Statistical characteristics of pre-summer rainfall over south China and associated synoptic conditions

Abstract

In this study, the climatological characteristics of pre-summer (April to June) rainfall over South China (SC) and the associated synoptic conditions are examined using 1980 – 2017 hourly rainfall observations and reanalysis data. The amount, frequency, and intensity of rainfall show pronounced regional variations and substantial changes between pre-and post-monsoon-onset periods. Owing to the more favorable thermodynamic conditions after monsoon onset over the South China Sea (SCS), rainfall intensifies generally over SC irrespective of the rainfall-event durations. Increased rainfall amounts in longer-duration (> 6 h) events were found over a designated west-inland region (west of 111°E), which are partially attributed to enhanced dynamic instability. In addition, rainfall events occur more frequently over the west-inland region, as well as coastal regions to the west of 118°E, but less over a designated east-inland region. Inland-region rainfall is closely linked to dynamic lifting driven by subtropical synoptic systems (low pressure and an associated front or shearline). The westward extension of the western North Pacific high and the eastward extension/movement of the front or shearline, interacting with the intra-period intensification of the southwesterly monsoonal flows, play important roles in providing high-θe (equivalent potential temperature) air to the west-and east-inland regions, respectively. Warm-sector coastal rain.