NATURE OF GLOBAL LARGE-SCALE SEA-LEVEL VARIABILITY IN RELATION TO ATMOSPHERIC FORCING - A MODELING STUDY

The relation between large-scale sea level variability and ocean circu lation is studied using a numerical model. A global primitive equation model of the ocean is forced by daily winds and climatological heat f luxes corresponding to the period from January 1992 to January 1994. T he physical nature of sea level's temporal variability from periods of days to a year is examined on the basis of spectral analyses of model results and comparisons with satellite altimetry and tide gauge measu rements. The study elucidates and diagnoses the inhomogeneous physics of sea level change in space and frequency domain. At midlatitudes, la rge-scale sea level variability is primarily due to steric changes ass ociated with the seasonal heating and cooling cycle of the surface lay er. In comparison, changes in the tropics and high latitudes are mainl y wind driven. Wind-driven variability exhibits a strong latitudinal d ependence in itself. Wind-driven changes are largely baroclinic in the tropics but barotropic at higher latitudes. Baroclinic changes are do minated by the annual harmonic of the first baroclinic mode and is lar gest off the equator; variabilities associated with equatorial waves a re smaller in comparison. Wind-driven barotropic changes exhibit a not able enhancement over several abyssal plains in the Southern Ocean, wh ich is likely due to resonant planetary wave modes in basins semienclo sed by discontinuities in potential vorticity. Otherwise, barotropic s ea level changes are typically dominated by high frequencies with as m uch as half the total variance in periods shorter than 20 days, reflec ting the frequency spectra of wind stress curl. Implications of the fi ndings with regards to analyzing observations and data assimilation ar e discussed.