Scale Analysis of Moist Thermodynamics in a Simple Model and the Relationship between Moisture Modes and Gravity Waves
Scale Analysis of Moist Thermodynamics in a Simple Model and the Relationship between Moisture Modes and Gravity Waves
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简单模型中潮湿热力学的尺度分析以及湿度模态与重力波之间的关系
DOI：
10.1175/jas-d-19-0121.1
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发表时间：
2019
影响因子：
3.1
通讯作者：
Inoue, Kuniaki
中科院分区：
文献类型：
--
作者：
Adames, Ángel F.;Kim, Daehyun;Clark, Spencer K.;Ming, Yi;Inoue, Kuniaki
对流耦合赤道波的观测和理论表明，它们可以分为两个不同的组。湿度模式是其热力学受湿度波动控制的波。另一方面，重力波群的热力学根源于浮力（温度）波动。在尺度分析的基础上，发现一个简单的无量纲参数——类似于罗斯贝数——可以解释导致这两个群存在的过程。该参数定义为Nmode，表示当异常对流持续足够长的时间，干燥重力波消除了对流区域的温度异常，满足弱温度梯度（WTG）平衡时，就会出现湿度模式。这个过程导致水分异常主导湿焓（或湿静态能量）的分布，从而主导波的演化。相反，当反常对流消除水分异常的速度比干重力波更快时，就会出现对流耦合重力波，从而将对流层调整至WTG平衡，从而导致温度控制湿焓的分布和演化。再分析数据的频谱分析表明，缓慢传播的波（cp~3 m s−1）很可能是水分模式，而快波（cp~30 m s−1）则表现出重力波行为，其间存在“混合水分重力”波。虽然这些发现是从高度理想化的框架中获得的，但假设它们可以扩展到理解 GCM 中对流耦合波的模拟以及更复杂现象的热力学。
Observations and theory of convectively coupled equatorial waves suggest that they can be categorized into two distinct groups. Moisture modes are waves whose thermodynamics are governed by moisture fluctuations. The thermodynamics of the gravity wave group, on the other hand, are rooted in buoyancy (temperature) fluctuations. On the basis of scale analysis, it is found that a simple nondimensional parameter—akin to the Rossby number—can explain the processes that lead to the existence of these two groups. This parameter, defined asNmode, indicates that moisture modes arise when anomalous convection lasts sufficiently long so that dry gravity waves eliminate the temperature anomalies in the convective region, satisfying weak temperature gradient (WTG) balance. This process causes moisture anomalies to dominate the distribution of moist enthalpy (or moist static energy), and hence the evolution of the wave. Conversely, convectively coupled gravity waves arise when anomalous convection eliminates the moisture anomalies more rapidly than dry gravity waves can adjust the troposphere toward WTG balance, causing temperature to govern the moist enthalpy distribution and evolution. Spectral analysis of reanalysis data indicates that slowly propagating waves (cp~ 3 m s−1) are likely to be moisture modes while fast waves (cp~ 30 m s−1) exhibit gravity wave behavior, with “mixed moisture–gravity” waves existing in between. While these findings are obtained from a highly idealized framework, it is hypothesized that they can be extended to understand simulations of convectively coupled waves in GCMs and the thermodynamics of more complex phenomena.
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