scholarly journals Influence of Stokes Drift Decay Scale on Langmuir Turbulence

2017 ◽  
Vol 47 (7) ◽  
pp. 1637-1656 ◽  
Author(s):  
Tobias Kukulka ◽  
Ramsey R. Harcourt
Keyword(s):  
Conceptual Framework ◽  
Climate Models ◽  
Side Surface ◽  
Surface Flux ◽  
Stokes Drift ◽  
Decay Length ◽  
Length Scale ◽  
Surface Boundary ◽  
Langmuir Turbulence ◽  
Physical Processes

AbstractAccurately scaling Langmuir turbulence (LT) in the ocean surface boundary layer (OSBL) is critical for improving ocean, weather, and climate models. The physical processes by which the structure of LT depends on surface waves’ Stokes drift decay length scale are examined. An idealized model for OSBL turbulent kinetic energy (TKE) provides a conceptual framework with three physical processes: TKE transport, dissipation, and production by the Craik–Leibovich (CL) vortex force (VF) associated with the Stokes drift shear. TKE profiles depend on OSBL depth h, surface roughness length z0, and wavenumber k through the nondimensional parameters kh and kz0. These parameters determine the rate and length scale for the dissipation of TKE produced by the CL-VF. For kz0 ≫ 1, TKE input by the CL-VF is governed by a surface flux with TKE rapidly decaying with depth. Only for kz0 < 1 can TKE penetrate deeper into the OSBL, with the TKE penetration depth controlled by kh. Turbulence-resolving large-eddy simulation results support this conceptual framework and indicate that the dominant Langmuir cell size scales with (kh)−1. Within the depth of dominant Langmuir cells, TKE dissipation is approximately balanced by CL-VF production. Shorter waves contribute less to deeper vertical velocity variance 〈w2〉 because the CL-VF is less effective in generating larger-scale LT. Depth-averaged 〈w2〉 scales with a modified Langmuir number Laϕ = (u*/usϕ)1/2, where u* denotes the water-side surface friction velocity and usϕ is a depth-integrated weighted Stokes drift shear or, equivalently, a spectrally filtered surface Stokes drift.

A novel method for directly obtaining the water vapor isotope surface flux for evaluating snow-atmosphere exchange processes

2020 ◽  
Author(s):  
Sonja Wahl ◽  
Hans Christian Steen-Larsen ◽  
Alexandra Zuhr ◽  
Joachim Reuder
Keyword(s):  
Climate Models ◽  
Water Cycle ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Flux ◽  
Surface Fluxes ◽  
Physical Processes ◽  
Surface Mass ◽  
Novel Method

&lt;p&gt;Water isotopologues offers a direct constraint on the physical processes controlling surface fluxes.&amp;#160; A novel method is presented which enables in-situ measurements of the water vapour isotope flux between the snow surface of the Greenland Ice Sheet and the atmosphere.&lt;/p&gt;&lt;p&gt;These observations have become possible by combining a cavity ring-down laser absorption spectroscopy analyzer with high frequency latent heat flux eddy-covariance measurements.&lt;/p&gt;&lt;p&gt;This new method reveals an isotope flux driven by the diurnal cycle.&lt;br&gt;Water isotopes can thus act as a natural tracer giving information of the physical processes such as the influence of turbulent fluxes in the water cycle. This allows the assessment of sublimation and deposition processes in the low accumulation zone of the interior Greenland Ice Sheet.&lt;br&gt;Therefore, we can provide a strategy to benchmark the parameterizations of surface mass balance and surface fluxes in regional climate models.&lt;/p&gt;

scholarly journals Wind–Wave Misalignment Effects on Langmuir Turbulence in Tropical Cyclone Conditions

2019 ◽  
Vol 49 (12) ◽  
pp. 3109-3126 ◽  
Author(s):  
Dong Wang ◽  
Tobias Kukulka ◽  
Brandon G. Reichl ◽  
Tetsu Hara ◽  
Isaac Ginis
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Reynolds Stress ◽  
Wind Wave ◽  
Stokes Drift ◽  
Scaling Analysis ◽  
Surface Boundary ◽  
Langmuir Turbulence ◽  
Near Surface ◽  
Momentum Budget

