Locally and remotely forced atmospheric circulation anomalies of Ningaloo Niño/Niña

Abstract

A recently identified climate mode called Ningaloo Nino (Nina) is associated with positive (negative) sea surface temperature (SST) anomalies off the west coast of Australia and negative (positive) sea level pressure (SLP) anomalies in the overlying atmosphere. By conducting a series of numerical experiments with an atmospheric general circulation model, generation mechanisms of the atmospheric circulation anomalies accompanied by Ningaloo Nino/Nina are examined. Even when SST is allowed to vary interannually only in the eastern South Indian Ocean, negative (positive) SLP anomalies are formed off the west coast of Australia in Ningaloo Nino (Nina) years, supporting the existence of local ocean–atmosphere interaction. When the model is forced by SST anomalies outside of the eastern South Indian Ocean, negative (positive) SLP anomalies are also generated in Ningaloo Nino (Nina) years owing to a Matsuno–Gill type response to atmospheric convection anomalies in the tropical Pacific. It is found that the latter impact is stronger in the current atmospheric general circulation model. Regarding climatic impacts, it is shown that Ningaloo Nino (Nina) induces wet (dry) anomalies over the northwestern part of Australia even when SST anomalies outside of the eastern South Indian Ocean are excluded from the SST forcing.