Anomalous convective activity over sub-tropical east Pacific during 2015 and associated boreal summer monsoon teleconnections
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The eastern Pacific Ocean received a record highest number of sub-tropical convective activities during boreal summer (June–September) of 2015, since last four decades. The associated rainfall distribution was also atypical with anomalously enhanced rainfall extending from equator to sub-tropical central-eastern Pacific. The present analysis reveals a pronounced meridional sea surface temperature (SST) gradient across central-eastern Pacific, with the mean SST exceeding 28 °C over sub-tropical north Pacific, setting up favorable conditions for these enhanced convective activities. It is found that these anomalous features promoted northward spanning of westerly anomalies and drastically modified the east–west circulation over sub-tropical north Pacific. This seems to induce large-scale subsidence over the off-equatorial monsoon regions of south and south-east Asia, thus constituting an east–west asymmetry over sub-tropical Indo-Pacific region. Based on our observational study, it can be concluded that the sub-tropical convective activities over east Pacific may play a pivotal role in mediating the Pacific-monsoon teleconnection through the unexplored meridional SST gradient across Pacific.
KeywordsEast Pacific storms Sub-tropical east–west asymmetry Meridional SST gradient Pacific-monsoon teleconnection
The authors thank three anonymous reviewers for the constructive comments. The authors acknowledge discussions with Dr. Harry Hendon, BOM, Melbourne, Australia. Dr. P. Terray is also acknowledged for his code on testing statistical significance and valuable suggestions. The CCCR, IITM is fully funded by the Ministry of Earth Sciences (MoES), Govt. of India.
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