Surface pressure and temperature anomalies in Argentina in connection with the Southern Oscillation

Abstract

The interannual surface variability of pressure and temperature over Argentina is studied in connection with the Southern Oscillation (SO). Thirty nine surface records of the 1959-92 period from Argentina were used to study the anomaly pattern of the negative SO phase. Surface pressure is significantly lower over most of the country during the negative SO phase. The stronger signal is over the west and center of the country where throughout the year there is a low pressure center that appears in every mean monthly map. This west low (WL) tends to be enhanced in its center to be displaced to the south during the negative SO phase. Over Central Argentina the seasonal response varies throughout the year being negative except in summer and stronger, near 1 hPa negative, in winter. According to this anomaly pattern, except in summer, the meridional gradient over Patagonia is weakened while the zonal gradient over the center and east of the country is enhanced. It is discussed how this pressure anomaly pattern is consistent with the respective surface temperature anomalies. In Patagonia the negative SO phase coincides with cooler temperatures, while in Central Argentina except in summer, warmer temperatures are observed during this phase although they are not statistically significant. In the central part of Argentina there is a marked regularity in the pressure behavior during a period of about three years that starts in the year before the negative SO phase. In Central Argentina during almost all negative SO phases, pressure is usually lower than in the preceding and in the following year. For instance, in the eight negative SO phases studied, the pressure was lower than the average of the preceding and following year. The probability of the observed regular sequences to happen by chance was calculated with the cumulative binomial distribution and it is very low. A similar behavior, though less regular, is also observed in Patagonia. The marked regularity of the pressure response to the negative SO phase in Argentina suggests that this response is linked to features that are common to all ENSO events. The Andes mountain interaction with the anomaly circulation induced by the anomalous ENSO convection seems responsible for the strong response over the WL.