Model characterization of the South American low-level flow during the 1997-1998 spring-summer season

Abstract

A relevant feature of the South American low-level circulation during the wet season is a poleward warm and moist current immediately to the east of the Andes often referred to as a low-level jet, because of its resemblance to the Great Plains low-level jet. Provided that the lack of observational data causes a great deal of uncertainty on the ability of analyses to describe diurnal fluctuations of sub-synoptic features like a low-level jet, this description has been carried out using the Eta regional model. Special emphasis has been given to the detection and characterization of a low-level jet (LLJ) east of the Andes, as a feature best developed at night and mesoscale cross-stream dimensions. This study describes the modeled northerly current east of the Andes during the 1997–1998 warm season, and progress on its mean characterization, including diurnal fluctuations and horizontal and vertical structure. From moisture budget calculations a net convergence of moisture flux is found over an area that includes the Del Plata basin, with a maximum southward flux through the northern boundary at low levels. While there are evidences to suggest that this model provides a realistic description of the local circulation, it is emphasized that observational data are needed to gain further understanding of the behavior of the South American low-level jet and its role upon the regional climate.