Effects of the Madden-Julian Oscillation on generalized frosts in central southern South America

SHIMIZU MARÍLIA ; GABRIELA V. MÜLLER

Mar del Plata

Congreso; XII Congreso Argentino de Meteorología; 2015

Centro Argentino de Meteorología

Extreme cold events can beextremely dangerous to the society, leading to damages in agriculture,livestock, and event deaths. The processes responsible for these cold eventsincludes complex interaction mechanisms at different atmospheric scales. The frostevents that affect central and northeastern Argentina are associated with adouble wave train in the subtropical and polar jet streams and to an intensepolar air advection. However, mechanisms that interacts with these wave trains,such the Madden Julian Oscillation, can alter the patterns of temperature,intensifying or weakening these cold events. This study aims to investigate theimpacts of the MJO phases on the extreme cold events on central southern SouthAmerica during the winter. The generalized frosts days are defined as days on which minimumtemperatures below 0º were recorded at more than 75% of meteorological stationsin the Pampas. The composites for the highest and lowest number of episodes inthe period of 1979-2010 of different meteorological variables were evaluated. MJOevents were defined using a MJO index based on empirical orthogonal functionsanalysis of zonal wind and Outgoing Longwave Radiation (OLR). The results showsthat the intensification of the cold events are associated with a single extratropicalwave train and the weakening are related with a double wave train, one at thetropics and another in the extratropics. Moreover, the position of theconvection associated with the MJO can influence the number of extreme coldevents and its intensity.