Cold and warm events over argentina and their relationship with the ENSO phases: risk evaluation analysis

摘要

The main purpose of this work is to provide a broad assessment of the influence of the El Nino-southern oscillation (ENSO) on the frequency of extreme temperature events throughout the year in Argentina. The cold and warm events, defined by the persistence of significant anomalies arising from the maximum and minimum temperatures, are more intense in the subtropical latitudes, north of Argentina (northeast for cold events and northwest for warm events), during the coldest months, and in the south (higher latitudes) in the warmest months. The persistence of the air masses is always greater in the north. The warm (cold) events have a preferential region of dissipation in the northwest (northeast) of Argentina, close to the Andes. The effect of the ENSO phases on the probability of occurrences of these events has a large inter-monthly variability. The different La Nina episodes are more homogeneous in relation to their effects and feasibility for the prediction of extreme temperatures within the region, especially for cold events. During La Nina episodes, all 2 month periods (except August-September) present a higher occurrence probability of very persistent and intense cold events, compared with Neutral months in different regions of the country. Conversely, the different El Nino episodes are more heterogeneous and, therefore, their effects on temperature are more varied and so less predictable. However, El Nino episodes exhibit a stronger signal, which is associated with the tropical air incursions that generate extreme warm events, particularly in winter. These events have a higher occurrence probability in the north and a lower one in the south during the months of June of November. Gold events have a lower occurrence probability in different regions, during the El Nino phase, in the period April to September. In some cases, the ENSO signal is stronger in daily temperature values than in monthly ones over Argentina.