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Dynamical responses of the west Pacific North Equatorial Countercurrent (NECC) system to El Niño events
Author(s) -
Zhao Jun,
Li Yuanlong,
Wang Fan
Publication year - 2013
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/jgrc.20196
Subject(s) - rossby wave , downwelling , ocean gyre , climatology , mesoscale meteorology , geology , oceanography , boundary current , upwelling , kelvin wave , ocean current , subtropics , fishery , biology
Analysis of data sets based on satellite measurements during 1992–2011 reveals pronounced interannual‐to‐decadal variations of the west Pacific North Equatorial Countercurrent (NECC) system, involving the intensity (INT), position ( Y CM ), and path length ( L CM ) of the surface NECC jet, together with the associated recirculation gyres and mesoscale eddies. During the 1997–1998 and 2009–2010 El Niño events, the NECC jet showed increased INT before, and decreased INT, northerly position, and lengthened path after the mature phase. During the 1993–1995 and 2002–2005 central Pacific warming events, it also showed increased INT but no evident changes in Y CM and L CM . The varied responses caused the different natures of individual El Niño events. In 1998 and 2010, reflected upwelling Kelvin waves south of the NECC jet, together with the downwelling Rossby waves north of it induced by the following strong La Niña events, weakened the NECC jet through geostrophy and shifted it northward. This process was however absent during the 1993–1995 and 2002–2005 events. Intensified NECC jet during warm conditions gives rise to anomalously active mesoscale eddies, which also contribute to the unstable states of the NECC system in 1998 and 2010. Hindcast with a linear Rossby wave model reveals a slow change of the western Pacific NECC system during the past 50 years. Since 1990s, low‐frequency variance of the NECC system has been dominated by quasi‐decadal signals and more closely associated with wind forcing in the western Pacific Ocean, which corresponds to the slow changes of the El Niño/Southern Oscillation (ENSO)‐related wind forcing pattern.