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1
Largeron, Yann, Chantal Staquet e Charles Chemel. "Turbulent mixing in a katabatic wind under stable conditions". Meteorologische Zeitschrift 19, n. 5 (1 ottobre 2010): 467–80. http://dx.doi.org/10.1127/0941-2948/2010/0346.
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Atkinson, J. F., e D. R. F. Harleman. "Wind-mixing experiments for solar ponds". Solar Energy 38, n. 6 (1987): 389–403. http://dx.doi.org/10.1016/0038-092x(87)90020-x.
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Chen, Shih-Nan, e Lawrence P. Sanford. "Axial Wind Effects on Stratification and Longitudinal Salt Transport in an Idealized, Partially Mixed Estuary*". Journal of Physical Oceanography 39, n. 8 (1 agosto 2009): 1905–20. http://dx.doi.org/10.1175/2009jpo4016.1.
Testo completoAbstract (sommario):
Abstract A 3D hydrodynamic model [Regional Ocean Model System (ROMS)] is used to investigate how axial wind influences stratification and to explore the associated longitudinal salt transport in partially mixed estuaries. The model is configured to represent a straight estuarine channel connecting to a shelf sea. The results confirm that wind straining of the along-channel salinity gradient exerts an important control on stratification. Two governing parameters are identified: the Wedderburn number (W) defined as the ratio of wind stress to axial baroclinic pressure gradient force, and the ratio of an entrainment depth to water depth (hs/H). Here W controls the effectiveness of wind straining, which promotes increases (decreases) in stratification during down-estuary (up-estuary) wind. The ratio hs/H determines the portion of the water column affected by direct wind mixing. While stratification is always reduced by up-estuary wind, stratification shows an increase-then-decrease transition when down-estuary wind stress increases. Such transition is a result of the competition between wind straining and direct wind mixing. A horizontal Richardson number modified to include wind straining/mixing is shown to reasonably represent the transition, and a regime diagram is proposed to classify the wind’s role on stratification. Mechanisms driving salt flux during axial wind events are also explored. At the onset and end of the wind events, barotropic adjustment drives strong transient salt fluxes. Net salt flux is controlled by the responses of subtidal shear dispersion to wind forcing. Moderate down-estuary winds enhance subtidal shear dispersion, whereas up-estuary winds always reduce it. Supporting observations from upper Chesapeake Bay are presented.
4
Hetland, Robert D. "Relating River Plume Structure to Vertical Mixing". Journal of Physical Oceanography 35, n. 9 (1 settembre 2005): 1667–88. http://dx.doi.org/10.1175/jpo2774.1.
Testo completoAbstract (sommario):
Abstract The structure of a river plume is related to the vertical mixing using an isohaline-based coordinate system. Salinity coordinates offer the advantage of translating with the plume as it moves or expanding as the plume grows. This coordinate system is used to compare the relative importance of different dynamical processes acting within the plume and to describe the effect each process has on the structure of the plume. Vertical mixing due to inertial shear in the outflow of a narrow estuary and wind mixing are examined using a numerical model of a wind-forced river plume. Vertical mixing, and the corresponding entrainment of background waters, is greatest near the estuary mouth where inertial shear mixing is large. This region is defined as the near field, with the more saline, far-field plume beyond. Wind mixing increases the mixing throughout the plume but has the greatest effect on plume structure at salinity ranges just beyond the near field. Wind mixing is weaker at high salinity classes that have already been mixed to a critical thickness, a point where turbulent mixing of the upper layer by the wind is reduced, protecting these portions of the plume from further wind mixing. The work done by mixing on the plume is of similar magnitude in both the near and far fields.
5
Breitschwerdt, D., e F. D. Kahn. "Turbulent Mixing in Wind-Blown HII Regions". International Astronomical Union Colloquium 120 (1989): 117–21. http://dx.doi.org/10.1017/s025292110002354x.
