EGU21-11054
https://doi.org/10.5194/egusphere-egu21-11054
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

New Method for Estimating Double-Diffusive Dissipation Rates

Leo Middleton1,2, Elizabeth Fine3, Jennifer MacKinnon4, Matthew Alford4, and John Taylor1
Leo Middleton et al.
  • 1DAMTP, University of Cambridge, Cambridge, UK
  • 2British Antarctic Survey, Cambridge, UK
  • 3Woods Hole Oceanographic Institution, Falmouth, US
  • 4Scripps Institution of Oceanography, UC San Diego, San Diego, US

Understanding the transport of heat in the Arctic ocean will be vital for predicting the fate of sea-ice in the decades to come. Small-scale turbulence is an important driver of heat transport and one of the major forms of this turbulence is known as `double-diffusive convection'. Double diffusion refers to a variety of turbulent processes in which potential energy is released into kinetic energy, made possible in the ocean by the difference in molecular diffusivities between salinity and temperature.  The most direct measurements of ocean mixing require sampling velocity or temperature gradients on scales <1mm, so-called microstructure measurements. Here we present a new method for estimating the energy dissipated by double-diffusive convection using temperature and salinity measurements on larger scales (100s to 1000s of metres). The method estimates the up-gradient diapycnal buoyancy flux, which is hypothesised to balance the dissipation rate. To calculate the temperature and salinity gradients on small scales we apply a canonical scaling for compensated thermohaline variance (or `spice') and project the gradients down to small scales. We apply the method to a high-resolution survey of temperature and salinity through a subsurface Arctic eddy (Fine et al. 2018) and compare the results with simultaneous microstructure measurements. The new technique can reproduce up to 70% of the observed dissipation rates to within a factor of 3. This suggests the method could be used to estimate the dissipation and heat fluxes associated with double-diffusive convection in regions without microstructure measurements. Finally, we show the method maintains predictive skill when applied to a sub-sampling of the CTD data at lower resolutions.

How to cite: Middleton, L., Fine, E., MacKinnon, J., Alford, M., and Taylor, J.: New Method for Estimating Double-Diffusive Dissipation Rates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11054, https://doi.org/10.5194/egusphere-egu21-11054, 2021.

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