Decadal change in east Asian summer monsoon circulation in the mid‐1990s

Abstract

A climate shift in the mid‐1990s in summertime circulation over east Asia is described and the dynamics associated with the climate shift are discussed. The east Asian summer monsoon has a large interdecadal variability as well as interannual variability. It is suggested herein that the east Asian summer monsoon has undergone a decadal change in the mid‐1990s. After the mid‐1990s, there has been a significant decrease in the strength of zonal winds near the subtropical jet over the east Asia as well as a distinct increase in precipitation in the southeastern part of China. This decrease of the strength of zonal winds over east Asia could be understood as a barotropic response to a steady forcing associated with heating from increased precipitation. These decadal changes are significantly predominant only in the summertime. Concurrently, there has been a remarkable increase in the number of the typhoon passing through the southeastern part of China. It is suggested that the distinctive increase of the typhoon passing may be partly responsible for the increased precipitation in the same area after the mid‐1990s.

Interdecadal change of summer precipitation over Eastern China around the late-1990s and associated circulation anomalies, internal dynamical causes

“…Huang and Yan [25,26] documented that, forced by the same external forcing, the circulation and planetary wave propagation varied under different basic flow. Accompanying the several interdecadal change of the summer precipitation over East Asia, the intensity and location of the subtropical upper-level westerly jet over East Asia exhibit notable interdecadal variations [11]. Thereby, the interdecadal change of the summer troposphere flow over East Asia may exert an important influence on the interdecadal change of summer climate over Eastern China.…”

“…Since then, many studies analyzed the interdecadal changes of the atmospheric circulations over East Asia and pointed out the weakening of the EASM since the mid-/late-1970s. Results revealed that the persistent precipitation decrease over North China and the summer climate change over East Asia around the mid-/late-1970s may be closely related to southward/westward-shifting of the western north Pacific subtropical high [4,5,14,15], the enhancement of the South Asia high [16,17], the troposphere cooling [18,19] and the enhancement and northward-shifting of subtropical westerly jet over East Asia [11]. Recently, Kwon et al [11] stated that the interdecadal increase of summer precipitation over the South China around the early-1990s was accompanied by the weakening of the subtropical high-level westerly jet over East Asia, and studies of Ding et al [20] and Wu et al [21] attributed the interdecadal climate change around the early-1990s to the low-level anticyclonic circulation anomalies over the western north Pacific.…”

An interdecadal change of tropical cyclone activity in the South China Sea in the early 1990s

“…For spatial distribution (Fig.1b) . In contrast with the SCS, there was a slight decrease in TC numbers in the NWP (fi gure not shown), refl ecting a negative relationship between the East Asian and NWP summer monsoon systems, as revealed by previous studies (Kwon et al, 2005). Seasonal variations of TCs for the two periods are displayed in Fig.2.…”

“…The relationship between the EA and WNP monsoons also shows a change around [1993][1994]. Correlation between the two monsoon subsystems was much stronger during 1994-2004than 1979-1993(Kwon et al, 2005. They argued that the leading mode of summer-mean precipitation over the EA and WNP regions changed from an ENSO-related mode during 1979-1993 to a WNP monsoon-related mode during 1994-2004.…”

“…This TIO warming forces a warm tropospheric Kelvin wave into the western Pacifi c (Xie et al, 2009), decreasing westerly wind shear in the SCS and increasing TC counts. Goh and Chan (2009) A few recent studies identify decadal changes during the mid-1990s in the East Asian (EA) and western North Pacifi c (WNP) summer monsoon regions (Kwon et al, 2005(Kwon et al, , 2007Yim et al, 2008), plus intraseasonal variability over the SCS (Kajikawa et al, 2009). The strength of zonal winds in the subtropical jet over the EA signifi cantly decreased after the mid-1990s, accompanying a distinct precipitation increase in southeast China (Kwon et al, 2007).…”