scholarly journals Numerical simulation of ice cover of saline lakes

2019 ◽  
Vol 55 (1) ◽  
pp. 152-163
Author(s):  
V. M. Stepanenko ◽  
I. A. Repina ◽  
G. Ganbat ◽  
G. Davaa
Keyword(s):  
Vertical Distribution ◽  
Freezing Point ◽  
Mixed Layer Depth ◽  
Ice Cover ◽  
Ice Thickness ◽  
Significant Shift ◽  
Layer Depth ◽  
Lake Model ◽  
Order Of Magnitude

A new version of 1D thermodynamic and hydrodynamic model LAKE 2.1 is presented. The model is supplemented with description of dynamics and vertical distribution of salinity in ice layer. Simulation results are compared to in situ and satellite data on water temperature and ice cover at Lake Uvs (Mongolia) from 2000 to 2015. We demonstrate that underestimation of mixed-layer depth by the model with standard k–ε closure during summer and autumn leads to significant shift of ice-on to earlier dates. If the effects of water salinity are neglected in the model, ice cover establishes 16–17 before the observed dates. This error is removed, if influence of salinity on water density and freezing point is included, still assuming the fresh ice. However, in this case, LAKE model underestimates the maximal winter ice thickness on average by ≈0.2 m. In turn, this discrepancy decreases an order of magnitude if dynamics and vertical distribution of salinity in ice are reproduced. Such an effect does not take place when using constant salinity value in ice.

scholarly journals Eastern Tropical Atlantic Mixed Layer Depth: Assessment of Methods from In Situ Profiles in the Gulf of Guinea from Coastal to High Sea

2019 ◽  
Vol 36 (1) ◽  
pp. 201-212
Author(s):  
Benjamin Kouadio N’Guessan ◽  
Aka Marcel Kouassi ◽  
Albert Trokourey ◽  
Elisée Toualy ◽  
Desiré Kouamé Kanga ◽  
...  
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Tropical Atlantic ◽  
Gulf Of Guinea ◽  
Layer Depth

scholarly journals Future projections of temperature and mixing regime of European temperate lakes

2019 ◽  
Vol 23 (3) ◽  
pp. 1533-1551 ◽  
Author(s):  
Tom Shatwell ◽  
Wim Thiery ◽  
Georgiy Kirillin
Keyword(s):  
Climate Warming ◽  
Mixed Layer Depth ◽  
Ice Cover ◽  
Climate Projections ◽  
Lake Model ◽  
Lake Morphology ◽  
Mixing Regime ◽  
Physical Response ◽  
Lake Characteristics

Abstract. The physical response of lakes to climate warming is regionally variable and highly dependent on individual lake characteristics, making generalizations about their development difficult. To qualify the role of individual lake characteristics in their response to regionally homogeneous warming, we simulated temperature, ice cover, and mixing in four intensively studied German lakes of varying morphology and mixing regime with a one-dimensional lake model. We forced the model with an ensemble of 12 climate projections (RCP4.5) up to 2100. The lakes were projected to warm at 0.10–0.11 ∘C decade−1, which is 75 %–90 % of the projected air temperature trend. In simulations, surface temperatures increased strongly in winter and spring, but little or not at all in summer and autumn. Mean bottom temperatures were projected to increase in all lakes, with steeper trends in winter and in shallower lakes. Modelled ice thaw and summer stratification advanced by 1.5–2.2 and 1.4–1.8 days decade−1 respectively, whereas autumn turnover and winter freeze timing was less sensitive. The projected summer mixed-layer depth was unaffected by warming but sensitive to changes in water transparency. By mid-century, the frequency of ice and stratification-free winters was projected to increase by about 20 %, making ice cover rare and shifting the two deeper dimictic lakes to a predominantly monomictic regime. The polymictic lake was unlikely to become dimictic by the end of the century. A sensitivity analysis predicted that decreasing transparency would dampen the effect of warming on mean temperature but amplify its effect on stratification. However, this interaction was only predicted to occur in clear lakes, and not in the study lakes at their historical transparency. Not only lake morphology, but also mixing regime determines how heat is stored and ultimately how lakes respond to climate warming. Seasonal differences in climate warming rates are thus important and require more attention.

