On the role of convective available potential energy (CAPE) in tropical cyclone intensification
On the role of convective available potential energy (CAPE) in tropical cyclone intensification
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DOI：
10.1080/16000870.2018.1433433
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发表时间：
2018-01
期刊：
影响因子：
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通讯作者：
Marguerite Lee;T. Frisius
中科院分区：
文献类型：
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作者：
Marguerite Lee;T. Frisius
摘要本文研究了对流有效势能（CAPE）在模拟热带气旋增强过程中的作用。此外，它还检验了“风致表面热交换”（WISHE）理论，其中在强化期间不存在CAPE。我们使用具有不同复杂性的模型层次结构。低阶热带气旋模式是最简单的模式。研究发现，WISHE理论假设的快速对流交换对CAPE的阻尼抑制了模型中的大幅增强。这一结果可以解释为在生长阶段二次循环对表面传热的优势。它导致低熵空气夹带进入眼壁，导致气旋减弱。其他模拟结果表明，增强速率随初始CAPE的增大而增大，且内核CAPE小于周围区域。用更复杂的Ooyama模型进行的研究也得到了类似的定性结果。在这个模型中，考虑了两种对流。第一个模型基于边界层的摩擦辐合，第二个模型描述了包括降水效率在内的对流调整。只有摩擦诱导对流支持热带气旋的增强，而第二种对流则对热带气旋有强烈的抑制作用。最后，在初始CAPE变化的情况下，采用复杂的非流体静力云模式CM1。该模型还揭示了在强化期间存在径向增加的CAPE。本研究的实验表明，径向CAPE梯度与增强速率呈正相关，这与WISHE模型的基本假设不一致。结果强调了二次环流在将高熵空气输送到热带气旋内核中的作用，因此应像Montgomery和Smith在旋转对流范式中所做的那样，在适当的强化理论中加以考虑。
Abstract This study addresses the role of convective available potential energy (CAPE) in the intensification of simulated tropical cyclones. Additionally, it also examines the ‘wind-induced surface heat exchange’ (WISHE) theory in which CAPE is non-existent during intensification. We use a hierarchy of models with different complexity. A low-order tropical cyclone model forms the simplest model. It is found that the damping of CAPE by fast convective exchange as assumed in the WISHE theory inhibits substantial intensification in the model. This result can be explained by the dominance of the secondary circulation over surface heat transfer in the growth stage. It leads to entrainment of low entropy air into the eyewall resulting in the weakening of the cyclone. Other simulations reveal that the intensification rate increases with increasing initial CAPE and that the inner core CAPE is smaller than that of the ambient region. Investigations with the more complex Ooyama model yield qualitatively similar results. In this model, two types of convection are considered. The first one is based on frictional convergence in the boundary layer and the second one describes a convective adjustment including a precipitation efficiency. Only frictionally induced convection supports tropical cyclone intensification while the second one strongly acts to dampen the cyclone. Finally, the complex nonhydrostatic cloud model CM1 is used where the initial CAPE is varied. This model also exposes the existence of radially increasing CAPE during intensification. The experiments of this study indicate a positive relationship between the radial CAPE gradient and the intensification rate which disagrees with the basic assumption of WISHE models. The results emphasise the role of the secondary circulation for transporting high entropy air into the tropical cyclone inner core, and therefore should be considered in a proper intensification theory as has been done in the rotating convection paradigm by Montgomery and Smith.