资源环境科技发展态势分析平台

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 2001-2018. The occurrence and duration of diurnal pulses 24 hours 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 ( 15h) 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.