SPATIAL AND TEMPORAL SCALES IN ALTIMETRIC VARIABILITY IN THE BRAZIL-MALVINAS CURRENT CONFLUENCE REGION - DOMINANCE OF THE SEMIANNUAL PERIODAND LARGE SPATIAL SCALES
C. Provost et Py. Letraon, SPATIAL AND TEMPORAL SCALES IN ALTIMETRIC VARIABILITY IN THE BRAZIL-MALVINAS CURRENT CONFLUENCE REGION - DOMINANCE OF THE SEMIANNUAL PERIODAND LARGE SPATIAL SCALES, J GEO RES-O, 98(C10), 1993, pp. 18037-18051
Two years of Geosat data are used to investigate the space and time sc
ales of the mesoscale variability in the Brazil-Malvinas Current confl
uence region. The mesoscale activity is highly inhomogeneous and aniso
tropic. The inhomogeneity is characterized by low values of sea level
variability in the Malvinas Current (less than 8 cm, i.e., eddy kineti
c energy less than 150 cm2 s-2), intermediate values in the Brazil Cur
rent (typically 16 cm/800 cm2 s-2) and high values in the Brazil-Malvi
nas frontal region (30 cm/1700 cm2 s-2). The anisotropy is marked with
meridional variances of velocity that are typically three times large
r than zonal ones in the region of maximum variability. Mesoscale vari
ations are dominated by relatively large spatial scales and low-freque
ncy fluctuations. Contrary to similar spectra derived from Geosat data
over the North Atlantic (Le Traon, 1991; Le Traon et al., 1990) or ov
er the whole southern ocean (Chelton et al., 1990) there is very littl
e energy at the annual period. In the mean spectrum, the energy is at
least 3 times smaller at the annual period than at the semiannual peri
od or at shorter periods. The semiannual signal, with length scales of
about 400-500 km, has a clear northward propagation and is maximum in
the frontal region. It is probably associated with the semiannual wav
e that dominates the atmospheric circulation in the southern hemispher
e. However, the mechanism responsible for this semiannual signal in th
e frontal region remains unclear. Beyond this dominant semiannual freq
uency, the altimetry-derived mesoscale fluctuations exhibit other ener
getic signals, especially signals at periods between 75 and 150 days a
nd spatial scales of 500-600 km with a westward propagation which have
characteristics consistent with the dynamics of barotropic Rossby wav
es.