热带季节内振荡与天气尺度扰动之相互作用

The Intraseasonal Oscillation [ISO; aka The Madden-Julian Oscillation (MJO)] is the most prominent mode of intraseasonal variability in the tropics. As it propagates eastward along the equator, the ISO exerts influences upon the weather and climate systems in various regions. Understanding the ISO structures and dynamics is the key to increasing the capability of extended-range weather forecasting. This proposal aims to use both the multi-agencies sponsored DYNAMO/CINDY2011 field campaign data plus new-generation high-resolution (20-50km) reanalysis data, and conduct numerical experiments to investigate the multi-scale structures of the ISO, as well as the physical processes of scale interaction over the tropics. The main tasks in this proposal consist of 1) making an analysis of how the ISO phase and its associated circulation affect the activity of high-frequency disturbances; 2) making a diagnosis of possible upscale feedback processes of synoptic-scale perturbations to the ISO (such as eddy momentum transport, atmospheric heating/moisture processes, and air-sea heat flux); and 3) clarifying the mechanisms of scale interaction by carrying out numerical experiments. The merit of this project is to advance the understanding of tropical climate dynamics, which may further benefit the development and improvement of model physics on ISO simulation and prediction.

季节内振荡为热带大气季节内尺度变化之主要模态，其发展与移动过程中对不同地区的天气和气候系统将产生显著影响，了解季节内振荡之特征结构与动力机制是提高延伸期预报能力之关键。本项目拟利用国际最新大型季节内振荡观测计划DYNAMO/CINDY2011数据和最新一代高分辨率（20-50 km）再分析资料，结合数值试验，对季节内振荡之多重尺度特征和尺度相互作用过程的物理机制进行研究。主要内容包含：1) 分析季节内振荡对流相位和环流场如何影响其波包内高频天气尺度扰动的结构与演化；2) 诊断热带天气尺度扰动可能的升尺度反馈过程（扰动动能传播、大气加热过程、水汽过程、海-气热通量）及各过程对季节内振荡发生、发展和移动的相对贡献；3) 数值敏感性试验验证观测诊断结果，并明确尺度相互作用之物理机制。项目研究成果将提升对热带气候动力过程之理解，且为改进模式模拟和预报季节内振荡提供依据。

本项目利用DYNAMO外场观测数据、最新高分辨率再分析数据并结合数值试验，研究季节内振荡（MJO）的多重尺度特征及其与高频天气尺度系统相互作用的物理过程。主要的研究成果：1）确认了海气相互作用对MJO发展和传播的关系，MJO的潜热通量有利对流增强，但不利于东传；2）然而MJO波包内的高频天气尺度扰动可以透过非线性海气相互作用反馈影响MJO的增强和东传；3）赤道对流耦合波动可透过垂直平流在MJO对流东侧引发西风趋势，有利MJO对流–环流系统的东传；4）MJO的位相和生命阶段对高频天气尺度产生不同的调控作用，天气尺度波动在赤道MJO对流中心及其西侧垂直东风切变地区较为活跃；5）数值敏感性试验证实了观测诊断结果，当模式中与潜热通量有关的高频天气尺度系统去掉后，MJO东传信号减弱。项目研究成果提升了对热带气候动力过程的理解，并提供了改进模式模拟和预报季节内振荡的依据。