High-frequency patterns of the atmospheric circulation over the Southern Hemisphere and South America

Daily 500-hPa geopotential height and 250-hPa meridional wind reanalyzed da ta obtained from the National Centers for Environmental Prediction are used to document austral winter (May to September) and summer (November to Marc h) high-frequency variability in the Southern Hemisphere (SH) midlatitudes for the 1990-1994 period. Empirical orthogonal function (EOF) technique is used to determine the high-frequency patterns for these variables in select ed areas. The high-frequency anomalous 500-hPa geopotential height patterns for two areas in the SH midlatitudes (the zonally global domain and the we stern hemisphere) and the high-frequency anomalous 250-hPa meridional wind patterns in the western hemisphere between 15 degrees N and 70 degrees S ar e discussed. The high-frequency winter and summer patterns for both variabl es feature a wavetrain structure in the SH midlatitudes which is related to synoptic-scale systems, such as cyclones and anticyclones associated with frontal zones. The dominant high-frequency patterns in the SH midlatitudes manifest in the eastern hemisphere while the secondary ones appear in the s outheastern Pacific. Analysis of the western hemisphere data reveal that th e wavetrain in the South American sector extends northeastward over the con tinent, thus affecting the regional weather conditions. An important result presented here concerns the preference of the intense synoptic systems in the eastern hemisphere and in the southeastern Pacific to occur in a sequen tial instead of an intermittent fashion. This result might have a potential for being used in weather monitoring.