Testo completoAbstract (sommario):
AbstractTurbulent mixing between an ionization bounded HII region and a hot shocked stellar wind (HSSW), which keeps it under pressure, is examined. Recently we have shown that acoustic disturbances can grow there to finite amplitude in a time scale which is comparable to the sound crossing time in the HII layer. The resulting turbulence will then stretch fluid elements and the frozen-in magnetic field. A condition under which turbulence can decay down to the viscous scale, where mixing is very efficient, is derived. For a uniform and plane parallel magnetic field Bo and a constant density ρo of the ambient medium, we find that efficient mixing takes place near the polar regions. Subsequently the rate of mass addition to the hot bubble is calculated and it is shown that catastrophic cooling is likely to occur. In the case of NGC 6334(A) it seems that this has just happened and we predict an upper limit for Bo of 4 x 10-5 gauss there. This model may also explain the existence of highly ionized species (e.g. OVI), soft X-rays and high velocity flows of the order of 100 km/s.
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Inoue, Ryuichiro, Michio Watanabe e Satoshi Osafune. "Wind-Induced Mixing in the North Pacific". Journal of Physical Oceanography 47, n. 7 (luglio 2017): 1587–603. http://dx.doi.org/10.1175/jpo-d-16-0218.1.
Testo completoAbstract (sommario):
AbstractTemporal variability of the winter input of wind energy flux (wind power) and its relationship to internal wave fields were examined in the North Pacific. The dominant long-term variability of the wind power input, estimated from a mixed layer slab model, was inferred from an empirical orthogonal function analysis, and it was found that variability partly corresponded to the strength and movement of the Aleutian low. Responses of the internal wave field to the input of wind power were examined for two winters with a meridional float array along 170°W at a sampling interval of 2 dbar. Time series of the vertical diffusivities inferred from density profiles were enhanced during autumn and winter. After comparing diffusivities inferred from densities sampled at 2- and 20-dbar intervals, Argo floats with a vertical resolution of 20 dbar were used to detect spatial and temporal variability of storm-related mixing between 700 and 1000 dbar in the North Pacific over a period of 10 years. Horizontal maps of inferred seasonal diffusivities suggested that the diffusivities were enhanced in autumn and winter. However, it is unlikely that there is a simple linear relationship between the input of wind power and the inferred mixing.
7
Breitschwerdt, D., e F. D. Kahn. "Turbulent mixing in wind-blown HII regions". Astrophysics and Space Science 216, n. 1-2 (giugno 1994): 297–301. http://dx.doi.org/10.1007/bf00982508.
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Eidnes, G., T. Utnes e T. A. McClimans. "Wind mixing of a stratified shear flow". Continental Shelf Research 6, n. 5 (gennaio 1986): 597–613. http://dx.doi.org/10.1016/0278-4343(86)90025-7.
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Liu, Jing-Wu, Su-Ping Zhang e Shang-Ping Xie. "Two Types of Surface Wind Response to the East China Sea Kuroshio Front*". Journal of Climate 26, n. 21 (16 ottobre 2013): 8616–27. http://dx.doi.org/10.1175/jcli-d-12-00092.1.
Testo completoAbstract (sommario):
Abstract Effects of the sea surface temperature (SST) front along the East China Sea Kuroshio on sea surface winds at different time scales are investigated. In winter and spring, the climatological vector wind is strongest on the SST front while the scalar wind speed reaches a maximum on the warm flank of the front and is collocated with the maximum difference between sea surface temperature and surface air temperature (SST − SAT). The distinction is due to the change in relative importance of two physical processes of SST–wind interaction at different time scales. The SST front–induced sea surface level pressure (SLP) adjustment (SF–SLP) contributes to a strong vector wind above the front on long time scales, consistent with the collocation of baroclinicity in the marine boundary layer and corroborated by the similarity between the thermal wind and observed wind shear between 1000 and 850 hPa. In contrast, the SST modulation of synoptic winds is more evident on the warm flank of the SST front. Large thermal instability of the near-surface layer strengthens temporal synoptic wind perturbations by intensifying vertical mixing, resulting in a scalar wind maximum. The vertical mixing and SF–SLP mechanisms are both at work but manifest more clearly at the synoptic time scale and in the long-term mean, respectively. The cross-frontal variations are 1.5 m s−1 in both the scalar and vector wind speeds, representing the vertical mixing and SF–SLP effects, respectively. The results illustrate the utility of high-frequency sampling by satellite scatterometers.
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Skyllingstad, Eric D., Jenessa Duncombe e Roger M. Samelson. "Baroclinic Frontal Instabilities and Turbulent Mixing in the Surface Boundary Layer. Part II: Forced Simulations". Journal of Physical Oceanography 47, n. 10 (ottobre 2017): 2429–54. http://dx.doi.org/10.1175/jpo-d-16-0179.1.
