Purpose of Review

Our understanding of the Madden-Julian Oscillation (MJO) and other tropical motion systems has significantly improved in recent years. This article reviews the contribution of moisture mode theory to this progress.

Recent Findings

Two realizations have contributed significantly to our understanding of the MJO: (1) Free tropospheric water vapor plays an important role in the occurrence and organization of tropical deep convection. (2) The latent heat released in convection is quickly transported around the tropics by gravity waves, the physical mechanism underpinning the weak temperature gradient (WTG) approximation. Simple models of the tropics that include (1) and (2) revealed the existence of moisture modes, waves in which water vapor plays a dominant role in their evolution. It was soon recognized that the MJO exhibits properties of moisture modes. The ensuing development and application of the so-called moisture mode theory of the MJO have led to the recognition that horizontal and vertical moisture advections are central to the propagation of the MJO, and that cloud-radiative heating is at least partially responsible for its maintenance. Moisture mode theory has also been applied to understand the MJO’s seasonality, Maritime Continent transit, and response to increasing CO₂. Recent work suggests that moisture mode theory can be extended beyond the MJO in order to explain the observed diversity of tropical motion systems.

Summary

A mounting body of evidence indicates that the MJO has properties of moisture modes. Extension of the theory beyond the MJO may help us further understand the processes that drive large-scale tropical circulations.

中文翻译：

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水分模态理论对加深我们对马登-朱利安涛动和其他热带扰动的理解的贡献

审查目的

近年来，我们对马登-朱利安涛动（MJO）和其他热带运动系统的了解有了显着提高。本文回顾了水分模式理论对此进展的贡献。

最近的发现

有两个认识对我们对 MJO 的理解做出了重大贡献：（1）自由对流层水汽在热带深对流的发生和组织中发挥着重要作用。 （2）对流释放的潜热通过重力波在热带地区快速传输，这是弱温度梯度（WTG）近似的物理机制。包括（1）和（2）在内的热带简单模型揭示了水分模式的存在，即水蒸气在其演化过程中起主导作用的波浪。人们很快就认识到 MJO 具有湿气模式的特性。随后，所谓的 MJO 水分模式理论的发展和应用使人们认识到，水平和垂直水分平流是 MJO 传播的核心，而云辐射加热至少部分负责其维持。 。湿度模式理论也被应用于理解 MJO 的季节性、海洋大陆凌日以及对 CO ₂增加的响应。最近的工作表明，水分模式理论可以扩展到 MJO 之外，以解释观测到的热带运动系统的多样性。

概括

越来越多的证据表明 MJO 具有湿气模式的特性。将理论扩展到 MJO 之外可能有助于我们进一步了解驱动大规模热带环流的过程。