Mesoscale Convective System Characterization over Plains and Topography in Southeastern South America

The continental region east of the Andes, covering the the plains of the north and centre of Argentina, south of Brazil, Paraguay and Uruguay, usually referred to as South Eastern South America (SESA), is known for its large and intense Mesoscale Convective Systems (MCSs) within which severe weather events develop. The deep convective systems in this region are associated with severe weather (e.g. intense precipitation, floods, damage winds, large hail, tornadoes.

This paper seeks to advance towards a characterization of the different stages of the life cycle (start, maturity and dissipation) of convective systems showing extreme properties, either in terms of intensity or precipitation, in the SESA region through a combined use of data from different satellite instruments (TRMM and GOES).

The most relevant results related to the life cycle of an average convective system that develops in the SESA region, show that the initial stage is characterized by the predominance of deep convective cells with high frequency of intensity Rain Precipitation Features (RPFs). While during the later stages to maturity, a high concentration of RPFs of extreme volumetric are present. This demonstrates that these systems develop vast areas of stratiform precipitation when system decay and dissipation occurs.

The central region of Argentina tends to be more active (in terms of onset of MCSs) towards the end of the afternoon (between 21Z and 00Z) during the warm season, while the northwestern area is shown to be in phase with radiative heating (between 18Z and 21Z). In particular, the west of Argentina, close to the topography, is presented as a favorable region for initiation of deep moisture convection during the warm season, which can then evolves towards a greater degree of organization and size, and develop into a MCS with extreme features. Plains areas are strongly related with the diurnal cycle evolution of the planetary boundary layer and the convergence of the low level jet, presenting a nocturnal extreme initiation and mature stage.

Advancing in the understanding of the interaction between topography and the onset of convective systems in the SESA region is a pending issue mainly due to lack of observations in (mainly lack of ground radars). Thus the present work aims to characterize systems that originate in a specific region close to the Andes which is shown to be highly favorable for the onset of the most intense MCSs that occur during the summer season in SESA regions: the region of the Sierras de Córdoba (SCBA), Northwestern Argentina (NOA) and Southern Plains (SP). Convective systems in the region of the SCBA are preferably initiated towards the end of the day and during the early evening hours, between 21Z and 00Z. They are very long-lived systems with lifetimes that in some cases can exceed 24 hours and even in extreme cases reach 60 hours of life, with a cloud field defined by IR data associated with large horizontal extent at the time of maturity (>250,000km2), exceeding about twice the average size of MCSs born in NOA and SP regions.