Journal
JOURNAL OF CLIMATE
Volume 29, Issue 12, Pages 4347-4359Publisher
AMER METEOROLOGICAL SOC
DOI: 10.1175/JCLI-D-15-0104.1
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Funding
- Special Fund for Public Welfare Industry (Meteorology) [GYHY201506013, GYHY201406022]
- National Basic Research Program 973'' [2012CB417403]
- Jiangsu Provincial Qinglan Project
- University of Reading Department of Meteorology
- NUIST
- National Centre for Atmospheric Science
- NERC [NE/I022841/1, NE/L01386X/1] Funding Source: UKRI
- Natural Environment Research Council [NE/L01386X/1, ncas10009, NE/I022841/1] Funding Source: researchfish
- Directorate For Geosciences
- Div Atmospheric & Geospace Sciences [1406601] Funding Source: National Science Foundation
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Previous studies have shown that the Indo-Pacific atmospheric response to ENSO comprises two dominant modes of variability: a meridionally quasi-symmetric response (independent of the annual cycle) and an antisymmetric response (arising from the nonlinear atmospheric interaction between ENSO variability and the annual cycle), referred to as the combination mode (C-mode). This study demonstrates that the direct El Nino signal over the tropics is confined to the equatorial region and has no significant impact on the atmospheric response over East Asia. The El Nino-associated equatorial anomalies can be expanded toward off-equatorial regions by the C-mode through ENSO's interaction with the annual cycle. The C-mode is the prime driver for the development of an anomalous low-level anticyclone over the western North Pacific (WNP) during the El Nino decay phase, which usually transports more moisture to East Asia and thereby causes more precipitation over southern China. An atmospheric general circulation model is used that reproduces well the WNP anticyclonic anomalies when both El Nino sea surface temperature (SST) anomalies as well as the SST annual cycle are prescribed as boundary conditions. However, no significant WNP anticyclonic circulation anomaly appears during the El Nino decay phase when excluding the SST annual cycle. The analyses herein of observational data and model experiments suggest that the annual cycle plays a key role in the East Asian climate anomalies associated with El Nino through their nonlinear atmospheric interaction. Hence, a realistic simulation of the annual cycle is crucial in order to correctly capture the ENSO-associated climate anomalies over East Asia.
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