Ocean Turbulence and Mixing Near the Shelf Break South-East of Nova Scotia
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Ocean Turbulence and Mixing Near the Shelf Break South-East of Nova Scotia Iossif Lozovatsky1 · Charlotte Wainwright1 · Edward Creegan2 · Harindra J. S. Fernando1,3 Received: 20 March 2020 / Accepted: 26 September 2020 © Springer Nature B.V. 2020
Abstract Formation of coastal fog was observed near the southern tip of Nova Scotia when warm, humid air was advected towards the shore over an area of colder water. The sea-surface temperature in the colder and higher salinity patch near the coast was below 14 °C compared to that of the surrounding sea of ≈ 17–18 °C. Measurements of stratification, currents, and the dissipation rate of turbulence kinetic energy (ε) on the Nova Scotia shelf, shelf break, and continental slope revealed the frequent occurrence of shear instability in the pycnocline. The probability of the gradient Richardson number (Ri) being less than a critical value of Ri cr 0.25 in the depth range 30–90 m exceeded 50% on the shelf and over the slope, and it was above 75% along the shelf break, while in the open ocean pycnocline the probability of Ri < 0.25 is below 5%. The cumulative distribution functions of the dissipation rate in the pycnocline south-east of Nova Scotia followed the Burr probability model with median values from 7.9 × 10−9 W kg−1 on the slope to 1.9 × 10−8 W kg−1 at the shelf break. The eddy diffusivity (K N ) estimates follow a generalized extreme value distribution with a high median value of K N 5.8 × 10−5 m2 s−1 at the shelf break. The diffusivity K N depended on Ri in general agreement with the parametrization previously suggested by Lozovatsky and Fernando (Philos Trans R Soc A 371:20120213, 2013) but with a higher level of mixing at Ri > 1. This could be relevant to the nature of turbulence generation near the shelf break by random wave instabilities in the pycnocline at high Richardson and high Reynolds numbers. Keywords Coastal fog · Probability distribution · Shear instability · Shelf break · Stratified turbulence
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Iossif Lozovatsky [email protected]
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Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN, USA
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U.S. Army Research Laboratory, White Sands Missile Range, NM, USA
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Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN, USA
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I. Lozovatsky et al.
1 Introduction Air–sea interaction is a fundamental process in the development of marine fog. Warm advection fog may occur when a warm and humid airmass propagates, with relatively low wind speed, over water with a substantially lower sea-surface temperature (e.g., Koraˇcin and Dorman 2017). In particular, conditions favourable for fog formation often emerge along the Canadian east coast during the summertime (e.g., Gultepe et al. 2007). Fog negatively affects visibility, transportation, and communications, as well as ecosystem functions, yet its predictability is amongst the poorest in meteorology (Fernando et al. 2020), in particular for coastal fog where the influence of atmosphere, ocean, and land
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