Contrast of local air–sea relationships between 10–20-day and 30–60-day intraseasonal oscillations during May–September over the South China Sea and western North Pacific

Abstract

Present study compares local air–sea relationship of 10–20-day and 30–60-day intraseasonal oscillations (ISOs) over the South China Sea (SCS) and western North Pacific (WNP) during May through September for the period 1998–2010. It is shown that sea surface temperature (SST) has a larger intraseasonal variance in the North Indian Ocean, the SCS, and subtropical WNP on the 30–60-day time scale, but in tropical WNP on the 10–20-day time scale. The local correlation of SST with rain, surface shortwave radiation (SWR) and latent heat flux (LHF) displays a southwest–northeast tilted structure on the 10–20-day time scale, but a broad west-east pattern with a larger correlation on the 30–60-day time scale. The time of SST leading rain is larger in off-equatorial regions than in near-equatorial regions for both types of ISOs, whereas the time of rain leading SST is larger in near-equatorial regions than in off-equatorial regions. A similar feature is seen for SWR, but an opposite feature for LHF. The atmospheric ISOs induce intraseasonal SST variations through cloud-radiation and wind-evaporation changes. The intraseasonal SST variations feedback on the atmosphere through modulation of atmospheric stability over off-equatorial regions on both timescales. The SST impacts on the atmosphere appear larger on the 30–60-day time scale than on the 10–20-day time scale. The distinct spatial patterns of local air–sea relationship on the two types of ISOs are associated with different spatial structures in both atmospheric ISO-associated SWR and LHF anomalies and SST-induced atmospheric stability anomalies.