Py. Letraon et P. Demey, THE EDDY FIELD ASSOCIATED WITH THE AZORES FRONT EAST OF THE MID-ATLANTIC RIDGE AS OBSERVED BY THE GEOSAT ALTIMETER, J GEO RES-O, 99(C5), 1994, pp. 9907-9923
Two years of Geosat data (November 1986 to December 1988) for the Azor
es-Madeira region of the North Atlantic are analyzed. The objective is
to study the eddy field associated with the terminal retroflection of
the Azores current. The rms variability of sea level anomaly is 4 to
8 cm, with maximum values between 33-degrees and 35-degrees-N being as
sociated with the Azores current and located on its northern flank. Hi
gher energy is observed during winter and during the year November 198
7 to November 1988. Analysis of velocities at crossovers reveals aniso
tropy with larger meridional velocity variances. This is the signature
of meanders and/or eddies elongated in the north-south direction. The
eddy-mean flow interaction is studied through the analysis of the Rey
nolds tensor. Meridional and zonal accelerations of the mean by the ed
dy field are consistent with retroflection of the Azores Current to th
e south and to the west. Spectral analyses show that the dominant sign
als have periods and wavelengths larger than 100 days and 300 km, resp
ectively. Propagation velocities are westward but slow (1.5 km/d). Syn
optic mapping of the eddy field shows the wavelike structure of the va
riability on the northern flank of the current. It is likely that the
wave generation is not directly due to an instability of the Azores cu
rrent but is attributable to a cause more to the east. Once formed, th
e wave interacts with the current in winter and forms meanders. Season
al variations of the surface circulation are finally analyzed from the
2-year-long time series of synoptic maps. There is a clear seasonalit
y in the surface circulation which generally appears to be consistent
with historical in situ measurements. In winter there is a strong mean
dering and a southward branching, while in summer the mean front is na
rrower and penetrates further to the east.