scholarly journals Wave-Induced Turbulence, Linking Metocean and Large Scales

2020 ◽  
Author(s):  
Alexander V. Babanin
Keyword(s):  
Wind Speed ◽  
Surface Waves ◽  
Ocean Circulation ◽  
Large Scale ◽  
Wave Climate ◽  
The Arctic ◽  
Arctic Seas ◽  
The Mean ◽  
Wave Induced ◽  
Wave Boundary

Abstract Until recently, large-scale models did not explicitly take account of ocean surface waves which are a process of much smaller scales. However, it is rapidly becoming clear that many large-scale geophysical processes are essentially coupled with the surface waves, and those include ocean circulation, weather, Tropical Cyclones and polar sea ice in both Hemispheres, climate and other phenomena in the atmosphere, at air/sea, sea/ice and sea/land interface, and many issues of the upper-ocean mixing below the surface. Besides, the wind-wave climate itself experiences large-scale trends and fluctuations, and can serve as an indicator for changes in the weather climate. In the presentation, we will discuss wave influences at scales from turbulence to climate, on the atmospheric and oceanic sides. At the atmospheric side of the interface, the air-sea coupling is usually described by means of the drag coefficient Cd, which is parameterised in terms of the wind speed, but the scatter of experimental data with respect to such dependences is very significant and has not improved noticeably over some 40 years. It is argued that the scatter is due to multiple mechanisms which contribute into the sea drag, many of them are due to surface waves and cannot be accounted for unless the waves are explicitly known. The Cd concept invokes the assumption of constant-flux layer, which is also employed for vertical profiling of the wind measured at some elevation near the ocean surface. The surface waves, however, modify the balance of turbulent stresses very near the surface, and therefore such extrapolations can introduce significant biases. This is particularly essential for buoy measurements in extreme conditions, when the anemometer mast is within the Wave Boundary Layer (WBL) or even below the wave crests. In this presentation, field data and a WBL model are used to investigate such biases. It is shown that near the surface the turbulent fluxes are less than those obtained by extrapolation using the logarithmic-layer assumption, and the mean wind speeds very near the surface, based on Lake George field observations, are up to 5% larger. The dynamics is then simulated by means of a WBL model coupled with nonlinear waves, which revealed further details of complex behaviours at wind-wave boundary layer. Furthermore, we analyse the structure of WBL for strong winds (U10 > 20 m/s) based on field observations. We used vertical distribution of wind speed and momentum flux measured in Topical Cyclone Olwyn (April 2015) in the North-West shelf of Australia. A well-established layer of constant stress is observed. The values obtained for u⁎ from the logarithmic profile law against u⁎ from turbulence measurements (eddy correlation method) differ significantly as wind speed increases. Among wave-induced influences at the ocean side, the ocean mixing is most important. Until recently, turbulence produced by the orbital motion of surface waves was not accounted for, and this fact limits performance of the models for the upper-ocean circulation and ultimately large-scale air-sea interactions. While the role of breaking waves in producing turbulence is well appreciated, such turbulence is only injected under the interface at the vertical scale of wave height. The wave-orbital turbulence is depth-distributed at the scale of wavelength (∼10 times the wave height) and thus can mix through the ocean thermocline in the spring-summer seasons. Such mixing then produces feedback to the large-scale processes, from weather to climate. In order to account for the wave-turbulence effects, large-scale air-sea interaction models need to be coupled with wave models. Theory and practical applications for the wave-induced turbulence will be reviewed in the presentation. These include viscous and instability theories of wave turbulence, direct numerical simulations and laboratory experiments, field and remote sensing observations and validations, and finally implementations in ocean, Tropical Cyclone, ocean and ice models. As a specific example of a wave-coupled environment, the wave climate in the Arctic as observed by altimeters will be presented. This is an important topic for the Arctic Seas, which are opening from ice in summer time. Challenges, however, are many as their Metocean environment is more complicated and, in addition to winds and waves, requires knowledge and understanding of ice material properties and its trends. On one hand, no traditional statistical approach is possible since in the past for most of the Arctic Ocean there was limited wave activity. Extrapolations of the current trends into the future are not feasible, because ice cover and wind patterns in the Arctic are changing. On the other hand, information on the mean and extreme wave properties is of great importance for oceanographic, meteorological, climate, naval and maritime applications in the Arctic Seas.

