Combining the Seasat data with the Geos-3 data into a monthly data
base, Menard [1988] studied the seasonal cycle of the North
Equatorial Counter Current and obtained encouraging comparisons of
the altimetry analysis with in-situ data and model simulations. Carton
[1989] studied the variation of the equatorial current systems using the
first year of the Geosat data. He also estimated the zonal sea surface
slopes associated with the current variabilities. A follow-up study was
conducted to examine the seasonal variations of the North Equatorial
Counter Current using two years' worth of the Geosat data [ Carton
and Katz, 1990]. The current maximum was found at 38
W
with peak transport of 40 Sv (1 Sv= 10
kg/sec). Extensive
intercomparisons were made between the Geosat data and various
in-situ data [ Carton and Katz, 1990, Arnault et al., 1990, 1992a].
Arnault et al. [1992b] made extensive comparisons of the
low-frequency variabilities between altimetry analysis and model
simulations. Interannual variabilities in the Gulf of Guinea related to
the 1986--87 El Niño were discussed. Arnault and Cheney
[1994] conducted further investigation using 4.5 years' worth of
improved Geosat data. They described 80% of the sea level variance
in terms of 3 empirical orthogonal functions and reported an increase
of the volume of the equatorial upper ocean during 1987--89,
indicative of the effect of the 1986--87 El Niño. Didden and
Schott [1992] examined the variabilities of the North Equatorial
Counter Current and the North Brazil Current using the Geosat data
and the World Ocean Circulation Experiment (WOCE) Community
Model and obtained good agreement between the two. Musman
[1992] reported evidence for the equatorial instability waves at
4
N and 4
S with a period of 25 days and a wavelength
of 970 km.