Cold fronts responsible for intense winds in the Santos Basin, Brazilian Southeast Offshore Region

Abstract

This work aimed to identify the synoptic conditions associated with the cold fronts (CFs) passage that causes intense winds in the Santos Basin. Furthermore, the atmospheric characteristics of the CFs, which generated intense (INTW) and moderate (MODW) winds in the studied area, were identified. For this purpose, INTW and MODW composites of CFs episodes were elaborated. First, the INTW and MODW cases were selected from the 10 m wind intensity observed in the Santos buoy, belonging to the Brazilian National Buoys Program. Satellite images and synoptic surface charts were analyzed to identify the synoptic systems responsible for INTW and MODW in the Santos buoy, keeping only the cases generated by CFs. From the comparison between the composites, it was possible to observe in INTW: (i) a stronger pressure gradient over the Santos Basin, with the isobars presenting an almost meridional position near the basin, which caused the intense winds registered in the buoy; (ii) a baroclinic trough at medium and high levels reaching the Santos Basin region, located westward of the surface system; (iii) stronger 1000-500 hPa layer thickness and dew point temperature gradients over the continent, reaching the Santos Basin region, and (iv) a colder and drier air mass over southern Brazil. On a large scale, the Rossby wave tracings were analyzed, where different wavenumbers were noticed for each composite. In INTW, the wavenumber was 2, while in MODW, it was 2 and 3. Finally, the main characteristics found in the composites were observed in the case studies.