scholarly journals Atmospheric Circulation Effects on Wind Speed Variability at Turbine Height

2007 ◽  
Vol 46 (4) ◽  
pp. 445-456 ◽  
Author(s):  
Katherine Klink
Keyword(s):  
Wind Speed ◽  
Pressure Gradient ◽  
Large Scale ◽  
Ground Level ◽  
The Arctic ◽  
Circulation Index ◽  
Regression Equations ◽  
Change Models ◽  
Wind Speeds ◽  
The North

Abstract Mean monthly wind speed at 70 m above ground level is investigated for 11 sites in Minnesota for the period 1995–2003. Wind speeds at these sites show significant spatial and temporal coherence, with prolonged periods of above- and below-normal values that can persist for as long as 12 months. Monthly variation in wind speed primarily is determined by the north–south pressure gradient, which captures between 22% and 47% of the variability (depending on the site). Regression on wind speed residuals (pressure gradient effects removed) shows that an additional 6%–15% of the variation can be related to the Arctic Oscillation (AO) and Niño-3.4 sea surface temperature (SST) anomalies. Wind speeds showed little correspondence with variation in the Pacific–North American (PNA) circulation index. The effect of the strong El Niño of 1997/98 on the wind speed time series was investigated by recomputing the regression equations with this period excluded. The north–south pressure gradient remains the primary determinant of mean monthly 70-m wind speeds, but with 1997/98 removed the influence of the AO increases at nearly all stations while the importance of the Niño-3.4 SSTs generally decreases. Relationships with the PNA remain small. These results suggest that long-term patterns of low-frequency wind speed (and thus wind power) variability can be estimated using large-scale circulation features as represented by large-scale climatic datasets and by climate-change models.

scholarly journals A Diagnostic Model of the Nordic Seas and Arctic Ocean Circulation: Quantifying the Effects of a Variable Bottom Density along a Sloping Topography

2008 ◽  
Vol 38 (12) ◽  
pp. 2685-2703 ◽  
Author(s):  
Signe Aaboe ◽  
Ole Anders Nøst
Keyword(s):  
Arctic Ocean ◽  
Ocean Circulation ◽  
Large Scale ◽  
The Arctic ◽  
Diagnostic Model ◽  
Large Scale Circulation ◽  
Nordic Seas ◽  
Variable Bottom ◽  
Canadian Basin ◽  
Baroclinic Transport

Abstract A linear diagnostic model, solving for the time-mean large-scale circulation in the Nordic seas and Arctic Ocean, is presented. Solutions on depth contours that close within the Nordic seas and Arctic Ocean are found from vorticity balances integrated over the areas enclosed by the contours. Climatological data for wind stress and hydrography are used as input to the model, and the bottom geostrophic flow is assumed to follow depth contours. Comparison against velocity observations shows that the simplified dynamics in the model capture many aspects of the large-scale circulation. Special attention is given to the dynamical effects of an along-isobath varying bottom density, which leads to a transformation between barotropic and baroclinic transport. Along the continental slope, enclosing both the Nordic seas and Arctic Ocean, the along-slope barotropic transport has a maximum in the Nordic seas and a minimum in the Canadian Basin with a difference of 9 Sv (1 Sv ≡ 106 m3 s−1) between the two. This is caused by the relatively lower bottom densities in the Canadian Basin compared to the Nordic seas and suggests that most of the barotropic transport entering the Arctic Ocean through the Fram Strait is transformed to baroclinic transport. A conversion from barotropic to baroclinic flow may be highly important for the slope–basin exchange in the Nordic seas and Arctic Ocean. The model has obvious shortcomings due to its simplicity. However, the simplified physics and the agreement with observations make this model an excellent framework for understanding the large-scale circulation in the Nordic seas and Arctic Ocean.

scholarly journals Variability of Daily Maximum Wind Speed across China, 1975–2016: An Examination of Likely Causes

