A laboratory study of open ocean barometric response

An attempt is made to explain the physical mechanism for the Mid-Ocean Dynamics Experiment (MODE) bottom pressure observations of Brown et al. (1975) by means of a joint laboratory and theoretical study. First, possible relevant effects in an f-plane model are considered, where pressure driving forms and transient effects can be evaluated. If atmospheric pressure change is local (of a standing wave nature), sea surface response increases with increasing subinertial frequency. If pressure changes are advective, sea surface response decreases with increasing speed. Overreaction of the free surface to forcing, causing overshoot, can occur when the free inertia-gravity modes of the basin are excited. Laboratory experiments are performed which agree with the theory of the local pressure change mechanism to within assinged experimental error.The study is extended to consider the response of an equivalent β-plane system in a more laboratory-oriented approach. It is found that the β-effect is important in the entire range of frequencies studied in the laboratory, with the response approaching that of an f-plane ocean at higher frequencies. The excitation of free planetary modes of the basin proves to be important in the barometric response, allowing for local oversoot and undershoot and for the generation of a substantial pressure signal at a distance from the driving, allowing a significant contribution to the incoherent bottom signal to be forced by distant atmospheric pressure disturbances in the ocean basin.