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A study on quasi-biweekly oscillation around Himalaya, Assam and Bangladesh regions

喜马拉雅、阿萨姆邦和孟加拉国地区准双周振荡研究

基本信息

批准号：
22340137
负责人：
YASUNARI Tetsuzo
金额：
$ 11.9万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2010
资助国家：
日本
起止时间：
2010 至 2012
项目状态：
已结题

项目摘要

This study elucidated a process of distinct rainfall fluctuation related to quasi-biweekly Oscillation (QBW) over Himalaya-Assam-Bangladesh (HAB) region, where one of the heaviest rainfall is observed in the world, by means of data analysis and a numerical simulation. QBW in rainfall became a dominant mode of intraseasonal oscillation since 1980s around Bangladesh. QBW in rainfall over HAB region is most active, especially in Meghalaya plateau and the western coast of Myanmar, in land areas of Asian monsoon. In active (break) phase of rainfall in QBW in the HAB region, a low-level westerly/southwesterly (easterly/southeasterly) is dominated there. The large zonal wind fluctuation is induced by westward propagating n=1 equatorial Rossby wave with a wave length of ~6000 km. Rainfall in active phase of QBW often shows a remarkable diurnal variation around the Meghalaya plateau.The variation is caused by diurnal variation of low-level jet around 900 hPa. Thestrong low-level flow transports abundant moisture to the southern slope of the Meghalaya Plateau during the active period, which triggers forced lifting and brings orographic rainfall. However, low-level wind during the inactive period is too weak to induce orographic rainfall. Thus, the distinct QBW in HAB region is strongly enhanced locally (~500Km) by the topographical features although atmospheric circulation causing the ISO has horizontal scale of ~6000 Km.

本文通过资料分析和数值模拟，揭示了世界上最大降水区之一的喜马拉雅-阿萨姆-孟加拉（HAB）地区降水的准双周振荡过程。自20世纪80年代以来，孟加拉国降水的QBW成为季节内振荡的主导模态。HAB地区降水中QBW最活跃，尤其是亚洲季风陆地区的梅加拉亚高原和缅甸西海岸。在暴雨活跃（中断）阶段，低层西风/西南风（东风/东南风）占主导地位。大的纬向风脉动是由波长约6000 km的n=1赤道Rossby波向西传播引起的。QBW活跃期的降水在梅加拉亚高原附近常表现出明显的日变化，这种变化是由900 hPa附近低空急流的日变化引起的。强低空气流在活跃期向梅加拉亚高原南坡输送了大量的水汽，触发了强迫抬升，带来了地形性降水。然而，低层风在非活跃期太弱，导致地形降雨。因此，虽然引起ISO的大气环流具有约6000 Km的水平尺度，但HAB区域的明显QBW在局部（约500 Km）被地形特征强烈增强。