Presented on December 19, 2025, by

Weixin Xu
Professor, Ph.D
School of Atmospheric Science
Sun Yat-sen University
Zhuhai, China

ABSTRACT:

Accurate forecasting of tropical cyclone (TC) intensity still faces great challenges, as intensity change is impacted by complex processes across multiple scales involving both environmental forcing and internal structures. The diurnal cycle of TCs is likely one such process. TCs show significant diurnal variations in many aspects, and one of the most spectacular diurnal cycle features is the radially outward propagation of a cooling signal in the upper-level clouds, the so-called diurnal pulse (DP). Model simulations suggested that DP may influence the TC’s internal structures and eventually the intensity. Based on long-term multi-satellite observations, this study addresses several important scientific questions regarding the DPs: 1) Do DPs occur in the deep convective layer or just at the upper-level cold clouds? 2) How do TC’s mean internal structures change in association with DP occurrence? 3) What are the relationships between DPs and TC intensity change, especially rapid intensification? This talk will present and discuss some interesting findings raised from the investigation of thousands of DP events and intensifying TC periods. Overall, DP implies a coherent pattern of the convective structure in the TC’s evolution and provides important implications for TC intensity change.