TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 55 (No. 3), pp. 385-394, 1999

Interdecadal Variations of ENSO Signals and Annual Cycles Revealed by Wavelet Analysis

Takashi Setoh1, Shiro Imawaki2, Alexander Ostrovskii2 and Shin-ichiro Umatani2

1Department of Earth System and Technology, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
2Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka 816-8580, Japan

(Received 18 September 1998; in revised form 2 November 1998; accepted 10 November 1998)

Abstract: Interdecadal variations of El Niño/Southern Oscillation (ENSO) signals and annual cycles appearing in the sea surface temperature (SST) and zonal wind in the equatorial Pacific during 1950-1997 are studied by wavelet, empirical orthogonal function (EOF) and singular value decomposition (SVD) analyses. The typical timescale of ENSO is estimated to be about 40 months before the late 1970s and 48-52 months after that; the timescale increased by about 10 months. The spatial pattern of the ENSO signal appearing in SST also changed in the 1970s; before that, the area of strong signal spread over the extratropical regions, while it is confined near the equator after that. The center of the strongest signal shifted from the central and eastern equatorial Pacific to the South American coast at that time. These SST fluctuations near the equator are associated with fluctuations of zonal wind, whose spatial pattern also shifted considerably eastward at that time. In the eastern equatorial Pacific, amplitudes of annual cycles of SST are weak in El Niño years and strong in La Niña years. This relation is not clear, however, in the 1980s and 1990s.


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