Marin F., Kestenare Elodie, Delcroix Thierry, Durand Fabien, Cravatte Sophie, Eldin Gérard, Bourdalle-Badie R. (2010). Annual reversal of the Equatorial intermediate current in the Pacific : observations and model diagnostics. Journal of Physical Oceanography, 40 (5), p. 915-933. ISSN 0022-3670.
Titre du document
Annual reversal of the Equatorial intermediate current in the Pacific : observations and model diagnostics
Journal of Physical Oceanography, 2010,
40 (5), p. 915-933 ISSN 0022-3670
A large reversal of zonal transport below the thermocline was observed over a period of 6 months in the western Pacific Ocean between 2 degrees S and the equator [from 26.2 Sv (1 Sv equivalent to 10(6) m(3) s(-1)) eastward in October 1999 to 28.6 Sv westward in April 2000]. To document this reversal and assess its origin, an unprecedented collection of ADCP observations of zonal currents (2004-06), together with a realistic OGCM simulation of the tropical Pacific, was analyzed. The results of this study indicate that this reversal is the signature of intense annual variability in the subsurface zonal circulation at the equator, at the level of the Equatorial Intermediate Current (EIC) and the Lower Equatorial Intermediate Current (L-EIC). In this study, the EIC and the L-EIC are both shown to reverse seasonally to eastward currents in boreal spring (and winter for the L-EIC) over a large depth range extending from 300 m to at least 1200 m. The peak-to-peak amplitude of the annual cycle of subthermocline zonal currents at 165 degrees E in the model is similar to 30 cm s(-1) at the depth of the EIC, and similar to 20 cm s(-1) at the depth of the L-EIC, corresponding to a mass transport change as large as similar to 100 Sv for the annual cycle of near-equatorial zonal transport integrated between 2 degrees S and 2 degrees N and between 410-and 1340-m depths. Zonal circulations on both sides of the equator (roughly within 2 degrees and 5.5 degrees in latitude) partially compensate for the large transport variability. The main characteristics of the annual variability of middepth modeled currents and subsurface temperature (e. g., zonal and vertical phase velocities, meridional structure) are consistent, in the OGCM simulation, with the presence, beneath the thermocline, of a vertically propagating equatorial Rossby wave forced by the westward-propagating component of the annual equatorial zonal wind stress. Interannual modulation of the annual variability in subthermocline equatorial transport is discussed.
