Simulation of two types of El Nio from different convective parameters

Abstract

Many recent studies have reported the presence of two types of El Nio events in observation: Cold Tongue (CT) El Nio and Warm Pool (WP) El Nio. We investigate the sensitivity of a model simulating two types of El Nio by changing a convective triggering parameter (Tokioka parameter). When deep convections are highly suppressed with a large Tokioka parameter, the model is capable of simulating distinct two-types of El Nio. However, the model has a problem in simulating two-types of El Nio distinctively when the Tokioka parameter is small, because the location of the maximum precipitation anomaly related to the CT El Nio is significantly shifted westward, leading to an atmospheric response pattern similar to that of the WP El Nio. Our results suggest that the mean precipitation over the eastern equatorial Pacific and the resultant zonal distribution in atmospheric feedback associated with ENSO can be one of the crucial factors for simulating two-types of El Nio.