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Ann. Geophys., 19, 83-97, 2001
www.ann-geophys.net/19/83/2001/
© European Geosciences Union 2001
Energetics of the summer circulation over South America
M. C. de Lima Moscati and V. B. Rao
Instituto Nacional de Pesquisas Espaciais/Ministério da Ciência e tecnologia - INPE/MCT 12.227-970 - São José dos Campos, SP - Brazil
Correspondence to: M. C. de Lima Moscati, (marley@met.inpe.br)
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 -χ∇2Φ,and Kχ to Kψ through the term f∇ψ ∙ ∇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 -χ∇2Φ and f∇ψ ∙ ∇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)
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