Atmospheric forcing of the oceanic semidiurnal tide

Abstract

The principal solar semidiurnal tide (S2) in the ocean is forced by the pressure loading of the atmospheric thermal tide as well as by the gravitational tidal potential. This paper examines the effects of adding the atmospheric S2 forcing to a forward tide model. When the model is forced only by the gravitational potential, the S2 relative elevation error with respect to pelagic tide gauges is anomalously poor. After atmospheric S2 forcing is added, the relative error reduces to levels seen in other tidal constituents. In the global average, the atmospherically forced S2 ocean tide is 14.7 percent as large as the gravitationally forced S2 tide, and differs by about 109.4 in phase, consistent with the relative amplitudes and phases of the atmospheric and gravitational S2 forcings. Because the S2 air tide is periodic, the oceanic S2 tide represents a particularly clean test of the ability of numerical models to successfully replicate the oceanic response to atmospheric pressure loading.