Teleconnection Patterns Associated with Extreme Frequency of Generalized Frosts. Part I: Rossby Waves Propagation Regions 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).

Based on the linear theory of Rossby wave propagation, wave propagation patterns associated with extreme occurrence of Generalized Frosts (GF) over the center and northwest of Argentina were identified in the Austral Hemisphere. Using the stationary wavenumber (Ks) it is possible to show the regions where the Rossby waves may or may not propagate. For different wavenumbers the corresponding waveguides were calculated for two basic states related to winters with extreme frequency of GF occurrence (maximum and minimum). As it would be expected from the theory the Ks distribution emphasize the jet stream as efficient waveguides, having its maximum zonally orientated. For the analyzed basic states it was found wavenumbers 6 and 7 along the subtropical jet. However, for the subpolar jet there were some differences in the wavenumbers distribution, in both basic states, although wavenumber 3 was the most predominant at high latitudes. From the wave theory analysis the main features that favor the large occurrence of GF are: i) an intense subtropical jet and a well define subpolar jet close to the South America; ii) an inhibition region of Rossby wave propagation (Ks=0) near the continent. On the other hand, the characteristics that do not favor GF are: 1) a weak subtropical jet near South America and a less defined subpolar jet over the Pacific Ocean; 2) Rossby wave inhibition region over the continent coincident with the entrance of synoptic systems region in South America. The observed difference between the two analyzed basic states indicates that Rossby wave propagation is conditioned by the basic states themselves, and the teleconection mechanism is favored during winters with maximum occurrence of GF. It seems that the maxima occurrence of GF is dependent of the interaction on the subtropical and subpolar waveguides near the South American continent.