An experimental investigation of evanescent wave propagation through a turning depth

The formation of internal waves from evanescent regions is studied experimentally with a Gaussian topography and varying natural frequency (N) profiles. When a topography is encompassed by an evanescent region, where N is less than the imposed excitation frequency, only evanescent waves are generated. The amplitude of these evanescent waves decay at an exponential rate while traveling vertically. An evanescent wave can become a propagating internal wave when it passes through a turning depth where N is equivalent to the excitation frequency. Two-dimensional experiments are performed with exponentially varying stratifications to investigate energy transmitted from an evanescent wave to a propagating internal wave. These experiments focus on how internal wave energy is influenced by the location of the topography relative to the turning depth and the ratio of natural frequency near the topography to the excitation frequency. Internal wave energy is estimated from the experiments using Synthetic Schlieren and compared to linear theory.