北半球温带反气旋的气候统计特征

利用美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)/美国国家大气研究中心(National Center for Atmospheric Research,NCAR)再分析资料,采用判定和追踪反气旋的客观方法统计分析了1948～2016年北半球冬季温带反气旋活动特征。研究发现,北半球温带反气旋主要活动在中东部的北太平洋、东北大西洋、北美的沿落基山脉东部和美国东部、欧亚的环地中海、伊朗高原、青藏高原以北且贝加尔湖以南地区。海洋上、北美洲和环地中海地区上的反气旋夏季频数最高,而伊朗高原、青藏高原以北且贝湖以南的反气旋均冬季最多。海洋上的反气旋生成区域分布较分散,且主要向偏东方向移动、发展,且具有季节变化。相比于海洋,大陆上反气旋生成的纬度较低,主要向东南方移动、发展。北美大陆上的反气旋夏季生成的较多,冬季移动范围较广。北半球反气旋年平均过程数呈缓慢上升趋势。夏季过程数最多,且从1970年开始呈上升趋势。欧亚地区的反气旋过程数最多,其次太平洋,大西洋最少,但是同一个区域的四季相差较小。反气旋的中心气压大值区的形态和高频区的分布形态相似,且中心气压有明显的季节变化。四季中冬季反气旋最强。秋冬季节是欧亚地区的反气旋最强,大西洋的最弱。春夏季大西洋的反气旋最强,欧亚地区的最弱。四季均是欧亚地区的反气旋的平均纬度较低,且冬季最低。北美地区的反气旋除秋季均是移动纬度范围最大的。反气旋数随生命史的变长而急剧下降,90%左右的反气旋的生命史在4 d内,四季均是大洋上的反气旋生命史较大陆上的长。

Statistical Characteristics of the Extratropical Anticyclonic Activities in Northern Hemisphere

Based on the National Centres for Environmental Prediction-National Center for Atmospheric Research (NCEP /NCAR) reanalysis data, the characteristics of extratropical anticyclonic activities in the northern hemisphere winter from 1948 to 2016 were statistically analyzed by using the objective method of identifying and tracking anticyclonic activities.The results show that the extratropical anticyclone in the northern hemisphere mainly actived in the east-central north Pacific Ocean, the eastern north Atlantic Ocean, the east along the Rocky Mountains and the east of the United States, the Mediterranean rim of Eurasia, the Iranian Plateau, the north of the Qinghai-Tibet Plateau and the south of Lake Baikal. The distribution of anticyclone was more concentrated on the European and North America continent, most of which were located in the middle and high latitudes, while the distribution of anticyclone was more dispersed on the Pacific and the Atlantic ocean than that on the land, with lower latitude position. The frequency of anticyclone in summer was the highest in the ocean, North America and the Mediterranean region, while the frequency of anticyclone in winter was the highest in the north of the Iranian Plateau, north of the Qinghai-Tibet Plateau and the south of Lake Baikal.The anticyclonogenic regions were dispersed on the ocean, which moved and developed towards the east, and presented seasonal variation. Compared with the ocean, the latitude of the continental anticyclone was lower, which mainly moved and developed to the southeast.In the North American continent, anticyclones were more generated in summer than in winter, and they moved within a larger range in winter. The annual frequency of anticyclone process in the northern hemisphere showed a gradual upward trend. In summer, the anticyclone frequency was most high, and it began to rise since 1970. The temporal and spatial distribution of extratropical anticyclones were further studied by zoning into 4 regions. It is found that the anticyclones in different regions presented different seasonal, interannual and interdecadal variations. Eurasia had the largest number of anticyclone processes, followed by the Pacific Ocean, and the Atlantic Ocean had smallest number, but there were slight seasonal differences for the same region. The high value area of the central pressure of the anticyclone had the similar distribution pattern to that the high frequency area, and the central pressure presented obvious seasonal change. The anticyclone was strongest in winter. As for the autumn and winter seasons, the anticyclone was the strongest in Eurasia and the weakest in the Atlantic Ocean. The Atlantic anticyclones were the strongest and weakest in Eurasia in spring and summer. There was little difference of anticyclonic intensity between oceans and continents in spring. The average latitude of anticyclones in Eurasia was lower than other three regions , and the lowest in winter. Except autumn, North American anticyclone had the largest movement latitude range of the four regions. About 90% of the anticyclones had a lifespan of within 4 days. The lifespan of anticyclone in the ocean was longer than that on land in the four seasons.