An experimental study of internal wave generation through evanescent regions

Internal waves are a complex phenomena that affect both the atmosphere and the ocean. Internal wave generation occurs uniquely in fluids which are stratified, or have varying density with respect 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 excitation frequency (ω) less than the local natural frequency 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 propagating waves will be generated and instead only evanescent waves will be formed. However, recent 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 experiments were performed to validate this theory as well as investigate the amount of kinetic energy found in the propagating internal waves.