热带太平洋年代际平均气候态变化与ENSO循环

文中用观测的热带太平洋海表温度资料、风应力资料和OLR资料，通过多时间尺度分析，将与ENSO有关的变化分为3个主要的分量，一是2～7a的ENSO循环尺度，二是8～20a的年代际尺度，三是20a以上的平均气候态变化。讨论了热带太平洋这种平均气候态变化的主要特征以及与ENSO循环的关系，并用耦合模式的数值试验来研究平均气候态的变化对ENSO循环的影响。结果表明热带太平洋的平均气候态在20世纪70年代后期发生了一次由冷态向暖态的变化，主要增暖区是沿赤道以及热带东太平洋的，海表温度变化最大中心可以达到0.6℃。伴随着海表温度的变化，赤道西太平洋的西风距平加强，赤道东太平洋的东风距平也加强，在赤道中太平洋形成了一个加强的辐合中心。年代际平均气候冷暖态的变化对ENSO最直接的线性影响是使ElNio位相增加，而形成ENSO冷位相和暖位相的不对称。另一方面较暖的平均气候态可能引起海洋和大气之间的耦合加强，导致ENSO循环振荡有所加强。

DECADAL CLIMATE CHANGE AND ENSO CYCLE

The observed strongest global climate variation on the interannual timescale is the El Nio - Southern Oscillation (ENSO) phenomenon, which is an irregular interannual oscillation resulting primarily from coupled ocean-atmosphere interaction in the tropical Pacific. Since 1970s the El Nio events have been stronger than the La Nina both on frequency and amplitude. Perhaps it links with the global climate warming. In this paper, sea surface temperature, wind stress and OLR data sets are diagnosed by using wavelet transform. The ENSO cycle (2-7 years ) signal and decadal variability ( 8-20 years ) are filtered out to form the data sets in order to investigate the features of the decadal climate change and its effect on ENSO cycle. Then the numerical experiments are designed to identify the effect by running a hybrid tropical Pacific coupled model.　　The main results of the paper can be outlined as follows:　　1)For the behavior of SSTA and wind stress in tropical Pacific by wavelet analysis, it is clear that not only the energy density of ENSO cycle ( 2-7 years) gets stronger during 1990s, but also does so the decadal oscillation ( 8-20 years). The long-term linear trend of climate change ( more than 20 years ) can be identified with a catastrophe climate change in 1976 from cold climate state turning to warm state.　　2)The main warming regions of the sea surface temperature after 1976 is the east tropical areas and extended westward along the equator with the maximum value up to 0.6℃.The main features of wind stress pattern are the increasing westerly anomaly in west tropical Pacific and easterly anomaly at east tropical Pacific so that low level convection occurs near the date line.　　3)However, the average state in the tropical Pacific in the 1990s is warmer than that in 1980s. This climate background change in the 1990s may cause the asymmetry of the warm and cold phases. On the other hand, the decadal oscillation has directly affected the ENSO cycle on both frequency and amplitude.