We present an experimental and numerical investigation of the effect of Coriolis forces on the axisymmetric collapse of a uniform mixed region in uniformly stratified fluid. Laboratory experiments were performed on a rotating table in which a mixed patch contained initially in a hollow cylinder was released and so excited internal waves whose properties were analyzed using synthetic schlieren. Numerical simulations restricted to an axisymmetric geometry were run with the experimental parameters to confirm the accuracy of the code and the validity of the axisymmetric approximation. The simulations were then run in larger domains and with wide-ranging parameters exploring the dependence of wave generation upon rotation and the aspect ratio of the mixed patch. Internal waves are found to be generated from the circumference of a shallow aspect-ratio mixed patch, with the radial and vertical wavelengths scaling as the mixed-layer depth. In rotating fluid, the energy spectrum revealed that pairs of wavepackets were generated, one with near-inertial frequencies and one with frequencies near the buoyancy frequency. Energy transport due to the waves was most significant during the first 6 wave periods. However, for very low Rossby number Ro similar to 0.1, internal wave generation continued over relatively longer times as a consequence of undulations of the geostrophically adjusting mixed patch. (C) 2015 AIP Publishing LLC.
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