Resposta da circulação no oceano Atlântico Tropical oeste ao Modo Meridional do Atlântico

Abstract

This work analyzed Atlantic Meridional Mode (AMM) influence on ocean circulation of Tropical Atlantic (TA) during extreme precipitation years. Were used temperature and current velocity data of SODA reanalysis, the dipole index and standardized precipitation anomalies in Fortaleza between 1980 and 2008. Positive and negative composites were chosen using years presenting, positive index and standardized precipitation anomalies below -0.5 (four drier years), and negative index and standardized precipitation anomalies above 0.5 (eight rainiest years), respectively. Surface and subsurface means and two meridional sections were performed on TA to make composites of each variable. In drier years, positive temperature anomalies prevail on east and northeast Brazilian coast and NEA region presents highest intensification of positive anomalies, which can cause droughts in Fortaleza. The opposite occurs in rainiest years. Small transport values were found for Equatorial Undercurrent (EUC) because the chosen section is close to its forming region. Higher EUC transport was find during AMM negative phase (rainiest years), the opposite of what was expected, being higher in March and April in both events. The North Brazilian Undercurrent/North Brazilian Current (NBUC/NBC) presents weakening during rainiest years and presents the biggest differences when the extreme precipitation years are compared, being always stronger in drier years. In drier years, with the NBUC/NBC intensification and positive temperature anomalies on east and northeast Brazilian coast, more heat is transported from the South hemisphere to the North hemisphere, which can increase the northern region temperatures. This temperature rise displaces the Intertropical Convergence Zone (ITCZ) northward, causing droughts in Fortaleza. The opposite occurs in rainiest years. Since the transports was similar in extreme precipitation years, it was not possible to find relationship between North Equatorial Countercurrent (NECC) and EUC with the occurrence of extreme precipitation years. Equatorial upwelling strengthens over the months in drier years due to east-west temperature gradient intensification. In drier years, downwelling in northeast Brazilian coast is enhanced by northeast trade winds intensification.