Mixing in theSouth China Seainduced by Large-Amplitude Internal Waves
Dr. Rolf Lueck
PhD. Physics and Oceanography, UniversityofBritish Columbia, 1979
President,RocklandScientific International Inc.
Specializing in physical oceanography;ocean turbulence and mixing; ocean instrumentation and measurement techniques; signal processing
Talk Abstract
The semi-diurnal tide oscillating over the ridge in theLuzonStraitregularly generates large-amplitude, non-linear, internal waves. These waves, which can be easily tracked by satellite imagery, propagate westward into theSouth China Seawhere they ultimately dissipate their energy. Vertical profiles of turbulence and fine-scale measurements taken recently over the Dongsha Plateau and near the Dongsha Reef indicate that these waves elevate the rate of turbulent mixing by a factor of 100 compared to ambient conditions. Over the Dongsha Plateau the rate of dissipation of kinetic energy was among the largest ever observed in the open ocean and the eddy diffusivity reached 103cm2 s–1.
Turbulence Measurements from a Glider
Dr. Fabian Wolk
PhD. Physical Oceanography,TokyoUniversityof Marine Science, 2007
Vice President,RocklandScientific International Inc.
President,RocklandOceanographic Services Inc.
Specializing in ocean turbulence measurements
Talk Abstract
To test the feasibility of measuring small-scale turbulence from an ocean glider, a self-contained package carrying velocity shear probes andFP07thermistors is deployed in a small lake on aSlocumocean glider. The package’s turbulence sensors are augmented by a high-resolution pressure sensor and a set of orthogonally mounted accelerometers monitoring the glider’s attitude and vibrations. The package is neutrally buoyant and does not limit the glider’s manoeuvrability. It attaches to the top of the glider’s fuselage with the turbulence sensors positioned just ahead of the glider nose. The package receives power from the glider and can record turbulence data independently for up to 35 days. Data from the a test in Ashumet Pond near Cape Cod show that vibration levels of the glider are generally small and do not interfere with the measurement of small-scale turbulence shear.The accelerometer spectra show vibration peaks at 28, 60, and 80 Hz, which are caused by vibrations of the glider’s tail fin assembly. These vibrations are stimulated by the action of the glider’s buoyancy pump, which acts at the top and bottom turn-around points, and by the action of the rudder, which is activated at regular intervals (~6 seconds) during the flight in order to control the heading of the glider. The vibration peaks have a small magnitude and narrow bandwidth and do not interfere with the shear probe spectrum. The shear probes resolved dissipation rates between 5x10-11W/kg in the quiescent layer below the thermocline and 5x10-7W/kg in the surface mixing layer. All measured shear spectra fit well with the Nasmyth Empirical Spectrum.
时间：11月30日下午3：00-5：30
地点：曾呈奎楼B-206
