Polar Outbreaks in South America and Cyclone/Anticyclone Climatological Tracks.

PEZZA, ALEXANDRE; MÜLLER GABRIELA V; AMBRIZZI, TÉRCIO

São Paulo

Workshop; II Workshop on Extreme Climatic and Paleoclimatic events in South America: Teleconnections between low and high Latitudes; 2003

In this work, it is presented a climatology (1973 ? 2002) of surface cyclone and anticyclone tracks associated with strong polar air outbreaks in Sao Paulo, Brazil, during wintertime. The trajectories have been determined through the use of the NCEP Reanalysis data applied to a robust automatic tracking scheme developed at the University of Melbourne (Australia). The tracks responsible for the cold advection (early stage) and for the enhanced radiational cooling (late stage) were composed for different polar air thresholds in Sao Paulo (daily low temperatures below zero, between zero and 2.5 degrees with or without frost on the ground, and above 2.5oC with frost occurrence). Our results indicate that there is a strong meridional displacement in most cases, particularly in relation to the anticyclones. For all cases, there is a couple cyclone/anticyclone associated (cold advection), but their intensities and trajectories are very variable. Some anticyclone tracks also presented a very large zonal displacement, beginning over the west Pacific. Regardless of the traditional thinking that strong anticyclones are always the major responsible for frost occurrence in the tropical area, it is shown that the cyclogenesis in the eastern coast of Southern Brazil and Argentina plays an important physical role not only in the polar outbreak itself, but, particularly, in the frost occurrence in Sao Paulo