A MODEL FOR THE GROWTH OF MUDWAVES IN THE PRESENCE OF TIME-VARYING CURRENTS

Mudwaves are produced in a model when a periodic current produces lee waves that alter the deposition-erosion rates of sediment at the bottom of an ocean. A technique, analogous to using a Lagrangian representation, for calculating the velocity perturbations associated with these lee waves is determined and then applied to a situation typical of one observed in the Argentine basin. The fact that the imposed current is variable results in the perturbation velocities also being time-dependent with two major time scales. One of these time scales is the period of the variable current, which is taken to be on the order of weeks; this is consistent with the dominant periods indicated in the data. The other time scale is on the order of a day or two and is associated with the time required for the time-dependent part of the imposed current (total current minus its time-averaged part) to cross a ridge; waves on this time scale are excited when the imposed current passes through a value that changes the character of the lee waves from vertically-propagating to bottom-trapped (or vice versa). The long-term erosion-deposition and mudwave growth rates are insensitive to the details of these shorter time scale variations.