Fine scale structure of convective mixed layer in ice-covered lake

Volkov, Sergey; Bogdanov, Sergey; Здоровеннов, Роман; Здоровеннова, Галина; Terzhevik, Arkady; Palshin, Nikolay; Bouffard, Damien; Kirillin, Georgiy

doi:10.1007/s10652-018-9652-2

Cited by 25 publications

(22 citation statements)

References 34 publications

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“…10 −10 m 2 s −3 . The characteristic scale of convective velocities (Deardorff, 1970) w * = (B R h S ) 1/3 ≈ 1.3 mm s −1 , which agrees well with previous reports on radiative convection under lake ice (Mironov et al, 2002;Kirillin et al, 2018;Volkov et al, 2019). These estimates of the convective velocities suggest that radiation was of minor importance for the mixing conditions in the boundary layer compared with the mean flow (cf.…”

Section: Solar Radiationsupporting

confidence: 90%

“…The values of short-period fluctuations of the flow velocity were used to calculate dissipation rates of TKE based on Kolmogorov's 1941 hypothesis on the self-similarity of the velocity structure functions using the method described by Wiles et al (2006). ε was derived as a coefficient in the semi- empirical equation for the velocity structure function D i (r) along the ith acoustic beam,…”

Section: Study Site and Field Methodsmentioning

confidence: 99%

“…(21); the ε values from three beams were compared for similarity and averaged. The detailed procedure of data postprocessing and the quality check is described by Kirillin et al (2018) and Volkov et al (2019).…”

Section: Study Site and Field Methodsmentioning

confidence: 99%

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Turbulence in the stratified boundary layer under ice: observations from Lake Baikal and a new similarity model

Kirillin

Aslamov

Козлов

et al. 2020

Hydrol. Earth Syst. Sci.

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Seasonal ice cover on lakes and polar seas creates seasonally developing boundary layer at the ice base with specific features: fixed temperature at the solid boundary and stable density stratification beneath. Turbulent transport in the boundary layer determines the ice growth and melting conditions at the ice-water interface, especially in large lakes and marginal seas, where large-scale water circulation can produce highly variable mixing conditions. Since the boundary mixing under ice is difficult to measure, existing models of ice cover dynamics usually neglect or parameterize it in a very simplistic form. We present the first detailed observations on mixing under ice of Lake Baikal, obtained with the help of advanced acoustic methods. The dissipation rate of the turbulent kinetic energy (TKE) was derived from correlations (structure functions) of current velocities within the boundary layer. The range of the dissipation rate variability covered 2 orders of magnitude, demonstrating strongly turbulent conditions. Intensity of mixing was closely connected to the mean speeds of the large-scale under-ice currents. Mixing developed on the background of stable density (temperature) stratification, which affected the vertical structure of the boundary layer. To account for stratification effects, we propose a model of the turbulent energy budget based on the length scale incorporating the dissipation rate and the buoyancy frequency (Dougherty-Ozmidov scaling). The model agrees well with the observations and yields a scaling relationship for the ice-water heat flux as a function of the shear velocity squared. The ice-water heat fluxes in the field were the largest among all reported in lakes (up to 40 W m −2 ) and scaled well against the proposed relationship. The ultimate finding is that of a strong dependence of the water-ice heat flux on the shear velocity under ice. The result suggests large errors in the heat flux estimations when the traditional "bulk" approach is applied to stratified boundary layers. It also implies that under-ice currents may have much stronger effect on the ice melt than estimated by traditional models.

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Section: Solar Radiationsupporting

confidence: 90%

Section: Study Site and Field Methodsmentioning

confidence: 99%

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Turbulence in the stratified boundary layer under ice: observations from Lake Baikal and a new similarity model

Kirillin

Aslamov

Козлов

et al. 2020

Hydrol. Earth Syst. Sci.

