Can geostrophic adjustment of baroclinic disturbances in the tropical atmosphere explain MJO events?,Quarterly Journal of the Royal Meteorological Society

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Can geostrophic adjustment of baroclinic disturbances in the tropical atmosphere explain MJO events?
Quarterly Journal of the Royal Meteorological Society ( IF 3.0 ) Pub Date : 2020-08-01 , DOI: 10.1002/qj.3884
Masoud Rostami _{1,

2} , Vladimir Zeitlin ₁

Affiliation

Using the two‐layer moist‐convective rotating shallow‐water model, we study the process of relaxation (adjustment) of localized large‐scale pressure anomalies in the lower equatorial troposphere, and show that it engenders coherent structures strongly resembling Madden–Julian Oscillation (MJO) events, as seen in vorticity, pressure, and moisture fields. We demonstrate that baroclinicity and moist convection substantially change the scenario of the quasi‐barotropic “dry” adjustment, which was established in the framework of the one‐layer shallow‐water model and consists, in the long‐wave sector, of the emission of equatorial Rossby waves, with dipolar meridional structure, to the west, and of equatorial Kelvin waves to the east. If moist convection is strong enough, a dipolar cyclonic structure, which appears in the process of adjustment as a Rossby‐wave response to the perturbation, transforms into a coherent modon‐like structure in the lower layer, which couples with a baroclinic Kelvin wave through a zone of enhanced convection and produces, at initial stages of the process, a self‐sustained slowly eastward‐propagating zonally dissymmetrical quadrupolar vorticity pattern. At the same time, a weaker quadrupolar structure of opposite sign arises in the upper layer, the whole picture similar to the active phase of MJO events. The baroclinic Kelvin wave then detaches from the dipole, which keeps slow eastward motion, and circumnavigates the Equator, catching up and interacting with the dipole.

中文翻译：

热带大气中斜压扰动的地转调节可以解释MJO事件吗？

利用两层湿对流旋转浅水模型，我们研究了赤道对流层下部局部大气压异常的松弛（调整）过程，并表明它产生了与马登-朱利安振荡强烈相似的相干结构（ MJO）事件，如在涡度，压力和湿度场中看到的。我们证明，斜压和湿对流大大改变了准正压“干”调整的方案，该方案是在单层浅水模型的框架内建立的，并且在长波范围内构成了对大气的排放。赤道的罗斯比波在西边具有偶极子午线结构，而赤道的开尔文波在东方。如果湿对流足够强，则为偶极气旋结构，在调整过程中表现为对扰动的罗斯比波响应，在下层转换为相干的模子状结构，并与斜压开尔文波耦合通过对流增强区域，并在初始阶段产生。在这个过程中，一个自我维持的，缓慢向东传播的带状不对称四极涡旋模式。同时，在上层出现了相反符号的较弱的四极结构，整个图像类似于MJO事件的活动阶段。然后斜压开尔文波从偶极子脱离，并保持缓慢的向东运动，并绕过赤道，追赶偶极子并与之相互作用。它与斜压开尔文波一起穿过对流增强区，并在该过程的初始阶段产生了一个自我维持的，缓慢向东传播的区域不对称的四极涡度图。同时，在上层出现了相反符号的较弱的四极结构，整个图像类似于MJO事件的活动阶段。然后斜压开尔文波从偶极子脱离，并保持缓慢的向东运动，并绕过赤道，追赶偶极子并与之相互作用。它与斜压开尔文波一起穿过对流增强区，并在该过程的初始阶段产生了一个自我维持的，缓慢向东传播的，区域不对称的四极涡度图。同时，在上层出现了相反符号的较弱的四极结构，整个图像类似于MJO事件的活动阶段。然后斜压开尔文波从偶极子脱离，并保持缓慢的向东运动，并绕过赤道，追赶偶极子并与之相互作用。整个情况类似于MJO事件的活动阶段。然后斜压开尔文波从偶极子脱离，并保持缓慢的向东运动，并绕过赤道，追赶偶极子并与之相互作用。整个情况类似于MJO事件的活动阶段。然后斜压开尔文波从偶极子脱离，并保持缓慢的向东运动，并绕过赤道，追赶偶极子并与之相互作用。

更新日期：2020-08-01

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