The 1986--87 El Niño was a major focus of the studies of the
tropical Pacific using the Geosat data. Cheney and Miller [1988] and
Miller et al. [1988] detected the Kelvin waves that initiated the El
Niño as the ocean's response to a burst of anomalous westerly
wind events (Kelvin wave is an edge wave involving the Earth's
gravity and rotation). Using 4-year long sea level time series
constructed from both the Geosat Geodetic Mission and the Exact
Repeat Mission, Miller and Cheney [1990] studied the budget of the
upper ocean water mass. They identified a seasonal exchange of upper
ocean water between the equatorial region (7
S--7
N) and
the region just to the north (8
N--20
N). This exchange
process was enhanced during the El Niño. The generation,
propagation, and reflection of Kelvin waves and Rossby waves (a
low-frequency wave caused by the vorticity of a rotating fluid) in the
equatorial wave guide were studied in detail [ White et al., 1990 a;
Delcroix et al., 1991; du Penhoat et al., 1992]. Extensive
comparisons were made between the Geosat observations and in-situ
observations from tide gauges and expendable bathythermographs
(XBTs) [ Tai et al., 1989; Cheney et al., 1989]. The Geosat data were
also compared to simulations of ocean general circulation models with
some success [ Cheney et al., 1989; Chao et al., 1993].
Evidence for equatorial waves in the strong shear region of the
equatorial current system was reported in the Seasat data [ Malarde et
al., 1987; Musman, 1989, 1992]. Characteristics of these waves were
studied in detail based on the Geosat data by Perigaud [1990], who
identified wave activities in two shear zones centered at 5
N
(between the South Equatorial Current and the North Equatorial
Counter Current) and 12
N (between the North Equatorial
Counter Current and the North Equatorial Current) with distinctively
different periods and wavelengths. She also found correlations of the
intensity of these waves to the seasonally varying strength of the
shears. Using the Geosat data with various in-situ data, Hansen and
Maul [1991] and Maul et al. [1992] studied the formation and
evolution of eddies in the eastern end of the North Equatorial Counter
Current. These eddies, having strong nonlinear character, were
formed during late fall when the current was strongest. Similar results
were obtained from the TOPEX/POSEIDON data [ Giese et al., 1994].
Busalacchi et al. [1994] demonstrated the unique aspect of
TOPEX/POSEIDON in observing the 20-30 day instability waves.