This work investigates the seasonal variability occurrence of cold and warm waves in the Brazilian State of Rio Grande do Sul and its relationships with El Niño and La Niña events. 39 years (1967-2005) temperature data series from 13 uniformly distributed meteorological stations over the State were used. The relationships between waves and ENOS were obtained from 2x2 contingence table analysis for the central months of each season. The statistical significance was evaluated using the Fisher exact test. It was observed that the seasonal variability of cold waves is different than the warm wave variability. There are more cold waves during the months with lowest minimum temperatures, and the warm waves have a more heterogeneous behavior. In most localities, the relationships between the occurrence of the warm waves and El Niño events are more significant in July. For La Niña and cold waves, the month with more significant relationships is April. In both cases, there are lags between the El Niño/La Niña occurrence and their impact in the setting of warm/cold waves.
cold waves; warm waves; ENSO; contingency tables
