TOPEX Outreach
Effects of Temporal Variations in the Ocean Surface

The gravitational perturbations induced by the moon and sun are the primary controlling influence of earth's solid & ocean tides. Although third-body effects from the otherplanets contribute, their magnitudes are negligible in comparison. Since the relative interaction/orientation of the earth-moon- sun system is known very accurately, its effect on the tide-generating potential at any point on earth can be determined rather precisely. This potential can be closely approximated by only the six constituents with the largest amplitude, all of which are diurnal (one cycle per day) or semi-diurnal (two cycles per day). The problem arises from the presence of continental boundaries & complex ocean floor topography and the effects of earth's rotation which introduce large errors in equilibrium predictions of these semi-diurnal and diurnal tides (not to mention the parameterization of friction in these models). Sophisticated models must take into account the time-varying motion of the solid earth, the time invariant latitudinally dependent portion of the deformation, and that portion due to ocean loading forces on the solid earth.

The inverse barometer correction is based on a direct proportionality of about 10 mm/mbar in the change in the sea surface height to changes in the sea surface atmospheric pressure. That is, the ocean surface is depressed in response to the increased atmospheric pressure. Problems can arise in this relationship near storms or near shore where other effects such as wind setup are correlated with pressure. Also, while the assumptions hold for weekly and longer periods, there is doubt as to short period ocean response having the same type of characterization.

Spacecraft Orbit Determination Error


Last Modified: Sat Jul 17, 1998