CONICET | Buscador de Institutos y Recursos Humanos

Maximum frequency of moist deep convection at night over northern central Argentina during summer is found both for environments dominated by convergence related to the presence of a low level jet to the east of the Andes but also when this feature is not present. Different processes related to the Andes mountain range as well as west-east gradients in surface characteristics influence the generation of mesoscale circulations that interact with surface friction and large-scale pressure gradients and may gradually force deep moist convection. These mesoscale circulations are associated with divergence/convergence patterns in the boundary layer. This work has been done using an enriched analysis for the summer 2002-2003, during which the South American Low-Level Jet Experiment (SALLJEX) was performed. SALLJEX aimed to monitor, quantify and analyze the low-level circulation over this region. SALLJEX data set provides a quantitative improvement in both spatial and temporal resolution over that of the operational network. In order to identify the convective systems and their life cycle IR brightness temperature data was employed at half hourly intervals with a horizontal resolution of 4km over the area between 10ºS-40ºS and 40ºW- 75ºW for the same period. Enriched analyses were generated ingesting all available data following a downscaling methodology, using RAMS. This model was applied to obtain analysis every three hours, with a horizontal resolution of 80 km covering mostly South America and an enhanced domain with 20 km resolution for the region encompassing Central and Northern Argentina, southern Brazil, Bolivia, Paraguay and Uruguay. This study addresses different genesis mechanisms of organized convection linked to mesoscale circulations in the mentioned region and a relationship is found between their diurnal cycles. With this objective case studies have been selected in weakly and strongly forced environments. Mesoscale circulation patterns are described in each case. An orogenic mesoscale convective system initiates at early evening and develops and decays during nighttime not supported by a low-level jet during its life cycle. Other cases correspond to an extended heat wave event over the region during which a deep thermal low pressure system over Northwestern Argentina developed to the lee of the Andes enhancing the low-level jet. Mesoscale circulations are altered once convection develops and dominates the different patterns. The results provide insight to perform further numerical experiments to isolate and find interaction between factors that control both the mesoscale circulations and the convection.