JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Poster

A (Atmospheric and Hydrospheric Sciences) » A-CG Complex & General

[A-CG45] [EE] Multi-scale ocean-atmosphere interaction in the tropical Indo-Pacific region

Sat. May 20, 2017 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL7)

[ACG45-P04] Onset of the Bay of Bengal summer monsoon and the seasonal timing of ENSO’s decay phase

*Shuyue Sun1,2, Rongcai Ren1, Guoxiong Wu1 (1.LASG, IAP, Chinese Academy of Sciences, 2.Univ. of Chinese Academy of Sciences)

Keywords:Bay of Bengal, Summer monsoon onset, Seasonal timing of ENSO's decay phase

Based on multiple sources of atmospheric and oceanic data, this study demonstrates a close relationship between the onset of the Bay of Bengal (BOB) summer monsoon (BOBSM) and the seasonal timing of ENSO’s decay phase. Through distinguishing ‘later-decay’ and ‘normal-decay’ ENSO events, it is found that a later/earlier onset of the BOBSM following El Niño/La Niña is mainly caused by later-decay ENSO events, while no significant changes in BOBSM onset can be identified between normal-decay El Niño and normal-decay La Niña events. Diagnosis of the related dynamic and thermodynamic processes further confirms that, for later-decay ENSO events that remain active until mid-April, persistent ENSO-induced ‘atmospheric-bridge’ processes can significantly modulate the lower tropospheric barotropic instability over the northern BOB by inducing a remarkable anomalous zonal SST gradient between the Indian Ocean and the western Pacific. Meanwhile, these processes alter the position of the South Asian high and the upper atmospheric divergence-pumping through the anomalous Walker circulation. A stronger vertical coupling between the upper and lower troposphere, which is crucial for BOBSM onset, thus appears anomalously earlier (later) following a later-decay La Niña (El Niño). In contrast, due to the earlier damping of normal-decay ENSO, the BOBSM onset processes are barely modulated.