Cold Extremes in Central Southern South America and the Possibility of Seasonal Forecast.

FERNANDEZ LONG, MARIA ELENA; MULLER, GABRIELA V

Beijing, China

Conferencia; Earth System Science Partnership (ESSP) Global Environmental Change Open Science Conference; 2006

This paper studies the relationship between the frequency of frosts in the wet Pampa region of southern South America and the Pacific Ocean SST as well as the PDO. The frequency of frosts is defined in terms of the number of days with frost, i.e. days with minimum temperature below 0ºC, over 50 weather stations in the region during the period 1964-2003. The wet Pampa is the main agricultural region of Argentina and its crop production is frequently affected by frosts. There is a  negative correlation between the Niño3 index and the frequency of frosts during fall, winter and spring, a result that is consistent with the fact that during warm (cold) Enso events there are less (more) frost events. The relationship becomes stronger when we consider the change in SSTs between summer and spring.  In this case, the negative correlation indicates an increase (decrease) in the number of winter frosts when the SST anomalies become colder (warmer) between the previous summer and the following spring. The relationship between the annual frequency of frost and the PDO index of the previous year is negative over most of the region, and the southern part shows an east (negative)-west (positive) dipole. The relationship found with the Enso phases and the PDO suggests the possibility of establishing the prevalent seasonal conditions for the development of frosts with enough advance so it could be of utility in agricultural planning.