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

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

JOURNAL OF GEOPHYSICAL RESEARCH

Año: 2004 p. 1 - 14

0148-0227

Surface thermal fronts in the southwestern Atlantic (SWA) Ocean are examined using9 years (1987–1995) of advanced very high resolution radiometer data. Fronts aredetected considering a gradient based edge detector. Sea surface temperature gradients arecalculated from 4 km resolution 5-day composite images covering the western ArgentineBasin south of 30
S. Variability in the position and intensity of the fronts from seasonal tointerannual timescales is characterized in six regions including different parts of theBrazil 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). Frontsin the SB-B, SB-M, MRF, and FE regions are controlled by the bathymetry. In the BM-Cregion the BCF and SAF appear to merge as a single front. This front does not presentlarge seasonal north-south excursions as previously described, though it pivots seasonallyaround a fixed point located approximately at 39.5
S, 53.5
W, changing its orientationfrom N-S in winter to NW-SE in summer. Consequently, on average, the front intersectsthe 1000 m isobath at 38
300S in summer and north of 37
S in winter. In the BC-O regionthe BCF has a U-shape centered at 53
W. The intensity of the fronts in each regionexcept in the FE region presents large seasonal variability. In the SB-B, BM-C, and BC-Oregions the frontal intensity is highest (>0.35
C/km) during austral winter, the annualcomponents explain 83, 67, and 71% of the total variance, respectively. In the SB-M andMRF regions the SAF is most intense (>0.25
C/km) in summer and fall; the annualcomponent 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 ZapiolaRise (centered at 45
S, 43
W) appears as a gradient-free region. Closed planetary potentialvorticity contours in this area suggest it is dynamically isolated.