A study on flow field and heat exchange anomalies on tropical pacific surface in the El Nino and La Nina events

Summary In this paper, based on the 2°×2° grid data COADS from 1950–1987 the flow field and heat exchange anomalies on the (11°S–11°N, 120° E-80°W) tropical Pacific surface (TPS) have been studied in El Nino and La Nina events. During El Nino, the zonal pressure gradient and trade winds decreased on the TPS, the tropical convergence strengthened on TPS, especially on the central TPS, the sensible and latent heat exchange increased, the net longwave radiation and incident solar radiation decreased and the net gain (loss)of heat reduced (increased) on the central and eastern TPS. During La Nina the results were opposite. Finally, two feedback mechanisms which include the dynamic, thermal and hydrological processes during El Nino and La Nina have been summarized and a conceptive model for El Nino-La Nina cycle is given. An estimated period for the El Nino-La Nina cycle is obtained.