INTERNAL WAVE GENERATION IN UNIFORMLY STRATIFIED FLUIDS .2. MOVING POINT SOURCES

The Green's function method is applied to the generation of internal g ravity waves by a moving point mass source. Arbitrary motion of a sour ce of arbitrary time dependence is treated using the impulsive Green's function, while 'classical' approaches of uniform motion of a steady or oscillatory source are recovered using the monochromatic Green's fu nction. Waves have locally the structure of impulsive waves, emitted a t the retarded time t(r) and having propagated with the group velocity ; at each position and time an implicit equation defines t(r), in term s of which the waves are written. A source both oscillating and moving generates two systems of waves, with respectively positive and negati ve frequencies, and when oscillations vanish these systems merge into one. Three particular cases are considered: the uniform horizontal and vertical motions of a steady source, and the uniform horizontal motio n of an oscillatory source. Waves spread downstream of the steady sour ce. For the oscillatory source they can extend both upstream and downs tream, depending on the ratio of the source frequency to the buoyancy frequency, and are contained inside conical wavefronts, parts of which are caustics. For horizontal motion, moreover, the steady analysis (b ased on the monochromatic Green's function) reveals the presence of tw o insignificant contributions overlooked by the unsteady analysis (bas ed on the impulsive Green's function), but which for an extended sourc e may become of the same order as the main contribution. Among those i s an upstream columnar disturbance associated with blocking.