Jp. Boulanger et C. Menkes, PROPAGATION AND REFLECTION OF LONG EQUATORIAL WAVES IN THE PACIFIC-OCEAN DURING THE 1992-1993 EL-NINO, J GEO RES-O, 100(C12), 1995, pp. 25041-25059
The TOPES/POSEIDON satellite, together with the Tropical Ocean and Glo
bal Atmosphere-Tropical Atmosphere Ocean (TOGA-TAO) array, provides oc
eanographic and atmospheric observations which allow a detailed study
of the equatorial Pacific variability. During the November 1992 to Dec
ember 1993 El Nino period, sea level, dynamic height, wind stress, sea
surface temperature, and surface zonal current data derived from TOPE
X/POSEIDON and TOGA-TAO measurements were used to describe the Pacific
ocean-atmosphere system and to understand the role played by long equ
atorial waves. A potentially important mechanism of the El Nino-Southe
rn Oscillation (ENSO), commonly referred to as the delayed action osci
llator, involves Kelvin and long Rossby waves and their reflections at
the Pacific western boundary. In order to investigate if this process
was at work during the period under study, a method for projecting TO
PEX sea level, TOGA-TAO dynamic height, and zonal wind stress onto mer
idional wave structures was designed both in unbounded and bounded reg
ions, The Kelvin and first three Rossby waves of the first baroclinic
mode are propagating at theoretical wave speeds in all data sets, Zona
l wind stress projections show that oceanic propagating wave features
are strongly linked to wind variability. Reflections are then examined
at both boundaries. At the eastern boundary most of the signal reflec
ted from incoming Kelvin waves is either counteracted by unfavorable w
ind forcing or strongly reinforced and therefore does not Seem to play
a significant role for generating the major Rossby wave signals durin
g the period under study, In the western Pacific, wind forcing, rather
than western boundary reflections, appears to be the main trigger for
returning Kelvin waves from the western Pacific to the eastern Pacifi
c. Simultaneously with the weakening of the extended 1991-1993 ENSO ev
ent, an upwelling Kelvin wave is observed propagating from the western
Pacific in September 1993 to the eastern Pacific in November 1993. Th
is scenario is consistent with some features of the delayed action osc
illator mechanism, where an upwelling Kelvin wave is systematically se
en returning from the western boundary to the east at the end of warm
events. However, here, contrary to the delayed action oscillator, most
of this returning Kelvin wave seems to be forced by a strong easterly
anomaly located in the western Pacific, rather than by reflection of
an upwelling first Rossby wave at the western boundary.