Combined effects of recent Pacific cooling and Indian Ocean warming on the Asian monsoon.

Atsuki Kumai,Hiroaki Ueda,Akio Kitoh,Shigeru Watanabe,Masamitsu Hayasaki,Yurisa Miki,Youichi Kamae

doi:10.1038/ncomms9854

Abstract

Recent research indicates that the cooling trend in the tropical Pacific Ocean over the past 15 years underlies the contemporaneous hiatus in global mean temperature increase. During the hiatus, the tropical Pacific Ocean displays a La Niña-like cooling pattern while sea surface temperature (SST) in the Indian Ocean has continued to increase. This SST pattern differs from the well-known La Niña-induced basin-wide cooling across the Indian Ocean on the interannual timescale. Here, based on model experiments, we show that the SST pattern during the hiatus explains pronounced regional anomalies of rainfall in the Asian monsoon region and thermodynamic effects due to specific humidity change are secondary. Specifically, Indo-Pacific SST anomalies cause convection to intensify over the tropical western Pacific, which in turn suppresses rainfall in mid-latitude East Asia through atmospheric teleconnection. Overall, the tropical Pacific SST effect opposes and is greater than the Indian Ocean SST effect.

Highlights

Recent research indicates that the cooling trend in the tropical Pacific Ocean over the past 15 years underlies the contemporaneous hiatus in global mean temperature increase
Noticeable positive rainfall anomalies occurred over the western Indian Ocean (WIO), probably associated with Indian Ocean warming[30,31]
The warming covered in the entire Indian Ocean, positive and negative rainfall anomalies coexist in the eastern Indian Ocean

Summary

Introduction

Recent research indicates that the cooling trend in the tropical Pacific Ocean over the past 15 years underlies the contemporaneous hiatus in global mean temperature increase. The tropical Pacific Ocean displays a La Nina-like cooling pattern while sea surface temperature (SST) in the Indian Ocean has continued to increase. Based on model experiments, we show that the SST pattern during the hiatus explains pronounced regional anomalies of rainfall in the Asian monsoon region and thermodynamic effects due to specific humidity change are secondary. The prolonged droughts over the Southern US and California[28] have been tied to the Pacific LNSST pattern It is unclear what changes have occurred in the Asian monsoon and to what extent they are due to the hiatus and decadal SST anomaly

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