Annual Cycle of Turbulent Dissipation Estimated from Seagliders

Abstract

The rate of dissipation of turbulent kinetic energy is estimated using Seaglider observations of vertical water velocity in the midlatitude North Atlantic. This estimate is based on the large-eddy method, allowing the use of measurements of turbulent energy at large scales O(1–10 m) to diagnose the rate of energy dissipated through viscous processes at scales O(1 mm). The Seaglider data considered here were obtained in a region of high stratification (1 × 10−4 < 1×10−2s−1), where previous implementations of this method fail. The large-eddy method is generalized to high-stratification by high-pass filtering vertical velocity with a cutoff dependent on the local buoyancy frequency, producing a year-long time series of dissipation rate spanning the uppermost 1,000 m with subdaily resolution. This is compared to the dissipation rate estimated from a moored 600 kHz acoustic Doppler current profiler. The variability of the Seaglider-based dissipation correlates with one-dimensional scalings of wind- and buoyancy-driven mixed-layer turbulence.