Climatology of mixed layer depth in the Gulf of Aden derived from in situ temperature profiles

2019 ◽  
Vol 75 (4) ◽  
pp. 335-347 ◽  
Author(s):  
Cheriyeri P. Abdulla ◽  
Mohammed A. Alsaafani ◽  
Turki M. Alraddadi ◽  
Alaa M. Albarakati
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Temperature Profiles ◽  
Gulf Of Aden ◽  
Layer Depth

In Situ Observations of Madden–Julian Oscillation Mixed Layer Dynamics in the Indian and Western Pacific Oceans

2012 ◽  
Vol 25 (7) ◽  
pp. 2306-2328 ◽  
Author(s):  
Kyla Drushka ◽  
Janet Sprintall ◽  
Sarah T. Gille ◽  
Susan Wijffels
Keyword(s):  
Heat Flux ◽  
Indian Ocean ◽  
Mixed Layer ◽  
Heat Budget ◽  
Mixed Layer Depth ◽  
Layer Depth ◽  
Temperature Variations ◽  
Central Indian Ocean ◽  
Mixed Layer Temperature

Abstract The boreal winter response of the ocean mixed layer to the Madden–Julian oscillation (MJO) in the Indo-Pacific region is determined using in situ observations from the Argo profiling float dataset. Composite averages over numerous events reveal that the MJO forces systematic variations in mixed layer depth and temperature throughout the domain. Strong MJO mixed layer depth anomalies (>15 m peak to peak) are observed in the central Indian Ocean and in the far western Pacific Ocean. The strongest mixed layer temperature variations (>0.6°C peak to peak) are found in the central Indian Ocean and in the region between northwest Australia and Java. A heat budget analysis is used to evaluate which processes are responsible for mixed layer temperature variations at MJO time scales. Though uncertainties in the heat budget are on the same order as the temperature trend, the analysis nonetheless demonstrates that mixed layer temperature variations associated with the canonical MJO are driven largely by anomalous net surface heat flux. Net heat flux is dominated by anomalies in shortwave and latent heat fluxes, the relative importance of which varies between active and suppressed MJO conditions. Additionally, rapid deepening of the mixed layer in the central Indian Ocean during the onset of active MJO conditions induces significant basin-wide entrainment cooling. In the central equatorial Indian Ocean, MJO-induced variations in mixed layer depth can modulate net surface heat flux, and therefore mixed layer temperature variations, by up to ~40%. This highlights the importance of correctly representing intraseasonal mixed layer depth variations in climate models in order to accurately simulate mixed layer temperature, and thus air–sea interaction, associated with the MJO.

scholarly journals Mixed layer variability and chlorophyll <i>a</i> biomass in the Bay of Bengal

2014 ◽  
Vol 11 (14) ◽  
pp. 3819-3843 ◽  
Author(s):  
J. Narvekar ◽  
S. Prasanna Kumar
Keyword(s):  
Mixed Layer ◽  
Bay Of Bengal ◽  
Mixed Layer Depth ◽  
Remote Sensing Data ◽  
Ekman Pumping ◽  
Layer Depth ◽  
Basin Scale ◽  
Deep Mixed Layer ◽  
Northern Bay Of Bengal

