Climate Controls of Tropical Cyclone Size: Rotation, Rossby Waves, and Climate Change

April 20, 2023

Dan Chavas

Hosted by Michael Bell

Abstract

Tropical cyclones cause widespread damage and loss of life globally each year. In a future warmer
climate, tropical cyclones are expected to have stronger maximum wind speeds, but could they also get
larger? This talk will discuss how I integrate theory, observations, idealized models, and global climate
models to understand what sets the size of tropical cyclones on Earth. I will focus in particular on how
size depends on both the Coriolis parameter and its meridional gradient. The latter acts as the strong
dynamical constraint on size in the Earth’s tropics, via a length scale traditionally known as the “Rhines
scale”. This length scale has long been used to explain properties of jet streams and the size of
extratropical cyclones, and I will demonstrate how this concept can be applied in a very simple manner to
explain why it limits the size of an isolated tropical cyclone. This work further provides novel insight into
the basic meaning of the Rhines scale itself in any context. These results suggest that storm size should
not change strongly with warming, which is corroborated by results from idealized and real-world GCM
simulations. The above insights will be combined with recent work linking storm properties to economic
damage to discuss whether landfalling storms are expected to become more damaging in the future.