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“…The evolution of under-ice profiles taken from ice-covered lakes (e.g., Farmer, 1975;Forrest et al, 2008;Volkov et al, 2018) show similar features and structure. The mean temperature T cml and the depth h cml both increase with time.…”

Section: Mixed-layer Convectionmentioning

confidence: 93%

Differential Heating Drives Downslope Flows that Accelerate Mixed‐Layer Warming in Ice‐Covered Waters

Ulloa

Winters

Wüest

et al. 2019

Geophysical Research Letters

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In ice-covered lakes, penetrative radiation warms fluid beneath a diffusive boundary layer, thereby increasing its density and providing energy for convection in a diurnally active, deepening mixed layer. Shallow regions are differentially heated to warmer temperatures, driving turbulent gravity currents that transport warm water downslope and into the basin interior. We examine the energetics of these processes, focusing on the rate at which penetrative radiation supplies energy that is available to drive fluid motion. Using numerical simulations that resolve convective plumes, gravity currents, and the secondary instabilities leading to entrainment, we show that advective fluxes due to differential heating contribute to the evolution of the mixed layer in waterbodies with significant shallow areas. A heat balance is used to assess the relative importance of differential heating to the one-dimensional effects of radiative heating and diffusive cooling at the ice-water interface in lakes of varying morphologies. Plain Language SummaryLake ice cover is one of the essential climate variables defined by the World Meteorological Organization. Its evolution is affected by direct meteorological forcing and by ice-penetrating radiation that heats near-surface waters and excites buoyancy-driven fluid motions. Both effects regulate water-to-ice heat transfer and thus the ice melting rate. We show how the warming of under-ice water is impacted by differential heating of the lake shallows and the resultant transport and mixing. We present a scaling analysis that quantifies how the rate of under-ice, mixed-layer warming depends on geometrical properties of the lake morphology. Accounting for differential heating and lateral transport is essential for processed-based models of ice-covered waterbodies that go beyond one-dimensional balances.

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“…For a discussion in the context of the global ocean, see, for example, Saenz et al (), and references therein, particularly Tailleux (). The cold, freshwater, Boussinesq framework employed here is directly applicable to flows near‐ice (see, e.g., Favier et al, ; Mondal et al, ; Toppaladoddi & Wettlaufer, ), radiatively driven convection in ice‐free water (Bouillaut et al, ; Lepot et al, ) and is particularly apt for ice‐covered inland waters (Kirillin et al, ; Leppäranta et al, ; Ulloa et al, ; Volkov et al, ) and supraglacial lakes (Christoffersen et al, ; Leeson et al, ).…”

Section: Introductionmentioning

confidence: 99%

Energetics of Radiatively Heated Ice‐Covered Lakes

Winters

Ulloa

Wüest

et al. 2019

Geophysical Research Letters

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We derive the mechanical energy budget for shallow, ice‐covered lakes energized by penetrative solar radiation. Radiation increases the available and background components of the potential energy at different rates. Available potential energy drives under‐ice motion, including diurnally active turbulence in a near‐surface convective mixing layer. Heat loss at the ice‐water interface depletes background potential energy at a rate that depends on the available potential energy dynamics. Expressions for relative energy transfer rates show that the pathway for solar energy is sensitive to the convective mixing layer temperature through the nonlinear equation of state. Finally, we show that measurements of light penetration, temperature profiles resolving the diffusive boundary layer, and an estimate of the kinetic energy dissipation rate can be combined to estimate the forcing rate, the rate of heat loss to the ice, and efficiencies of the energy pathways for radiatively driven flows.

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Fine scale structure of convective mixed layer in ice-covered lake

Cited by 25 publications

References 34 publications

Turbulence in the stratified boundary layer under ice: observations from Lake Baikal and a new similarity model

Turbulence in the stratified boundary layer under ice: observations from Lake Baikal and a new similarity model

Differential Heating Drives Downslope Flows that Accelerate Mixed‐Layer Warming in Ice‐Covered Waters

Energetics of Radiatively Heated Ice‐Covered Lakes

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