2020 ◽  
Vol 33 (7) ◽  
pp. 2793-2816 ◽  
Author(s):  
Gangfeng Zhang ◽  
Cesar Azorin-Molina ◽  
Deliang Chen ◽  
Jose A. Guijarro ◽  
Feng Kong ◽  
...  
Keyword(s):  
Wind Speed ◽  
Large Scale ◽  
Southern Oscillation ◽  
Vertical Wind Shear ◽  
Maximum Wind Speed ◽  
The Arctic ◽  
Risk Governance ◽  
Daily Maximum ◽  
Near Surface ◽  
Maximum Wind

AbstractAssessing change in daily maximum wind speed and its likely causes is crucial for many applications such as wind power generation and wind disaster risk governance. Multidecadal variability of observed near-surface daily maximum wind speed (DMWS) from 778 stations over China is analyzed for 1975–2016. A robust homogenization protocol using the R package Climatol was applied to the DMWS observations. The homogenized dataset displayed a significant (p < 0.05) declining trend of −0.038 m s−1 decade−1 for all China annually, with decreases in winter (−0.355 m s−1 decade−1, p < 0.05) and autumn (−0.108 m s−1 decade−1; p < 0.05) and increases in summer (+0.272 m s−1 decade−1, p < 0.05) along with a weak recovery in spring (+0.032 m s−1 decade−1; p > 0.10); that is, DMWS declined during the cold semester (October–March) and increased during the warm semester (April–September). Correlation analysis of the Arctic Oscillation, the Southern Oscillation, and the west Pacific modes exhibited significant correlation with DMWS variability, unveiling their complementarity in modulating DMWS. Further, we explored potential physical processes relating to the atmospheric circulation changes and their impacts on DMWS and found that 1) overall weakened horizontal airflow [large-scale mean horizontal pressure gradient (from −0.24 to +0.02 hPa decade−1) and geostrophic wind speed (from −0.6 to +0.6 m s−1 decade−1)], 2) widely decreased atmospheric vertical momentum transport [atmospheric stratification thermal instability (from −3 to +1.5 decade−1) and vertical wind shear (from −0.4 to +0.2 m s−1 decade−1)], and 3) decreased extratropical cyclones frequency (from −0.3 to 0 month decade−1) are likely causes of DMWS change.

Growth of Wave Height with Retreating Ice Cover in the Arctic

2020 ◽  
Author(s):  
Changlong Guan ◽  
Jingkai Li
Keyword(s):  
Arctic Ocean ◽  
Surface Waves ◽  
Wave Height ◽  
Open Water ◽  
Ice Cover ◽  
Wave Climate ◽  
Least Square ◽  
The Arctic ◽  
The Arctic Ocean ◽  
Wave Heights

&lt;p&gt;For the Arctic surface waves, one of the most uncontroversial viewpoints is that their escalation in the past few years is mainly caused by the ice extent reduction. Ice retreat enlarges the open water area, i.e., the effective fetch, and thus allows more wind input energy and available distance for wave evolution. This knowledge has been supported by a few previous studies on the Arctic waves which analyzed the correlation between time-series variations in wave height and ice coverage. However, from the perspective of space, the detailed relationship between retreating ice cover and increasing surface waves is not well studied. Hence, we performed such a study for the whole Arctic and its subregions, which will be helpful for a better understanding of the wave climate and for forecasting waves in the Arctic Ocean.&lt;/p&gt;&lt;p&gt;Wave data are produced by twelve-year (2007-2018) hindcasts of summer melt seasons (May-Sept.) and numerical tests with WAVEWATCH III. When a viscoelastic wave-ice model and a spherical multiple-cell grid are applied, simulated wave heights agree with available buoy data and previous research. After the validations, simulated significant wave heights over twelve-year summer melt seasons are used to demonstrate the detailed relationship between the escalation of wave height and reduction of ice extent for the whole Arctic and seven subregions. Through least square regression, we find that the mean wave height in the Arctic Ocean will increase by 0.071m (10&lt;sup&gt;6&lt;/sup&gt;km&lt;sup&gt;2&lt;/sup&gt;)&lt;sup&gt;-1&lt;/sup&gt; when the ice extent is smaller than 9.4&amp;#215;10&lt;sup&gt;6&lt;/sup&gt;km&lt;sup&gt;2&lt;/sup&gt;, and roughly 51% is contributed by the enlarged fetch. By analyzing the nondimensional wave energy and comparing the simulated wave height with Wilson IV, we prove the swell is widespread during the summertime in the current Arctic Ocean. Furthermore, we also display the variations in probabilities of occurrence of large waves as ice-edge retreats in seven subregions. Assuming that an ice free period occurs in the Arctic in September, the model results show that the simulated mean wave height is approximately 1.6m and the large waves occur much more frequently, which mean that the growth rate of wave height will be higher if the minimum ice extent keeps reducing in the future.&lt;/p&gt;

