Energetics of the high frequency disturbances over South America

Abstract

The energetics of the high frequency disturbances over South America are studied using composite maps of cyclone systems. The composite maps are constructed with filtered geopotential height data at 1000 hPa for the days when negative anomalies at the base grid point 70° W, 45° S exceeded two standard deviations below the mean. The cyclone system composite has 61 cases. The spatial distribution of the available potential energy of the high frequency disturbances is similar to what is seen for the Northern Hemisphere extratropical cyclones. The energy cycle of the high-pass filtered anomalies showed that these disturbances grow by baroclinic conversion. During the growing phase, energy fluxes coming into the region and nonconservative sources are also important, although barotropic instability seems to play some role over the Pacific Ocean. At the mature stage the disturbances showed barotropic decay and radiate energy out of the region.