Tropical Warm Pool Surface Heat Budgets and Temperature: Contrasts between1997/98 El Niño and 1998/99 La Niña

Abstract

Seasonal to interannual variations of the net surface heating (FNET) and its relationship to sea surface temperature tendency (dTs/dt) in the tropical eastern Indian and western Pacific Oceans are studied for the period October 1997–September 2000. The surface heat fluxes are derived from the Special Sensor Microwave Imager and Japanese Geostationary Meteorological Satellite radiance measurements. It is found that the magnitude of solar heating is larger than that of evaporative cooling, but the spatial variation of the latter is significantly larger than the former. As a result, the spatial patterns of the seasonal and interannual variability of FNET are dominated by the variability of evaporative cooling. Seasonal variations of FNET and dTs/dt are significantly correlated, except for the equatorial western Pacific. The high correlation is augmented by the high negative correlation between solar heating and evaporative cooling. The change of FNET between the 1997/98 El Niño and 1998/99 La Niña is significantly larger in the tropical eastern Indian Ocean than that in the tropical western Pacific. For the former region, reduced evaporative cooling arising from weakened winds during El Niño is generally associated with enhanced solar heating due to reduced cloudiness, leading to enhanced interannual variability of FNET. For the latter region, reduced evaporative cooling due to weakened winds is generally associated with reduced solar heating arising from increased cloudiness, and vice versa. Consequently, the interannual variability of FNET is reduced. The correlation between interannual variations of FNET and dTs/dt is weak in the tropical western Pacific and eastern Indian Oceans, indicating the importance of ocean dynamics in affecting the interannual SST variation.