Annual and Monthly Trends in Frost Days in the Wet Pampa

FERNANDEZ LONG, MARÍA ELENA; MULLER, GABRIELA VIVIANA

Foz do Iguazu, Brasil

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

AMS

The aim of this paper is to evaluate the annual and monthly trends (March-October) of frost days, as defined by days when the minimum temperature is below 0ºC at the meteorological stations of the central-eastern region of Argentina, called the wet Pampa. This was done for the 1964-2003 period. The annual analysis presents a no significant negative spatial average of trend of the frost frequency, when considering an average for the whole region. The regional analysis indicates pronounced variations in the northeast zone of the wet Pampa. One of the stations with a singular behavior is Sauce Viejo (Santa Fe province), which has a significant negative trend. On the other hand, the stations near Sauce Viejo like Paraná, Concordia and Ceres show an opposite, although not significant, sign. It stands out on the southern part of the region two sub regions with a well defined east-west dipole. To the west it is seen a nucleus with significant negative trend (Santa Rosa, Pigüé, General Pico, Bordenave and Anguil). The eastern nucleus shows significant positive trends (Coronel Suarez and Tandil). Finally, it was found that the annual minimum temperature has a positive (negative) trend in those places where the frequency of frosts shows a negative (positive) trend. The spatial average of trends in the autumn months present decreasing values. From May the trends have a differential behavior, starting to show the center-south region of Buenos Aires province with a positive trend. During the winter, the months of June and August present negative spatial average of trends with stronger values in August. In the north of the studied region the trend becomes positive in Ceres and Concordia. However in July a positive spatial average of trends is seen, contrast with the annual trend. On the other hand, there is negative trend in the minimum temperature, which is particularly significant in Tandil. In spring there is a non homogeneous behavior. September has a negative spatial average of trend seen in the south-east of Buenos Aires, with some isolated meteorological stations presenting the same positive trend. However in October this trend is only maintained for Coronel Suarez. November presents very few frost events, this being the reason why it is not considered in the analysis of the trends.