西北太平洋季内振荡的多尺度扰动及其对热带气旋生成的调制研究

An intimate association between tropical cyclone (TC) genesis and intraseasonal oscillation (ISO) over the western North Pacific has been widely documented. Moreover, the ISO over the western North Pacific exhibit a pronounced multi-scale organization, including the two dominant ISO modes, its strong modulation on synoptic waves, as well as its close linkage to the monsoon trough variability. Despite of many existing studies in this field, it remains largely unknown regarding the key processes responsible for the intraseasonal modulation of TC activity, which leaves us disadvantaged in conducting extended-range TC predictions. This proposed research is aimed at improved understanding of key physics in regulating tropical cyclone (TC) activity on intraseasonal time scales. Three main objectives will be carried out during this study: (1) to investigate the evolution features of ISO, including its propagation, vertical / horizontal structures, and accompanying energy exchange and transport. The relationship between ISO and monsoon trough variability as well as synoptic scale disturbances will be closely explored; (2) to examine the effect of multi-scale circulation and their interactions during the evolution of ISO on monsoon trough variation. The key dynamical and thermo-dynamical processes closely associated with intraseasonal variability of monsoonal circulation as well as activity of synoptic disturbances will be investigated. Meanwhile, physical processes for the transition from synoptic-scale disturbances to TC will be studied and a conceptual model of TC genesis will be proposed; (3) to conduct suites of numerical experiments with ideal cases,sensitive cases and specifically selected observed cases to further validate the mechanisms derived in (2) on the multi-scale interactions between ISO, monsoon trough, synoptic disturbances, and TC genesis. Results of this study will greatly improve our understanding of the essential physical processes in modulating intraseasonal variability of TC activity, which provide scientific foundation for the predictability of TC on intraseasonal time scales. This study will thus benefit short-term climate prediction of TC activities over the western North Pacific based on both statistical and dynamical approaches.

本项目试图以多尺度环流相互作用为切入点，从季风槽活动变化的角度揭示季内振荡(ISO)调制西北太平洋热带气旋(TC)生成的物理机制。为此，将（1）利用观测资料系统分析ISO的结构传播特征和能量演变过程，揭示其传播过程中季风槽活动、天气尺度扰动、TC生成的季内演变规律及其它们之间的关联；（2）研究ISO传播过程中不同尺度环流系统及相互作用对季风槽活动的影响，应用动力学理论和能量诊断方法探讨与季风环流有关的动力和热力过程在天气尺度扰动季内变化中所扮演的角色，并理解天气尺度扰动发展为TC的物理过程，从而给出可能概念模型；（3）通过设计一系列理想、典型年份个例模拟和敏感性试验，验证资料诊断和理论分析所得到的结果，揭示影响TC生成的关键因子和重要物理过程。预期项目完成将有助于揭示TC季内变化的物理本质，同时也为西北太平洋TC季内/延伸期和短期气候预测提供科学的理论依据。

2014-2016年项目执行期间，按照计划书的研究内容和科学目标展开系统研究。利用多套高分辨再分析资料和数值模式，通过资料分析和动力诊断等手段针对低频振荡对西北太平洋（WNP）热带气旋（TC）生成的调制作用及其机理进行了深入的研究。经过3年的研究，在低频振荡对西北太平洋热带气旋生成的调制研究方面取得了较多的创新研究成果。共发表相关的研究论文共16篇，其中在国际主流Journal of Climate, Climate Dynamics, Journal of Advances in Modelling Earth Systems, Journal of Applied Meteorology and Climatology 等学术刊物上发表SCI(E)收录论文12篇。项目全面并部分超额完成项目计划书的研究任务和科学目标。.项目的主要研究成果归纳如下：1)系统地考察了WNP夏季季内振荡(ISO:MJO与QBWO)的传播特征和伴随着ISO传播的大尺度环流场尤其季风槽的演变特征，及其与WNP TC之间的关系，揭示了夏季ISO对WNP TC的显著调制作用；2)定量分析了夏季ISO诱发的不同大尺度环境因子调制WNP TC的贡献，揭示了中层相对湿度和低层相对涡度是两个关键环境因子；3）首次分析了ISO对五类大尺度环流型（季风切变线、热带辐合带、季风涡旋，东风波、热带气旋能量频散）相联系的WNP TC的影响，加深了对夏季ISO对WNP TC的大尺度调制过程的认识; 4)系统地分析了夏季ISO对WNP TC初始扰动之一-天气尺度波列的调制作用，从动力和能量角度揭示了影响天气尺度波列发展的关键因子，分析了夏季ISO对天气尺度波列发展的调制，并进一步发展为TC的物理过程， 揭示了ISO调制TC生成的可能物理本质。5）揭示了路径是海盆尺度热带气旋强度变化尤其是强台风的关键因子；发现了WNP TC活动年代际变化的另一种可能的物理原因-PDO与ENSO年代际关系的调整及MJO-TC关系的年代际关系的调整；完善了WNP TC季节活动理论模式系统；获得了WNP TC气候变化的新认识。.本项目的研究成果加深理解ISO对WNP TC季内生成的调制作用，揭示了WNP TC季内变化的可能物理机制，获得了WNP TC气候变化的新认识，为WNP TC延伸期预报和气候预测提供了科学的理论基础。