Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Estudio de los mecanismos que llevan a la formación y evolución de las líneas secas en la Argentina.

Study of the mechanisms leading to the formation and evolution of drylines in Argentina

Auteur :  : Bechis, Hernán

Université de soutenance : Universidad de Buenos Aires

Grade : Doctor de la Universidad de Buenos Aires en el área de Ciencias de la Atmósfera y los Océanos 2020

Résumé
Drylines are air-mass boundaries, characterized by a strong moisture contrast at low levels. In Argentina, forecasters and the meteorological community in general recognize drylines as a relevant characteristic of the summer circulation. Strong humidity gradients usually develop between the arid elevations of the Patagonian Plateau and the Central Argentinian Plains, in the absence of a well-defined low-level front. These air-mass boundaries are frequently oriented in an NW-SE direction and are sometimes associated with the development of storms that, under favorable conditions, can lead to severe weather events. While the drylines represent an important component of the regional low-level atmospheric circulation, little is known about them beyond the general knowledge provided by operational experience. In this work, the first reanalysis-based synoptic climatology of these drylines is presented, in addition to studying the processes that act in the formation and evolution of the most characteristic drylines. The results obtained based on reanalysis are complemented with high-resolution numerical modeling tools, which allows the analysis of both the synoptic and mesoscale processes involved. The results show that drylines are more frequent between the North Patagonian Plateau and the Central Argentinean Plains. These drylines form at the confluence between a warm and moist airmass driven by a nortwesterly flow, and drier air flowing east over the Northern Patagonian Plateau. The dry air originates above the Pacific maritime boundary layer and experiences lee subsidence after crossing the Andes range, creating an area of warm and dry air aloft. This area is advected east and northeast over nothern Patagonia, where the strong surface warming and associated vertical mixing transport it downward. The development of a cyclonic circulation in that region, associated with the surface heating and the advance of an upper-level disturbance, together with the anticyclonic circulation to the north creates a confluent pattern, strongly frontogenetic for the humidity field, which leads to the formation of a dryline.

Présentation (RDI UBA)

Version intégrale