Wave Disturbances and Their Role in the Maintenance, Structure, and Evolution of a Mesoscale Convection System
Wave Disturbances and Their Role in the Maintenance, Structure, and Evolution of a Mesoscale Convection System
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DOI：
10.1175/jas-d-18-0348.1
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发表时间：
2019-12
影响因子：
3.1
通讯作者：
Shushi Zhang;D. Parsons;Yuanzu Wang
中科院分区：
文献类型：
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作者：
Shushi Zhang;D. Parsons;Yuanzu Wang
本研究对在夜间平原对流抬升（PECAN）野外考察期间观测到的一个夜间中尺度对流系统（MCS）进行了调查。在该MCS之前观测到一系列波状特征，并且在其中一次扰动之后发生了广泛的对流触发（CI）。利用WRF - ARW模式进行模拟，以了解这些扰动的动力学及其对MCS的影响。在这些模拟中，由于空气向上流过冷池并越过冷池使逆温层抬升，在高空逆温层内形成了一个“抬升的涌浪”。当涌浪在MCS之前传播时，这种抬升创造了一个更有利于深对流的环境，使得MCS由于涌浪尾流中的对流触发而离散传播。斯考勒参数在一定程度上有利于这种波能的捕获，尽管环境的某些方面演变得符合n = 2模式深对流层重力波的预期。高空逆温层内的涌浪让人联想到两层流体力学理论所预测的扰动，这与近期一些研究形成对比，那些研究表明涌浪通常是由稳定的夜间边界层内的气流与对流产生的冷池之间的相互作用引发的。基于这种两层方法并考虑地形以及逆温层下方充分混合层的理想化模拟表明，抬升的涌浪为白天的飑线提供了一种可能的机制，使其能够消除大平原上空经常出现的逆温层顶，特别是在天气扰动环境中，垂直切变可能有利于波能的捕获。
This study investigates a nocturnal mesoscale convective system (MCS) observed during the Plains Elevated Convection At Night (PECAN) field campaign. A series of wavelike features were observed ahead of this MCS with extensive convective initiation (CI) taking place in the wake of one of these disturbances. Simulations with the WRF-ARW Model were utilized to understand the dynamics of these disturbances and their impact on the MCS. In these simulations, an “elevated bore” formed within an inversion layer aloft in response to the layer being lifted by air flowing up and over the cold pool. As the bore propagated ahead of the MCS, the lifting created an environment more conducive to deep convection allowing the MCS to discretely propagate due to CI in the bore’s wake. The Scorer parameter was somewhat favorable for trapping of this wave energy, although aspects of the environment evolved to be consistent with the expectations for an n = 2 mode deep tropospheric gravity wave. A bore within an inversion layer aloft is reminiscent of disturbances predicted by two-layer hydraulic theory, contrasting with recent studies that suggest bores are frequently initiated by the interaction between the flow within stable nocturnal boundary layer and convectively generated cold pools. Idealized simulations that expand upon this two-layer approach with orography and a well-mixed layer below the inversion suggest that elevated bores provide a possible mechanism for daytime squall lines to remove the capping inversion often found over the Great Plains, particularly in synoptically disturbed environments where vertical shear could create a favorable trapping of wave energy.