Rossby Wave Propagation and its Relationship with Severe Frosts Over South America.

MULLER, GABRIELA V; AMBRIZZI, TÉRCIO

Clivar Exchanges

Año: 2006 vol. 11 p. 16 - 19

1026-0471

The hypothesis that an anomalous heating in the occidental tropical Pacific can generate propagation of a Rossby wave towards South America favoring the occurrence of generalized frosts is tested using the ray tracing technique. The waves starting point was based on the OLR austral winter negative anomaly composites during the maximum occurrence of GF +ó. The ray paths showed that the wavenumber 3 was the only one to reach South America. This result is in agreement with numerical simulations using the same basic state. In this case a clear Pacific South American pattern is observed. For the analysis using a GF -ó flux, the ray path and propagation patterns were very different and any Rossby wave passed through the South American continent. Through ray tracing analysis and in agreement with some previous numerical and observational studies, anomalous convection over the tropical west Pacific can generate a Rossby wave pattern that will favor extreme generalized frosts over the Wet Pampa in Argentina. This work emphasizes how important is the atmospheric basic state variability to influence these events and indicates a specific analysis tool to study these patterns.