The Influence of Shear on Deep Convection Initiation. Part II: Simulations
The Influence of Shear on Deep Convection Initiation. Part II: Simulations
复制标题
切变对深层对流引发的影响。
DOI：
10.1175/jas-d-21-0144.1
复制
发表时间：
2022
影响因子：
3.1
通讯作者：
Nowotarski, Christopher J.
中科院分区：
文献类型：
--
作者：
Peters, John M.;Morrison, Hugh;Nelson, T. Connor;Marquis, James N.;Mulholland, Jake P.;Nowotarski, Christopher J.
本文通过一系列数值模拟的结果，对第一部分中介绍的垂直风切变在深对流形成中的作用进行了评估。该假说指出，“超过宽度和剪切阈值的初始潮湿上升气流将随着时间的推移在逐渐加深的转向流中'扎根'，增加它们的低层云相对流和流入量，扩大，随后降低它们对蒸发驱动稀释的敏感性，朝着准稳定的自我维持状态发展。第一部分提出了一个理论模型，体现了假设的关键要素，并在多维环境参数空间内探讨了该模型的行为。在这里研究的模拟中，无论是在DCI的时间演变方面，还是在DCI对环境参数的敏感性方面，与理论模型的行为都非常相似。值得注意的是，无论是模拟和理论模型的经验，在结果的分歧，即新生的云是窄于一个给定的初始半径R0阈值迅速衰减和那些以上thereR0阈值进行DCI。在理论模型中的一个重要假设，即云的相对流动的背景环境VCR决定云radiusR，在模拟中仔细检查。结果表明，风暴诱导的入流是小的相对于VCR超过几公里的上升气流边缘，和VCR因此起着主导作用，在输送条件不稳定空气的上升气流。从而验证了VCR在测定R中的关键作用。
This study evaluates a hypothesis for the role of vertical wind shear in deep convection initiation (DCI) that was introduced in Part I by examining behavior of a series of numerical simulations. The hypothesis states, “Initial moist updrafts that exceed a width and shear threshold will ‘root’ within a progressively deeper steering current with time, increase their low-level cloud-relative flow and inflow, widen, and subsequently reduce their susceptibility to entrainment-driven dilution, evolving toward a quasi-steady self-sustaining state.” A theoretical model that embodied key elements of the hypothesis was developed in Part I, and the behavior of this model was explored within a multidimensional environmental parameter space. Remarkably similar behavior is evident in the simulations studied here to that of the theoretical model, both in terms of the temporal evolution of DCI and in the sensitivity of DCI to environmental parameters. Notably, both the simulations and theoretical model experience a bifurcation in outcomes, whereby nascent clouds that are narrower than a given initial radiusR0threshold quickly decay and those above theR0threshold undergo DCI. An important assumption in the theoretical model, which states that the cloud-relative flow of the background environmentVCRdetermines cloud radiusR, is scrutinized in the simulations. It is shown that storm-induced inflow is small relative toVCRbeyond a few kilometers from the updraft edge, andVCRtherefore plays a predominant role in transporting conditionally unstable air to the updraft. Thus, the critical role ofVCRin determiningRis validated.
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