-afternoon precipitation (LAP) mode and the morning precipitation (MP) mode. Under the EAP mode, the rainfall starts to increase from midnight and reaches its peak in the early afternoon. The nocturnal to morning rainfall generally concentrates on the northeastern Pearl River Delta (PRD) and along the coastline. The coastal rainfall is initiated from the convergence zone induced by the strong onshore wind, and is further enhanced via the establishment of land breeze in the early morning. The northeastern PRD center is mainly attributed to the windward mechanical lifting associated with the strong low-level wind. The afternoon rainfall is pronounced over inland and exhibits significantly regional diversity. The eastern inland rainfall develops from the early-morning rainfall over the northeastern PRD, whereas the eastward propagating rainbelts associated with frontal activities are responsible for the formation of western inland rainfall. The LAP mode features a late-afternoon peak, which is triggered and developed locally with favorable thermal-dynamic conditions over the western inland South China. The MP mode exhibits a single early-morning peak. Nocturnal to morning rainfall is prominent on the northeastern PRD and near-offshore region. The near-offshore rainfall is basically induced by the convergence between the onshore wind and land breeze in the early morning, which further propagates far offshore in the morning due to effects of gravity wave.