The 2016 record-breaking marine heatwave in the Yellow Sea and its association with atmospheric circulation anomalies

Abstract

Marine heatwaves (MHWs) are becoming more frequent and intense, and they have been investigated in many regions of the world. However, few studies have been focused on MHWs of the China’s marginal seas and their mechanism. In this study, we examined the characteristics and associated atmospheric circulation anomalies of the 2016 Yellow Sea MHW, a record hot event in observational history. It was found that the MHW was directly caused by greater-than-normal solar radiation and weak wind speeds which reduced upper oceanic mixing and caused substantial warming of the stratified surface layer. These were in turn associated with an unusually fractured western Pacific subtropical high (WPSH) and the distinctly more active transmission of Madden-Julian Oscillation (MJO) eastward to the western Pacific in August 2016. The MJO seems to have played a leading role in causing the atmospheric anomalies, which triggered a more frequent tropical cyclone activity, splitting the WPSH into two parts. The western segment of the WPSH combined with the continental high to form an abnormally positive geopotential height at the west of 120ºE, causing strong subsiding flows at its east and extremely high solar radiation. An unambiguous cyclonic circulation anomaly in the lower troposphere, encompassing much of the northwestern Pacific, reduced the surface wind speed in the Yellow Sea. Therefore, a stratified surface layer coincided with a rapid increase in solar radiation under the background of the seasonally abnormal atmospheric circulation were thus a key to the extreme 2016 Yellow Sea MHW.