Graduate Lecture Series: Tim Cronin (EAPS)

Speaker: 
Tim Cronin (EAPS)
Date: 
Friday, March 9, 2018 - 4:30pm
Location: 
54-915

Understanding Hurricanes by Drying Them Out

Our understanding of dynamics in our real moist atmosphere is strongly informed by idealized dry models. It is widely believed that tropical cyclones (TCs) are an intrinsically moist phenomenon – relying fundamentally on evaporation and latent heat release – yet recent numerical modeling work has found formation of dry axisymmetric tropical cyclones from a state of dry radiative-convective equilibrium. What can such “dry hurricanes” teach us about intensity, structure, and size of real moist tropical cyclones in nature? Are dry TCs even stable in 3D? What about surfaces that are nearly dry but have some latent heat flux – can they also support TCs?

To address these questions, we use experiments with a convection-permitting model to simulate radiative-convective equilibrium in a doubly-periodic geometry with rotation, and subject to constant tropospheric radiative cooling. We use a homogeneous surface with fixed temperature and with surface saturation vapor pressure scaled by a factor 0-1 relative to that over pure water – allowing for continuous variation between moist and dry limits. We also explore cases with surface enthalpy fluxes that are uniform in space and time, where partitioning between latent and sensible heat fluxes is specified directly.

We find that a completely moist surface yields a TC-world where multiple vortices form spontaneously and persist for tens of days. A completely dry surface can also yield a parallel dry TC-world with many vortices that are even more stable and persistent. Spontaneous cyclogenesis, however, is impeded for a range of low to intermediate surface wetness values, and by the combination of large rotation rates and a dry surface. These findings have the potential to test theories of how tropical cyclogenesis works, and suggest that physically realizable fluid dynamical experiments should yield hurricane-like cyclones under the right conditions.

About the Speaker

Tim Cronin is an Assistant Professor of Atmospheric Science in Earth, Atmospheric, and Planetary Sciences at MIT. The focus of his research is on the role of regional-scale atmospheric dynamics, radiative transfer, and coupled surface-atmosphere interactions in the climate system. He combines pencil-and-paper theory and simplified numerical models of the atmosphere to test hypotheses about climate sensitivity, climates of the distant past, and interactions between weather and climate.

About the Series

The Graduate Lecture Series [GLS] is a weekly lecture featuring EAPS Professors geared towards EAPS Graduate Students, Researchers and Postdocs. Lectures usually take place on Fridays from 4:30-5:30 pm in 54-915 unless otherwise noted (term-time only). For more information please contact: Allison Provaire, provaire@mit.edu.