摘要:采用观测分析和数值试验等方法，分析夏季南亚高压与热带季节内振荡（ISO）之间的关系，并对两者之间的相互作用进行量化诊断，探讨其物理过程。主要结果表明：南亚高压ISO与热带ISO活动关系密切，当热带ISO处于印度洋位相（第1、2、3位相），则南亚高压东脊点位置偏西，当ISO处于太平洋位相（第5、6、7位相），则南亚高压东脊点位置偏东。与热带ISO关系最密切的是南亚高压东部附近区域，即东亚—西太平洋地区（15°～25°N，110°～140°E），该关键区也是南亚高压ISO最显著区域。在热带ISO的调制下，关键区对流层大气垂直结构产生斜压性异常变化，导致高层南亚高压东脊点的东伸（西退）对应中低层西太平洋副热带高压西脊点的东退（西伸）。在南亚高压与热带ISO之间关系中，主要是热带ISO对南亚高压的影响，南亚高压东部关键区ISO强度40%来源于热带ISO的贡献，而南亚高压对热带ISO平均强度的影响很弱。热带ISO影响南亚高压的物理过程如下，热带ISO从印度洋向东传播至西太平洋时，强对流产生分支，部分由于东亚—西太平洋的有利夏季风背景转为向北传播，ISO向北传播过程中对流强度进一度加强，这就相当于存在一个赤道非对称热源。在热源的作用下，大气产生异常响应，在热源的西北侧，即东亚—西太平洋地区，对流层低层为气旋性环流异常、位势高度负异常，对流层高层为反气旋性环流异常、位势高度正异常，从而导致南亚高压东脊点偏东。而当热带ISO处于印度洋位相时，大气异常响应与上述相反，南亚高压东部位势高度降低，南亚高压东脊点西撤。
关键词:季节内振荡(ISO)/
南亚高压/
东脊点/
斜压/
东伸/
西退
Abstract:The relationship between the tropical ISO (intraseasonal oscillation) and the intraseasonal variation of the SAH (South Asian high) in boreal summer and the associated physical mechanisms are investigated by using both the observational data analysis and numerical model experiments. The results indicate that the intraseasonal variation of SAH is closely related to the tropical ISO activity. The eastern edge of SAH shifts westward when the active phase of the tropical ISO appears in Indian Ocean (including Phase 1, 2, and 3), and shifts eastward when the ISO appears in Pacific (including Phase 5, 6 and 7). The most sensitive region in response to the tropical ISO forcing is over the eastern part of SAH, which is the region connecting East Asia and western Pacific (15°–25°N, 110°–140°E). The vertical profile of tropospheric atmosphere in the region exhibits a baroclinic structure. An eastward extension (westward retreat) of the eastern edge of SAH corresponds well to an eastward retreat (westward extension) of the western edge of the WPSH (western Pacific subtropical high) in the middle and lower troposphere. The intraseasonal variability of SAH is primarily affected by the tropical ISO. About 40% of the variability in the key region is attributed to the tropical ISO, whereas the influence of the SAH on the tropical ISO is weak. The physical processes by which the tropical ISO affects SAH are summarized as follows: As the tropical ISO moves from the Indian Ocean to the western Pacific, part of the convection branches out and propagates northward under the favorable background state of the summer monsoon, which further strengthens the convection. To the northwest of the ISO heat source, cyclonic circulations and negative height anomalies (anticyclonic circulation and positive height anomalies) appear in the lower (upper) troposphere, which leads to the eastward extension of SAH. However, when the tropical ISO appears in the Indian Ocean, the atmospheric circulation responses are in general opposite to the above, leading to the westward retreat of SAH.
Key words:Intraseasonal oscillation (ISO)/
South Asian high (SAH)/
Eastern edge of SAH/
Baroclinicity/
Eastward extension/
Westward retreat
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