中国气温变化的两个基本模态的诊断和模拟研究

我国地域辽阔，气候复杂多变，在全球变暖的背景下研究中国近百年来的气温变化具有重要的意义。为此我们重建了中国东部71个站1880—2004年四季气温距平序列。通过EOF分析发现了中国气温变化的2种最基本的模态：东部一致变化和关内关外相反变化。这2种模态不随季节变化，而且在不同时期也是稳定的。通过研究这2种模态与变暖趋势的关系发现，20世纪80年代以来的变暖主要是由于第一模态在该时期持续的正位相增强造成的；而20世纪20~40年代的变暖主要是由于第二模态所呈现的正位相所造成的。此外，我们检验了这2种模态在大气环流模式（CAM）中的表现。结果表明：121年（模式中1880—2000年）的集合模拟在一定程度上可以重现第一模态的变化，而第二模态则仅在冬季表现明显。最后，以冬季为例，利用1880—2004年重建及观测的500 hPa高度场资料，通过合成分析进一步研究了这2种模态的环流机制：第一模态正位相对应纬向环流增强，表现在地面气温分布上为东部一致变暖。而负位相则对应东亚大槽加深，东部地区一致变冷。第二模态正位相对应的环流分布则为从东亚北部到阿留申为负距平，东亚到北太平洋中纬度为正距平；对应地面气温分布为关内变暖关外变冷。负位相时环流分布基本相反。这样的环流机制得到了模式研究的支持。

Diagnostic and Modeling Study of the Two Basic Modes of Surface Air Temperature and Its Variation in China

Because of its particular geographical condition, the climate of China vary from one region to another. Thus, studies of the spatial patterns of temperature variance in the context of global warming in the past one hundred years are very meaningful. Using the constructed and observational data, we obtained a series of surface temperature anomaly over Eastern China in four seasons during the period of 1880 2004. EOF analysis was applied on this sequence, and it is found that two basic spatial patterns, which are independent of seasonal cycle, dominate the variation of surface temperature in China. The two leading EOF eigenvectors are: (1) Eastern China experiences a consistent change; (2) Northeastern China exhibits an opposite change compared with the rest parts of China. Moreover, detailed analysis shows that the warming since the 1980s in China is chiefly caused by the persistently increasing in positive phase of EOF 1 mode since 1976. The warming during the period of the 1920s 1940s can be mainly attributed to the positive phase of EOF 2 mode. Besides the diagnostic analysis, the results from an ensemble numerical simulation were also examined, using the same methods and approaches as above. It should be noted that the first mode can be captured by an Atmospheric General Circulation Model forced by observational sea surface temperature and sea ice data. However, this model failed to present the second mode except for boreal winter (DJF). Furthermore, because of the relatively steady performance of the two modes in winter, the circulation patterns in 500 hPa level for these two modes were investigated by composite analysis on both the observational and modeled data. The results from the two kinds of data show conformably that the positive phase of the first mode corresponds to the enhanced zonal circulation in winter, which leads to the warming in eastern China, while the negative phase corresponds to the circulation structure that the East Asia trough is deepening, which leads to the coherent cold in Eastern China. The second mode is affected by the large scale of high level anomaly centers. The positive phase corresponds to the situation that from northern East Asia to Aleutian is controlled by negative geopotential height anomaly and from East Asia to northern Pacific Ocean in middle latitude is covered by positive anomaly, resulting in the cold anomaly on surface in northeast and warm anomaly in the rest parts. The circulation pattern of the negative phase is almost in the opposite condition.