Convection On the Edge
Convection On the Edge
复制标题
边缘对流
DOI：
10.1029/2019ms001820
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发表时间：
2019
影响因子：
6.8
通讯作者：
C. Hohenegger
中科院分区：
文献类型：
--
作者：
J. Windmiller;C. Hohenegger
无论是在理想化的研究还是在观测中，热带海洋上空的深层对流通常在对流活跃区域的边缘增强。这里使用辐射对流平衡研究的稳态来详细研究对流的边缘强化，以单个对流簇为标志，在该簇的边缘深层对流强化。通过将深层对流的空间分布与已知对对流重要的不同变量进行比较，研究了边缘强化的原因及其对簇面积的依赖性。模拟分析表明，边缘的特点是触发对流的可能性增加，而不是更强的上升气流。特别是，虽然潮湿区域的边缘在热力学上并不更有利，但我们发现强烈的表面收敛，因此在该边缘处存在动力提升。显示表面收敛是由两个相反的流引起的。一方面，正如之前的辐射对流平衡模拟所预期的那样，存在低水平的流入流向潮湿区域。另一方面，地表存在正密度异常，这是对流活跃区域内不断形成冷池的结果，形成了超冷池。由于低层流入的速度与超冷池边界的潜在传播速度大致匹配，这些相反的流动解释了该区域边缘存在强收敛。由此产生的抬升是否会导致深层对流的形成取决于大规模的不稳定性。
Deep convection over tropical oceans often appears intensified at the edge of convectively active regions, both in idealized studies and in observations. This edge intensification of convection is studied in detail here, using the steady state of a radiative‐convective equilibrium study, marked by a single convective cluster with deep convection intensified at the edge of this cluster. The cause for edge intensification and its dependence on the cluster area is investigated by comparing the spatial distribution of deep convection to different variables known to be important for convection. Analysis of the simulation suggests that the edge is marked by an increased probability for the triggering of convection rather than by stronger updrafts. In particular, while the edge of the moist region is not thermodynamically more favorable, we find strong surface convergence and therefore dynamical lifting at this edge. The surface convergence is shown to result from two opposing flows. On the one hand, there is, as expected from previous radiative‐convective equilibrium simulations, a low‐level inflow directed toward the moist region. On the other hand, there is a positive density anomaly at the surface which is the result of continuously forming cold pools within the convectively active region, creating a super‐cold‐pool. As the velocity of the low‐level inflow approximately matches the potential propagation speed of the super‐cold‐pool boundary, these opposing flows explain the presence of strong convergence at the edge of this region. Whether the resulting lifting induces the formation of deep convection is shown to depend on the large‐scale instability.