Upscale feedback of high-frequency winds on seasonal SST change over the tropical western North Pacific during boreal summer

Abstract

Present study compares the contribution of low-frequency (> 90-day) and high-frequency (< 90-day) variation-related latent heat flux (LHF) to seasonal sea surface temperature (SST) change during boreal summer. It is revealed that both low- and high-frequency LHFs have prominent but opposite contributions to seasonal SST change in the tropical western North Pacific (WNP) during boreal summer. The feedback of high-frequency LHF on the seasonal SST change in the WNP is strong during El Nino events but weak during La Nina events. The difference in the feedback of high-frequency LHF is due to two factors. One is the background surface wind and the other is the intensity of high-frequency wind fluctuations. The high-frequency LHF displays a large non-linear dependence on surface wind under the weak background surface wind during El Nino developing summers, which leads to an accumulation of high-frequency daily LHF in summer mean. The high-frequency wind variability is large over the WNP during El Nino developing summers, which further enhances the accumulation of high-frequency daily LHF. The strong background surface wind and relatively weak high-frequency wind variability during La Nina developing summers are unfavorable for the accumulation of high-frequency daily LHF. This leads to a small summer mean of high-frequency LHF so that the upscale feedback of high-frequency wind variations on seasonal SST change is weak in the WNP during La Nina developing summers.