The Stirring Tropics: Theory of Moisture Mode–Hadley Cell Interactions
The Stirring Tropics: Theory of Moisture Mode–Hadley Cell Interactions
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搅拌热带：水分模式理论 - 哈德利细胞相互作用
DOI：
10.1175/jcli-d-23-0147.1
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发表时间：
2023
影响因子：
4.9
通讯作者：
Mayta, Víctor C.
中科院分区：
文献类型：
--
作者：
Adames Corraliza, Ángel F.;Mayta, Víctor C.
本文用一个平面上的线性两层模型研究了大尺度波与Hadley环流的相互作用。一个线性的非正交湿度梯度决定了理想化Hadley胞的强度。信风处于热成风平衡状态，温度梯度较弱。平均纬向湿度梯度是不稳定的天气尺度（水平尺度为1000公里）的湿度模式，向西平流的信风，让人想起海洋热带低压波。经向水汽平流导致水汽模态从“水汽涡旋不稳定性”（MVI）发展而来，导致极向涡动水汽通量增加纬向平均纬向水汽梯度，从而削弱Hadley环流。以纬向平均纬向湿度梯度为代价的波的放大意味着一个尺度下的潜能级联。涡动水汽通量与Hadley环流的涡动水汽梯度的再生相反。这些Hadley细胞水分模式的相互作用让人想起准地转相互作用，除了波活动是由于柱水分方差，而不是位涡方差。这种相互作用可以导致水分模式活动和Hadley细胞强度中的捕食者-被捕食者循环，这类似于ITCZ分解。本文认为水汽模态是中纬度斜压波的热带模拟。MVI类似于斜压不稳定性，以干斜压涡旋搅动感热的相同方式搅动潜能。这些结果表明，水分模式稳定的Hadley细胞，并可能是重要的，因为后者在全球能源transfer.Significance StatementThe热带的特点是稳定的环流，如Hadley细胞以及动物园的热带天气系统。尽管我们对两者的理解都取得了进展，但对平均环流和天气系统如何相互作用知之甚少。在这里，我们表明，热带波可以通过从哈德利环流中提取水分来增长，从而削弱它。它们还将水分输送到高纬度地区。我们的研究结果挑战了哈德利环流是热带地区唯一的能量输送者的观点，相反，我们支持热带波对全球能量平衡也至关重要的观点。它们通过搅拌使潮湿区域干燥并使干燥区域湿润。
Interactions between large-scale waves and the Hadley cell are examined using a linear two-layer model on anfplane. A linear meridional moisture gradient determines the strength of the idealized Hadley cell. The trade winds are in thermal wind balance with a weak temperature gradient (WTG). The mean meridional moisture gradient is unstable to synoptic-scale (horizontal scale of ∼1000 km) moisture modes that are advected westward by the trade winds, reminiscent of oceanic tropical depression–like waves. Meridional moisture advection causes the moisture modes to grow from “moisture-vortex instability” (MVI), resulting in a poleward eddy moisture flux that flattens the zonal-mean meridional moisture gradient, thereby weakening the Hadley cell. The amplification of waves at the expense of the zonal-mean meridional moisture gradient implies a downscale latent energy cascade. The eddy moisture flux is opposed by a regeneration of the meridional moisture gradient by the Hadley cell. These Hadley cell–moisture mode interactions are reminiscent of quasigeostrophic interactions, except that wave activity is due to column moisture variance rather than potential vorticity variance. The interactions can result in predator–prey cycles in moisture mode activity and Hadley cell strength that are akin to ITCZ breakdown. It is proposed that moisture modes are the tropical analog to midlatitude baroclinic waves. MVI is analogous to baroclinic instability, stirring latent energy in the same way that dry baroclinic eddies stir sensible heat. These results indicate that moisture modes stabilize the Hadley cell and may be as important as the latter in global energy transport.Significance StatementThe tropics are characterized by steady circulations such as the Hadley cell as well as a menagerie of tropical weather systems. Despite progress in our understanding of both, little is known about how the mean circulations and the weather systems interact with one another. Here we show that tropical waves can grow by extracting moisture from the Hadley cell, thereby weakening it. They also transport moisture to higher latitudes. Our results challenge the notion that the Hadley cell is the sole transporter of energy out of the tropics and instead favor a view where tropical waves are also essential for the global energy balance. They dry the humid regions and moisten the drier regions via stirring.