Intensified Springtime Deep Convection over the South China Sea and the Philippine Sea Dries Southern China

Zhenning Li,Chundi Hu,Song Yang,Bian He

doi:10.1038/srep30470

Abstract

Springtime rainfall, accounting for 25–40% of the annual rainfall in southern China, exerts great agricultural and socioeconomic impacts on the region. In the recent decades, southern China has experienced a significant declining trend of precipitation in boreal spring. Meanwhile, precipitation has increased over the South China Sea and the Philippine Sea (SCS-PhS). This paper presents observational and modeling evidences suggesting that the intensified latent heating released by the convection over SCS-PhS leads to suppressed springtime rainfall over southern China. Moisture budget analysis indicates that the drying trend over southern China is due mainly to weakened convergence of moisture flux, which is controlled by a heat-induced anomalous overturning circulation reinforced by the convection over SCS-PhS. Further idealized simulations support the feature that the heat-induced overturning circulation and its corresponding anomalous cyclone can be well established in several days under the spring mean flow condition. Thus, this rapid dynamic process is associated with both the intraseasonal-to-interannual variations and the long-term change of the springtime rainfall over southern China.

Highlights

Fully-coupled CGCM simulations, and idealized AGCM experiments, we demonstrate that the enhanced latent heating released by the convection over SCS-PhS leads to suppressed SRSC
Moisture budget analysis indicates that the drying trend over inland southern China is due mainly to the anomalous negative convergence term in convergence of vertically integrated moisture flux (CVIMF), which is controlled by a heat-induced overturning circulation from the reinforced convection over SCS-PhS
In summer, above normal convective activity over the western tropical Pacific tends to be associated with anticyclonic anomalies over the mid-latitudes, giving rise to dry and hot summer days[26]

Summary

Introduction

The 80-year mean result from the fully-coupled CESM with comprehensive CAM4 physics resembles the response in the idealized simulations, albeit the smoother patterns (Fig. 4d). The resemblance between the idealized simulations (Fig. 4a–c) and the fully-coupled experiments (Fig. 4d) provides evidence that a heat-induced overturning circulation directly links the springtime rainfalls over SCS-PhS and southern China. The enhanced convection heating over SCS-PhS causes local SLP decrease, low-level cyclone, and anomalous ascending motion, while forces descending motion, low-level divergence, and reduced rainfall over southern China.

Results

Conclusion