青藏高原夏季风强弱年波包传播特征分析

采用1996—2005年NCEP/NCAR 600 hPa逐日再分析资料,利用高原季风指数定义和波包传播的诊断方法(WPD),研究了高原夏季风强弱年(1998年和1997年)不同发展阶段的波包传播特征。研究表明,在高原夏季风开始前,都存在着季风的加强期,期间高原地区都有来自乌拉尔山—巴尔喀什湖地区向东传播的波包和来自阿拉伯海、阿拉伯半岛地区向西传播的波包。当乌拉尔山向高原地区的波包传播减弱,高原地区波包传播主要来自西太平洋地区时,高原夏季风爆发。在高原夏季风爆发后,存在着季风的加强期、维持期和减弱期等不同阶段。季风加强期间,强年(1998年)主要是从西太平洋地区向西传播到高原的波包值,而弱年(1997年)西太平洋地区几乎没有向西传播到高原的波包;季风维持期间,强年(1998年)表现出高原地区波包大值区向四周频散的趋势,而弱年(1997年)反映出与强年(1998年)相反的特征,高原地区有来自阿拉伯海、阿拉伯半岛地区和西太平洋地区传播来的波包;季风结束减弱期间,乌拉尔山地区的波包值再次向东传播影响到高原地区。最后分析波包强中心对应着天气系统扰动能量的中心,并且与天气系统也有较好的对应关系,波包强中心的传播常常与槽脊的移动相联系。

The Distinguishing Characteristics of Wave-Packet Propagation in Strong/Weak Qinghai-Xizang Plateau Summer Monsoon Year

Using the daily NCEP/NCAR reanalysis of 600 hPa geopotential height field from 1996 to 2005 and the concept of Plateau monsoon index(PMI) and method of WPD investigate the different wave-packet characteristics in different stages of the strong/weak(1998/1997) year.(1) The Plateau summer monsoon characteristics calculated by PMI of 1997 and 1998 show that: Its strength is very different in the different phases,so this paper divide it to three phases(intensive and permanent and weakly days)and discussing it separately,the result also show the characteristic is distinct in strong/weak summer monsoon.(2) During the intensive days that before the Plateau summer monsoon break up,Plateau region has strongly wave-packet propagating eastward where come from Ural-Balkash Lake and propagating westward where come from Arabian Sea and Araby whatever in the strong or weak year,but wave-packet value in the strong monsoon year is higher than in the weak monsoon year.When Ural area wave-packet propagation become weak,and Plateau region wave-packet propagation mainly come from western Pacific Ocean,Plateau summer monsoon break up.(3) In the intensive days after Plateau summer monsoon onset,average wave-packets in Plateau region is strong and mainly propagating from west Pacific ocean in strong monsoon year,but weak in weak monsoon year.In the permanent days the average wave-packet in Plateau region is very strong and disperse to around in strong monsoon year,then average value become lower because of dispersion,but weak monsoon year shows the opposite characteristics,Plateau region has wave-packets propagation which come from Arabian Sea and Araby and west Pacific ocean,and the average wave-packet is weak.(4) In the weakly days while Plateau summer monsoon come to an end,the characteristics of Plateau summer monsoon begin translate to water monsoon and the average wave-packet is higher than before and the wave-packet in Ural region propagating northward in strong summer monsoon year(1998).In the end it indicate that the center of wave-packet is corresponding to the perturbation energy center for weather system,and the center of wave-packet propagation has relationship with the movement of trough and wedge.