The South American Low Level Jet Experiment (SALLJEX), planned over the past five years by scientists in Argentina, Brazil, Bolivia, Paraguay, and the US, will be launched November 15, 2002, for 13 weeks to intensively measure the atmosphere over central South America in order to better understand and model the flow of moist air from the Amazon basin through the low level jet east of the Andes to the breadbasket region of southeastern South America where it feeds summertime storms and exerts controlling influences on droughts and floods. The field campaign enhances observations over one of the largest over-land atmospheric data voids on the planet. The existing balloon sounding network over South America is augmented with additional sites in northern Chile, northwestern Argentina, Bolivia, Paraguay, Peru and western Brazil. Up to eight balloon launches per day will be taken to resolve the diurnal (day-night) cycle during moderate to strong occurrences of the jet. The surface rain gauge network is also being enhanced in the region with an additional 1200 sites. The ground-based observations are augmented by wind and moisture measurements made along and across the core of the jet by a NOAA P-3 aircraft, stationed with the field operations center in the city of Santa Cruz, Bolivia. Upon completion of the field program, researchers will utilize the data collected to better understand and model the characteristics of the low level jet, particularly the diurnal cycle of wind and precipitation. NOAA and NSF sponsor the participation of US scientists in the experiment.