Hawaiian Ocean Mixing Experiment: Nearfield: SeaSoar/LAMP Operations

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

9819530 Rudnick A large coordinated experiment (HOME: Hawaiian Ocean Mixing Experiment) is underway near the Hawaiian Ridge to determine whether sites with rough topography are responsible for the mixing of the global ocean. The goals are to identify the major energy pathways for ocean mixing and achieve an approximate energy budget for the region. The Near-field experiment of the HOME project focuses on the investigation of the dynamical processes in the immediate vicinity of the Hawaiian Ridge, and especially the response to barotropic tidal forcing including generation of low- and high-mode internal waves, propagation and turbulent dissipation and mixing. This sub-project will focus on quantifying the role of advection, and measuring the evolution of shear, stratification and dissipation, especially in the off-shore direction. Two instrument systems, SeaSoar and LAMP (Long-term Autonomous Microstructure Profiler) will be deployed to conduct surveys of the upper ocean. The SeaSoar is a towed vehicle capable of undulating between the surface and 400 m, completing a cycle every 3 km at a tow speed of 8 knots. Measured variables include temperature, salinity, pressure, and fluorescence. Velocity and shear will be measured using a shipboard Doppler Sonar. Repeated surveys consisting of several long offshore legs will achieve both fine horizontal and vertical resolution and wide range. The Nearfield SeaSoar component will, to some extent, revolve around the detailed measurements from FLIP. The time series obtained from FLIP are Eulerian, so changes will be both local and advective. The SeaSoar survey will resolve the horizontal structure advecting past FLIP, placing its velocity and density measurements into mesoscale context. The unique contribution of SeaSoar will be the ability to calculate statistics that require horizontal resolution and range. For example, the complete vertical and horizontal wavenumber-frequency spectrum is realizable from the combination of FLIP and SeaSoar measurements. Augmenting the SeaSoar work will be LAMP (Long-term Autonomous Microstructure Profiler), which is an autonomous profiler (based on the SOLO) outfitted with microstructure temperature probes, a Sea-Bird CTD, and an internal flash card. LAMP provides both temporal resolution and broader coverage than otherwise possible. After the survey resolves the current field, four LAMPs will be periodically seeded into the survey box where they will drift through and eventually out of the region. They will provide additional spatial sampling of the thermal dissipation c rates and the density field, as well as some profiles of c further off the ridge to help place the Nearfield measurements into a larger context.