The South American low‐level jet east of the Andes during the 1999 LBA‐TRMM and LBA‐WET AMC campaign

Abstract

The present study describes some observed surface and upper‐air features of the low‐level jet (LLJ) and southerly jet (SJ). Our results suggest the existence of this low‐level circulation to the east of the Andes that transports moisture from tropical South America toward the south during the warm/wet season of 1999. We explore the synoptic variability, diurnal variation, and alternations between LLJ and SJ episodes by using a combination of surface and high‐resolution upper‐air observations (1 to 8 soundings per day) and global reanalysis. Our results show strong synoptic fluctuations; with the LLJ more frequent than SJs. The LLJ has stronger winds in the afternoon and its core of maximum winds is located between 1600 and 2000 m above the surface. Special observational efforts, such as the pilot balloon sounding network in Bolivia (Pan American Climate Studies Sounding Network [PACS‐SONET] program), the Large‐Scale Biosphere‐Atmosphere (LBA) Experiment‐WET Atmospheric Mesoscale Campaign (AMC), and Tropical Rainfall Measuring Mission (TRMM)‐LBA in Southwest Amazonia, have provided upper‐air information with high temporal and spatial resolution to describe the structure of both the LLJ and the SJ during the January–April 1999 period.