An experimental study of internal wave generation through evanescent regions

Internal waves are a complex phenomena that af-fect both the atmosphere and the ocean. Internal wave generation occurs uniquely in fluids which are stratified, or have varying density with re-spect to height. The natural frequency (N) is a fluid property that is defined by the rate of density change within the fluid. Internal waves are generated in stratified fluids when an excita-tion frequency (ω) less than the local natural fre-quency occurs. If the reverse is true, then only evanescent waves, or waves with an exponentially decaying amplitude, are generated. Within the ocean the natural frequency is not constant and in some locations can decrease with depth [1]. In these locations it has been assumed that no prop-agating waves will be generated and instead only evanescent waves will be formed. However, re-cent research has indicated that evanescent waves can become propagating internal waves when the natural frequency increases past the value of the original excitation frequency. Laboratory experi-ments were performed to validate this theory as well as investigate the amount of kinetic energy found in the propagating internal waves.