Oslo fjord, 20-23 June, 2011, CTD and Dissipation rates

Dissipation rates: Dissipation rates of turbulent kinetic energy were obtained from the microstructure shear data using standard methods, as describe in more detail by e.g. Arneborg and Liljebladh (2009). Basically, the shear probes measure how one transverse velocity component changes along the path of the profiler. From the shear variance one can calculate the dissipation rate under the assumption of isotropic turbulence. However, since the sensors do not cover the complete wave-number range o

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Dissipation rates: Dissipation rates of turbulent kinetic energy were obtained from the microstructure shear data using standard methods, as describe in more detail by e.g. Arneborg and Liljebladh (2009). Basically, the shear probes measure how one transverse velocity component changes along the path of the profiler. From the shear variance one can calculate the dissipation rate under the assumption of isotropic turbulence. However, since the sensors do not cover the complete wave-number range of the shear variance, the dissipation rates are obtained by fitting the observed shear spectrum to the universal Nasmyth spectrum for that component. This is done in 50% overlapping 512 point segments, and the resulting estimates of dissipation rate are averaged into 0.5 m bins. In the present case, the main problem with this method is that the velocity of the sensor tip through the water is estimated from the rate of change of the pressure. The velocity through the water enters the calculation of dissipation rates to the power of 4, so small errors in the velocity give considerable errors in the dissipation rate. As discussed in Klymak and Gregg (2004) this may cause large problem in a hydraulic jump where the vertical velocities can be large relative to the sinking velocity of the profiler. As proposed by Klymak and Gregg (2004) we also considered a constant velocity rather than that calculated from the pressure, but found no significant differences in the results. The results presented here are therefore obtained by using the traditional method.

Temperatures: The NTC channel is based on an fp07 fast thermistor, which designed for fast response rather than stability. The TEMPcor channel is based on an Pt100 sensor with better accuracy (+/- 0.01 deg C) but slower response. The raw temperatures are corrected for response time before averaging.

The conductivity sensor is a 7-pole cell with specified accuracy of about +/- 0.05mS/cm. Show less..