Core Dynamics of the MJO
Core Dynamics of the MJO
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DOI：
10.1175/jas-d-20-0193.1
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发表时间：
2020-10
影响因子：
3.1
通讯作者：
Ji Eun Kim;Chidong Zhang
中科院分区：
文献类型：
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作者：
Ji Eun Kim;Chidong Zhang
马登-朱利安振荡（MJO）是一个大尺度的向东移动的系统，主导着热带亚季节扰动，对全球天气气候产生深远的影响。自发现以来的近半个世纪里，尽管人们提出了许多理论进行了深入的研究，但对MJO最基本的动力学还没有达成共识。在这项研究中，使用一个简单的分析方法，我们发现了一个解决方案的线性赤道浅水方程的动量阻尼，类似于一个谐振子。这个解决方案展示了观测到的MJO的关键特征：在行星尺度上的季节内周期性和向东传播。与将MJO解释为水分演变中出现的新的变异模式的理论相反，我们的解决方案强调MJO的核心在于水分没有明确波动的动态。水分仍然在为MJO的核心动力学提供能量方面发挥作用，并确定理论所需的等效深度值。能量来源可能来自热带随机强迫，也可能来自热带外。MJO的尺度选择来自尺度相关的响应，尺度无关的瑞利阻尼。我们还表明，这里介绍的MJO解决方案再现所观察到的燕尾结构和纬向风和位势的MJO之间的相位关系，以及MJO和开尔文波之间的过渡的连续性。在MJO的反馈机制的作用也讨论了使用相同的简单的数学框架。
The Madden–Julian oscillation (MJO) is a large-scale eastward-moving system that dominates tropical subseasonal perturbations with far-reaching impacts on global weather–climate. For nearly a half century since its discovery, there has not been a consensus on the most fundamental dynamics of the MJO, despite intensive studies with a number of theories proposed. In this study, using a simple analytical approach, we found a solution to the linear equatorial shallow-water equations with momentum damping that resembles a harmonic oscillator. This solution exhibits the key characteristics of the observed MJO: its intraseasonal periodicity at the planetary scale and eastward propagation. In contrast to theories that interpret the MJO as a new mode of variability emerging from the evolution in moisture, our solution emphasizes that the core of the MJO resides in the dynamics without explicit fluctuations in moisture. Moisture still plays a role in supplying energy to the core dynamics of the MJO, and determining the value of the equivalent depth required by the theory. The energy source may come from stochastic forcing in the tropics or from the extratropics. The scale selection for the MJO comes from scale-dependent responses to scale-independent Rayleigh damping. We also demonstrate that the MJO solution introduced here reproduces the observed swallowtail structure and the phase relation between zonal wind and geopotential of the MJO, and the continuum nature of the transition between the MJO and Kelvin waves. Roles of feedback mechanisms in the MJO are also discussed using the same simple mathematical framework.