Sea Surface Temperature and Atmospheric Circulation features associated to the argentinean andean rivers streamflow variability

ARANEO, DIEGO C.; COMPAGNUCCI, ROSA H.

Foz do Iguaçu, Brasil

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

American Meteorological Society - Brazilian Institute for Space Research (INPE)

The objective of this paper focuses on revealing the main characteristics of the conditions of Atmospheric Circulation and Sea Surface Temperature (SST) associated with the fluctuations of flow in the Atuel and the Chubut rivers, whose temporal behaviors represent the temporal variations found in the rivers of the Cuyo and North Patagonia regions. The relationship between streamflows and SST is significant in large areas of the Southern Hemisphere (SH) central Pacific. However, the Atuel variability seems to be highly linked to El niño / Southern Oscillation (ENSO) patterns with strong signal in the tropical-equatorial Pacific and the Indian Ocean, whereas the Chubut seems to be less associated with the ENSO, showing signal restricted to the SH central subtropical Pacific. High streamflows in the Atuel zone are associated with frequent passage of northwest-southeast oriented lows moving over the subtropical Pacific that induce moisture convergence from lower latitudes and its advection toward the Andean region. The lows reaching the central Chilean coast would produce upward air motion with intense snowstorms in the high mountains and downward air motion with relative high pressures leeward the Andes. Hence, over northeastern Argentina and southern Brazil, a later cyclogenesis would be produced and an increase in baroclinicity linked to a frontal zone with consequent moisture convergence from Brazil, upward air motion and high pre-frontal temperatures. In cases of high streamflows in the Chubut zone, the lows from the Pacific would reach the Chilean coast at higher latitudes, crossing over the natural further low Andes with no discontinuity and transporting moisture from subtropical latitudes. The subtropical low systems are linked to a remarkable reduction of the westerlies owing to higher frequency of highs from the southern Pacific. Some researchers associate these highs with equatorial SST anomalies and the decadal ENSO-like variability and they may take part of a wave-train from the Indian Ocean extended over the southern Pacific. The wave-train can be observed with the correlation between the Atuel streamflows and the geopotential height, but not for the Chubut streamflows. Inverse circulation and SST features would be associated to low streamflows in the studied regions.