Teleconnection Patterns and Rossby Wave Propagation Associated to Generalized Frosts over Southern South America?

MÜLLER GABRIELA V; AMBRIZZI TÉRCIO

Climate Dynamics

Springer Link

Año: 2007 vol. 29 p. 1432 - 1894

1432-0894

Based on previous observational studies of themean atmospheric circulation leading to generalized frosts(GF) in central Southern South America, it is possible toestablish a hypothesis that specific large scale patterns areassociated to the frequency of occurrence of these eventsthrough the propagation of Rossby waves remotely excited.This hypothesis is tested here through a teleconnectionanalysis for austral winters which present an extreme frequencyof occurrence of GF in southeastern South America,particularly over the Wet Pampa area in Argentina.Rossby wave propagation regions are identified for twobasic states given by the composition of winters withmaximum and minimum frequency of GF occurrence,during the 1961-1990 period. The stationary wavenumberKs indicates the regions where the Rossby wave propagationis permitted and those where it will be inhibited (Ks = 0), highlighting the importance of the jets as waveguides.Nevertheless, differences exist between both basicstates analyzed. These differences indicate that the locationsfor wave generation and its later evolution are conditionedby the basic state. Results are validated through abaroclinic model, which simulates the Rossby wave patternsresponsible for the teleconnection. Numerical experimentsconfirm that the principal wave activity takes placeinside the subtropical and polar jets. In particular, for thebasic state with maximum frequency of GF occurrence, thewave trains propagating inside the subtropical and polarwaveguides merge just before entering the continent, asshown by the observations prior to the occurrence of GFevents. This configuration favors the development of anintense south wind anomaly with large meridional extensionwhich results in the intensification of anticycloniccirculation in southern South America. A conceptual modelis presented to summarise all these results.