Abstract
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.
Highlights
On 21 July 2001 a number of severe storms developed over the region of Camaguey, Cuba, which were observed by radar
The cloud merger was observed to occur in Sim3, demonstrating that the environmental conditions were favorable for the merger and they were provided by the 3-D ambient initial field of Sim1
The influence of the 3-D field in the occurrence of the cloud merger observed in Sim1 was studied in this paper
Summary
On 21 July 2001 a number of severe storms developed over the region of Camaguey, Cuba, which were observed by radar. A numerical simulation (Sim1) was performed in order to realistically reproduce the development of the storms observed that day. A case representing the merger between cells at different stages of development was correctly reproduced by the simulation and was 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 propagation motion of the cells and the increase in precipitation, due to the growth of the area after merger, were correctly reproduced. Simulated clouds matched the main characteristics of the observed radar echoes, though in some cases, reflectivity peaks and horizontal areas were overestimated. The results of Sim are described in the first part of this study
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