NONLINEAR FRICTION EFFECT IN AIR PRESSURE-GENERATED SEA-LEVEL VARIATIONS

The propagation and damping of long waves produced by atmospheric pres sure waves in shallow seas, where quadratic bottom friction has to be taken into account, was studied analytically. Forced circular motion o f the open sea, in which quadratic friction is without higher harmonic s, was analyzed and a solution at the fundamental frequency for a narr ow channel was obtained. Particular attention was paid to the changes of elevation amplitude and coefficient of linear friction in both case s along the resonance lines in the OMEGA - K plane. For the open sea f orced close to the resonance, the elevation amplitude changes from the inverted barometer response, when the angular frequency is equal to t he Coriolis frequency f, to an congruent-to 25 times higher response, when the angular frequency is 3 f. For a narrow channel forced at the resonance, the response and coefficient of linear bottom friction are proportional to the square root of the frequency, achieving changes of one order of magnitude for the angular frequency between zero and the Coriolis frequency. In both cases, the drag coefficient of the bottom friction was supposed to be congruent-to 3 x 10(-3) the depth of the sea 100 m, and the amplitude of the atmospheric wave 10 cm in elevatio n units.