Role of the western tropical Pacific in the North Pacific regime shift in the winter of 1998/1999

Hyun Su Jo, Sang Wook Yeh, Benjamin Kirtman

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Abstract

In this study, we examine the role of the western tropical Pacific in the North Pacific regime shift during the winter (December-January-February) of 1998/1999. The North Pacific regime shift in the winter of 1998/1999 is characterized by a dipole-like structure along 40N where significant warming is prominent in the western and central North Pacific. This shift might have been associated with an abrupt warming in the western tropical Pacific after 1998/1999, in the North Equatorial Current (NEC) bifurcation region (8N-18N, 125E-160E) in particular. The NEC bifurcation region experiences a regime shift from cooling to warming during the 1998/1999. Consequently, the Kuroshio current, which originates in the NEC bifurcation region, could transport the anomalous warm water into the North Pacific. In addition, a sudden shift in the NEC bifurcation latitude to the south also contributes to the 1998/1999 regime shift in the North Pacific. We suggest a possible mechanism that could have caused the regime shift in the NEC bifurcation region during the 1998/1999. An abrupt deepening of the thermocline depth in the NEC bifurcation region from 1997/1998 to 1998/1999, which is associated with the biggest El Niño in 1997/1998 and a subsequent La Niña event in 1998/1999, plays a role in initiating the shift in the NEC bifurcation region. Subsequently, the frequent occurrence of the La Niña events after 1998/1999 plays a role in maintaining the regime shift toward warming by sustaining a deepening of the thermocline depth.

Original languageEnglish (US)
Pages (from-to)6161-6170
Number of pages10
JournalJournal of Geophysical Research C: Oceans
Volume119
Issue number9
DOIs
StatePublished - Sep 1 2014

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Keywords

  • NEC bifurcation region
  • regime shift
  • western tropical Pacific

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Oceanography

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