On the topic of oceanic variability near the Coriolis frequency; generation mechanisms, observations, and implications for interior mixing

• Main Author: Kilbourne, Byron
• Other Authors: Girton, James B
• Format: Thesis
• Language: English
• Published: 2015
• Subjects: Physical oceanography; oceanography; Langmuir; Pacific; Southern Ocean; Weller
• Online Access: http://hdl.handle.net/1773/34108

Thesis (Ph.D.)--University of Washington, 2015 Internal waves with frequency near the Coriolis frequency, the frequency of oscillations due to the Coriolis acceleration (commonly denoted by the symbol f), are ubiquitous throughout the world’s oceans. However, observational constraints on their global energetics and impact on subsurface mixing remain sparse. This study investigates near-inertial (inertial and Coriolis frequency are used interchangeably) waves in the Southern Ocean using measurements of water velocity made by Electromagnetic Autonomous Profiling Explorers (EM-APEX). Initial observations from the eastern Pacific showed that coherent near-inertial waves were episodic and enhanced at mid-depth between 500 and 1000 m. The observed waves showed depth-integrated horizontal kinetic energy between 1 and 7 kJ m^−2, with an average of 1.6 kJ m^−2, and a typical group velocity of 40 m d^−1. These observations imply an average energy flux of 3 mW m^−2 at the mixed layer base decreasing to approximately 25% of that value at 1500 m. Simulations of near-inertial surface currents forced with reanalysis winds along each float track agree with observed surface currents from EM-APEX, provided that mixed layer depth is restricted to the layer of weakest observable stratification, interpreted as the maximum depth which remains mixed over an inertial period. Simulations using the Price-Weller-Pinkel model, which permits time varying stratification, provides a better match to the observations; emphasizing the importance of near-surface stratification in amplifying wind power input. These simulations indicate an average wind power input of 3mW m^−2 in the eastern Pacific sector of the Southern Ocean. The thickness of the active mixing-layer, the turbulent layer in contact with wind stress, is needed to accurately estimate wind power input. Vertical shear, Langmuir cells, and buoyant convection were investigated as possible mechanisms for maintaining turbulent mixing within the mixing-layer. Over 90% of the observed ...