Wave Glider Measurements of Turbulent Fluxes and Bulk Meteorological Quantities in the Wave Boundary Layer

During the Coupled Air Sea Processes and Electromagnetic ducting Research west coast field campaign (CASPER-West), several offshore platforms were instrumented with turbulence-resolving and bulk meteorological sensors. One major asset was the Liquid Robotics WaveGlider SV2, named Thresher, which was deployed from the R/V Sally Ride on October 4, 2017 approximately 42 km south of Point Mugu. Thresher followed an oval track spanning 10 km east to west travelling approximately at 0.5 m/s for 15 days. It hosted several atmospheric sensors including a 3-D ultrasonic wind anemometer (Gill WindMaster Pro), inertial motion unit (VectorNav VN100), and several vertical levels of bulk temperature/relative humidity (Rotronic HC2-S3) and one multi-parameter weather sensor (Vaisala WXT520). The sonic anemometer sensing volume was mounted at 1 m above the ocean surface. R/P FLIP was stationed nearby, approximately 7 km away from the center of the oval track, which hosted similar instrumentation to measure a profile of turbulent fluxes and bulk quantities.

Aboard Thresher, three-component flow velocity and sonic temperature were sampled at 20-Hz from the wind anemometer and synchronized with the IMU, which yielded the capability to retrieve the 3-D wind components after platform motion correction. Therefore, the momentum and sensible heat fluxes can be directly calculated with the eddy-covariance method from the 3-D wind components and sonic temperature perturbation quantities. Simultaneously, ocean waves parameters were derived from the IMU motion measurements, thus, allowing the wave-induced turbulent motion to be subtracted out of the "total" measured turbulence.

In this analysis, both eddy-covariance and inertial-dissipation methods will be used to derive turbulent momentum fluxes. The momentum fluxes from the aforementioned methods will be examined and evaluated to quantify momentum fluxes with and without the wave-induced motion, as well as, within various wave and stability regimes. It is expected that the variability in the turbulent fluxes contained in the wave boundary layer would affect the near-surface bulk temperature and water vapor profile, which is important for the refractivity profile and thus for EM ducting conditions. These turbulent and bulk quantities will be compared to those measured on R/P FLIP.