The Atmospheric Boundary Layer and the Initiation of the MJO
The Atmospheric Boundary Layer and the Initiation of the MJO
复制标题
大气边界层和 MJO 的启动
DOI：
10.1175/jcli-d-23-0210.1
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发表时间：
2023
影响因子：
4.9
通讯作者：
Brewer, W. Alan
中科院分区：
文献类型：
--
作者：
Johnson, Richard H.;de Szoeke, Simon P.;Ciesielski, Paul E.;Brewer, W. Alan
印度洋是马登-朱利安涛动（MJO）频繁发生的地点。MJO形成过程中的对流演化与云下大气混合层（ML）密切相关。进入形成中的积云的大部分空气要经过云底；因此，ML的属性对于确定云开发的性质至关重要。低气压的性质和深度受水平平流、降水驱动冷池和垂直运动的影响。为了解决MJO启动期间的ML行为，使用了2011/12 MJO实验动力学（DYNAMO）的数据。在10月MJO开始之前的一段时间里，研究船revellev的观测结果被用来记录ML及其变化。在10月1日至12日的抑制期，混合层深度从~ 500米增加到~ 700米，使得更大比例的边界层热气流到达上升凝结层，从而促进云的增长。ML热收支定义了一个平衡混合层深度，该深度可以准确诊断DYNAMO对流抑制期间的混合层深度，前提是包括水平平流。热带气旋的平流明显受到南暖流区低层对流外流的影响。研究结果还表明，卷云及其通过降低ML辐射冷却速率对ML深度和对流发展的远程影响之间存在联系。平衡混合层的涌现行为对用参数化云和湍流尺度运动模式模拟MJO具有重要意义。
The Indian Ocean is a frequent site for the initiation of the Madden–Julian oscillation (MJO). The evolution of convection during MJO initiation is intimately linked to the subcloud atmospheric mixed layer (ML). Much of the air entering developing cumulus clouds passes through the cloud base; hence, the properties of the ML are critical in determining the nature of cloud development. The properties and depth of the ML are influenced by horizontal advection, precipitation-driven cold pools, and vertical motion. To address ML behavior during the initiation of the MJO, data from the 2011/12 Dynamics of the MJO Experiment (DYNAMO) are utilized. Observations from the research vesselRevelleare used to document the ML and its modification during the time leading up to the onset phase of the October MJO. The mixed layer depth increased from ∼500 to ∼700 m during the 1–12 October suppressed period, allowing a greater proportion of boundary layer thermals to reach the lifting condensation level and hence promote cloud growth. The ML heat budget defines an equilibrium mixed layer depth that accurately diagnoses the mixed layer depth over the DYNAMO convectively suppressed period, provided that horizontal advection is included. The advection at theRevelleis significantly influenced by low-level convective outflows from the southern ITCZ. The findings also demonstrate a connection between cirrus clouds and their remote impact on ML depth and convective development through a reduction in the ML radiative cooling rate. The emergent behavior of the equilibrium mixed layer has implications for simulating the MJO with models with parameterized cloud and turbulent-scale motions.
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