In this study, the role of diabatic heating/cooling in outer rainbands (ORBs) in the formation and evolution of the secondary eyewall of a numerically simulated tropical cyclone (TC) is investigated. This is done through a series of sensitivity experiments under idealized conditions using a high-resolution cloud-resolving atmospheric model. The results show that artificially increasing diabatic heating in rainbands enhances convective activities in ORBs and leads to an earlier secondary eyewall formation (SEF), and later the faster weakening and earlier dissipation of the primary eyewall. Reducing diabatic heating in ORBs weakens the rainbands and delays the SEF but prolongs the duration of the double eyewall structure if the SEF occurs. Reducing diabatic cooling in ORBs enhances convective activity in rainbands but has little effect on convection in the primary eyewall prior to the SEF. However, it results in a widened eyewall structure and a stronger TC after the eyewall replacement. Increasing diabatic cooling in ORBs largely suppresses convection in rainbands and prohibits the SEF. These results demonstrate that diabatic heating/cooling in ORBs plays important roles in the SEF and evolution. Since diabatic heating/cooling in rainbands is sensitive to the near-core environmental relative humidity, our results demonstrate the critical importance of large-scale environmental moist condition to the formation and evolution of secondary eyewall in TCs. In addition, it is also found that when the area-averaged diabatic heating rate in ORBs becomes similar in magnitude to that in the primary eyewall, the secondary eyewall forms.

中文翻译：

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外雨带非绝热加热/冷却在数值模拟热带气旋次生眼壁形成和演变中的作用


在本研究中，研究了外雨带 （ORB） 中非绝热加热/冷却在数值模拟热带气旋 （TC） 次级眼壁形成和演变中的作用。这是通过使用高分辨率云分辨大气模型在理想化条件下进行的一系列灵敏度实验来完成的。结果表明，人为增加雨带中的非绝热增强了 ORB 中的对流活动，并导致次级眼壁形成 （SEF），随后初级眼壁的更快减弱和更早消散。减少 ORB 中的非绝热会削弱雨带并延迟 SEF，但如果 SEF 发生，则会延长双眼壁结构的持续时间。减少 ORB 中的非绝热冷却增强了雨带中的对流活动，但对 SEF 之前主眼壁的对流影响不大。然而，它会导致眼壁结构变宽，眼壁置换后 TC 更强。ORB 中非绝热冷却的增加在很大程度上抑制了雨带中的对流并禁止了 SEF。这些结果表明，ORB 中的非绝热加热/冷却在 SEF 和进化中起着重要作用。由于雨带中的非绝热加热/冷却对近核心环境相对湿度敏感，我们的结果表明大尺度环境湿润条件对 TCs 中次生眼壁的形成和演变至关重要。此外，还发现当 ORB 中的面积平均非绝热加热速率在幅度上与主眼壁中的热速率相似时，会形成次级眼壁。