Testo completoAbstract (sommario):
AbstractGeneration of ocean surface boundary layer turbulence and coherent roll structures is examined in the context of wind-driven and geostrophic shear associated with horizontal density gradients using a large-eddy simulation model. Numerical experiments over a range of surface wind forcing and horizontal density gradient strengths, combined with linear stability analysis, indicate that the dominant instability mechanism supporting coherent roll development in these simulations is a mixed instability combining shear instability of the ageostrophic, wind-driven flow with symmetric instability of the frontal geostrophic shear. Disruption of geostrophic balance by vertical mixing induces an inertially rotating ageostrophic current, not forced directly by the wind, that initially strengthens the stratification, damps the instabilities, and reduces vertical mixing, but instability and mixing return when the inertial buoyancy advection reverses. The resulting rolls and instabilities are not aligned with the frontal zone, with an oblique orientation controlled by the Ekman-like instability. Mean turbulence is enhanced when the winds are destabilizing relative to the frontal orientation, but mean Ekman buoyancy advection is found to be relatively unimportant in these simulations. Instead, the mean turbulent kinetic energy balance is dominated by mechanical shear production that is enhanced when the wind-driven shear augments the geostrophic shear, while the resulting vertical mixing nearly eliminates any effective surface buoyancy flux from near-surface, cold-to-warm, Ekman buoyancy advection.
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Gille, S. T., M. M. Carranza, R. Cambra e R. Morrow. "Wind-induced upwelling in the Kerguelen Plateau Region". Biogeosciences Discussions 11, n. 6 (5 giugno 2014): 8373–97. http://dx.doi.org/10.5194/bgd-11-8373-2014.
Testo completoAbstract (sommario):
Abstract. In contrast to most of the Southern Ocean, the Kerguelen Plateau supports an unusually strong spring chlorophyll (Chl a) bloom, likely because the euphotic zone in the region is supplied with higher iron concentrations. This study uses satellite wind, sea surface temperature (SST), and ocean color data to explore the impact of wind-driven processes on upwelling of cold (presumably iron-rich) water to the euphotic zone. High wind speeds typically correlate with cold sea surface temperatures, implying that wind-mixing leads to enhanced vertical mixing. Negative wind-stress curl also correlates with cold SSTs, implying that Ekman pumping can further enhance upwelling, and coupling between winds and SSTs associated with mesoscale eddies can locally modulate the wind-stress curl. Kerguelen has a significant wind shadow on its downwind side, which generates a wind-stress curl dipole that shifts location depending on wind direction. This leads to locally enhanced Ekman pumping on the downstream side of the Kerguelen Plateau, where Chl a blooms are observed most years.
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Stanley, Geoff J., e Oleg A. Saenko. "Bottom-Enhanced Diapycnal Mixing Driven by Mesoscale Eddies: Sensitivity to Wind Energy Supply". Journal of Physical Oceanography 44, n. 1 (1 gennaio 2014): 68–85. http://dx.doi.org/10.1175/jpo-d-13-0116.1.
Testo completoAbstract (sommario):
Abstract It has been estimated that much of the wind energy input to the ocean general circulation is removed by mesoscale eddies via baroclinic instability. While the fate of this energy remains a subject of research, arguments have been presented suggesting that a fraction of it may get transferred to lee waves that, upon breaking, result in bottom-enhanced diapycnal mixing. Here the authors propose several parameterizations of this process and explore their impact in a low-resolution ocean–climate model, focusing on their impact on the abyssal meridional overturning circulation (MOC) of Antarctic Bottom Water. This study shows that, when the eddy energy is allowed to maintain diapycnal mixing, the abyssal MOC generally intensifies with increasing wind energy input to the ocean. In such a case, the whole system is driven by the wind: wind steepens isopycnals and generates eddies, and the (parameterized) eddies generate small-scale mixing, driving the MOC. It is also demonstrated that if the model diapycnal diffusivity, eddy transfer coefficient, and surface climate are decoupled from the winds, then stronger wind stress in the Southern Ocean may lead to a weaker MOC in the abyss—in line with previous results. A simple scaling theory, describing the response of the abyssal MOC strength to wind energy input, is developed, providing a better insight on the numerical results.
