Intraseasonal variability of the North Brazil Undercurrent forced by remote winds

Abstract

[1] Intraseasonal signals with periods of 2 to 3 weeks in near-surface alongshore current measurements are detected from four moorings (K1-K4) deployed from 2000 to 2004 at the 11 S section close to the Brazilian coast as part of the German CLIVAR Tropical Atlantic Variability Project. This section crosses the path of the North Brazil Undercurrent, the most powerful western boundary current in the South Atlantic Ocean. We investigate the origin of this intraseasonal variability of the North Brazil Undercurrent by relating the oceanic oscillation of the alongshore currents to its atmospheric counterpart, the meridional wind stress. On average, the results indicate a well-defined lagged (10 days) correlation ($0.6) structure between meridional wind stress and alongshore currents. The oceanic region with the highest cross-correlations is identified as a relatively narrow band along the Brazilian coast, from 22 -36 S and 40 -50 W, bounded in the north by an eastward change in coastline orientation. The cross-wavelet transform establishes the common power between the time series of meridional wind stress and alongshore currents, predominantly during austral winter and spring. These signals propagate equatorward with an alongshore speed of 285 AE 63 km day À1 , consistent with Coastal Trapped Wave theory.

Interannual to decadal changes in the western boundary circulation in the Atlantic at 11°S

“…The variability in NBUC and DWBC transport at 5°S and 11°S in the Atlantic is investigated using seven ship cruises, two mooring time series (2000-2004 and 2013-2014), and a numerical simulation. While former studies relying on direct observations focused more on intraseasonal to interannual variability of transports and velocity [Dengler et al, 2004;Schott et al, 2005;Veleda et al, 2012], the focus of this study is on interannual to decadal changes in transports, velocity, salinity, and oxygen at this location.…”

When Bergmann's rule fails: evidences of environmental selection pressures shaping phenotypic diversification in a widespread seabird

“…velocity) (Richardson and Walsh ). SPSP is also influenced by the Equatorial Undercurrent, which flows in the opposite direction (eastward), approximately 80 m deep (Veleda et al ). It decelerates when it reaches the SPSP archipelago, generating vortices on the east side and increasing the residence time of nutrients around the SPSP (Araujo and Cintra ), as commonly observed around seamounts (Mullineaux and Mills ).…”

Indirect investigations of the Atlantic Meridional Overturning changes in the South Atlantic Ocean in numerical models for the 20th century

“…As mentioned before, the NBUC originates south of 10°S from the SEC bifurcation (e.g. Stramma & England (1999a), , Harper (2000), Wienders, Arhan & Mercier (2000), Scho et al (2005), Rodrigues, Rothstein & Winbush (2007), Silva et al (2009), Veleda et al (2012) and the bifurcation position has a direct effect in this current seasonal variability. Previous studies, using mooring data at 11°S show that the NBUC core has a dominant uctuation with a periodicity of two months (SCHO et al, 2005;SCHUCKMANN, 2006).…”

“…is subsurface ow, proposed by Scho & Böning (1991), was rst described (as NBUC) by Stramma, Fischer & Reppin (1995) using velocity data. It is a strong western boundary current, with a nearshore core position, approximately 50km from Brazilian coast, reaching down about 900m in depth, with maximum speed of about 0.65m·s −1 at 180 to 250m on average (SCHO et al, 2005;VELEDA et al, 2012). As mentioned before, the NBUC originates south of 10°S from the SEC bifurcation (e.g.…”