Department of Atmospheric Sciences | University of Illinois
Atmospheric Sciences | Colloquia

Atmospheric sciences colloquia

Atmospheric sciences colloquia

skip to events

Seminar coordinator: Asst. Prof. Ryan Sriver (rsriver at illinois.edu)

calendar tabs

  •  All 
  • Grid
  • Month
  • Week
  • Day
  • (Selected tab) Detail

Event Detail Information

Event Detail Information

"Influence of cloud-radiative forcing on tropical cyclone structure"

Speaker Professor Robert Fovell, Department of Atmospheric and Oceanic Sciences, UCLA
Date Dec 4, 2013
Time 3:00 pm  
Location Room 114 of the Transportation Building
Sponsor Department of Atmospheric Sciences, University of Illinois
Contact Shirley Palmisano
Phone 217-244-5737
Event type Graduate colloquium
Views 1157

We demonstrate how and why cloud-radiative forcing (CRF), the interaction of hydrometeors with longwave and shortwave radiation, can influence tropical cyclone structure through "semi-idealized" integrations of the Hurricane Weather Research and Forecasting (HWRF) model and an axisymmetric cloud model. Averaged through a diurnal cycle, CRF consists of pronounced cooling along the anvil top and weak warming through the cloud, which locally reverses the large net cooling that occurs in the troposphere under clear-sky conditions. CRF itself depends on the microphysics parameterization, and represents one of the major avenues through which simulations are sensitive to microphysical assumptions.

 

By itself, CRF enhances convective activity in the tropical cyclone's outer core, leading to a wider eye, a broader tangential wind field, and a stronger secondary circulation. This forcing also functions as a positive feedback, assisting in the development of a thicker and more radially extensive anvil than would otherwise have formed. Our simulations clearly show that the weak (primarily longwave) warming within the cloud anvil is the major component of CRF, directly encouraging stronger upper tropospheric radial outflow as well as slow, yet sustained, ascent throughout the outer core. In particular, this ascent leads to enhanced convective heating, which in turn broadens the wind field, as demonstrated with dry simulations using realistic heat sources.

 

As a consequence, improved tropical cyclone forecasting in operational models may depend on proper representation of cloud-radiative processes, as they can strongly modulate the size and strength of the outer wind field that can potentially influence cyclone track as well as the magnitude of the storm surge.

If you would like to subscribe to an RSS feed of DAS seminars, use: DAS Seminar RSS feed.

link for robots only