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 w et season is a poleward warm and moist current immediately to the east of t he Andes often referred to as a low-level jet, because of its resemblance t o the Great Plains low-level jet. Provided that the lack of observational d ata causes a great deal of uncertainty on the ability of analyses to descri be diurnal fluctuations of sub-synoptic features like 3 low-level jet, this description has been carried out using the Eta regional model. Special emp hasis has been given to the detection and characterization of a low-level j et (LLJ) east of the Andes, as a feature best developed at night and mesosc ale cross-stream dimensions. This study describes the modeled northerly cur rent east of the Andes during the 1997-1998 warm season, and progress on it s 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. Whil e there are evidences to suggest that this model provides a realistic descr iption of the local circulation, it is emphasized that observational data a re needed to gain further understanding of the behavior of the South Americ an low-level jet and its role upon the regional climate.