A Thermodynamic Perspective on Steady-State Tropical Cyclones
A Thermodynamic Perspective on Steady-State Tropical Cyclones
复制标题
稳态热带气旋的热力学视角
DOI：
10.1175/jas-d-20-0140.1
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发表时间：
2020
影响因子：
3.1
通讯作者：
G. Bryan
中科院分区：
文献类型：
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作者：
Raphaël Rousseau;R. Rotunno;G. Bryan
热带气旋最大强度的理论假设是稳定状态。然而，在运行数十天的模拟中，许多TC倾向于在稳定在最终平衡稳态（ES）之前从堆芯中的早期稳态（CS）显著地衰减。这种衰变提出了一个问题，即CS或ES是否应该被用作与最大强度理论的比较。为了了解CS和ES之间的差异，我们研究了TC衰减的原因，并试图模拟TC在100天内具有稳定强度。使用轴对称云模型1，我们发现，CS TC衰减是由于一个大规模的下沉区域干燥。这种干燥在轴对称模式中非常明显，因为浅层到中层对流没有足够精确地表示以湿润下沉区的空气。在沉降区增加水分松弛项的模拟和没有任何水分的干旋风都保持稳定状态超过100天，在启动期后没有明显衰减。这些模拟结果表明，TC模拟的衰减是由于不可逆的去除降水结合在沉降区缺乏增湿机制。一旦消除这些条件中的任何一个，衰减就会消失，CS和ES强度变得基本相等。
Theories for the maximum intensity of tropical cyclones (TCs) assume steady state. However, many TCs in simulations that run for tens of days tend to decay considerably from an early steady state in the core (CS), before stabilizing at a final equilibrium steady state (ES). This decay raises the question of whether CS or ES should be used as a comparison to the maximum intensity theories. To understand the differences between CS and ES, we investigate why TCs decay and attempt to simulate a TC with steady intensity over a 100-day period. Using the axisymmetric Cloud Model 1, we find that the CS TC decay is due to a large-scale drying of the subsidence region. Such a drying is very pronounced in axisymmetric models because shallow-to-midlevel convection is not represented accurately enough to moisten air in the subsidence region. Simulations with an added moisture relaxation term in the subsidence region and dry cyclones without any moisture both remain in a steady state for over 100 days, without decaying appreciably after the spinup period. These simulations indicate that the decay in TC simulations is due to the irreversible removal of precipitation combined with the lack of a moistening mechanism in the subsidence region. Once either of these conditions is removed, the decay disappears and the CS and ES intensities become essentially equivalent.