Abstract. The mixed layer is the most variable and dynamically active part of the marine environment that couples the underlying ocean to the atmosphere and plays an important role in determining the oceanic primary productivity. We examined the basin-scale processes controlling the seasonal variability of mixed layer depth in the Bay of Bengal and its association with chlorophyll using a suite of in situ as well as remote sensing data. A coupling between mixed layer depth and chlorophyll was seen during spring intermonsoon and summer monsoon, but for different reasons. In spring intermonsoon the temperature-dominated stratification and associated shallow mixed layer makes the upper waters of the Bay of Bengal nutrient depleted and oligotrophic. In summer, although the salinity-dominated stratification in the northern Bay of Bengal shallows the mixed layer, the nutrient input from adjoining rivers enhance the surface chlorophyll. This enhancement is confined only to the surface layer and with increase in depth, the chlorophyll biomass decreases rapidly due to reduction in sunlight by suspended sediment. In the south, advection of high salinity waters from the Arabian Sea and westward propagating Rossby waves from the eastern Bay of Bengal led to the formation of deep mixed layer. In contrast, in the Indo–Sri Lanka region, the shallow mixed layer and nutrient enrichment driven by upwelling and Ekman pumping resulted in chlorophyll enhancement. The mismatch between the nitrate and chlorophyll indicated the inadequacy of present data to fully unravel its coupling to mixed layer processes.

scholarly journals ACC Subduction by Mesoscales

2019 ◽  
Vol 49 (12) ◽  
pp. 3263-3272
Author(s):  
V. M. Canuto ◽  
Y. Cheng
Keyword(s):  
Antarctic Circumpolar Current ◽  
Mesoscale Model ◽  
Mixed Layer Depth ◽  
Fold Increase ◽  
Layer Depth ◽  
Surface Drifter ◽  
Order Of Magnitude ◽  
Overall Performance ◽  
Circumpolar Current ◽  
2D Model

AbstractThe mesoscale contribution to subduction in the Southern Ocean was studied by Sallée and Rintoul in 2011 (SR11) using the following mesoscale model. The adiabatic (A) regime was modeled with the Gent–McWilliams streamfunction, the diabatic (D) regime was modeled with tapering functions, the D–A interface was taken to be at the mixed layer depth, and the mesoscale diffusivity either was a constant or was given by a 2D model. Since the resulting subductions were an order of magnitude smaller than the data of ±200 m yr−1 as reported by Mazloff et al. in 2010, SR11 showed that if, instead of the above model-dependent mesoscale diffusivities, they employed the ones reported in 2008 by Sallée et al. from surface drifter observations, the subductions compared significantly better to the data. On those grounds, SR11 suggested a 10-fold increase of the diffusivity. In this work, we suggest that, since the mesoscale diffusivity is but one component of a much large mesoscale parameterization, one should first assess the latter’s overall performance followed by an assessment of the predicted Antarctic Circumpolar Current (ACC) subduction. We employ the mesoscale model formulated by Canuto et al. in 2018 and 2019 that includes recent theoretical and observational advances and that was assessed against a variety of data, including the output of 17 other OGCMs. The ACC diffusivities compare well to drifter data from Sallée et al., and the ACC subduction rates are in agreement with the data.

scholarly journals Has Sverdrup's critical depth hypothesis been tested? Mixed layers vs. turbulent layers

2014 ◽  
Vol 72 (6) ◽  
pp. 1897-1907 ◽  
Author(s):  
Peter J. S. Franks
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Critical Depth ◽  
Layer Depth ◽  
Poor Indicator ◽  
Active Turbulence ◽  
Mixed Layers ◽  
Vertical Scales ◽  
Over Time

Abstract Sverdrup (1953. On conditions for the vernal blooming of phytoplankton. Journal du Conseil International pour l'Exploration de la Mer, 18: 287–295) was quite careful in formulating his critical depth hypothesis, specifying a “thoroughly mixed top layer” with mixing “strong enough to distribute the plankton organisms evenly through the layer”. With a few notable exceptions, most subsequent tests of the critical depth hypothesis have ignored those assumptions, using estimates of a hydrographically defined mixed-layer depth as a proxy for the actual turbulence-driven movement of the phytoplankton. However, a closer examination of the sources of turbulence and stratification in turbulent layers shows that active turbulence is highly variable over time scales of hours, vertical scales of metres, and horizontal scales of kilometres. Furthermore, the mixed layer as defined by temperature or density gradients is a poor indicator of the depth or intensity of active turbulence. Without time series of coincident, in situ measurements of turbulence and phytoplankton rates, it is not possible to properly test Sverdrup's critical depth hypothesis.

