Eventos extremos de gelo marinho no Mar de Weddell e sua relação com o Anticiclone Subtropical do Anticiclone Subtropical do Atlântico Sul.

Abstract

In Brazil, we are under the influence of the South American Monsoon System (SAMS), which irregularly distributes precipitation over a big part of the territory, concentrating the rains in the summer season. In winter, one of the systems responsible for modifying climatic conditions is the South Atlantic Subtropical High (SASH), which generates a high pressure zone that tends to advance over the continent and inhibit precipitation. In the summer, SASH has a climatological position positioned to the east and contributes to the entry of moisture from the ocean. Antarctica also plays a role in the planet's climate, as it has connections to distant regions via polar air masses, frontal systems, cyclones and stormtracks. In this study, the role of Weddell Sea ice during its extreme retraction (SIER) and expansion (SIEE) events was analyzed in order to understand its capacity to affect SASH circulation, indirectly affecting precipitation on the continent. In addition, the role of sea ice of Weddell Sea in the polarity of the Southern Annular Mode (SAM) index was compared. To achieve these objectives, the following data were used: NSIDC sea ice extent between 1981-2015; Data from the Era-Interim climate reanalysis, provided by the ECMWF, between 1981-2015; Precipitation gridded data provided by the dataset of Xavier, King and Scanlon (2017); Monthly SAM index obtained through CPC / NOAA, between 1981-2015. The extreme events of the months of February / March and September / October were obtained using the percentiles technique, and the years referring to the percentiles of 10% and 90% were analyzed, with lag of one month also being analyzed (lag=0 and lag=+1). After determining the events, atmospheric fields were generated for pressure anomalies at sea level, geopotential height at 500 hPa, zonal wind at 250 hPa and precipitation in Brazil, at a statistical significance of 10%. The monthly SAM index was compared to the years of SIER and SIEE. The results indicated that SIER events in the WS during the analyzed months cause a possible weakening in the SASH and the polar jet stream, while strengthening the subtropical jet stream and the surface pressure in the WS, resulting in a decrease in rainfall in the tropical region of Brazil, with a probable suppression of the activity of the South Atlantic Convergence Zone (SACZ). The opposite conditions were observed during SIEE events. In the analysis of the SAM index and the extreme events of sea ice, it was verified the previous relation raised by Raphael et. al (2010) and Parise et. al (2015), with the SIER events in the WS having a greater influence in the signal of the SAM for the negative phase. Both results confirm the importance of the Antarctic sea ice in the atmospheric circulation, both in the propagation of transient systems and in precipitation in Brazil, evidencing the necessity of including these factors in the national monitoring and forecasting for a better planning and management of water, energy and agricultural resources.