Analytical study of sea level response to atmospheric pressure forcing in a barotropic model
© Moncef Boukthir
The atmospheric pressure-driven sea level changes are analytically investigated using a barotropic model with flat bottom in an infinite b-plane ocean configuration. The validity of the inverted barometer assumption is found to be dependent on the time and space scales considered. In particular, at subinertial frequencies and horizontal scales longer than the Rossby radius of deformation, a geostrophic adjustment is possible. Thus, an isostatic response at a given frequency/horizontal wavenumber band is not at all valid but contains potentially information about ocean dynamics. For periods shorter than 3 days and for large scale forcing, the bottom pressure perturbation may reaches 8-25% of the atmospheric pressure amplitude and meridional transport integrated over the depth may be of the order of several Sverdrups. When dealing with moving forcing, it appears that eastwards pressure variability promotes and isostatic adjustment while westwards forcing tends to give rise to rather non-isostatic behaviour. The analysis of satellite altimetric data and their use, for example, in an-oceanic numerical models must then be done with some care particularly when the pressure - driven sea level signal contains potentially useful information about ocean dynamics.