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Quasi‐biennial winds in the far western equatorial Pacific phase‐Locking El Niño to the seasonal cycle
Author(s) -
Clarke Allan J.,
Shu Lianghua
Publication year - 2000
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/1999gl010506
Subject(s) - climatology , el niño southern oscillation , pacific decadal oscillation , wind stress , geology , madden–julian oscillation , pacific ocean , annual cycle , oceanography , atmospheric sciences , geography , convection , meteorology
At El Niño/Southern Oscillation (ENSO) frequencies, the ocean is mainly driven by zonal equatorial winds. Using zonal equatorial Pacific wind stress for the last 8 El Niños, we demonstrate that anomalous equatorial westerly winds typically begin to blow in the far western Pacific in about November prior to the El Niño year and then slowly move eastward, amplifying and reaching a maximum in the central Pacific in about the following October. The key phase‐locking in the far western Pacific winds that leads to calendar‐year phase‐locking in El Niño appears to be associated with quasi‐biennial (QB) variability in the zonal wind. Recent theory suggests that evaporation and the seasonal wind cycle in the far‐western equatorial Pacific are crucial to the generation of the QB variability. The biennial wind‐stress phase‐locking explains why there is a spring persistence barrier in often used ENSO indices.