AbstractThis study utilizes a large-eddy simulation (LES) approach to systematically assess the directional variability of wave-driven Langmuir turbulence (LT) in the ocean surface boundary layer (OSBL) under tropical cyclones (TCs). The Stokes drift vector, which drives LT through the Craik–Leibovich vortex force, is obtained through spectral wave simulations. LT’s direction is identified by horizontally elongated turbulent structures and objectively determined from horizontal autocorrelations of vertical velocities. In spite of a TC’s complex forcing with great wind and wave misalignments, this study finds that LT is approximately aligned with the wind. This is because the Reynolds stress and the depth-averaged Lagrangian shear (Eulerian plus Stokes drift shear) that are key in determining the LT intensity (determined by normalized depth-averaged vertical velocity variances) and direction are also approximately aligned with the wind relatively close to the surface. A scaling analysis of the momentum budget suggests that the Reynolds stress is approximately constant over a near-surface layer with predominant production of turbulent kinetic energy by Stokes drift shear, which is confirmed from the LES results. In this layer, Stokes drift shear, which dominates the Lagrangian shear, is aligned with the wind because of relatively short, wind-driven waves. On the contrary, Stokes drift exhibits considerable amount of misalignments with the wind. This wind–wave misalignment reduces LT intensity, consistent with a simple turbulent kinetic energy model. Our analysis shows that both the Reynolds stress and LT are aligned with the wind for different reasons: the former is dictated by the momentum budget, while the latter is controlled by wind-forced waves.

scholarly journals How robust and (un)certain are regional climate models over the Himalayas?

2014 ◽  
Vol 8 (6) ◽  
pp. 6251-6270 ◽  
Author(s):  
A. P. Dimri
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Regional Climate ◽  
Regional Climate Models ◽  
Surface Flux ◽  
Western Himalayas ◽  
Subgrid Scale ◽  
Model Resolution ◽  
Physical Processes ◽  
Event Scale

Abstract. Regional Climate Model(s) (RCMs) are sensitive towards presentation of regional climate of Indian winter monsoon (IWM) over the western Himalayas (WH). They illustrate robust nature in representing regional climate at mountain scale and even at event scale. While downscaling outputs, from these models, at basin level for hydrological and glaciological studies, it is found that RCMs fail to provide realistic figures. And hence, in the present paper, using the Siachen glacier basin as a reference, debate and deliberation on RCMs' uncertainly and high order of deviation from real observations is presented. Results from RCMs thus need "further tuning" if they are used for hydrological and glacier studies. Reasons for such uncertainties could be due to the improper representation of topography, missing subgrid scale processes, surface flux characteristics, various physical processes etc. at such finer model resolution and scale. At present, this paper only deliberates and brings out issues pertaining to such complexities to provide an insight for future course of studies, if understood correctly.

scholarly journals Characteristics of Langmuir Turbulence in the Ocean Mixed Layer

2009 ◽  
Vol 39 (8) ◽  
pp. 1871-1887 ◽  
Author(s):  
Alan L. M. Grant ◽  
Stephen E. Belcher
Keyword(s):  
Wave Field ◽  
Mixed Layer ◽  
Friction Velocity ◽  
Surface Friction ◽  
Stokes Drift ◽  
Length Scale ◽  
Langmuir Turbulence ◽  
Eddy Simulation ◽  
Lack Of Information ◽  
Velocity Scale

Abstract This study uses large-eddy simulation (LES) to investigate the characteristics of Langmuir turbulence through the turbulent kinetic energy (TKE) budget. Based on an analysis of the TKE budget a velocity scale for Langmuir turbulence is proposed. The velocity scale depends on both the friction velocity and the surface Stokes drift associated with the wave field. The scaling leads to unique profiles of nondimensional dissipation rate and velocity component variances when the Stokes drift of the wave field is sufficiently large compared to the surface friction velocity. The existence of such a scaling shows that Langmuir turbulence can be considered as a turbulence regime in its own right, rather than a modification of shear-driven turbulence. Comparisons are made between the LES results and observations, but the lack of information concerning the wave field means these are mainly restricted to comparing profile shapes. The shapes of the LES profiles are consistent with observed profiles. The dissipation length scale for Langmuir turbulence is found to be similar to the dissipation length scale in the shear-driven boundary layer. Beyond this it is not possible to test the proposed scaling directly using available data. Entrainment at the base of the mixed layer is shown to be significantly enhanced over that due to normal shear turbulence.

