Brazil Malvinas Frontal System as seen from 9 years of advanced very high resolution radiometer data

Abstract

Surface thermal fronts in the southwestern Atlantic (SWA) Ocean are examined using 9 years (1987–1995) of advanced very high resolution radiometer data. Fronts are detected considering a gradient based edge detector. Sea surface temperature gradients are calculated from 4 km resolution 5‐day composite images covering the western Argentine Basin south of 30°S. Variability in the position and intensity of the fronts from seasonal to interannual timescales is characterized in six regions including different parts of the Brazil Current Front (BCF) and the Subantarctic Front (SAF): Shelf Break‐Brazil (SB‐B), Brazil Malvinas Collision (BM‐C), Brazil Current‐Overshoot (BC‐O), Shelf Break‐Malvinas (SB‐M), Malvinas Return Flow (MRF), and Falkland Escarpment (FE). Fronts in the SB‐B, SB‐M, MRF, and FE regions are controlled by the bathymetry. In the BM‐C region the BCF and SAF appear to merge as a single front. This front does not present large seasonal north‐south excursions as previously described, though it pivots seasonally around a fixed point located approximately at 39.5°S, 53.5°W, changing its orientation from N‐S in winter to NW‐SE in summer. Consequently, on average, the front intersects the 1000 m isobath at 38°30′S in summer and north of 37°S in winter. In the BC‐O region the BCF has a U‐shape centered at 53°W. The intensity of the fronts in each region except in the FE region presents large seasonal variability. In the SB‐B, BM‐C, and BC‐O regions the frontal intensity is highest (>0.35°C/km) during austral winter, the annual components explain 83, 67, and 71% of the total variance, respectively. In the SB‐M and MRF regions the SAF is most intense (>0.25°C/km) in summer and fall; the annual component of the intensity fluctuations explains 29 and 38% of the total variance, respectively. In the FE region the annual component of frontal intensity explains only 17% of the variability. In the six regions, important interannual variability is found. The Zapiola Rise (centered at 45°S, 43°W) appears as a gradient‐free region. Closed planetary potential vorticity contours in this area suggest it is dynamically isolated.