Internal wave generation from rough topography

Through laboratory experiments we examine internal wave generation above and in the lee of finite-amplitude periodic topography having various degrees of roughness. We show that internal waves are generated not only by flow over the hills but also by flow over “boundary-trapped” lee waves and by vigorous turbulence created in the lee of sharp-crested hills. For low values of the excitation frequency, linear theory well predicts the internal wave frequencies but significantly overestimates the wave amplitudes because it neglects processes associated with boundary layer separation. When the excitation frequency exceeds the buoyancy frequency, turbulence results in the excitation of internal waves with frequencies approximately 0.72±0.05 of the buoyancy frequency and vertical displacement amplitudes ranging between 1.5% and 2% of the horizontal wavelength.