Dynamical Aquaplanet Experiments with Uniform Thermal Forcing: System Dynamics and Implications for Tropical Cyclone Genesis and Size
Dynamical Aquaplanet Experiments with Uniform Thermal Forcing: System Dynamics and Implications for Tropical Cyclone Genesis and Size
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DOI：
10.1175/jas-d-19-0001.1
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发表时间：
2019-07
影响因子：
3.1
通讯作者：
D. Chavas;K. Reed
中科院分区：
文献类型：
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作者：
D. Chavas;K. Reed
热带气旋发生和大小对纬度的动态依赖性的现有假设主要取决于科里奥利参数 f。这些假设通过具有均匀热力的动态水行星实验进行了测试，其中行星自转速率和行星半径相对于地球值而变化；控制模拟还与当今的地球模拟进行了比较。风暴发生率崩溃为对 f 的准普遍依赖，在临界纬度处达到最大值，其中反 f 尺度和莱茵尺度相等。距赤道的最小成因距离由赤道莱茵河（或形变）尺度设定，而不是由 f 的最小值设定。外部风暴的大小定性地遵循两个长度尺度中较小的一个，包括在控制模拟中随着纬度赤道 45° 缓慢增加，类似于地球模拟。峰值尺寸的纬度与不同行星半径的临界纬度成比例，但与自转速率无关，可能是因为成因特别依赖于 f。峰大小和峰堆积密度的范围紧密相连。结果表明，时间效应和风暴间相互作用可能对规模动态具有重要意义。更一般地说，临界纬度将两种区域分开：1）混合波浪-气旋赤道带，其中波浪效应很强，莱茵河规模可能限制风暴规模；2）充满气旋的极冠，其中波浪效应较弱，气旋持续存在。大行星极限预测世界几乎被长期风暴覆盖，相当于 f 平面。总体而言，球形几何形状对于理解类地行星上的热带气旋的起源和大小可能很重要。
Existing hypotheses for the dynamical dependence of tropical cyclone genesis and size on latitude depend principally on the Coriolis parameter f. These hypotheses are tested via dynamical aquaplanet experiments with uniform thermal forcing in which planetary rotation rate and planetary radius are varied relative to Earth values; the control simulation is also compared to a present-day Earth simulation. Storm genesis rate collapses to a quasi-universal dependence on f that attains its maximum at the critical latitude, where the inverse-f scale and Rhines scale are equal. Minimum genesis distance from the equator is set by the equatorial Rhines (or deformation) scale and not by a minimum value of f. Outer storm size qualitatively follows the smaller of the two length scales, including a slow increase with latitude equatorward of 45° in the control simulation, similar to the Earth simulation. The latitude of peak size scales with the critical latitude for varying planetary radius but not rotation rate, possibly because of the dependence of genesis specifically on f. The latitudes of peak size and peak packing density scale closely together. Results suggest that temporal effects and interstorm interaction may be significant for size dynamics. More generally, the critical latitude separates two regimes: 1) a mixed wave–cyclone equatorial belt, where wave effects are strong and the Rhines scale likely limits storm size, and 2) a cyclone-filled polar cap, where wave effects are weak and cyclones persist. The large-planet limit predicts a world nearly covered with long-lived storms, equivalent to the f plane. Overall, spherical geometry is likely important for understanding tropical cyclone genesis and size on Earthlike planets.