scholarly journals Comments on “Langmuir Turbulence and Surface Heating in the Ocean Surface Boundary Layer”

2018 ◽  
Vol 48 (2) ◽  
pp. 455-458 ◽  
Author(s):  
Yign Noh ◽  
Yeonju Choi
Keyword(s):  
Boundary Layer ◽  
Ocean Surface ◽  
Large Eddy Simulations ◽  
Surface Heating ◽  
Length Scale ◽  
Surface Boundary ◽  
Langmuir Turbulence ◽  
Surface Boundary Layer ◽  
Obukhov Length ◽  
Large Eddy

AbstractUsing large-eddy simulations (LES) it is shown that the depth of a diurnal thermocline h should be scaled by the Zilitinkevich scale LZ, not by the Monin–Obukhov length scale LMO, contrary to the proposition by Pearson et al. Their argument to explain the slower increase of h than LMO using the effect of the preexisting thermocline is also invalid.

Interaction of Langmuir Turbulence and Inertial Currents in the Ocean Surface Boundary Layer under Tropical Cyclones

2018 ◽  
Vol 48 (9) ◽  
pp. 1921-1940 ◽  
Author(s):  
Dong Wang ◽  
Tobias Kukulka ◽  
Brandon G. Reichl ◽  
Tetsu Hara ◽  
Isaac Ginis ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Tropical Cyclones ◽  
Ocean Surface ◽  
Stokes Drift ◽  
Surface Boundary ◽  
Langmuir Turbulence ◽  
Surface Boundary Layer ◽  
Wave Forcing ◽  
Inertial Currents

AbstractBased on a large-eddy simulation approach, this study investigates the response of the ocean surface boundary layer (OSBL) and Langmuir turbulence (LT) to extreme wind and complex wave forcing under tropical cyclones (TCs). The Stokes drift vector that drives LT is determined from spectral wave simulations. During maximum TC winds, LT substantially enhances the entrainment of cool water, causing rapid OSBL deepening. This coincides with relatively strong wave forcing, weak inertial currents, and shallow OSBL depth , measured by smaller ratios of , where denotes a Stokes drift decay length scale. LT directly affects a near-surface layer whose depth is estimated from enhanced anisotropy ratios of velocity variances. During rapid OSBL deepening, is proportional to , and LT efficiently transports momentum in coherent structures, locally enhancing shear instabilities in a deeper shear-driven layer, which is controlled by LT. After the TC passes, inertial currents are stronger and is greater while is shallower and proportional to . During this time, the LT-affected surface layer is too shallow to directly influence the deeper shear-driven layer, so that both layers are weakly coupled. At the same time, LT reduces surface currents that play a key role in the surface energy input at a later stage. These two factors contribute to relatively small TKE levels and entrainment rates after TC passage. Therefore, our study illustrates that inertial currents need to be taken into account for a complete understanding of LT and its effects on OSBL dynamics in TC conditions.

scholarly journals A global perspective on Langmuir turbulence in the ocean surface boundary layer

2012 ◽  
Vol 39 (18) ◽  
Author(s):  
Stephen E. Belcher ◽  
Alan L. M. Grant ◽  
Kirsty E. Hanley ◽  
Baylor Fox-Kemper ◽  
Luke Van Roekel ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Ocean Surface ◽  
Global Perspective ◽  
Surface Boundary ◽  
Langmuir Turbulence ◽  
Surface Boundary Layer

scholarly journals High-Fidelity Simulations of a Linear HPT Vane Cascade Subject to Varying Inlet Turbulence

