Large-scale air-sea interactions in the tropical western Pacific on interannual and intraseasonal time scales

(1) The interannual variability of the main thermocline in the tropical western Pacific along the 137°E longitude line is reflected primarily in the quasi-biennial oscillation (QBO) time scale. Each dominant eastward-propagating QBO mode is extracted by applying a complex EOF analysis to the sea surface temperature (SST) and 700 mb zonal wind anomaly fields over the tropical Indian and Pacific Oceans. (2) Two air-sea coupled modes; ie intraseasonal and interannual modes, are statistically extracted using the complex EOF analysis. There exist remarkable differences in the air-sea coupling of the intraseasonal time scale compared with the interannual time scale. (3) The growth of the atmospheric 30-60 day oscillation over the equatorial western Pacific is even affected by high SST above a threshold value of 28°-28.5°C. The intraseasonal variations, especially with 40-60 day scales are predominant when the mean SST over the warm water region is in the range of 29°-29.5°C. There exists strong air-sea coupling on the intraseasonal time scale in the warm water region. -from Author