A Indo-Pacific SST teleconnection pattern during ENSO

This study examines the teleconnection between Indian and Pacific Ocean SSTs during ENSO using coupled atmosphere-ocean GCM (CGCM) simulations. In one simulation, the oceanic component of the CGCM includes only the tropical Pacific Ocean (i.e., the Pacific Run). In another simulation, both the Indian and Pacific Oceans are included in the ocean model component (i.e., the Indo-Pacific Run). There are three major findings of this study.

First, we identify a dominant Indo-Pacific SST pattern that is closely assocaited with the ENSO cycle. This patterns includes five major SST features: 1) the Pcific ENSO SST anomalies, 2) a east-west SST anomaly dipole in the equatorial Indian Ocean, 3) a noth-south oscillating SST anomaly dipole of the Indian Ocean, 4) a SST anomaly dipole off the coast of North America (the Northeastern Pacific), and 5) a SST anomly dipole off the coast of Asian continent (the Southwesten Pacific). Those features are clearly observed during the 1997-98 El Nino event. The north-south oscillating of Indian Ocean SST is found to play an important role in the ENSO-Monsoon linkage.

Second, we find that the air-sea interactions in the Indian Ocean are different from those in the Pacific Ocean. For example, surface heat flux is an active forcing to the interannual warming of the Indian Ocean, while it is a passive damping to the ENSO warming in the Pacific. The air-sea interactions involved in generating the dominant Indo-Pacific SST teleconnection pattern will be discussed.

Thrid, it is also found that the magnitude and frequency of the ENSO cycle are significantly affected by an active Indian Ocean. The Indo-Pacific Run produces larger amplitude and longer period of the ENSO cycle than the Pacific Run. Also, the active Indian Ocean allows a the Indo-Pacific Run to produce a strong interdecadal ENSO variability. During one decade, there are almost no warm ENSO event but persistent cold ENSO events. In another decade, warm ENSO amplitude can be as large as 3 degree C.