Understanding the Role of Convective Cold Pools in Hurricane Rainfall and Land Surface Interactions

Convective cold pools in the atmosphere form when rainfall evaporation creates a downdraft of cold, dense air. These cold pools spread out along the surface, often triggering new convection and influencing local weather patterns. In hurricanes, cold pools play an important role in the formation of new rainbands by interacting with the inflow and lifting of warm air. The initiation of a cold pool creates a sharp increase in latent heat flux at its edge, which removes moisture from the underlying soil and transfers it to the atmosphere. Therefore, cold pools in landfalling hurricanes could be a significant factor in the transfer of soil moisture to the atmosphere. The effects of cold pools on latent heat transfer and hurricane rainband structures have been demonstrated in idealized simulation studies; however, studies using real-world simulations are still limited.

To assess the impact of cold pools on hurricane rainfall, a modified version of the Hurricane Weather Research and Forecasting model (HWRFxUT) is used to simulate 10 recent landfalling hurricanes along the Gulf Coast. The model is configured with an operational 9 km, 3 km, and 1 km nested domain setup over the contiguous United States. Model experiments are performed for each hurricane case by modifying the rainfall evaporation rate by 20%, 50%, and 80% in the Ferrier-Aligo microphysics scheme used for the simulations. The results are compared with the control experiments, which are conducted without any modification to the microphysics scheme.

Cold pools in the vicinity of hurricanes are identified using a watershed algorithm. The features of these cold pools are compared across each experiment, and their impact on hurricane rainfall, intensity, and track is analyzed. The changes in the exchange of sensible and latent heat fluxes between the land surface and atmosphere in the presence of cold pools near the storm are also specifically analyzed. The findings highlight the crucial role of convective cold pools in modulating hurricane dynamics and suggest that accurate representation of these processes is crucial for improving forecasts of landfalling hurricanes.