A study of the triggering mechanisms for deep convection in the Tropics using a Mesoscale Model: Hector events during SCOUT-O(3) and TWP-ICE campaigns. (3.10)

One of the purposes of SCOUT-O(3) (Stratosphere-Climate Links with emphasis on the Upper Troposphere and Lower Stratosphere) campaign was to improve our understanding of the interaction between convection and the tropical tropopause layer. Within the framework of SCOUT-O(3) project a study on Hector events has been carried out. Hector is a deep convective cell developing on Tiwi Islands during the pre-monsoon period and break monsoon period. In this study two Hector events are investigated: 30 November 2005 a multicells event occurred during SCOUT-O(3) campaign, and a single cell developed on 6 February 2006 during the TWP-ICE (Tropical Warm Pool International Cloud Experiment) campaign. The first event was characterized by two cells: the first cell downdraft triggering the second cell. The second Hector event was characterized by a cell triggered by the interaction of a previous convective cell and the south breeze front. The dynamics and thermodynamics of both events have been analyzed using the mesoscale model MM5V3 (Fifth-Generation Mesoscale Model Version 3). A few preliminary experiments have been performed to the aim of tuning the MM5 for the tropics; to this purpose two parameters are considered as the mass flux in the convective scheme and the condensation nuclei in the microphysical parameterization. Satellite and Radar images are used together with MM5V3 results to investigate the triggering mechanisms of the two Hector events. The MM5 results for the Hector event of Nov 30, 2005 shows a slightly lower Hector first cell, whereas the second one is very well reproduced, suggesting a stronger triggering acting in this second case. Moreover, the structure and the precipitation produced are in good agreement with the observation. For Feb 6, 2006 MM5 shows a shortcoming in the timing of maximum development of Hector (I h earlier), but the structure and the precipitation are in good agreement with the observations. Finally, numerical experiments are performed to the aim of investigating the triggering factor for the two Hector events, which allows for assessing type A for the first cell of November 30, 2005 and type B for the second cell of November 30, 2005 and February 6, 2006 event. (C) 2008 Elsevier B.V. All rights reserved.