Interannual variability of temperature spells over Argentina

This work is aimed at studying the interannual variability of surface temperature cold spells and warm spells due to cold-and warm-air incursions. The effect of the ENSO event on the occurrence of extreme spells having three different indices was studied. In order to track changes during the 1959/96 period, spell parameters, persistence and intensity, have been studied from daily temperatures. The number of extreme spells per year show low frequency variability plus a biennial variability, which is more important in its intensity than in its persistence, and in summer rather than in winter. The number of extreme warm spells increases until the end of the sixties and seventies, reflecting an increase of northeasterly flow. From then onwards, the trend starts to decline significantly over northern Argentina. The interannual variability of extreme winter cold spells increases from the 80's onwards, indicating the variation of anticyclone permanence over the country. Cases are more numerous in the latest years. Extreme spell occurrence in northern Argentina is closely linked to the El Nino phenomenon. Winter warm spells are more persistent in an El Nino (0) year and more intense and persistent in the year following El Nino. In summer, however, there is either no difference, or the relationship is reversed, resulting in more intense situations in November and December in the case of La Nina. Cold spells reaching the northeastern most part of the country are more persistent when La Nina occurs, the conclusion being that the region would be affected by extreme cold spells when La Nina is active.