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E. GERBER, Hermann, Glendon M. FRICK, Jorgen B. JENSEN e James G. HUDSON. "Entrainment, Mixing, and Microphysics in Trade-Wind Cumulus". Journal of the Meteorological Society of Japan 86A (2008): 87–106. http://dx.doi.org/10.2151/jmsj.86a.87.
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Rasmussen, Bjarke. "Stratification and wind mixing in the Southern Kattegat". Ophelia 42, n. 1 (settembre 1995): 319–34. http://dx.doi.org/10.1080/00785326.1995.10431511.
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Grant, Alan L. M., e Stephen E. Belcher. "Wind-Driven Mixing below the Oceanic Mixed Layer". Journal of Physical Oceanography 41, n. 8 (1 agosto 2011): 1556–75. http://dx.doi.org/10.1175/jpo-d-10-05020.1.
Testo completoAbstract (sommario):
Abstract This study describes the turbulent processes in the upper ocean boundary layer forced by a constant surface stress in the absence of the Coriolis force using large-eddy simulation. The boundary layer that develops has a two-layer structure, a well-mixed layer above a stratified shear layer. The depth of the mixed layer is approximately constant, whereas the depth of the shear layer increases with time. The turbulent momentum flux varies approximately linearly from the surface to the base of the shear layer. There is a maximum in the production of turbulence through shear at the base of the mixed layer. The magnitude of the shear production increases with time. The increase is mainly a result of the increase in the turbulent momentum flux at the base of the mixed layer due to the increase in the depth of the boundary layer. The length scale for the shear turbulence is the boundary layer depth. A simple scaling is proposed for the magnitude of the shear production that depends on the surface forcing and the average mixed layer current. The scaling can be interpreted in terms of the divergence of a mean kinetic energy flux. A simple bulk model of the boundary layer is developed to obtain equations describing the variation of the mixed layer and boundary layer depths with time. The model shows that the rate at which the boundary layer deepens does not depend on the stratification of the thermocline. The bulk model shows that the variation in the mixed layer depth is small as long as the surface buoyancy flux is small.
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Polnikov, V. G. "Model of Vertical Mixing Induced by Wind Waves". Fluid Dynamics 55, n. 1 (gennaio 2020): 20–30. http://dx.doi.org/10.1134/s0015462820010103.
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Gong, Wenping, Zhongyuan Lin, Yunzhen Chen, Zhaoyun Chen e Heng Zhang. "Effect of winds and waves on salt intrusion in the Pearl River estuary". Ocean Science 14, n. 1 (28 febbraio 2018): 139–59. http://dx.doi.org/10.5194/os-14-139-2018.
Testo completoAbstract (sommario):
Abstract. Salt intrusion in the Pearl River estuary (PRE) is a dynamic process that is influenced by a range of factors and to date, few studies have examined the effects of winds and waves on salt intrusion in the PRE. We investigate these effects using the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system applied to the PRE. After careful validation, the model is used for a series of diagnostic simulations. It is revealed that the local wind considerably strengthens the salt intrusion by lowering the water level in the eastern part of the estuary and increasing the bottom landward flow. The remote wind increases the water mixing on the continental shelf, elevates the water level on the shelf and in the PRE and pumps saltier shelf water into the estuary by Ekman transport. Enhancement of the salt intrusion is comparable between the remote and local winds. Waves decrease the salt intrusion by increasing the water mixing. Sensitivity analysis shows that the axial down-estuary wind, is most efficient in driving increases in salt intrusion via wind straining effect.
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Zhai, Xiaoming, Richard J. Greatbatch, Carsten Eden e Toshiyuki Hibiya. "On the Loss of Wind-Induced Near-Inertial Energy to Turbulent Mixing in the Upper Ocean". Journal of Physical Oceanography 39, n. 11 (1 novembre 2009): 3040–45. http://dx.doi.org/10.1175/2009jpo4259.1.
