太平洋表层海温的年代际变化

众所周知，ENSO(El Nino/ Southern Oscillation)是发生在热带太平洋的年际时间尺度上最强的气候信号，与 El Nino (La Nina)相应的正(负)海温距平(SSTA)主要分布于赤道中东太平洋地区(Rasmusson et al.，1982)。相对于热带太平洋的年际ENSO现象，人们注意到北太平洋海平面气压(SLP)存在更长周期的年代际变化(Trenberth et al.，1994)，有人认为这与北太平洋的表层温度(SST)变化有关(Latif et al.，1994)，也有人认为与热带SST的异常关系更为密切(Jacobs et al.，1994)。20世纪80年代后的ENSO事件和20世纪60，70年代有明显的差别(Wang，1995)，20世纪90年后El Nino发生频数增加，并且在1997和1998年出现了20世纪最强的一次Nino事件(McPhaden，1999)。因此，不论是作为大气年代际变化可能的一个驱动因子，还是作为年际ENSO的背景场，从整体上了解太平洋SST的年代际时间尺度上的时、空变化特征都是十分重要的。

INTERDECADAL VARIABILITY OF THE SEA SURFACE TEMPERATURE IN THE PACIFIC

Temporal and spatial characteristics of interdecadal SST variability of the North Pacific Ocean were investigated and its effect on ENSO was discussed. Interdecadal variability in SST obviously exists in both the tropical and north Pacific Ocean, while it is relatively weak in the equatorial Pacific and SST changes in the north Pacific possess lower frequencies. 1977 was a turning point for interdecadal SST variations (from cold to warm) in the equatorial Pacific as well as for the SST principal mode (EOF1) of the Pacific SST in terms of temporal change. But the north Pacific changed from warm to cold period from 1973, which is attributed mainly to the second mode. Both equatorial and north Pacific Ocean has turned to warm period since 1990. Revealed by the first mode, SST oscillation of the middle latitude North Pacific Ocean and its adjacent area are out of phase, while oscillation of the north Pacific was revealed by the second mode. Significant impact of interdecadal changes of equatorial SST on ENSO strength is shown. It seems that warm decadal background is a prerequisite condition for frequent and strong ENSO events.