Abstract: Turbulence in the Wake of an Internal Solitary Wave Train

 

 

Authors: Louis Goodman and Zhankun Wang

Turbulence measurements were made from the autonomous underwater vehicle, T-REMUS, as a part of the 2006 Layered Organization in the Coastal Ocean (LOCO) experiment, which took place in a very shallow region of Monterey Bay at nighttime in the summer of 2006.  The T-REMUS vehicle contains a variety of the micro and fine scale sensors as well as supporting “hotel” sensors which monitor its position and performance. The vehicle was run in an 5o yoyo mode over an across isobaths track of 2.5 km for 8 hours and from 1 meter from the surface to 4 meters above the bottom. The experiment took place during a time period of very light wind forcing, little air sea exchange, and weak tidal flow. Turbulence, characterized by kinetic energy dissipation rates of e>10-7 Watts/kg  and buoyancy Reynolds numbers of Reb>1000, was observed in the lee of a large amplitude, high frequency, non linear internal wave train.  Using a modal eKdV model along with the observed values of internal wave displacement and local buoyancy frequency we show that internal wave induced shear and strain were not sufficiently strong to affect the mean local Richardson number. However,  observations were shown to be compatible with the theory of Moum et al. (2003) of internal wave induced vertical strain enhancing the background shear and lowering the local Richardson number sufficiently to produce turbulence.  Calculation of the effect of this turbulence on the internal wave train suggested a turbulent decay distance of 1.4 km.