Examining the Impact of Cloud-Radiative Interactions on the Development of Tropical Cyclone

Abstract:

This study examines the role of cloud-radiative interactions in regulating tropical cyclone (TC) genesis and intensification using satellite measurements and the WRF model. Latent heating is considered to be the main energy source for the development of TCs and tropical waves (TWs). A recent study used CloudSat measurements of cloud ice water content as a proxy for latent heating and showed that TCs with greater cloud ice water content tend to intensify over the next 24 hours. However, the extent of enhanced ice water content, which spreads across 500 km of the TC center, greatly exceeds the high impact area of latent heating in influencing TC intensity which is generally only important near the storm center. Such an inconsistency implies that it may be the radiative heating from clouds, rather than latent heating, which is primarily responsible for TC intensification. In addition, previous modeling studies have shown that cloud-radiative interactions play a critical role in the development of tropical convective systems at its early stage, aggregating energy and nurturing a storm. To examine the impact of cloud radiative heating on the development of storms, we used NASA Clouds and the Earth’s Radiant Energy System (CERES) data set to calculate cloud radiative heating in each 2001 to 2011 storm over the Atlantic Ocean. The results show that developing TWs and TCs on average have a greater amount of cloud radiative heating than non-developing groups; that is, cloud radiative heating in developing TWs and TCs is greater within five degrees latitude/longitude of the storm center, while it is less outside five degrees latitude/longitude, than do non-developing TWs and TCs. The clear structural differences between developing and non-developing storms inspired us to use the Weather and Research Forecasting model (WRF) in order to examine the effect of cloud-radiative interactions on the development of storms. We conducted two sets of simulations, one with regular cloud-radiative interactions and the other with uniformly prescribed longwave radiative heating profiles. We found that the storms with regular cloud-radiative interactions tend to develop at a faster rate, especially for those with a weaker initial vortex. These results imply that cloud-radiative interactions may be the key to triggering TC genesis. Additional details of TC analyses will be further highlighted during the conference.