Orographic precipitation in the tropics: understanding the convective environment and rainfall statistics

Building upon the orographic precipitation studies of Smith et al. (2009), this work is intended to estimate statistical parameters and the background environment for the convective clouds that will be encountered in the upcoming DomEX (Dominica Experiment) field project during the spring of 2011. Using over two years of high-rate rain gauge data from the island of Dominica, we have determined the average width of the convective cells that are dominant in this tropical regime as well as their average advective time scale and intensity. These statistical measures of orographic convection were also applied to model output from large eddy simulations (Kirshbaum and Smith 2009). Statistical properties derived from both observations and models were interpreted by constructing an idealized geometrical model of the convective rainshafts. Through these methods, we characterize the width, speed and intensity of orographically forced precipitating convective cells in the tropics.

The analysis was taken a step further by examining the thermodynamic conditions and cloud characteristics of the western Tropical Atlantic area using data from the RICO project (Rain In Cumulus over the Ocean). The RICO project used the same Wyoming King Air research aircraft in a region very close to where DomEX will take place. To gain a better understanding of the conditions and properties of the upstream environment, RICO data was analyzed for variables including aerosol and CCN concentrations, degree of conditional instability, updraft speeds, entrainment downdrafts, and cloud droplet size. Knowledge of the anticipated convective systems and background environment will improve our analysis during the DomEX field project next spring.