Mechanisms of Warm Water Volume Changes in the Tropical Pacific, as Inferred From Space-Based Observations

Details Mechanisms of Warm Water Volume Changes in the Tropical Pacific, as Inferred From Space-Based Observations Mechanisms of Warm Water Volume Changes in the Tropical Pacific, as Inferred From Space-Based Observations

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmos11a1463b&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #OS11A-1463

Physics

4215 Climate And Interannual Variability (1616, 1635, 3305, 3309, 4513), 4513 Decadal Ocean Variability (1616, 1635, 3305, 4215), 4522 Enso (4922)

Scientific paper

Observational and modelling studies showed that variations of Warm Water Volume (WWV) in the tropical Pacific mainly consist of a zonal seesaw pattern in the equatorial band at the ENSO time scale, and a meridional seesaw pattern between the equatorial and off-equatorial regions at the ENSO and decadal (PDO) time scales. The meridional seesaw pattern is reminiscent of the ENSO recharge / discharge oscillator theory, and WWV changes in the equatorial band can be used to improve ENSO prediction. This study aims at analyzing the mechanisms responsible for the WWV changes during the period 1992-2005, both in the equatorial (5°N-5°S) and off-equatorial regions. This will be done relying on sea level data derived from the TOPEX/Poseidon and Jason missions and wind stress measurements from the ERS satellite mission. The WWV changes in the 5°N-5°S equatorial box are derived from sea level changes, assuming the ocean behaves like a 1.5-layer ocean. Changes in this WWV are analyzed in terms of geostrophic and Ekman transports filling up or draining the equatorial box. The geostrophic transports in the upper layer are computed from surface geostrophic currents (derived from sea level gradients) and statistical current profiles obtained from TAO/TRITON moorings and cruise measurements. These satellite-derived geostrophic transports in the upper layer are validated against in situ hydrographic measurements. The Ekman transports are computed from the wind stress data alone. The relative roles of geostrophic and Ekman transports in changing the equatorial WWV will be discussed, focussing in particular on the effects of propagating equatorial Kelvin and Rossby waves because they affect the basin-scale sea level gradients and related geostrophic currents. The off-equatorial WWV changes, as well as the tight relationships with the equatorial WWV changes, are finally analyzed. It will be shown in particular than the observed north-south asymmetry of the WWV recharge / discharge (not accounted for in the recharge / discharge oscillator theory) results from specific symmetrical and non-symmetrical wind stress curl patterns and associated Sverdrup transports. Idealized wind stress fields and linear model results will be used to complete our understanding of the mechanisms responsible for this asymmetry.

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