印度洋偶极子对孟加拉湾秋季气旋年际变化的调制过程

Bay of Bengal (BoB) frequently suffered the severe disasters because of the hitting of the tropical cyclone (TC). The four cyclones of the top-10 deadliest cyclones in the history occurred in BoB. It is, therefore, very important to study BoB TC. Except the annual cycle, the interannual cycles is also the typical characters of BoB TC. Due to the most BoB TCs formed in the BoB-TC fall (October-November) peak time, the interannual variability of BoB TC was notably showed in the fall peak time. IOD generally reaches the mature period during the boreal fall, and its mature period overlaps the fall peak time of BoB TC well. There, hence, exists the phase lock between them. According to the statistics result, the positive (negative) phase of IOD mode results the less (more) TCs genesis in BoB during October-November. This proposal prepares to develop the diagnosis method in order to quantitively estimate the impact of each environment factor on fall-peak-time BoB TC frequency during IOD. Meanwhile, it would explore the possible process through which the circulation anomaly caused by IOD makes the potential influence to the environment factors (including vorticity, vertical wind shear, relative humidity, sea surface temperature and air temperature). Based on above-mention work, it would be understood well that IOD modulates the interannual cycle of fall-peak-time BoB TC. This study is not only beneficial to understand the story on BoB-TC interannual cycle, but also helpful to further research the trend of BoB-TC interannual activity under the global warming background.

孟加拉湾（BoB）受气旋影响严重，导致最多人员伤亡的前十名气旋中有四个发生在该海域，因此孟加拉湾气旋（BoB_TC）是当今气旋研究中的重点问题。除了典型的季节特征, BoB_TC还存在明显的年际变化。由于BoB_TC主要发生在秋季（10-11月）峰值期，因此它的年际变化显著体现在秋季峰值上。印度洋偶极子(IOD)强盛期发生在秋季，与BoB_TC秋季峰值存在位相锁定关系，所以IOD可通过引起印度洋环流变异进而影响秋季BoB_TC。统计表明IOD正（负）位相中秋季BoB_TC明显偏少（多）。对此，本项目发展诊断方法定量评估IOD中各环境因子对秋季BoB_TC频数的影响。探究IOD引起的BoB区域环流异常影响环境因子的物理过程。在此基础上，构建IOD调制秋季BoB_TC年际变化的物理框架。本项目不仅有助于增进理解BoB_TC的年际变化，还可以为研究全球变暖背景下BoB_TC变化趋势提供参考。

孟加拉湾（BoB）受气旋影响严重，导致最多人员伤亡的前十名气旋中有四个发生在该海域，因此孟加拉湾气旋（BoB_TC）是当今气旋研究中的重点问题。除了典型的季节特征,BoB_TC还存在明显的年际变化。由于BoB_TC主要发生在秋季（10-11月）峰值期，因此它的年际变化显著体现在秋季峰值上。印度洋偶极子(IOD)强盛期发生在秋季，通过统计分析发现IOD强盛期与BoB_TC秋季峰值存在位相锁定关系，所以IOD通过引起印度洋环流变异进而影响秋季BoB_TC。统计结果显示IOD正（负）位相中秋季BoB_TC明显偏少（多）。对此，本项目发展诊断方法定量评估IOD中各环境因子对秋季BoB_TC频数的影响。研究结果指出IOD正（负）位相时，虽然海表温度异常发生在南半球的IOD东极区，但是根据Gill理论， 在赤道以北的孟加拉湾地区出现与东极区类似的反气旋（气旋）Rossby波响应，该地区大气环流呈现气旋（反气旋）异常，通过Ekman抽吸作用，影响中层大气的水汽，最终调制秋季BoB_TC生成频数偏少（多）。这一诊断研究清晰揭示出IOD引起的BoB区域环流异常影响环境因子的物理过程与内在机制。并在此基础上，构建IOD调制秋季BoB_TC年际变化的物理框架。本项目不仅有助于增进理解BoB_TC的年际变化，还可以为研究全球变暖背景下BoB_TC变化趋势提供参考。此外该研究结果对保障该地区海上航行安全，中缅输油管线建设，以及BoB及其周边地区防灾减灾部署都有重要意义。