Interannual Salinity Variability Associated With the Central Pacific and Eastern Pacific El Ninos in the Tropical Pacific

Ocean reanalysis products and observations are used to analyze the differences between the two types of El Nino in terms of interannual salinity variability in the tropical Pacific; a budget analysis for mixed layer (ML) salinity (MLS) is performed in the region. The center of negative MLS anomalies associated with the central Pacific (CP) El Nino tends to move further westward in winter along the equator, as compared with the eastern Pacific (EP) El Nino. The oscillation period with the EP El Nino is found to be approximately 10 years, longer than that with the CP El Nino (approximately 6-8 years). Our budget analyses further reveal that surface advection, surface forcing, and subsurface effect are the three main contributors to ML tendency of interannual salinity anomalies, which are regionally dependent. In the eastern edge of the warm pool (WP), surface advection makes a larger contribution (about 40-60%) to the MLS budget, and subsurface effect (about 20%) and surface forcing (about 20-40%) are relatively smaller. The subsurface effects on the MLS tendency tend to compensate for the imbalance induced by the surface forcing and advection: A weakened MLS tendency occurs with the CP El Nino, whereas an enhanced MLS tendency occurs with the EP El Nino, respectively. The MLS tendency leads the Nino3.4 SST by 8-10 months for the EP El Nino, whereas there is no such apparent lead/lag relationship for the CP El Nino. It is demonstrated that the relationships between the interannual sea surface temperature (SST) variability and MLS budget terms can be a clear indicator to distinguish the two types of El Nino.