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大气科学  2007 

夏季热带东风急流的结构、变化及其与亚非季风降水的关系

DOI: 10.3878/j.issn.1006-9895.2007.05.16

Keywords: 热带东风急流,季风降水,垂直环流

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Abstract:

使用NCEP/NCAR再分析资料研究热带东风急流(TEJ)的长期变化及其与亚非降水分布的关系。用150~100hPa纬向风代表TEJ,并定义了一个指数(TEJI)来度量急流的变率。分析发现,TEJ主要覆盖了热带地区从日界线向西延伸到非洲西海岸的大片地区,其核心位于150~100hPa印度半岛南部10°N~15°N,中心风速超过30m/s。急流中线大致位于70°E,以东是急流的入口区,以西是出口区。在入口区急流轴线有两个分支,南支位于0°~10°N,呈西北东南走向,北支位于10°N~20°N,呈西南东北走向。TEJ存在40~60天和20~30天的季节内振荡周期,以及2~4年和7~10年的周期变化。出现暖事件时TEJ减弱,出现冷事件时TEJ加强。TEJ存在明显的年代际变化,1978年是其气候突变点,突变前为强TEJ时期,突变后TEJ显著减弱。亚洲和中非的主要降水带、对流区、高层辐散及大尺度上升运动都出现在东风急流入口区的右侧及出口区的左侧,但出口区西非的情况略显复杂。在急流的入口区和出口区存在两个近于相反的垂直环流,它们与降水分布密切有关。在急流的入口区,强TEJ年其垂直环流更强,其右侧的降水也更大;但在急流的出口区,强、弱TEJ年的垂直环流没有明显差异,其左侧的降水也没有明显差异。

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