Title: Alignment and Intensification of Weak Tropical Cyclones in Vertical Wind Shear
Lecturer: Dr. Robert Rogers（Asia-Pacific Typhoon Collaborative Research Center）
Inviter: Prof. Kun Zhao
Time: Wednesday May 20, 2026 at 10:00 AM
Venue: Lecture Hall D103, School of Atmospheric Sciences
Abstract: Predicting the genesis and intensification of weak tropical cyclones (TCs) is a challenging yet critical problem. Such systems have a weak rotational constraint, are dominated by divergent flow, and are vulnerable to hostile environments such as vertical wind shear and dry air. Circulations are often misaligned between low- and mid-levels, sometimes by distances of O(100 km). The formation of an aligned circulation is a key step in this process. Understanding how this alignment occurs in this regime is important for better prediction of intensification, including rapid intensification. Downshear reformation is one pathway for this alignment in which the low-level center (LLC) redevelops underneath an existing midlevel center (MLC), downshear of the LLC, and in presence of deep convection and widespread precipitation in the vicinity of the MLC. What has not been adequately understood are the multiscale processes responsible for alignment, particularly the role that precipitation structure plays and how environmental features can promote (or inhibit) the evolution of precipitation structures to one which is favorable to vortex alignment and TC intensification.
This talk will focus on the environmental features thought to be important in promoting precipitation structure that facilitates downshear reformation. In particular, the thermodynamic environment, including stability and moisture profiles, are examined using composites of dropsondes released from low- and high-altitude aircraft in the Atlantic and Pacific basins. An emphasis is placed on how these parameters vary in a shear-relative framework and whether differences in these thermodynamic conditions can distinguish developing from non-developing weak TCs and what processes may contribute to modifying the thermodynamic conditions. Additionally, an overview will be provided of a project that is just now being undertaken to explore these issues in coastal China, using a combination of ground-based Doppler radar, dropsonde measurements from manned and unmanned aircraft, reanalysis datasets, and numerical modeling studies. Hypotheses that relate vertical shear structure and evolution, thermodynamic conditions resulting from these shear characteristics, and vortex evolution toward an aligned (or non-aligned) state will be presented.
Brief introduction to the speaker: Robert Rogers is Science Director and Chief Scientist for Typhoon Observations and Research for the Asia-Pacific Typhoon Collaborative Research Center in Shanghai. He is Co-Chief Editor of Tropical Cyclone Research and Review, Editor of Journal of Geophysical Research – Atmospheres, and Associate Editor of Journal of Atmospheric Sciences. He Co-Chaired the 10th International Workshop on Tropical Cyclones from the World Meteorological Organization in 2022 and Chaired the 3rd and 4th International Workshop on Tropical Cyclones – Landfall Processes in 2014 and 2017. His research interests include tropical cyclone structure and intensity change, convective and precipitation processes, and aircraft observations and numerical modeling of tropical cyclones.