Testo completoAbstract (sommario):
Abstract Wind-induced near-inertial energy has been believed to be an important source for generating the ocean mixing required to maintain the global meridional overturning circulation. In the present study, the near-inertial energy budget in a realistic model of the North Atlantic Ocean driven by synoptically varying wind forcing is examined. The authors find that nearly 70% of the wind-induced near-inertial energy at the sea surface is lost to turbulent mixing within the top 200 m and, hence, is not available to generate diapycnal mixing at greater depth. Assuming this result can be extended to the global ocean, it is estimated that the wind-induced near-inertial energy available for ocean mixing at depth is, at most, 0.1 TW. This confirms a recent suggestion that the role of wind-induced near-inertial energy in sustaining the global overturning circulation might have been overemphasized.
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Rousseau-Rizzi, Raphaël, e Kerry Emanuel. "An Evaluation of Hurricane Superintensity in Axisymmetric Numerical Models". Journal of the Atmospheric Sciences 76, n. 6 (1 giugno 2019): 1697–708. http://dx.doi.org/10.1175/jas-d-18-0238.1.
Testo completoAbstract (sommario):
Abstract Potential intensity (PI) is an analytical bound on steady, inviscid, axisymmetric hurricane wind speed. Studies have shown that simulated hurricane azimuthal wind speed can greatly exceed a PI bound on the maximum gradient wind. This disparity is called superintensity (SI) and has been attributed to the contribution of the unbalanced flow to the azimuthal wind. The goals of this study are 1) to introduce a new surface wind PI (PIs), based on a differential Carnot cycle and bounding the magnitude of the surface winds; 2) to evaluate SI in numerical simulations with respect to diagnostic PI bounds on gradient wind (PIg), azimuthal wind (PIa), and surface wind (PIs); and 3) to evaluate the validity of each PI bound based on the SI computations. Here, we define superintensity as the normalized amount by which each version of PI is exceeded by the quantity it bounds. Axisymmetric tropical cyclone simulations are performed while varying the parameterized turbulent mixing as a way of estimating SI in the inviscid limit. As the mixing length decreases, all three bounded wind speeds increase similarly from a sub-PI state to a marginally superintense state. This shows that all three forms of PI evaluated here are good approximations to their respective metrics in numerical simulations.
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Dyson, J. E. "Interstellar Wind-Blown Bubbles". International Astronomical Union Colloquium 120 (1989): 136–45. http://dx.doi.org/10.1017/s0252921100023654.
Testo completoAbstract (sommario):
Summary‘Classical’ stellar wind-driven bubbles are either energy or momentum driven, and evolve in smooth media containing only radial density gradients. Real bubbles are produced from winds from moving stars and which blow into non-homogeneous media. The resulting mixing of clump material can produce a variety of thermal, dynamical and chemical effects. In this review we discuss some of the modifications to classical bubbles which ensue, using observational examples where appropriate.
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Puls, Joachim. "Physical and Wind Properties of OB-Stars". Proceedings of the International Astronomical Union 3, S250 (dicembre 2007): 25–38. http://dx.doi.org/10.1017/s1743921308020310.
Testo completoAbstract (sommario):
AbstractIn this review, the physical and wind properties of OB-stars are discussed, with particular emphasis on metallicity dependence and recent results from the flames survey of massive stars. We summarize the relation between spectral type and Teff, discuss the status quo of the “mass-discrepancy”, refer to the problem of “macro-turbulence” and comment on the distribution of rotational velocities. Observational constraints on the efficiency of rotational mixing are presented, and magnetic field measurements summarized. Wind properties are reviewed, and problems related to weak winds and wind-clumping highlighted.
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Bonin, Timothy A., Brian J. Carroll, R. Michael Hardesty, W. Alan Brewer, Kristian Hajny, Olivia E. Salmon e Paul B. Shepson. "Doppler Lidar Observations of the Mixing Height in Indianapolis Using an Automated Composite Fuzzy Logic Approach". Journal of Atmospheric and Oceanic Technology 35, n. 3 (marzo 2018): 473–90. http://dx.doi.org/10.1175/jtech-d-17-0159.1.