scholarly journals A parametric model of surface waves as applied to the Arctic seas

2021 ◽  
pp. 515-530
Author(s):  
V. Cheshm Siyahi ◽  
V.N. Kudryavtsev ◽  
M.V. Yurovskaya
Keyword(s):  
Surface Waves ◽  
Parametric Model ◽  
The Arctic ◽  
Arctic Seas

scholarly journals Simulation of the Arctic—North Atlantic Ocean Circulation with a Two-Equation K-Omega Turbulence Parameterization

2018 ◽  
Vol 6 (3) ◽  
pp. 95 ◽  
Author(s):  
Sergey Moshonkin ◽  
Vladimir Zalesny ◽  
Anatoly Gusev
Keyword(s):  
Prandtl Number ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Large Scale ◽  
Mixed Layer Depth ◽  
Ocean Dynamics ◽  
Dynamics Simulation ◽  
The Arctic ◽  
Buoyancy Frequency ◽  
Physical Factors

The results of large-scale ocean dynamics simulation taking into account the parameterization of vertical turbulent exchange are considered. Numerical experiments were carried out using k − ω turbulence model embedded to the Institute of Numerical Mathematics Ocean general circulation Model (INMOM). Both the circulation and turbulence models are solved using the splitting method with respect to physical processes. We split k − ω equations into the two stages describing transport-diffusion and generation-dissipation processes. At the generation-dissipation stage, the equation for ω does not depend on k. It allows us to solve both turbulence equations analytically that ensure high computational efficiency. The coupled model is used to simulate the hydrophysical fields of the North Atlantic and Arctic Oceans for 1948–2009. The model has a horizontal resolution of 0.25 ∘ and 40 σ -levels along the vertical. The numerical results show the model’s satisfactory performance in simulating large-scale ocean circulation and upper layer dynamics. The sensitivity of the solution to the change in the coefficients entering into the analytical solution of the k − ω model which describe the influence of some physical factors is studied. These factors are the climatic annual mean buoyancy frequency (AMBF) and Prandtl number as a function of the Richardson number. The experiments demonstrate that taking into account the AMBF improves the reproduction of large-scale ocean characteristics. Prandtl number variations improve the upper mixed layer depth simulation.

Low-Frequency Climate Response of Quasigeostrophic Wind-Driven Ocean Circulation

2012 ◽  
Vol 42 (2) ◽  
pp. 243-260 ◽  
Author(s):  
Rafail V. Abramov ◽  
Andrew J. Majda
Keyword(s):  
Climate Change ◽  
Ocean Circulation ◽  
Linear Response ◽  
Large Scale ◽  
Response Times ◽  
Low Frequency ◽  
External Perturbation ◽  
Climate Dynamics ◽  
The Mean ◽  
General Response

