Interdiurnal Surface Pressure Variations in Brazil: Their Spatial Distributions, Origins and Effects

Abstract

A study is made of the spatial correlation of interdiurnal surface pressure variations in Brazil. Pressure oscillations that occur in southern Brazil, associated with midlatitude synoptic systems, are shown to be positively correlated with pressure oscillations near the equator. The correlation maxima show an eastward displacement with increasing lag. Interannual variability in the correlation coefficients is discussed and related to variability in the intensity and frequency of midlatitude systems, which affect the region. Some Southern Hemisphere synoptic systems have a marked effect on convective activity over the Amazon Basin, with the area of maximum activity showing an eastward displacement with time. A principal component analysis reveals that only the patterns of the first four eigenvectors have readily identifiable causes. These are associated with large-scale features, such as planetary waves and blocking, and typical wintertime, summertime and springtime patterns. The corresponding eigenvalues explain ∼85–95% of the total variance.