Understanding Essential Dynamics and Predictability of Madden-Julian Oscillation (MJO)

这项研究的总体目标是促进对控制Madden-Julian振荡(MJO)传播和发展的基本机制的理解，并提高动力模式模拟和预测季节内变化的能力。通过多模式诊断分析和使用耦合气候模式的数值试验，将探讨MJO缓慢东传和启动/加强的根本原因。MJO遥相关可以反馈到它自己向东传播的过程也将被研究。将被检验的第一个假设集中在决定MJO向东传播的机制上。耦合的Kelvin-Rossby波结构和MJO对流与低压异常之间的位相差异表明，MJO的缓慢东传可能主要是由与赤道低频波相关的动力过程的对流相互作用驱动的。因此，低频波的耦合和摩擦水汽辐合形成的大尺度对流复合体(包络)可能是MJO东移的基本驱动力。局地水汽变化、水汽平流、平均态湿静能(SST)分布、地表熵通量交换、高尺度动量、热量和水汽的涡动输送、环境垂直切变和平流、温带涡旋活动通量、海气混合层相互作用等都能不同程度地改变传播速度。第二个假说涉及加强和维持MJO的机制。对流与波动动力学的相互作用本身并不会产生不稳定性。然而，附加的摩擦水汽辐合与在浅层和稠密云中释放的潜热相互作用，可以通过将平均状态有效湿静能转换为MJO有效势能和动能，为MJO加强产生行星尺度的不稳定性。水汽平流、地面蒸发-风反馈、MJO与高尺度的热量、水汽和动量涡旋输送的相互作用、热带以外的能量传播也可能对MJO的启动和放大起重要作用。

The overall goal of the research is to advance understanding of fundamental mechanisms governing the propagation and development of Madden-Julian Oscillation (MJO) and to improve the ability of dynamical models to simulate and predict intraseasonal variability. Fundamental causes for slow eastward propagation and initiation/intensification of the MJO will be investigated through multi-model diagnostic analysis, and numerical experiments using coupled climate models. Processes through which the MJO teleconnection may feedback to its own eastward propagation will also be examined. The first hypothesis that will be tested focuses on mechanisms determining eastward propagation of the MJO. The coupled Kelvin-Rossby wave structure and the phase difference between the MJO convection and the low pressure anomaly suggest that slow eastward propagation of MJO may be essentially driven by convective interaction with dynamical processes associated with low-frequency equatorial waves. Thus, the coupling low frequency waves and the large scale convective complex (envelope) by frictional moisture convergence may serve as a basic driver for the MJO moving eastward. The local change of moisture, moisture advection, mean state moist static energy (thus SST) distribution, surface entropy flux exchange, upscale eddy transport of momentum, heat and moisture, environmental vertical shear and advection, the extratropical eddy activity flux, and atmosphere-ocean mixed layer interaction can all further modify propagation speed to various degrees. The second hypothesis deals with mechanisms responsible for intensification and maintenance of the MJO. The convective interaction with wave dynamics alone does not generate instability. However, the additional frictional moisture convergence interacting with the latent heat released in shallow and congestus clouds can generate planetary scale instability for MJO intensification through conversion of mean state available moist static energy to MJO available potential and kinetic energy. The moisture advection, the surface evaporation-wind feedback, the interaction between MJO and upscale eddy transport of heat, moisture and momentum, the energy propagation from outside of the tropics may also important for initiation and amplification of the MJO.