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Decadal Variability in the Large-Scale Sea Surface Height Field of the South Pacific Ocean: Observations and Causes

Bo Qiu(1) and Shuiming Chen(1)

(1) University of Hawaii at Manoa, 1000 Pope Road, Honolulu, HI 96822, United States


Large-scale sea surface height (SSH) changes in the extratropical South Pacific Ocean are investigated using satellite altimetry data of the past 12 years. In the midlatitude region south of 30S, the decadal SSH signals are dominated by an increasing trend in both the western basin around New Zealand and the eastern basin centered around 45S and 105W, and a decreasing trend in the central South Pacific Ocean poleward of 50S. Spatially-varying, low-frequency SSH signals are also found in the tropical region of 10-25S where the decadal SSH trend is negative in the eastern basin, but positive in the western basin. To clarify the causes for these observed spatially-varying SSH signals, we adopted a 1.5-layer reduced-gravity model that includes the wind-driven baroclinic Rossby wave dynamics and the responses forced by SSH changes along the South American coast. The model hindcasts the spatially-varying decadal trends in the midlatitude and the eastern tropical regions well. Accumulation of the wind-forced SSH anomalies along Rossby wave characteristics is found to be important for both the long-term trends and their reversals in recent years. While it has little impact upon the midlatitude interior SSH signals, the boundary forcing associated with the time-varying SSH signals along the South American coast is crucial for the observed SSH signals of all timescales in the eastern tropical South Pacific basin.


Workshop presentation


                 Last modified: 07.10.03