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

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 3 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.