Synoptic and Climatological Characterization of Post-Frontal Rainfall Events in Rio De Janeiro

Abstract In the City of Rio de Janeiro (CRJ), light to moderate rain can occur even after the total displacement of a Frontal System (FS) over the State. This phenomenon is known as precipitation from “sea circulation effect”, but there is no documentation about this, being restricted to the knowledge of the local servers. This study aims to characterize this phenomenon climatology (2000-2013), and to identify the associated synoptic conditions. From all the FS passages through CRJ, using satellite imagery and observed precipitation, the events were classified into three categories: No-Rain Post Front (NRPF), Rainy Post Front (RPF) and Excluded Post Front (EPF). The results show that more than half of the events are EPF (52%), 32% are NRPF and 16% are RPF. The EPF cases are more frequent in summer, NRPF in winter and spring, and RPF in fall. The composites from NRPF and RPF using ERA-Interim Reanalysis indicate that the post-frontal precipitation is associated with the convergence of strong southerly winds while reaching the continent, leading to the formation of precipitating stratiform clouds, even though the FS is no longer active in the region.