Weakening Relationship between East Asian Summer Monsoon and Asian-Pacific Oscillation after 1990s

Wei Hua,Xin Wang,Zouxin Lin,Guangzhou Fan

doi:10.1155/2019/6012301

Abstract

The East Asian summer monsoon (EASM), which is an important influencing summer climate of East Asia, is associated with large-scale change of the land-sea thermal contrast. The Asian-Pacific Oscillation (APO) can modulate the EASM because it not only represents the upper-tropospheric zonal land-sea thermal contrast over Asia and the Pacific region, but it also affects the sea surface temperature (SST) over the North Pacific, which can tune the land-sea thermal contrast for the EASM. This study revealed weakening of the APO-EASM relationship since the 1990s. It was found that the relationship between the APO and the EASM during 1948–1990 (1991–2016) was statistically significant (insignificant). Further study indicated that the APO was concurrent with significant positive SST in the central North Pacific and subtropical central-western Pacific during 1948–1990, which contributed to the shift of the Pacific Decadal Oscillation (PDO) from its cold to warm phase and led to a weakened EASM. The APO-related SST and atmospheric circulation anomalies were found statistically to be insignificant during 1991–2016, which indicates a weakening of influence of the APO on shift of the PDO, and even a weaker link to the EASM.

Highlights

IntroductionEoretically, the East Asian summer monsoon (EASM) is regarded as one of the consequences of the land-sea thermal contrast between East Asia and its adjacent oceans [7]
Introduction e EastAsian summer monsoon (EASM) has complex spatiotemporal features that are distinct from other monsoons such as the South Asian monsoon and the North American summer monsoon [1,2,3]. e spatial extent of the East Asian summer monsoon (EASM) covers areas of the tropics, subtropics, and midlatitudes and its intensity, onset, and duration are the main factors that determine the summer climate anomalies in East Asia, which can cause various disasters such as floods, landslides, and drought [4,5,6].eoretically, the EASM is regarded as one of the consequences of the land-sea thermal contrast between East Asia and its adjacent oceans [7]
Based on several gridded datasets, this work compared the correlation of the EASM with the Asian-Pacific Oscillation (APO) between 1948–1990 and 1991–2016. e results revealed a remarkable difference in the correlation between the APO and the EASM after the 1990s. e possible mechanisms for the weakening of the APO-EASM relationship were discussed, and the main findings are summarized in the following

Summary

Introduction

Eoretically, the EASM is regarded as one of the consequences of the land-sea thermal contrast between East Asia and its adjacent oceans [7]. Various indices have been defined based on pressure, potential height, and temperature to quantitatively describe the land-sea thermal contrast between East Asia and the adjacent oceans [9,10,11,12]. A significant positive relationship between the APO and the EASM variation has been documented [14,15,16]. Both the EASM and the APO have interannual and interdecadal variations, and the question arises: how stable is the long-term interrelationship between the Advances in Meteorology

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Discussion

Conclusion