Feedback of 10–20-day intraseasonal oscillations on seasonal mean SST in the tropical Western North Pacific during boreal spring through fall

Abstract

The present study documents the factors for year-to-year changes in the intensity of 10–20-day intraseasonal oscillations (ISOs) and investigates the feedback of the 10–20-day ISO intensity on seasonal mean sea surface temperature (SST) change in the tropical western North Pacific during boreal spring through fall. An analysis of local correlation reveals a significant negative correlation of the 10–20-day ISO intensity and the seasonal mean SST tendency in the tropical western North Pacific during spring, summer, and fall, suggesting a plausible feedback of the ISO intensity on seasonal mean SST anomaly. The 10–20-day ISO intensity change over the tropical western North Pacific is influenced by El Nino-Southern Oscillation (ENSO) through modulation of vertical shear of zonal winds, lower-level moisture, and upward motion. Due to the phase dependence of location of these ENSO-induced background field changes, the ISO intensity is subject to ENSO influence in different regions during the three seasons. The feedback of the 10–20-day ISO intensity on local seasonal mean SST change in the tropical western North Pacific is demonstrated by separating latent heat flux anomalies into components on different time scales. The ISO-induced latent heat flux anomalies may accumulate in a season and overcome interannual anomalies due to seasonal mean changes. Thus, the ISO-induced surface heat flux change may play an important role in the seasonal mean SST anomaly in the tropical western North Pacific.