Variability of the oceanic surface and subsurface layers in the warm pool associated with the atmospheric northward-propagating intraseasonal variability

Abstract

Abstract The variability of the oceanic surface and subsurface layers associated with the northward-propagating intraseasonal variability (ISV) in northern summer were examined in the western North Pacific (WNP) warm pool, using satellite and in-situ observation data. Analyses of satellite observation data revealed that the SST decreases when a convection maximum of the ISV passes. The sea-surface temperature (SST) difference (maximum minus minimum) was about 1.5 to 2.0 °C. In the southern part of the warm pool, the SST abruptly decreased just before the convection maximum. Examination of Argo float data revealed that the temperature profile shifted upward before the convection peak. During this period, the mixed-layer depth (MLD) did not largely change despite strong sea-surface wind and diabatic cooling. According to the sea-surface wind data, a large cyclonic wind-stress curl was identified just north of the convection center associated with a small Coriolis parameter. The upward Ekman pumping appears to contribute to the maintenance of a shallow mixed layer and the abrupt cooling of SST. After the rapid cooling, the SST was almost constant although the mixed layer was deepened. However, in the northern part where the Ekman pumping was relatively small, the SST decreased in accordance with the increase of MLD throughout the cooling period. It was suggested that the air-sea coupling in the off-equatorial region differs from that on the equator.