An interdecadal change in August Indochina Peninsula precipitation-ENSO relationship around 1980

A prominent change occurred in the relationship between August Indochina Peninsula (ICP) precipitation and tropical Pacific sea surface temperature (SST) around 1980. More August ICP precipitation falls in La Nina developing years during 1959-1979, but in El Nino developing years during 1983-2003. The relation change is associated with a change in the evolution of equatorial Pacific SST anomalies. During 1959-1979, negative SST anomalies develop in the equatorial eastern Pacific (EEP) in early spring and extend westward. They cause anomalous southwesterly and reduce surface latent heat flux (LHF) over the tropical western North Pacific (WNP), inducing positive SST anomalies there in early summer. Negative SST anomalies form in the tropical South Indian Ocean (SIO) due to LHF increase attributed to a local air-sea interaction process in preceding winter and a remote forcing of negative EEP SST anomalies in late spring-early summer. More August ICP precipitation is due to anomalous ascent induced by a Rossby wave response to positive WNP SST anomalies and a cross-equatorial vertical circulation due to negative SIO SST anomalies. During 1983-2003, positive SST anomalies form in the equatorial central Pacific (ECP) in late spring and extend eastward. Negative SST anomalies develop in the tropical southeastern Indian Ocean (SEIO) due to sustained LHF increase induced by both preceding winter negative SST anomalies and late spring-early summer positive SST anomalies in the EEP. More August ICP precipitation is induced by a Rossby wave response to positive ECP SST anomalies and a cross-equatorial vertical circulation due to negative SEIO SST anomalies.