Comparison of the Observed Mixed Layer Depth in the Lee of the Hawaiian Island to the Modeled Mixed Layer Depth of the Regional Navy Coastal Ocean Model

2013 ◽  
Vol 47 (1) ◽  
pp. 55-66 ◽  
Author(s):  
Jeffery Todd Rayburn ◽  
Vladimir M. Kamenkovich
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Coastal Ocean ◽  
Ocean Model ◽  
Sea Surface ◽  
Height Anomaly ◽  
Surface Mixed Layer ◽  
Layer Depth ◽  
Coastal Ocean Model

AbstractThis study evaluates the ability of the Hawaii Regional Navy Coastal Ocean Model to accurately predict the depth of the surface mixed layer in the lee of the Hawaiian Islands. Accurately modeling the depth of the surface mixed layer in this complex wake island environment is important to naval operations because the area hosts numerous training exercises. The simulated data were compared to CTD data collected from sea gliders, and tests for correlation were conducted. For mixed layer depths that did show correlation, match-paired t tests were used to determine the significance of the correlations. It was determined that the Hawaii Regional Navy Coastal Ocean Model has difficulty accurately predicting the depth of the surface mixed layer. It was also determined that the model has difficulty with unusual oceanographic features such as mode water eddies. These features are too uncommon and short-lived to be depicted in the climatology data. The climatology data are a major component of the synthetic profiles that the model generates, and these profiles tend to smooth out the unusual subsurface isothermal layer.List of AbbreviationsBT ‐ bathythermographsCCE ‐ cold core eddyCOAMPS ‐ Coupled Ocean/Atmosphere Mesoscale Prediction SystemCTD ‐ conductivity, temperature, and depthGDEM ‐ Generalized Digital Environmental ModelIR ‐ infraredMLD ‐ mixed layer depthMODAS ‐ Modular Ocean Data Assimilation SystemMOODS ‐ Master Oceanographic Observation DatasetNCODA ‐ Navy Coupled Ocean Data AssimilationNCOM1 ‐ Hawaii Regional Navy Coastal Ocean Model with in situ assimilationNCOM2 ‐ Hawaii Regional Navy Coastal Ocean Model without in situ assimilationPAVE ‐ Profile Analysis and Visualization EnvironmentSSHa ‐ sea surface height anomaly derived from altimetrySST ‐ sea surface temperatureWCE ‐ warm core eddy

scholarly journals Annual Salt and Energy Budget Beneath an Antarctic Fast Ice Cover

1985 ◽  
Vol 6 ◽  
pp. 182-186 ◽  
Author(s):  
Ian Allison ◽  
C. M. Tivendale ◽  
G. R. Copson
Keyword(s):  
Water Temperature ◽  
Fresh Water ◽  
Ice Cover ◽  
Ice Thickness ◽  
Salt Balance ◽  
Oceanic Heat Flux ◽  
Effective Removal ◽  
Salinity Increase ◽  
Fast Ice

Water temperature and salinity profiles were measured to a depth of 300 m below a fast ice cover near Mawson, Antarctica over a full annual cycle. Together with measurements of ice thickness and salinity, they are used to determine the heat and salt balance of the ice/ocean system at this site. The energy balance of the ocean is related to measured energy fluxes at the surface.Throughout the winter there is a net advection of salty water to the site which enhances the salinity increase in the water due to brine ejected from ice. After the ice reaches its maximum thickness there is considerable advection of warmer water which both raises the water temperature at the site and provides heat for the large oceanic heat flux previously reported for Mawson. The rate of this heat advection increases as the ice extent around Antarctica decreases. The ice partially meltsin situand breaks out in mid January. This effective removal of fresh water is balanced by a large influx of melt water from the continental ice sheet. The fresh water, initially near the surface, becomes well mixed to depths of greater than 200 m by strong storms in the ice free period from mid January to early April.

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