Intraseasonal Air–Sea Interaction in the Tropical Indian and Pacific Oceans

Abstract

The relationships between intraseasonal (periods <100 days) variations of convection, sea surface temperature (SST), surface wind stress, and surface fluxes of latent heat and radiation in the warm pool of the equatorial Indian and western Pacific Oceans are examined using 7 yr of gridded outgoing longwave radiation (OLR), SST, and surface stress and latent heat flux based on European Centre for Medium-Range Weather Forecasts analyses. In the warm pool region enhanced evaporation, which results from enhanced surface westerlies, lags enhanced convection by ?1 week. Intraseasonal SST fluctuations lag decreased evaporation by ?1 week and decreased convection (which implies increased insolation) by ?2 weeks, suggesting that anomalous latent heat flux and surface insolation drive SST changes on intraseasonal timescale. The relationship between anomalous SST, surface wind stress and surface fluxes of latent heat and shortwave radiation for the Madden?Julian oscillation (MJO), which dominates the intraseasonal variability of convection and surface winds over the warm pool, is developed. Spatially coherent SST anomalies, with amplitude of ?1/3°C, develop in the Indian Ocean and propagate eastward along with the large-scale convective anomaly, but with 1/4 cycle lag. The SST anomalies in the Indian Ocean are postulated to be driven predominantly by surface insolation anomalies associated with the anomalous large-scale convection. The SST anomalies in the western Pacific are postulated to be driven by a combination of anomalous latent heat flux and insolation. The differing behavior in each ocean reflects structural changes of the MJO as it evolves through its life cycle. Data collected during TOGA COARE are used to quantify the role of surface heat flux anomalies for driving the SST changes in the western Pacific.