Abstract Linear response to external perturbation through the fluctuation–dissipation theorem has recently become a popular topic in the climate research community. It relates an external perturbation of climate dynamics to climate change in a simple linear fashion, which provides key insight into physics of the climate change phenomenon. Recently, the authors developed a suite of linear response algorithms for low-frequency response of large-scale climate dynamics to external perturbation, including the novel blended response algorithm, which combines the geometrically exact general response formula using integration of a linear tangent model at short response times and the classical quasi-Gaussian response algorithm at longer response times, overcoming numerical instability of the tangent linear model for longer times due to positive Lyapunov exponents. Here, the authors apply the linear response framework to several leading empirical orthogonal functions (EOFs) of a quasigeostrophic model of wind-driven ocean circulation. It is demonstrated that the actual nonlinear response of this system under external perturbation at leading EOFs can be predicted by the linear response algorithms with adequate skill with moderate errors; in particular, the blended response algorithm has a pattern correlation with the ideal response operator on the four leading EOFs of the mean state response of 94% after 5 yr. In addition, interesting properties of the mean flow response to large-scale changes in wind stress at the leading EOFs are observed.

The ocean response to changes of the Greenland Ice sheet in a warming climate

2020 ◽  
Author(s):  
Marianne S. Madsen ◽  
Shuting Yang ◽  
Christian Rodehacke ◽  
Guðfinna Aðalgeirsdóttir ◽  
Synne H. Svendsen ◽  
...  
Keyword(s):  
Mass Loss ◽  
Ocean Circulation ◽  
Large Scale ◽  
Climate Model ◽  
Variable Mass ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Model System ◽  
Meridional Overturning Circulation ◽  
The Arctic

&lt;p&gt;During recent decades, increased and highly variable mass loss from the Greenland ice sheet has been observed, implying that the ice sheet can respond to changes in ocean and atmospheric conditions on annual to decadal time scales. Changes in ice sheet topography and increased mass loss into the ocean may impact large scale atmosphere and ocean circulation. Therefore, coupling of ice sheet and climate models, to explicitly include the processes and feedbacks of ice sheet changes, is needed to improve the understanding of ice sheet-climate interactions.&lt;/p&gt;&lt;p&gt;Here, we present results from the coupled ice sheet-climate model system, EC-Earth-PISM. The model consists of the atmosphere, ocean and sea-ice model system EC-Earth, two-way coupled to the Parallel Ice Sheet Model, PISM. The surface mass balance (SMB) is calculated within EC-Earth, from the precipitation, evaporation and surface melt of snow and ice, to ensure conservation of mass and energy. The ice sheet model, PISM, calculates ice dynamical changes in ice discharge and basal melt as well as changes in ice extent and thickness. Idealized climate change experiments have been performed starting from pre-industrial conditions for a) constant forcing (pre-industrial control); b) abruptly quadrupling the CO&lt;sub&gt;2&lt;/sub&gt; concentration; and c) gradually increasing the CO&lt;sub&gt;2&lt;/sub&gt; concentration by 1% per year until 4xCO&lt;sub&gt;2&lt;/sub&gt; is reached. &amp;#160;All three experiments are run for 350 years.&lt;/p&gt;&lt;p&gt;Our results show a significant impact of the interactive ice sheet component on heat and fresh water fluxes into the Arctic and North Atlantic Oceans. The interactive ice sheet causes freshening of the Arctic Ocean and affects deep water formation, resulting in a significant delay of the recovery of the Atlantic Meridional Overturning Circulation (AMOC) in the coupled 4xCO&lt;sub&gt;2&lt;/sub&gt; experiments, when compared with uncoupled experiments.&lt;/p&gt;

The Norwegian node for the European Multidisciplinary Seafloor and water column Observatory

2020 ◽  
Author(s):  
Thibaut Barreyre ◽  
Ilker Fer ◽  
Bénédicte Ferré
Keyword(s):  
Water Column ◽  
Ocean Circulation ◽  
Large Scale ◽  
Water Mass ◽  
Critical Role ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Global Ocean ◽  
Fram Strait ◽  
Nordic Seas

