Teleconnection Patterns Associated with Extreme Frequency of Generalized Frosts. Part II: Origin and Evolution of The Rossby Waves Propagation Patterns in the Austral Hemisphere

MÜLLER GABRIELA V; AMBRIZZI, TÉRCIO

Foz do Iguazu, Brasil

Conferencia; 8th International Conference on Southern Hemisphere Meteorology and Oceanography; 2006

American Meteorological Society (AMS).

The Southern Hemisphere teleconnection patterns associated with extremes of occurrence of Generalized Frosts (GF) over Central-Northwestern Argentina are investigated through a General Circulation Baroclinic Model (GCBM) in order to better understand the dynamical mechanisms linked to these meteorological systems. Some characteristics of the basic states to be used here were described in the Part I of this work, i.e., they were divided in two winter groups, one with the maxima (+ó) occurrence of GF and another with minima (-ó) occurrence during the 1961-1990 period.  The perturbed forcing in the numerical experiments is positioned over the regions where the basic state analysis for +ó and ?ó indicates the generation Rossby wave patterns that could lead to GF over the South American continent. From the numerical simulation of the stationary wave pattern with origin in the subtropical Indian Ocean, it is possible to see that the wave activity follows the subtropical and subpolar waveguides but with different propagation patterns for each basic state. In particular, for the +ó flux, the wave train propagates along the subtropical and subpolar jet until near the South America south cone, where their phase coincide just before entering the continent, in agreement with observations in the days previous to GF occurrence. For the -ó simulations, despite the propagation obtained along subtropical and polar latitudes, no wave phase coincidence is observed near the South American continent. In addition, a numerical experiment with the heating forcing over the tropical west Pacific Ocean, to mimic the convection observed in the +ó basic state, was carried out. The simulated Rossby wave pattern reaches South America, creating a southerly wind anomaly in all the southern part of the continent, although is not able to reproduce the pattern shown by the observations which, in turn, coincides with the one obtained in the previous experiment with the forcing over the Indian Ocean. These results suggest that despite of the role played by the subtropical and subpolar waveguides to generate the GF, the position of the initial perturbation is also quite important.