Seasonal climatology of cold fronts in south-central South America from an automated detection system

Abstract

The cold fronts (CF) operating in south and south-central South America are the main ones responsible for heavy rain, thunderstorms with strong winds, and accentuated temperature drops. This study aimed to perform a seasonal climatology of CF’s displacement and intensity in the region above mentioned. A computational algorithm was developed called the Normalized Cold Front Detection Index (NCFI) for detecting and characterizing CFs through the CFSR and CFSv2 reanalysis data, using the meridional component of the wind at 10 meters and the air temperature at 2 meters. Ten areas were delimited: five coastal and five continentals. Seasonal climatology showed a higher frequency in winter, when these systems are more intense, averaging 20 per year. The patterns of displacement and intensity exhibited a decrease in CFs as they advanced toward lower latitudes. The synoptic analysis and the accumulated precipitation composites revealed that the CFs that act in the spring concentrated the accumulated precipitation in Santa Catarina’s western portion. In the summer, convection cells are responsible for storms and poorly distributed rain. In the autumn, rainfall is associated with CFs and maritime circulations, impacting Rio Grande do Sul and the west and north of Santa Catarina. In the winter, CFs dominate the precipitation pattern. According to the NCFI, spring, autumn, and winter cases are categorized as intense, while summer cases are moderate.