Asymmetry of the Indian Ocean Basin-wide SST Anomalies: Roles of ENSO and IOD.

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Title:	Asymmetry of the Indian Ocean Basin-wide SST Anomalies: Roles of ENSO and IOD.
Authors:	洪志誠;Chi-Cherng Hong;Tim Li;H. Lin;Y.-C. Chen
Contributors:	地球環境暨生物資源學系(含環境教育與資源碩士班)
Keywords:	ENSO;Indian Ocean;Oceanic mixed layer;Ocean models;Sea surface temperature
Date:	2010-07
Issue Date:	2014-01-17 19:30:31 (UTC+8)
Abstract:	A basinwide warming (cooling) in the Indian Ocean is observed following the El Niño (La Niña) mature phase, with the amplitude of the warming being significantly larger than the cooling. A composite analysis reveals that the amplitude asymmetry (positive skewness) between the warm and cold Indian Ocean basinwide sea surface temperature anomaly pattern (IOB) appears only when ENSO is concurrent with the Indian Ocean dipole (IOD). The amplitude asymmetry becomes insignificant during the ENSO-only and the IOD-only events. The physical mechanism for the amplitude asymmetry is investigated by analyzing the mixed layer heat budget based on the Simple Ocean Data Assimilation (SODA) 2.0.2 data. It is found that the positive skewness in the IOD west pole (IODW) is mainly caused by the asymmetry of ocean temperature advection, whereas the positive skewness in the IOD east pole (IODE) is caused by the asymmetry of the surface heat flux anomaly (primarily shortwave radiation) in response to the ENSO remote forcing. The asymmetry of the mixed layer depth (MLD) between warm and cold events is another factor contributing to the IOB positive skewness. The MLD in IODE during the warm events (27 m) is shallower than that of the cold events (45 m), resulting a larger (smaller) temperature tendency during the warm (cold) events. In contrast, the MLD in IODW during the warm events (44 m) is deeper than that of the cold events (37 m). Because the positive skewness in IODW is caused by the ocean temperature advection and the surface heat flux plays a damping role, a larger (smaller) MLD leads to a weaker (stronger) thermodynamic damping. Thus the asymmetry of MLD in both IODE and IODW favors a greater basinwide warming than cooling.
Relation:	Journal of Climate，Vol. 23, Issue 13，Pages 3563-3576
Appears in Collections:	[Department of Earth and Life Science] Periodical Articles

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