Simple models of tidal transience: The steady state signal

Abstract

The nature of the tidal response to latitudinally localized transient changes in tidal forcing is examined using simple theoretical models. The major conclusions are (1) the initial tidal response is an outward propagating signal that oscillates with tidal frequency (steady state signal); (2) the diurnal steady state signal propagating from low latitudes is cut off at latitudes poleward of turning latitudes and exhibits exponential decay; (3) a few thousand kilometers from a localized source the steady state signal should exhibit long vertical wavelengths over a few scale heights, with shorter wavelength variations above and below; (4) the unsteadiness of tides observed locally can depend upon the spectrum of free waves excited; and (5) the setup times suggest that the tide can be unsteady to a significant extent. Theory suggests that tidal transience might be an important generator of normal modes, contribute significantly to short-term tidal variability, and help explain the complex tidal behavior observed at high latitudes.