The radially outward propagating diurnal signal in the upper-level clouds (diurnal pulse) is a prominent cyclical feature of tropical cyclones (TCs). This study examines relationships between diurnal pulses and TC intensity changes using satellite Infrared data from 2001 to 2018. The occurrence and duration of diurnal pulses 24 hr prior to or during TC intensity change are strongly correlated with TC intensification rate. Rapidly intensifying (RI) TCs have a markedly higher frequency (60%–80%) of very long-duration pulse (15 hr) and significantly longer mean pulse duration than steady-state (40%–50%) and gradually intensifying TCs (50%–60%). Long-duration pulses are infrequent in weakening TCs (20%–30%). Diurnal pulse frequency and duration are highly correlated with the initial cloud-top cooling rate and very cold-cloud fraction in the inner core, but less related to the initial TC intensity. In short, strong diurnal pulsing of cold clouds is an evident signature prior to or during the RI of TCs.

中文翻译：

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快速增强的热带气旋中冷云的强烈昼夜脉动

上层云中径向向外传播的昼夜信号（昼夜脉冲）是热带气旋（TC）的显着周期性特征。本研究利用 2001 年至 2018 年的卫星红外数据研究了昼夜脉冲与 TC 强度变化之间的关系。 TC 强度变化之前或期间 24 小时的昼夜脉冲的发生和持续时间与 TC 增强率密切相关。快速增强 (RI) TC 具有明显更高的频率 (60%–80%) 的极长持续时间脉冲 (15 小时）和比稳态 (40%–50%) 和逐渐增强的 TC (50%–60%) 显着更长的平均脉冲持续时间。长期脉冲在减弱的 TC 中很少见 (20%–30%)。昼夜脉冲频率和持续时间与初始云顶冷却速率和内核非常冷的云分数高度相关，但与初始 TC 强度相关性较小。简而言之，在 TC RI 之前或期间，冷云的强烈昼夜脉冲是一个明显的特征。