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Ann. Geophys., 20, 717-727, 2002
www.ann-geophys.net/20/717/2002/
© European Geosciences Union 2002
Transport of potential vorticity and Eliassen-Palm fluxes for two contrasting years: 1995–1996 (La Niña) and 1997–1998 (El Niño)
S. H. Franchito, V. Brahmananda Rao, J. P. R. Fernandez, and S. R. Chapa
Centro de Previsão de Tempo e Estudos Climtáicos, CPTEC Instituto Nacional de Pesquisas Espaciais, INPE CP 515, 12201-970, São José dos Campos, SP, Brazil
Correspondence to: S. H. Franchito (fran@cptec.inpe.br)
Abstract. Potential vorticity
transport (PV)-Eliassen and Palm (EP) cross sections are studied for two
contrasting years: 1995–1996 (La Niña) and 1997–1998 (El Niño). The
results show that the largest differences in PV transport-EP fluxes between El
Niño and La Niña events occur in winter in both hemispheres, but the changes
are higher in the Northern Hemisphere. PV transport-EP fluxes are stronger in
both July 1997 and January 1998 than in July 1995 and January 1996,
respectively, indicating stronger baroclinic activity in the El Niño year
compared to the La Niña year. The changes in PV transport seem to be due
mainly to the changes in eddy heat fluxes. Due to the increase in the wind
shear the Eady growth rate is stronger in the 1997–1998 El Niño compared to
1995–1996 La Niña. Consequently, the zonal winds are stronger in the El
Niño event, although the location of the jet streams is almost the same in
both the contrasting years. However, in the Southern Hemisphere, there are two
regions of maxima Eady growth rate in July 1997 and a double jet is observed
while a single jet is seen in July 1995 associated with only one maximum of
Eady growth rate. In the case of summer, there is little difference in PV
transport-EP fluxes between the two contrasting years in the hemispheres,
although they are slightly higher in the El Niño event than in the La Niña
event.
Key words. Meteorology and
atmospheric dynamics (climatology; general circulation)
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