Observational and modeling studies of Upper-air wave trains over the Pacific Ocean and wintertime polar outbreak in Southeastern Brazil

Observational evidence and modeling for the southern hemisphere teleconnection patterns in austral winter, are examined through upper and lower-level circulation, using NCEP reanalysis for the period June-August 1979-98. Rossby wave activity has been linked to cold surges into southeastern Brazil. The occurrence of polar outbreaks and freezes in subtropical Brazil has been associated with circulation features in both tropics and extra tropics, that resemble wave trains originated somewhere on the western Pacific, and that propagate all the way across to the Pacific towards South America. This variability is coupled to large-scale changes in the temperature and pressure fields in South America south of the equator, and to convection in northern South America. This represents a wave like, result of local anomalies in the atmospheric circulation over the western Pacific and their influence on the temperature conditions in the remote areas of southern and southeastern Brazil.

In this study we examine the observed near-surface and upper-level atmospheric circulation, air temperature and convection anomalies that leads to strong surface cooling in southern Brazil during austral wintertime (JJA), on time scales of less than a month, as represented by a composite of strong cold surge cases detected in southern Brazil. This is an attempt to identify and isolate the forcing of the wave train and to study their propagation throughout the Pacific Ocean before, during, and after freeze events episodes in southern Brazil, and allowing a forecasts of these events. Baroclinic modeling was performed to identify the possible source region of these waves in the western Atlantic, and to study the dependence of the intensity of the cold surge and the location/intensity of the wave sources. We expect to prove that the cold outbreaks due to incursions of polar air into tropical and subtropical Brazil, and the day-to-day variations of surface air temperature on those regions may be driven by wave activity originating in the western Pacific, that travel across the Pacific, and once reaching the west coast of South America

are directed toward the equator to the east of the Andes.