北半球500 hPa高度场定常波不平稳性分析

An analysis on the unsteadiness of Northern Hemispheric 500 hpa height stationary waves

中文关键词:  500 hPa位势高度场，定常波不平稳性，定常波不平稳度，气候脆弱带，环流成因

英文关键词:500hPa geopotential height field, Stationary wave anomaly, Stationary wave deviation degree, Vulnerable climate zone, General circulation system

中文摘要:

      提出并阐明Lorenz环流分解意义下的定常波不平稳性概念，它是月平均图上纬向波动分量气候变率与定常波强度相对大小的表征。根据Lorenz环流分解，定义全域(局域)定常波不平稳度 ( )，分析了北半球500 hPa位势高度场定常波强度较大的30°—60°N纬带的定常波不平稳性，结果表明：(1) 全域定常波不平稳带位置存在季节性北进、南退过程。平稳的定常波出现在冬季的35°—55°N的中纬度带和夏季的副热带地区（35°N以南），分别与冬季的东亚大槽、北美槽和较弱的欧洲槽，以及夏季的副热带高压等系统相联系。不平稳度的高值中心出现在春季的35°N和夏季的50°N，这与定常波强度季节变化和月平均图上槽脊位置、强度年际异常有关。(2) 局域定常波不平稳度存在着明显的纬向不对称性。平稳带通常位于定常波的强槽强脊所控制的区域，而不平稳带通常位于定常波强度较弱的区域。副热带(35°N及以南) 局域定常波不平稳度冬强于夏，中纬度(35°N及以北)则夏强于冬。夏季局域定常波不平稳度地理分布具有复杂的结构。但无论冬夏，北欧是定常波最不平稳的地区，北美大陆附近的定常波则相对平稳。(3) 夏季，从华北经东北至北太平洋存在一个定常波不平稳度高值带，其高值中心位于中国黑龙江省东部(45°N，130°E)，主要影响中国北方(东北、华北、西北)，可能是该区夏季气候脆弱带的环流成因。 

英文摘要:

      A definition of stationary wave anomalies is given based on the Lorenz decomposition of the atmospheric circulation, and monthly variations of the zonal component of stationary waves relative to the mean are illustrated. A deviation index ( )for global (local) stationary waves is used to analyze the stationary wave anomalies in the latitude band 30°-60°N, where the stationary waves in the Northern Hemisphere 500 hPa geopotential height field is significantly strong. The following results are obtained: (1) the devoation index characterizes the spatial temporal variance of global stationary waves in the 30°-60°N belt, and this anomalous belt advances southward and then retreats northward in the course of seasonal march. Steady stationary waves occur in mid-latitudes (35°-55°N) in winter and in the subtropical zone (south of 35°N) in summer. Specifically, they are associated respectively with the major troughs of East Asia and North America and the weaker European trough in winter, and the relatively steady subtropical high system in summer. A high value center of the deviation index appears at 35°N in spring and 50°N in summer, which reflects the seasonal variation of the strength of stationary waves and that of their zonal distributions. (2) The degree of deviation for local stationary waves clearly shows a zonal asymmetry. The steady zones of stationary waves are always located in the areas controlled by strong troughs or ridges, whereas the anomalous ones are in the areas where the stationary wave intensity is weak. The degree of deviation for local stationary waves in the subtropics (south of 35°N) is larger in winter than in summer, and the reverse is true in the mid-latitude region (north of 35°N). The summertime distribution of the deviation index on the whole shows a rather complicated structure. However, North Europe is the most anomalous area for local stationary waves, as represented by a high value of in both summer and winter, while over the North American Continent (about 120°-60°W), is slightly less than 1 in summer, indicating that the stationary waves in this region are more steady than those over other mid-and high-latitude regions. (3) From North China to the Northwest Pacific, there is a high value zone of in summer, with its center (45°N，130°E) located to the east of Heilongjiang Province, which impacts the northern areas of China. This may explain why these areas experience large interannual climate variabilities in summer. It is proposed that the degree of deviation is an intrinsic characteristic of stationary waves, and it can be of the same importance as the intensity and the energy spectrum structure of stationary waves in the study of the general circulation system.