In this note, changes in temperature extremes over a 40-yr period are analyzed, based on daily minimum and maximum temperatures over Argentina. Trend analysis was performed on seasonal means, standard deviations, and extremes (5th and 95th percentiles) over the 1959-98 period. The strongest (positive) changes over time occurred in mean summer minimum temperature, whereas the standard deviation decreased. Mean maximum temperatures mostly decrease over time in summer over northern Argentina, but they increase in Patagonia (southern Argentina). Generally, negative trends were obtained in the number of cold nights and warm days per summer, while the number of warm nights and cold days has increased at certain locations. Patagonia shows many stations with an increasing number of warm days and nights in winter and a decreasing number of cold days and nights in summer. The summer mean temperature is more sensitive to extremes than the winter one. In summer, the increase in mean temperature is more strongly related to the increase in the number of warm days and nights than to a decrease in the number of cold days and nights. In winter, the region with the highest correlation was found in Patagonia, while in the most productive area (La Pampa, Argentina), very little or nonsignificant association exists between mean temperature and the occurrence of warm or cold days.

This paper describes the statistical characteristics and temporal variability of the urban heat island (UHI) intensity in Buenos Aires using 32-year surface meteorological data with 1-h time intervals. Seasonal analyses show that the UHI intensity is strongest during summer months and an "inverse" effect is found frequently during the afternoon hours of the same season. During winter, the UHI effect is in the minimal. The interannual trend and the seasonal variation of the UHI for the main synoptic hours for a longer record of 48 years are studied and associated to changes in meteorological factors as low-level circulation and cloud amount. Despite the population growth, it was found a negative trend in the nocturnal UHI intensity that could be explained by a decline of near clear-sky conditions, a negative trend in the calm frequencies and an increase in wind speed. Urban to rural temperature differences and rural temperatures are negatively correlated for diurnal and nocturnal hours both for annual and seasonal scales. This result is due to the lower interannual variability of urban temperatures in comparison to rural ones.

The aim of this study is to analyse the interannual variability of monthly climatic indices of extreme daily temperature in the central-north region of Argentina throughout a year and its relationship with the atmospheric circulation. The impact of El Niño-Southern Oscillation (ENSO) over different temperature indices throughout the year is specially analysed. Globally used indices in the 1970-2010 period are utilized for this purpose. The trends of temperature extremes show warming conditions in several months, especially in October and November. In order to find possible forcings of extreme temperature in the region at monthly scale, the co-variability with other circulation monthly time series such as changes in the intensity of Southern Hemisphere semi-permanent anticyclones and the intensity of the subtropical jet were studied. The main finding was a systematic shift of the South Atlantic anticyclone towards the west over the decades in June and August, which might hinder the cold advections over the region surveyed. Moreover, the influence of the variation on the intensity of the subtropical jet over extreme events showed significant positive (negative) correlations between the intensity of the jet and the frequency of cold (warm) indices in a great number of months. Finally, the influence of the ENSO phases on each of the temperature extremes analysed was studied. It was found that under El Niño conditions, minimum temperatures are affected quite evenly throughout the year, fostering the occurrence of warm nights. The impact of the El Niño event on the maximum extreme temperatures, however, shows seasonal differences. Between July and September warm days conditions are fostered, while between November and February the opposite (cold days) can be seen. This results in a decrease in the temperature range in the region surveyed during the summer months under El Niño conditions.