Wind Speed and Gas Flux Through Air Water Interface
The Scenario
Understanding the relationship between wind speed and gas flux through the air-water interface has long been a goal of oceanographers, limnologists and engineers. While considerable data exist for relating gas exchange to wind speed in low to moderate winds, almost no data have been available for extreme wind conditions.
The Challenge
Laboratory measurements suffer from fixed boundaries that influence mixing, wave development and bubble injection, while measurements in natural waters require small, robust, accurate and fast equilibrating dissolved gas sensors that can be deployed in a setting that has sufficient fetch for sea state development.
The Solution
Working with Drs Eric D’Asaro and Craig McNeil at the Applied Physics Lab of the University of Washington, scientists and engineers at Pro-Oceanus Systems developed the Hurricane GTD™. The Hurricane GTD™ features the exceptional accuracy and stability of the original Pro-Oceanus GTD-Pro™, but instead of a flat gas transfer interface, the Hurricane GTD™ uses the patented Pro-Oceanus supported tubular interface. The savings in size and weight and the faster equilibration times provided by the tubular interface allow the instrument to be integrated into the APL neutrally buoyant float fitted with other sensors. Noting that dissolved nitrogen can be calculated from gas tension, dissolved oxygen, temperature and salinity the researchers dropped their floats into the paths of hurricanes to obtain data on mixed layer depth, mixing intensity, and concentrations of oxygen and nitrogen. The result is a new understanding of surface layer dynamics including gas exchange under extreme forcing.
Summary
The Pro-Oceanus Systems HGTD™ was developed to provide a smaller, lighter weight and faster equilibrating total dissolved gas sensor that features the same accuracy and stability as the Pro-Oceanus GTD-Pro™ . This new sensor was integrated with the University of Washington APL neutrally buoyant float and dropped into the paths of hurricanes to measure gas exchange at high wind speeds.
D’Asaro, E. and C. McNeil 2007. Air–sea gas exchange at extreme wind speeds measured by autonomous oceanographic floats. J. Mar. Sys., 66, 92-109.