Best Practices for Comparing Ocean Turbulence Measurements across Spatiotemporal Scales

The turbulent energy dissipation rate in the ocean can be measured by using rapidly sampling microstructure shear probes, or by applying a finescale parameterization to coarser-resolution density and/or shear profiles. The two techniques require measurements that are on different spatiotemporal scales and generate dissipation rate estimates that also differ in spatiotemporal scale. Since the distribution of the measured energy dissipation rate is closer to lognormal than normal and fluctuates with the strength of the turbulence, averaging the two approaches on equivalent spatiotemporal scales is critical for accurately comparing the two methods. Here, microstructure data from the 1997 Brazil Basin Tracer Release Experiment (BBTRE) is used to demonstrate that comparing averages of the dissipation rate on different spatiotemporal scales can generate spurious discrepancies of up to a factor of order 10 in regions of strong turbulence and smaller biases of up to a factor of 2 in the presence of weaker turbulence. SIGNIFICANCE STATEMENT: Ocean turbulence is more commonly weak than strong. This implies that measurements of ocean turbulence that are made over small time and length scales will measure weak turbulence more often than those that measure turbulence averaged over a large area and a long time. Therefore, comparing the two measurement methods can lead to a mismatch that is due to the statistics of turbulence opposed to inherent differences in the methods. While it is important for oceanographers to compare different measurement methods, care needs to be taken to ensure that equivalent quantities are being compared. This note is important since it explains a key consideration necessary for accurately comparing ocean turbulence measurements.

Automated summary

The dissipation rate of turbulent energy in the ocean can be measured using different techniques on various spatiotemporal scales, which may lead to discrepancies in estimates, especially in regions with strong turbulence. Comparing the results of these measurements is important for accurate assessment of ocean turbulence, but requires careful consideration of the equivalent spatiotemporal scales to ensure valid comparisons.