The Brazil Malvinas frontal system as seen from nine years of AVHRR data

SARACENO, M., C. PROVOST, A. PIOLA, J. BAVA, AND A. GAGLIARDINI

Nice, France

Conferencia; EGS - AGU - EUG Joint Assembly; 2003

Surface thermal fronts in the Southwestern Atlantic (SWA) Ocean are examined using nine years of Advanced Very High Resolution Radiometer data. Sea surface temperature gradients are calculated from 4km resolution 5-day composites covering the western Argentine Basin south of 30∞S. Six regions including different parts of the Brazil Current Front (BCF) and of the Subantarctic Front (SAF) are used to characterize the variability of the intensity and position of the fronts, from seasonal to interannual timescale: shelf break front-Brazil (SBF-B), Brazil-Malvinas front collision (BMF-C) and overshoot (BMF-O), shelf break front-Malvinas (SBF-M), Malvinas Return front (MRF) and Falkland Escarpment front (FEF). All frontal locations, except for the BMF-C, are controlled by the bathymetry. The BMF-C changes its direction from NS in winter to NW-SE in summer and intersects the 1000m isobath at 38∫ 30´ S in summer and near 37∫S in winter. In the overshoot region the BMF reaches 45∞S in winter and has a U-shape, whereas in summer it remains north of 43∞S. This meridional fluctuation has significant periodicity at two years, four months, and 45 days. Seasonal variability is the strongest signal of the intensity of the fronts. The SBF-B and BMF-C display the highest intensity (> 0.35∞C/km) during the Austral winter and the annual component explains more than 60% of the total variance. The MRF and FEF are most intense (> 0.33∞C/km) in fall and winter and the annual signal is weaker. The intensity of the MRF is highest (~0.28∞C/km) in late summer. Interannual variability of the intensity is also found and possible sources discussed. The intensity of MRF appears to be related to shifts of the BMF-C. The negative correlation between changes in the transport of the Malvinas Current at 41∞S and the intensity of the MRF suggest that weak Malvinas Current transports lead to eastward penetrations of the BMF-C and enhanced the intensity of the MRF.