2017 ◽  
Author(s):  
Richard Pichler ◽  
Richard D. Sandberg ◽  
Gregory Laskowski ◽  
Vittorio Michelassi
Keyword(s):  
Heat Flux ◽  
Turbulence Intensity ◽  
Side Surface ◽  
Suction Side ◽  
Transition Process ◽  
Length Scale ◽  
Length Scales ◽  
Inflow Turbulence ◽  
High Turbulence ◽  
Turbulence Length

The effect of inflow turbulence intensity and turbulence length scales have been studied for a linear high-pressure turbine vane cascade at Reis = 590,000 and Mis = 0.93, using highly resolved compressible large-eddy simulations employing the WALE turbulence model. The turbulence intensity was varied between 6% and 20% while values of the turbulence length scales were prescribed between 5% and 20% of axial chord. The analysis focused on characterizing the inlet turbulence and quantifying the effect of the inlet turbulence variations on the vane boundary layers, in particular on the heat flux to the blade. The transition location on the suction side of the vane was found to be highly sensitive to both turbulence intensity and length scale, with the case with turbulence intensity 20% and 20% length scale showing by far the earliest onset of transition and much higher levels of heat flux over the entire vane. It was also found that the transition process was highly intermittent and local, with spanwise parts of the suction side surface of the vane remaining laminar all the way to the trailing edge even for high turbulence intensity cases.

scholarly journals Implementation of a boundary layer heat flux parameterization into the Regional Atmospheric Modeling System (RAMS)

2008 ◽  
Vol 8 (4) ◽  
pp. 14311-14346 ◽  
Author(s):  
E. L. McGrath-Spangler ◽  
A. S. Denning ◽  
K. D. Corbin ◽  
I. T. Baker
Keyword(s):  
Carbon Dioxide ◽  
Boundary Layer ◽  
Heat Flux ◽  
Lower Layer ◽  
Bowen Ratio ◽  
Surface Flux ◽  
Atmospheric Modeling ◽  
Surface Energy Budget ◽  
Stress Factors ◽  
Surface Boundary

Abstract. The response of atmospheric carbon dioxide to a given amount of surface flux is inversely proportional to the depth of the boundary layer. Overshooting thermals that entrain free tropospheric air down into the boundary layer modify the characteristics and depth of the lower layer through the insertion of energy and mass. This alters the surface energy budget by changing the Bowen ratio and thereby altering the vegetative response and the surface boundary conditions. Although overshooting thermals are important in the physical world, their effects are unresolved in most regional models. A parameterization to include the effects of boundary layer entrainment was introduced into a coupled ecosystem-atmosphere model (SiB-RAMS). The parameterization is based on a downward heat flux at the top of the boundary layer that is proportional to the heat flux at the surface. Results with the parameterization show that the boundary layer simulated is deeper, warmer, and drier than when the parameterization is turned off. These results alter the vegetative stress factors thereby changing the carbon flux from the surface. The combination of this and the deeper boundary layer change the concentration of carbon dioxide in the boundary layer.

scholarly journals Forecasting circulation in the Cilician Basin of the Levantine Sea

2006 ◽  
Vol 3 (5) ◽  
pp. 1481-1514 ◽  
Author(s):  
E. Özsoy ◽  
A. Sözer
Keyword(s):  
Boundary Conditions ◽  
Initial Conditions ◽  
Eastern Mediterranean ◽  
Model Performance ◽  
Surface Flux ◽  
Mediterranean Coast ◽  
Open Boundary ◽  
Surface Boundary ◽  
Open Boundary Conditions ◽  
Levantine Sea

Abstract. The Cilician Basin/Shelf Model is adapted for studying the shelf circulation in the Cilician Basin – Gulf of İskenderun region of the Levantine Basin of the Eastern Mediterranean between the Turkish Mediterranean coast, Syria and the island of Cyprus. The model initial conditions and open boundary conditions are supplied by the ALERMO regional model of the Levantine Sea, while interactive surface flux boundary conditions are specified by an atmospheric boundary layer sub-model using calculated water properties and surface atmospheric variables supplied by the Skiron atmospheric model, within the nested modelling approach of the MFSTEP (Mediterranean Forecasting System: Towards Environmental Predictions) project. Sensitivity tests are performed for alternative surface boundary conditions. Model performance for shelf/meso-scale forecasts is demonstrated.

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