北大西洋年际变率的海气耦合模式模拟II:热带太平洋强迫

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

利用一个全球海气耦合模式(BCM),结合观测资料,讨论了热带太平洋强迫对北大西洋年际气候变率的影响。研究表明,BCM能够相对合理地模拟赤道太平洋的年际变率模态及相应的海温距平型和大气遥相关型,尽管其准3年的振荡周期过于规则。来自数值模式和观测上的证据都表明,北大西洋冬季海温的主导性变率模态,即自北而南出现的“-+-”的海温距平型,受到来自热带太平洋强迫的显著影响,其正位相与赤道中东太平洋冷事件相对应。换言之,赤道太平洋暖事件的发生,在太平洋-北美沿岸激发出PNA遥相关型,进而通过在北大西洋产生类似NAO负位相的气压距平型,削弱本来与NAO正位相直接联系的三核型海温距平。北大西洋三核型海温距平对热带太平洋强迫的响应,要滞后2—3个月的时间。

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 Nino mode and the associated global SST anomalies and the atmospheric tele-connection 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 tri-polar 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-ag estimation.