Clouds and Radiation in a Mock‐Walker Circulation
Clouds and Radiation in a Mock‐Walker Circulation
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DOI：
10.1029/2020ms002196
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发表时间：
2021-02
影响因子：
6.8
通讯作者：
Levi G. Silvers;T. Robinson
中科院分区：
文献类型：
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作者：
Levi G. Silvers;T. Robinson
Walker环流将热带西太平洋的深层大气对流区域与东太平洋的浅对流、对流层下沉和层积云云层连接起来。本研究的目的是更好地了解沃克环流、云系统和相互作用辐射之间的多尺度相互作用。为了做到这一点，我们使用理想边界条件，用全物理一般环流模型模拟模拟沃克环流。我们的实验使用双周期域，网格间距分别为1、2、25和100公里。因此，我们跨越了从大气环流模式（GCMs）到云系统解析模式（crm）的范围。我们的模型来自地球物理流体动力学实验室大气GCM （AM4.0）。我们发现GCM - like实验和CRM - like实验模拟的模拟Walker环流存在实质性差异。类似CRM的试验有更多的高层云、更强的翻转环流和更少的降水。类似GCM的实验中，低层云的比例要大20%。这些差异导致大气对长波云辐射效应（LWCRE）变化的响应相反。活跃的LWCRE导致gcm降水增加，而CRMs降水减少。LWCRE导致环流的上升分支变窄，并大大增加了大尺度云参数化降水的比例。这项工作表明，模拟-沃克环流是辐射对流平衡的有用推广，包括大尺度环流。
The Walker circulation connects the regions with deep atmospheric convection in the western tropical Pacific to the shallow‐convection, tropospheric subsidence, and stratocumulus cloud decks of the eastern Pacific. The purpose of this study is to better understand the multi‐scale interactions between the Walker circulation, cloud systems, and interactive radiation. To do this we simulate a mock‐Walker Circulation with a full‐physics general circulation model using idealized boundary conditions. Our experiments use a doubly‐periodic domain with grid‐spacing of 1, 2, 25, and 100 km. We thus span the range from General Circulation Models (GCMs) to Cloud‐system Resolving Models (CRMs). Our model is derived from the Geophysical Fluid Dynamics Laboratory atmospheric GCM (AM4.0). We find substantial differences in the mock‐Walker circulation simulated by our GCM‐like and CRM‐like experiments. The CRM‐like experiments have more upper level clouds, stronger overturning circulations, and less precipitation. The GCM‐like experiments have a low‐level cloud fraction that is up to 20% larger. These differences leads to opposite atmospheric responses to changes in the longwave cloud radiative effect (LWCRE). Active LWCRE leads to increased precipitation for our GCMs, but decreased precipitation for our CRMs. The LWCRE leads to a narrower rising branch of the circulation and substantially increases the fraction of precipitation from the large‐scale cloud parameterization. This work demonstrates that a mock‐Walker circulation is a useful generalization of radiative convective equilibrium that includes a large‐scale circulation.