On the Varying Responses of East Asian Winter Monsoon to Three Types of El Nino: Observations and Model Hindcasts

Using observational data and model hindcasts produced by a coupled climate model, we examine the response of the East Asian winter monsoon (EAWM) to three types of El Nino: eastern Pacific (EP) and central Pacific I (CP-I) and II (CP-II) El Ninos. The observational analysis shows that all three El Nino types weaken the EAWM with varying degrees of impact. The EP El Nino has the largest weakening effect, while the CP-II El Nino has the second largest, and the CP-I El Nino has the smallest. We find that diverse El Nino types impact the EAWM by altering the responses of two anomalous anticyclones during El Nino mature winter: the western North Pacific anticyclone (WNPAC) and Kuroshio anticyclone (KAC). The WNPAC responses are controlled by the Gill response and Indian Ocean warming processes that both respond to the eastern-to-central tropical Pacific precipitation anomalies. The KAC responses are controlled by a poleward wave propagation responding to the northwestern tropical Pacific precipitation anomalies. We find that the model hindcasts significantly underestimate the weakening effect during the EP and CP-II El Ninos. These underestimations are related to a model deficiency in which it produces a too-weak WNPAC response during the EP El Nino and completely misses the KAC response during both types of El Nino. The too-weak WNPAC response is caused by the model deficiency of simulating too-weak eastern-to-central tropical Pacific precipitation anomalies. The lack of KAC response arises from the unrealistic response of the model's extratropical atmosphere to the northwestern tropical Pacific precipitation anomalies.

Automated summary

Through observational data and model hindcasts, it was discovered that different types of El Nino have varying effects on the East Asian winter monsoon, with EP and CP-II El Ninos showing the most significant weakening impact.