The PI's propose to develop a capability to measure temperature microstructure over large areas and for extended times. This will permit sampling suspected mixing 'hot spots' over larger areas and for longer periods than affordable with ships, measuring in areas not frequented by ships, or where the weather is too severe for ship-based observations. To meet this scientific objective, the PI's propose to add temperature microstructure as one of the optional sensors available with Autonomous Profiling Explorers (APEXs) floats. Because these floats can be programmed to restrict their profiling range to stay within water masses, they will allow simultaneous Lagrangian observations of mixing rates and T,S changes. The addition would consist of two thermistors to detect the microstructure, a small external signal-conditioning package, an internal electronics board and software for processing the data and mounts for additional batteries and modification to the ballasting. The data will be added to the existing data stream transmitted every time a float surfaces. Only a small amount of additional processing will be required ashore.
Broader Impacts
The Tmicro-APEX floats could allow for global spatial coverage of turbulent mixing variability in the ocean and help to identify its temporal variability. This global understanding of ocean mixing from measurements will help constrain the mixing rates that are parameterized in global and regional ocean models. The proposed instrumentation development will offer the opportunity to have a standardized microstructure measurement package accessible to a broad sector of the experimental physical oceanographic community. It should stimulate numerous investigations that overtime will provide a significantly improved understanding of the global dissipation processes and their variability.
After testing in the Puget Sound, a float was launched south of Oahu in January 2011 and profiled successful for several weeks. Figure 2 shows the first and fifth profiles, taken almost a day apart. Diapycnal diffusivities, Kp, calculated from xT averaged about 10−5 m2 s−1 during the first profile, except for a sharp event near 4 MPa. The fifth profile again found strong mixing there, but, in addition, mixing intensity increased by nearly a decade in the 150 m below the spike. Because the data are too limited to be scientifically interesting, we have not yet written a paper describing the float. It is planned for this year, but since the float went to sea, Gregg and Miller retired. Gregg is working part time but has to put analysis of a more recent experiment first owing to interactions with PIs on that project. This development, however, spawned several others at APL that have collected far more data than our test deployment. Tom Sanford added Tmicro probes to about a dozen EM-APEX probes used in several ONR experiments, and Luc Rainville put them on gliders used during several ONR experiments. During ITOP, good data were returned throughout a deployment of several months, indicating that problems with the Rockland probes are not systematic.
