A numerical study of cell merger over Cuba – Part I: implementation of the ARPS/MM5 models

On 21 July 2001 a number of severe storms de- veloped over the region of Camaguey, Cuba, which were ob- served by radar. A numerical simulation was performed in order to realistically reproduce the development of the storms observed that day. The mesoscale model MM5 was used to determine the initial, boundary and update conditions for the storm-scale simulation with the model ARPS. Changes to the source code of ARPS were made in order to assimilate the output from the MM5 as input data and a new land-use file with a 1-km horizontal resolution for the Cuban territory was created. A case representing the merger between cells at different stages of development was correctly reproduced by the simu- lation and is in good agreement with radar observations. The state of development of each cell, the time when the merger occurred, starting from the formation of clouds, the propa- gation motion of the cells and the increase in precipitation, due to the growth of the area after the merger, were correctly reproduced. Simulated clouds matched the main characteris- tics of the observed radar echoes, though in some cases, re- flectivity tops and horizontal areas were overestimated. Max- imum reflectivity values and the heights where these maxi- mum values were located were in good agreement with radar data, particularly when the model reflectivity was calculated without including the snow. The MM5/ARPS configuration introduced in this study, improved sensibly the ability to sim- ulate convective systems, thereby enhancing the local fore- casting of convection in the region.