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首页> 外文期刊>Climate dynamics >Dynamics of distinct intraseasonal oscillation in summer monsoon rainfall over the Meghalaya-Bangladesh-western Myanmar region: covariability between the tropics and mid-latitudes
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Dynamics of distinct intraseasonal oscillation in summer monsoon rainfall over the Meghalaya-Bangladesh-western Myanmar region: covariability between the tropics and mid-latitudes

机译：梅加拉亚邦-孟加拉-西部缅甸西部地区夏季风季风中不同季节内振荡的动态：热带与中纬度之间的协变性

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摘要

Detailed spatiotemporal structures for the sub-monthly-scale (7-25 days) intraseasonal oscillation (ISO) in summer monsoon rainfall and atmospheric circulation were investigated in South Asia using high-quality rainfall and reanalysis datasets. The Meghalaya-Bangladesh-coast of the western Myanmar (MBWM) region is the predominant area of submonthly-scale ISO in the Asian monsoon regions. The distinct rainfall ISO is caused by a remarkable alternation of low-level zonal wind between westerly and easterly flows around the Gangetic Plain on the same timescales. In the active ISO phase of the MBWM, a strong low-level westerly/southwesterly flows around the plain and a center of cyclonic vorticity appears over Bangladesh. Hence, a local southerly flows toward the Meghalaya Plateau and there is strong southwesterly flow towards the coast along southeastern Bangladesh and western Myanmar, resulting in an increase in orographic rainfall. Rainfall also increases over the lowland area of the MBWM due to the low-level convergence in the boundary layer under the strong cyclonic circulation. The submonthly-scale low-level wind fluctuation around the MBWM is caused by a westward moving n = 1 equatorial Rossby (ER) wave. When the anticyclonic (cyclonic) anomaly related to the ER wave approaches the Bay of Bengal from the western Pacific, humid westerly/southwesterly (easterly/southeasterly) flows enhance around the Gangetic Plain on the northern fringe of the anticyclone (cyclone) and in turn promote (reduce) rainfall in the MBWM. Simultaneously, robust circulation signals are observed over the mid-latitudes. In the active phase, cyclonic anomalies appear over and around the TP, having barotropic vertical structure and also contributing to the enhancement of low-level westerly flow around the Gangetic Plain. In the upper troposphere, an anticyclonic anomaly is also observed upstream of the cyclonic anomaly over the TP, having wavetrain structure. The mid-latitude circulation around the TP likely helps to induce the distinct ISO there in conjunction with the equatorial waves. Thus, the distinct ISO in the MBWM is strongly enhanced locally (～ 500 km) by the terrain features, although the atmospheric circulation causing the ISO has a horizontal scale of ～ 6,000 km or more, extending across the whole Asian monsoon system from the tropics to mid-latitudes.
机译：使用高质量的降雨和再分析数据集，对南亚夏季季风降雨和大气环流中每个月以下尺度（7-25天）的季节内振荡（ISO）的详细时空结构进行了调查。缅甸西部（MBWM）地区的Meghalaya-Bangladesh-Coast是亚洲季风区域次月级ISO的主要区域。独特的降雨ISO是由于在相同的时间尺度上恒河平原周围的西风和东风之间低空纬向风的显着交替引起的。在MBWM的活动ISO阶段，强烈的低水平西风/西南风围绕平原流动，并且在孟加拉国上方出现了旋风涡旋中心。因此，当地向南流向梅加拉亚高原，向西南流向沿孟加拉国东南部和缅甸西部的海岸，导致地形降雨增加。由于强旋风循环下边界层的低水平收敛，MBWM低地地区的降雨也增加了。 MBWM周围的次月尺度低水平风波动是由向西移动的n = 1赤道Rossby（ER）波引起的。当与ER波有关的反气旋（气旋）异常从西太平洋到达孟加拉湾时，西风/西南风（东/东风）的湿气流在反气旋（旋风）北缘的恒河平原周围流动增强，反过来又反过来促进（减少）MBWM中的降雨。同时，在中纬度地区观测到了强劲的环流信号。在活动期，气旋异常出现在TP上方和周围，具有正压垂直结构，也有助于增强恒河平原周围的低层西风流动。在对流层上方，在TP上方的旋风异常上游也观察到了反旋风异常，具有波列结构。 TP周围的中纬度环流很可能有助于与赤道波一起在那诱发不同的ISO。因此，尽管造成ISO的大气环流的水平尺度从热带地区延伸到整个亚洲季风系统，但由于地形特征，MBWM中独特的ISO局部增强了（约500 km）。到中纬度。

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