&lt;p&gt;NorEMSO is a coordinated, large-scale deep-ocean observation facility to establish the Norwegian node for the European Multidisciplinary Seafloor and water column Observatory (EMSO). The project aims to explore the under-sampled Nordic Seas to gain a better understanding of the critical role that they play in our climate system and global ocean circulation. An overarching scientific objective is to better understand the drivers for the temporal and spatial changes of water mass transformations, ocean circulation, acidification and thermo-chemical exchanges at the seafloor in the Nordic Seas, and to contribute to improvement of models and forecasting by producing and making available high quality, near real time data. NorEMSO will achieve this by combining expansion of existing and establishment of new observatory network infrastructure, as well as its coordination and integration into EMSO.&lt;/p&gt;&lt;p&gt;NorEMSO comprises of three main components: moored observatories, gliders, and seafloor and water column observatory at the Mohn Ridge (EMSO-Mohn).&lt;/p&gt;&lt;p&gt;Moored observation systems include an array of four moored observatories located at key positions in the Nordic Seas (Svin&amp;#248;y, Station M, South Cape, and central Fram Strait).&lt;/p&gt;&lt;p&gt;Gliders will be operated along five transects across both the Norwegian and the Greenland Seas to monitor circulation and water mass properties at those key locations. Transects in the Norwegian and Lofoten basins will focus on monitoring the Norwegian Atlantic Current, and a transect in Fram Strait will monitor properties and variability in the return Atlantic Water along the Polar Front in the northern Nordic Seas. In addition, transects in the Greenland and Iceland Seas will address the water mass transformation processes through wintertime open ocean convection, and the southbound transport of surface water from the Arctic Ocean and dense water that feeds the lower limb of the Atlantic Meridional Overturning Circulation in the East Greenland Current.&lt;/p&gt;&lt;p&gt;EMSO-Mohn will establish, at the newly discovered hydrothermal site on the Mohn Ridge, a fixed-point seabed-water-column-coupled and wireless observatory with a multidisciplinary approach &amp;#8211; from geophysics and physical oceanography to ecology and microbiology. It is primarily directed at understanding hydrothermal fluxes and associated hydrothermal plume dynamics in the water column and how it disperses in an oceanographic front over the Mohn Ridge.&lt;/p&gt;&lt;p&gt;Following EMSO philosophy, NorEMSO will provide data and platforms to a large and diverse group of users, from scientists and industries to institutions and policy makers. The observations will serve climate research, ocean circulation understanding, numerical operational models, design of environmental policies, and education.&lt;/p&gt;

scholarly journals Interannual characteristics of an 80 km resolution diagnostic Arctic ice–ocean model

1991 ◽  
Vol 15 ◽  
pp. 155-162 ◽  
Author(s):  
John E. Ries ◽  
William D. Hibler
Keyword(s):  
Ocean Circulation ◽  
Large Scale ◽  
Eddy Viscosity ◽  
Barents Sea ◽  
Arctic Basin ◽  
Ocean Model ◽  
The Arctic ◽  
Atmospheric Forcing ◽  
Ice Edge ◽  
Arctic Ice

Seasonal simulations with large-scale coupled ice–ocean models have reproduced many features of the ice and ocean circulation of the Arctic Ocean and the Greenland and Norwegian seas (e.g. Hibler and Bryan, 1987; Semtner, 1987). However, the crude resolution and high lateral eddy viscosity used by these models prevent the simulation of many of the smaller-scale seasonal features and tend to produce sluggish circulation. Similarly, the use of a single year’s atmospheric forcing prevents the simulation of features on an interannual time-scale. As an initial step towards addressing these issues, an 80 km diagnostic Arctic ice–ocean model is constructed and integrated over a three-year period using daily atmospheric forcing to drive the model. To examine the effect of topographic resolution and eddy viscosity on model results, similar simulations were performed with a 160 km-resolution model. The results of these simulations are compared with one another, with buoy drift in the Arctic Basin, and with observed ice-edge variations. The model results proved most sensitive to changes in horizontal resolution. The 80 km results provided a more realistic and robust circulation in most areas of the Arctic and improved the modelled ice edge in the Barents Sea, while also successfully simulating the interannual variation in the region. Although it performed better than the 160 km model, the 80 km model still produced too large an ice extent in the Greenland Sea. No significant improvement in the ice-edge prediction was observed by varying the lateral eddy viscosity. The results indicate that problems remain in the vertical resolution in shallow regions, in treating penetrative convection, and in the simulation of inflow into the Arctic Basin through the Fram Strait.

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