OCEAN-ATMOSPHERE COUPLED MODEL SIMULATION OF NORTH ATLANTIC INTERANNUAL VARIABILITY II：TROPICAL TELE-CONNECTION

The contribution of the tropical Pacific forcing to the North Atlantic interannual time scale variability is addressed by using the output of a global ocean-atmosphere coupled model namely Bergen Climate Model (BCM) in combination with the observational data. Evaluations on the simulated interannual variability of the equatorial and tropical Pacific sea surface temperature (SST) indicate that the BCM model has an acceptable performance in reproducing both the El Ni o mode and the associated global SST anomalies and the atmospheric teleconnection patterns, although the simulated warm events have a prudish regular time period of approximately 3 year, which is a common problem for many ocean atmosphere coupled models. Evidences from both the simulation and the observation all support that the dominant mode of the interannual time scale SST variability of the North Atlantic, appearing as a tri polar pattern spanning the basin meridionally, is partly forced by the atmospheric teleconnections originated from the middle and eastern equatorial Pacific. Positive phase of the tri polar North Atlantic SST mode corresponds to a cold event in the equatorial Pacific. In other words, the occurrence of an equatorial Pacific warm event can provoke a Pacific North American tele connection pattern (PNA) over the Pacific North America domain, which further modulates the sea level pressure (SLP) change over the North Atlantic. The SLP anomaly pattern partly resembles the situation of a negative phase of the NAO. Since a strong NAO is always associated with a robust tri polar structure SST anomaly pattern, the weakened NAO pattern accordingly leads to weaker tripolar SST anomalies. Further analyses prove that the response of the North Atlantic SST to the equatorial Pacific forcing has a lag time of 2-3 months. Both the model simulation and the observation support this time agestimation.