A numerical study of cell merger over Cuba – Part II: sensitivity to environmental conditions

Abstract. In the first part of this study, an external 3-D ambient field (3d-field) was used to initiate a simulation (Sim1). In this paper, the influence of the 3-D field in the occurrence of the cloud merger simulated in Sim1 is studied. The surface convergence was very important to supply the lifting necessary for the development of new the convection. The interaction of the gust front from an old cloud with the environmental wind, as well as the interaction between the two gust fronts, were the main factors that enhanced the surface convergence. A favorable perturbation pressure gradient was also found to intensify this mechanism. The formation and development of a new cloud from the cloud bridge was the main feature for the occurrence of the cloud merger.

The influence of the wind shear components and the relative humidity (RH) in the occurrence of the cloud merger was also analyzed. The parallel wind shear component and the large RH present in the zone of study had a positive contribution to the occurrence of the cloud merger. However, the perpendicular wind shear component did not provide the main forced lifting which would be capable of generating the new convection along the direction between interacting clouds.

A high resolution simulation corroborated that the cloud merger was correctly simulated and it was not obtained by unrealistic effects due to the coarse resolution employed. It evidenced that when the horizontal resolution is improved, the life cycle of each cloud and the different processes related to their interactions are better described.