Effects of the South Asian Monsoon Intraseasonal Modes on Genesis of Low Pressure Systems over Bangladesh
Effects of the South Asian Monsoon Intraseasonal Modes on Genesis of Low Pressure Systems over Bangladesh
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DOI：
10.1175/jcli-d-16-0360.1
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发表时间：
2017-04-01
影响因子：
4.9
通讯作者：
Fujinami, Hatsuki
中科院分区：
文献类型：
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作者：
Hatsuzuka, Daisuke;Fujinami, Hatsuki
准双周振荡（QBW）是孟加拉国夏季降水的主要季节内模态。QBW的活跃阶段通常伴随着低压系统（LPS），如涡型低压。本研究探讨了两个季节内模态，QBW和北方夏季季节内振荡（BSISO），在孟加拉国的LPS的成因在29个夏季风季节的影响。每日滞后复合对流和低层大气环流的活跃阶段的情况下，LPS（LPS的情况下）和无LPS（非LPS的情况下）的基础上，在孟加拉国QBW降雨。在QBW模态中，从西太平洋到孟加拉湾（BoB）的反气旋异常向西传播在这两种情况下都是常见的。然而，在LPS的情况下，反气旋中心位于略偏东的非LPS的情况下，这导致更强的气旋性涡孟加拉国和周围。相反，BSISO模式显示了两种情况之间的相反相位：在LPS情况下（非LPS情况下），气旋（反气旋）异常从赤道向北传播到BoB。在LPS的情况下，在BSISO模式的气旋异常增强的西风（东风）流在活跃阶段的孟加拉国的BoB（孟加拉国），导致在北方BoB和孟加拉国的气旋性涡度的增强，在QBW模式的合作。这些结果表明，无论是QBW和BSISO模式有显着的环境条件的LPS在孟加拉国的成因影响。
The quasi-biweekly oscillation (QBW) is a dominant intraseasonal mode in summer rainfall over Bangladesh. Active phases of the QBW are often accompanied by low pressure systems (LPSs) such as vortex-type lows. This study investigated the effects of two intraseasonal modes, the QBW and the boreal summer intraseasonal oscillation (BSISO), on the genesis of LPSs over Bangladesh during 29 summer monsoon seasons. Daily lag composites of convection and low-level atmospheric circulation were constructed for active-phase cases with LPSs (LPS case) and without LPSs (non-LPS case) based on rainfall in the QBW over Bangladesh. In the QBW mode, a westward propagation of an anticyclonic anomaly from the western Pacific to the Bay of Bengal (BoB) is common in both cases. However, the anticyclonic center in the LPS case is located slightly to the east of that in the non-LPS case, which results in stronger cyclonic vorticity over and around Bangladesh. In contrast, the BSISO mode shows an opposite phase between the two cases: a cyclonic (anticyclonic) anomaly propagating northward from the equator to the BoB in the LPS case (non-LPS case). In the LPS case, the cyclonic anomaly in the BSISO mode enhances the westerly (easterly) flow over the BoB (Bangladesh) in the active phase, resulting in the enhancement of cyclonic vorticity over the northern BoB and Bangladesh, in cooperation with the QBW mode. These results suggest that both the QBW and BSISO modes have significant influence on the environmental conditions for LPS genesis over Bangladesh.