South American Cold Surges: Types, Composites, and Case Studies

Abstract

This paper examines the climatological, large-scale, and synoptic-scale aspects of South American cold surges using NCEP-NCAR gridded reanalyses for the 1992-96 period. Three common cold surge types are identified on the basis of a thickness (1000-850 hPa) criteria: type 1-a transient surge associated with weak anticyclone development east of the Andes in the absence of ridging aloft, type 2-a strong and persistent surge associated with dynamic anticyclogenesis aloft and strong surface anticyclone development east of the Andes, and type 3-a surge east of the Brazilian coastal mountains. Cold surges are most common during the winter and spring (Jun-Nov), accounting for 189 of the 256 events (74%).