Redistribution zonale et méridienne de masse aux échelles ENSO et décennale dans le Pacifique tropical

Abstract : The main modes of interannual climate variability in the tropical Pacific are identified using satellite data for the 1993-99 period and a linear model forced by observed wind for the 1964-99 period. The first mode is typical of ENSO variability. It consists of a zonal seesaw pattern in sea level around a fulcrum at the dateline, associated with an equatorial patch of zonal wind centered near the dateline. The second mode consists of a meridional seesaw pattern in sea level around a fulcrum at 5°N, associated with opposite zonal wind anomalies in the northwestern and southeastern parts of the tropical Pacific. The second mode, particularly active during the very strong 1982-83 and 1997-98 El Niño events, statistically leads ENSO by several months. Its temporal function seems to include a decadal component. Mass transports (0-200 m) associated with both modes of variability are simulated. The first mode is characterised by predominant zonal transports. The second mode, mainly associated with meridional geostrophic transports across 5°N, can be described as a low-frequency, asymmetric recharge oscillator. An OGCM forced by atmospheric reanalysis is then used for the 1951-99 period. It proves able to reproduce the modes of variability described above. The model outputs are validated against surface currents, warm water transports, dynamic height and sea level data. The simulated dynamic height includes a partly artificial linear trend. The origin of this trend is identified in the wind forcing. Subtropical cells, which may play an important role in the decadal variability of the tropical Pacific are simulated. The model shows, in agreement with available data, that the increase of the equatorial SST during the last decades could be linked to a decrease of the meridional transports in the pycnocline.
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Gaël Alory. Redistribution zonale et méridienne de masse aux échelles ENSO et décennale dans le Pacifique tropical. Milieux et Changements globaux. Université Paris 6, 2002. Français. ⟨tel-01171601⟩

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