Articles | Volume 19, issue 1
31 Jan 2001
 | 31 Jan 2001

Energetics of the summer circulation over South America

M. C. de Lima Moscati and V. B. Rao

Abstract. We have investigated the energetics of the summer circulation over tropical and extratropical South America. The kinetic energy equations of divergent (Kχ ) and rotational (Kψ) motion are utilized. All the terms of these equations are calculated on each day for five summers (November-February 1985–1990), using global wind analysis from the National Meteorological Center (NMC), now National Centers for Environmental Prediction (NCEP). The regional kinetic energy balance showed that the energy cycle over South America during the summer is, A P E to Kχ through the term -χ2Φ,and Kχ to Kψ through the term fψ ∙ ∇χ. In the literature, several dominant oscillation modes have been noted over South America, namely the annual cycle, inter-annual, seasonal, intraseasonal, and high frequency scales, as revised by Lima. Results of the power spectrum analysis of kinetic energy terms indicate several statistically significant peaks and these have been confirmed with a fouth-order Butterworth filter. A well-defined mode, with a period around 30 days, was detected in the terms -χ2Φ and fψ ∙ ∇χ, likely associated with Madden-Julian Oscillation (MJO). Later, we discuss the local kinetic energy balance using Mak’s local energetics scheme. We attempted to verify how the intraseasonal component interacts with other dominant oscillations over South America, such as seasonal cycle and high frequency disturbances,. It is noted that the major interactions among the three temporal scales occur mainly close to the South Atlantic Convergence Zone (SACZ) region. The temporal scale interactions in the Bolivian High (BH) and Northeast Brazil Low (NL) are distinct, and the dominant temporal scales may change from year to year.

Key words. Meteorology and atmospheric dynamics (climatology, general circulation, tropical meteorology)