Tropical Meteorology Special Symposium
20th Conference on Climate Variability and Change


Modeling Studies of Island Induced Convective Activities in Puerto Rico Region

Melissa Sheffer, Florida Institute of Technology, Melbourne, FL; and S. Chiao and I. Matos

This study is aimed to investigate the convective activities that are induced by small islands in the Caribbean. It is often observed by satellite that tropical dendritic cumulus form off the leeward coast of many Caribbean islands. Some of the dendritic cumulus can become convective systems that affect the island of Puerto Rico. It is still a challenge to forecast such small scale convective activities development. Based on the Froude number (Fr = U/Nh; U = average wind speed in m/s, N = Brunt-Väisälä Frequency, and h = mountain height in meters), small islands such as (e.g., Vieques and Culebra to the east of Puerto Rico) are not able to produce any island wake in terms of shallow cumulus clouds. The working hypothesis of this study is that those small islands play an essential role in the development of convective activities over Puerto Rico. The Weather Research and Forecasting (WRF) model is employed to understand what parameters cause the convective initiation on Puerto Rico, and to determine if the clouds are forced by an island heating effect or other dynamical processes. The WRF model is configured with 3 nested domains at 4 km, 1 km and 250 m, respectively.

There are four cases that were identified: June 26, July 20, August 8, and August 20 of 2006. These cases are categorized into wet (with precipitation) and dry (without precipitation) conditions. Preliminary results demonstrated that topography from both Puerto Rico and the small islands of Vieques and Culebra influenced the convective initiation that forms on Puerto Rico. Despite the Froude number, which states island wakes cannot occur from these islands, convergence is observed in a diurnal cycle on the leeward coast of Vieques, which is, in part, due to a blocking effect. The island topography effect will be examined more in-depth with different sensitivity experiments, such as different flow regimes and moisture conditions. Additionally, high resolution (i.e., 250 meter grid spacing) idealized simulations will be conducted to examine the formation of island wakes and dendritic cumulus.

Joint Poster Session 3, Tropical Cyclones and Climate Change Poster Session
Monday, 21 January 2008, 2:30 PM-4:00 PM, Exhibit Hall B

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