Interannual Influences of the Surface Potential Vorticity Forcing over the Tibetan Plateau on East Asian Summer Rainfall

Chen Sheng,Yimin Liu,Shaoyu Zhang,Bian He,Guoxiong Wu

doi:10.1007/s00376-021-1218-4

Abstract

The influences of interannual surface potential vorticity forcing over the Tibetan Plateau (TP) on East Asian summer rainfall (EASR) and upper-level circulation are explored in this study. The results show that the interannual EASR and associated circulations are closely related to the surface potential vorticity negative uniform leading mode (PVNUM) over the TP. When the PVNUM is in the positive phase, more rainfall occurs in the Yangtze River valley, South Korea, Japan, and part of northern China, less rainfall occurs in southern China, and vice versa. A possible mechanism by which PVNUM affects EASR is proposed. Unstable air induced by the positive phase of PVNUM could stimulate significant upward motion and a lower-level anomalous cyclone over the TP. As a result, a dipole heating mode with anomalous cooling over the southwestern TP and anomalous heating over the southeastern TP is generated. Sensitivity experiment results regarding this dipole heating mode indicate that anomalous cooling over the southwestern TP leads to local and northeastern Asian negative height anomalies, while anomalous heating over the southeastern TP leads to local positive height anomalies. These results greatly resemble the realistic circulation pattern associated with EASR. Further analysis indicates that the anomalous water vapor transport associated with this anomalous circulation pattern is responsible for the anomalous EASR. Consequently, changes in surface potential vorticity forcing over the TP can induce changes in EASR.

Highlights

East Asian summer rainfall (EASR) affects East Asian countries, including China, Japan, and Korea (Ding and Chan, 2005; Kubota et al, 2016; Zhou et al, 2019)
In Expt3 (Fig. 7c), the response of atmospheric circulation with the “CCA” pattern is very similar to the midlatitude Asian summer (MAS) pattern related to EASR (Figs. 3d–f). These results indicate that the dipole heating mode induced by surface TPPV forcing can lead to a realistic MAS pattern, which is important for the formation of the anomalous EASR
The present study investigates the relationship between the surface Potential vorticity (PV) forcing over the Tibetan Plateau (TP) and EASR and the associated circulation on the interannual timescale and the possible mechanism

Summary

Introduction

East Asian summer rainfall (EASR) affects East Asian countries, including China, Japan, and Korea (Ding and Chan, 2005; Kubota et al, 2016; Zhou et al, 2019). The onset, formation, and evolution of the Asian summer monsoon are closely related to the thermal forcing of the TP (Wu and Zhang, 1998; Hsu and Liu, 2003). More complex experiments, considering increasing TP heights from zero to its contemporary height (Chen et al, 1999; Liu, 1999; Kitoh, 2004; Jiang et al, 2008), have indicated that Asian summer monsoon rainfall shifts northward from the Indian Ocean to inland Asia as TP height increases. Certain studies (Liu and Yin, 2002; Liang et al, 2005) have illustrated that the onset and evolution of the Asian summer monsoon is sensitive to the location and height of the TP. Little insight is given about the intrinsic combined effects of dynamic and thermodynamic forcing of the TP in the literature

Objectives

Results

Conclusion