Distilling the mechanism for the Madden–Julian Oscillation into a simple translating structure,Quarterly Journal of the Royal Meteorological Society

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Distilling the mechanism for the Madden–Julian Oscillation into a simple translating structure
Quarterly Journal of the Royal Meteorological Society ( IF 3.0 ) Pub Date : 2021-06-21 , DOI: 10.1002/qj.4114
Geoffrey K. Vallis ₁

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This article presents a minimal model of the Madden–Julian Oscillation (MJO), isolating a robust mechanism that leads to the observed characteristic pattern and eastward propagation. A localized heat source at the Equator leads to a Gill-like pattern in the geopotential, with moist air converging toward the heat source. Over a fairly wide range of parameters, the moisture convergence is found to be slightly to the east of the heat source, with moist air advected in from the east along the Kelvin lobe meeting slightly drier air advected meridionally around the Rossby lobes. The associated condensation then gives rise to a heat source that also is east of the original one, thus causing the pattern itself to propagate east with dryer regions both to the east and west of the region of precipitation. The speed of the propagation is limited by the ability of the moisture advection to move the condensational heat source; it thus scales with the fluid speed which is induced by the convective heat source, and so with the strength of the convective heating, and not with a gravity wave speed. The propagation speed also increases with the nominal offset between the centre of the pattern and the subsequent moistening and condensation. In the real world this distance, as well as the level and coherence of condensation, are determined not only by the location of moisture convergence but also by the complex physics of convection in the tropical environment. Thus, even though the underlying MJO mechanism is itself not complicated, its reproduction will depend rather sensitively on model parameters in simulations with comprehensive numerical models.

中文翻译：

将 Madden-Julian Oscillation 的机制提炼成一个简单的转换结构

本文提出了马登-朱利安振荡 (MJO) 的最小模型，隔离了导致观察到的特征模式和向东传播的稳健机制。赤道的局部热源导致地势中出现类似鳃的模式，潮湿的空气会向热源汇聚。在相当广泛的参数范围内，发现湿气会聚稍微偏向热源的东面，潮湿空气沿着开尔文瓣从东面平流进入，与稍微干燥的空气在罗斯比瓣周围沿子午平流相遇。然后相关的冷凝产生一个热源，它也位于原始热源的东边，从而导致模式本身向东传播，降水区域的东部和西部都有干燥区域。传播速度受水分平流移动凝结热源的能力的限制；因此，它与由对流热源引起的流体速度成比例，因此与对流加热的强度成比例，而不是与重力波速度成比例。传播速度也随着图案中心与随后的润湿和凝结之间的标称偏移而增加。在现实世界中，这个距离以及凝结的水平和连贯性不仅取决于湿气汇聚的位置，还取决于热带环境中复杂的对流物理。因此，即使潜在的 MJO 机制本身并不复杂，它的再现将相当敏感地依赖于具有综合数值模型的模拟中的模型参数。

更新日期：2021-08-04

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