Interaction of cold fronts with the Brazilian Plateau: a climatological analysis

摘要

Complex orography of elevated terrain and numerous peaks can act as an important physical barrier to the atmospheric flow and can generate a range of meteorological phenomena. The objective of this study is to investigate the effect of the Brazilian Plateau on the spatial distribution of cold fronts and their climatology for the period between 1979 and 2010 using Climate Forecast System Reanalysis data. The cold fronts are detected and divided into three groups, according to their frequency and trajectory over South America: the continental fronts are referred to as the AN group; the fronts that pass over the coastal region of Sao Paulo are referred to as the SP group; and the fronts that pass over the two areas are referred to as the ANSP group. Composites of means and anomalies of atmospheric variables are constructed for each group. The investigation focuses on the orographic effects of the Brazilian Plateau on the climatology of the cold fronts. The Brazilian Plateau affects the spatial distribution ofmaximum and minimum frontal frequency. The number of cold fronts over the elevated regions of the Brazilian Plateau is significantly lower than in the surrounding regions. The maximum frontal frequency is found to the east of the Andes and a secondary maximum is found along the Southeast coast of Brazil. The main effect of the Brazilian Plateau on the mean and anomaly fields of meteorological variables is to block the dry and cool post-frontal air at lower atmospheric levels. The most significant anomalies are found in the ANSP group of cold fronts, which are more intense and move more rapidly eastward. On the other hand, the AN cold front group is the most frequent, but the weakest and easily affected by the Brazilian Plateau orography.