Regional analysis of the inverted barometer effect over the global ocean using TOPEX/POSEIDON data and model results

Crossover sea level differences from almost 5 years of TOPEX/POSEIDON data are regressed against corresponding differences in atmospheric pressure (-D elta p(a)), and the regression coefficient (alpha) is examined for deviatio ns from the value of similar to 1 cm/mbar expected under a pure inverted ba rometer (IB) signal. Only crossovers within each 10-day repeat cycle are us ed. We focus on variability at the shortest periods where non-IB response i s more likely. Results indicate a marked tendency to have alpha < 1 cm/mbar , with values in the general range of 0.8-1 cm/mbar in middle and high lati tudes and 0.4-0.8 cm/mbar in the tropics. Effects of errors in Delta p(a) a nd altimeter data seem small to explain all of the observed IB deviations, which imply then positive correlations between Delta p(a) and dynamic sea l evel Delta eta' (sea level adjusted for an IB signal). A simple constant-de nsity ocean model is used to help interpret the regression results. Only ef fects of winds and p(a) on Delta eta' are considered. Model-based alpha est imates agree qualitatively with the data estimates. On the basis of the mod el results, wind-driven Delta eta' signals contribute importantly to the sp atial variability of ct observed at middle land high latitudes. This is par ticularly evident in the Southern Ocean, where strongest wind-driven effect s on alpha coincide with regions of anomalous ambient potential vorticity g radients and different vorticity dynamics. In contrast; the observed decrea se in a toward low latitudes is due to a true dynamic response to p(a) most ly at periods shorter than 10 days. The stronger non-IB signals suggest a r esponse closer to resonance and may be due to the richer resonance spectrum in the tropics. The non-IB signals are largely remotely driven and therefo re weakly correlated with local p(a). Thus regression results tend to under estimate the importance of the nonisostatic response in the tropics but als o at higher latitudes.