北太平洋涛动的季节演变及其与我国冬春气候异常的联系

本文利用NCEP/NCAR再分析资料和我国160站的观测资料,首先定义了季节平均的北太平洋涛动(NPO)指数,在此基础上分析了不同季节中NPO的时空变化特征,特别对冬季和春季NPO与我国气温、降水异常的关系作了研究.结果表明,作为北太平洋地区海平面气压(SLP)年际变化的第二模态,NPO具有相当正压的结构,在地面表现为...

The Seasonal March of the North Pacific Oscillation and Its Association with the Interannual Variations of China's Climate in Boreal Winter and Spring

Based on the monthly mean NCEP/NCAR reanalysis dataset and the observed surface air temperature and precipitation from 160 China stations, the seasonal march of the North Pacific Oscillation (NPO) and its association with the interannual variations of China's climate in boreal winter and spring are investigated in this paper. By employing the Empirical Orthogonal Function (EOF) analysis method, the NPO is identified as the second EOF mode of the monthly mean Sea Level Pressure (SLP) field over the North Pacific. The seasonal mean NPO indices are then defined as the average of the monthly mean indices for each season. Wavelet analysis reveals that the significant periods of the NPO indices are below 8 years for all the four seasons, indicating strong interannual variability and weak interdecadal variability of the NPO. Besides, the winter mean NPO index experiences significant linear trend towards its positive polarity. For all the seasons, NPO is featured with a large-scale meridional dipole in the SLP field over the North Pacific region and resembles the western Pacific pattern in the middle troposphere. The two surface centers are located around Aleutian Islands and the northwest of Hawaii, respectively. Their positions vary a little with season. Comparatively the south center experiences more zonal movement and the north center bears more meridional movement. Vertically the NPO is featured with an equivalent barotropic structure in summer and tilts a little westward with height for the rest three seasons. To put the NPO jet fluctuation in perspective, the positive phase of NPO is characterized by a northward shift and downstream extension of the East Asian jet stream especially in the jet exit region. The NPO variability is influential for the China's climate. Regression analysis indicate that during boreal winter the positive phase of NPO favors significant southerly anomalies along the coasts of East Asia, which may bring warm and moisture air from the south. Consequently, significant warming is observed over most areas of eastern China as well as the eastern part of the Tibetan Plateau. Meanwhile, more precipitation is observed over southeastern China, the Huaihe River valley, and several stations of northwestern China. During boreal spring, the influence of NPO is mainly confined to North China. More precipitation and weak cooling can be observed over this region in the positive phase of NPO. Such changes may be accounted for by the NPO-associated anomalous low-level wind convergence and the secondary circulation around the entrance of East Asian jet stream. In addition to the simultaneous influences, it is further found that the wintertime NPO is closely related to the temperature and precipitation of the following spring. If the NPO phase is positive in the preceding winter, significant warming will be observed over northern China and southwestern China in the following spring. Meanwhile, about 20% more-than-normal precipitation will be observed over southwestern China. Therefore, the wintertime NPO may act as a potential predictor for the climate of the following spring in China.