Testo completoAbstract (sommario):
AbstractA Halo Photonics Stream Line XR Doppler lidar has been deployed for the Indianapolis Flux Experiment (INFLUX) to measure profiles of the mean horizontal wind and the mixing layer height for quantification of greenhouse gas emissions from the urban area. To measure the mixing layer height continuously and autonomously, a novel composite fuzzy logic approach has been developed that combines information from various scan types, including conical and vertical-slice scans and zenith stares, to determine a unified measurement of the mixing height and its uncertainty. The composite approach uses the strengths of each measurement strategy to overcome the limitations of others so that a complete representation of turbulent mixing is made in the lowest km, depending on clouds and aerosol distribution. Additionally, submeso nonturbulent motions are identified from zenith stares and removed from the analysis, as these motions can lead to an overestimate of the mixing height. The mixing height is compared with in situ profile measurements from a research aircraft for validation. To demonstrate the utility of the measurements, statistics of the mixing height and its diurnal and annual variability for 2016 are also presented. The annual cycle is clearly captured, with the largest and smallest afternoon mixing heights observed at the summer and winter solstices, respectively. The diurnal cycle of the mixing layer is affected by the mean wind, growing slower in the morning and decaying more rapidly in the evening with lighter winds.
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Kawaguchi, Yusuke, Shigeto Nishino e Jun Inoue. "Fixed-Point Observation of Mixed Layer Evolution in the Seasonally Ice-Free Chukchi Sea: Turbulent Mixing due to Gale Winds and Internal Gravity Waves". Journal of Physical Oceanography 45, n. 3 (marzo 2015): 836–53. http://dx.doi.org/10.1175/jpo-d-14-0149.1.
Testo completoAbstract (sommario):
AbstractA fixed-point observation using the R/V Mirai was conducted in the ice-free northern Chukchi Sea of the Arctic Ocean during September of 2013. During the program the authors performed repeated microstructure measurements to reveal the temporal evolution of the surface mixed layer and mixing processes in the upper water column. The shelf region was initially characterized by a distinct two-layer system comprising a warmer/fresher top layer and a colder/saltier bottom layer. During the two-week observation period, the top-layer water showed two types of mixing processes: near-surface turbulence due to strong wind forcing and subsurface mixing due to internal gravity waves. In the first week, when the top layer was stratified with fresh sea ice meltwater, turbulent energy related to internal waves propagated through the subsurface stratification, resulting in a mechanical overturning near the pycnocline, followed by enhanced mixing there. In the second week, gale winds directly stirred up the upper water and then established a deeper homogenous layer. The combination of internal wave mixing and wind-driven turbulence may contribute to releasing the oceanic heat into the atmosphere, consequently promoting the preconditioning of surface water freezing.
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Nikurashin, Maxim, e Geoffrey Vallis. "A Theory of Deep Stratification and Overturning Circulation in the Ocean". Journal of Physical Oceanography 41, n. 3 (1 marzo 2011): 485–502. http://dx.doi.org/10.1175/2010jpo4529.1.
Testo completoAbstract (sommario):
Abstract A simple theoretical model of the deep stratification and meridional overturning circulation in an idealized single-basin ocean with a circumpolar channel is presented. The theory includes the effects of wind, eddies, and diapycnal mixing; predicts the deep stratification in terms of the surface forcing and other problem parameters; makes no assumption of zero residual circulation; and consistently accounts for the interaction between the circumpolar channel and the rest of the ocean. The theory shows that dynamics of the overturning circulation can be characterized by two limiting regimes, corresponding to weak and strong diapycnal mixing. The transition between the two regimes is described by a nondimensional number characterizing the strength of the diffusion-driven compared to the wind-driven overturning circulation. In the limit of weak diapycnal mixing, deep stratification throughout the ocean is produced by the effects of wind and eddies in a circumpolar channel and maintained even in the limit of vanishing diapycnal diffusivity and in a flat-bottomed ocean. The overturning circulation across the deep stratification is driven by the diapycnal mixing in the basin away from the channel but is sensitive, through changes in stratification, to the wind and eddies in the channel. In the limit of strong diapycnal mixing, deep stratification is primarily set by eddies in the channel and diapycnal mixing in the basin away from the channel, with the wind over the circumpolar channel playing a secondary role. Analytical solutions for the deep stratification and overturning circulation in the limit of weak diapycnal mixing and numerical solutions that span the regimes of weak to strong diapycnal mixing are presented. The theory is tested with a coarse-resolution ocean general circulation model configured in an idealized geometry. A series of experiments performed to examine the sensitivity of the deep stratification and the overturning circulation to variations in wind stress and diapycnal mixing compare well with predictions from the theory.
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Brody, Sarah R., e M. Susan Lozier. "Characterizing upper-ocean mixing and its effect on the spring phytoplankton bloom with in situ data". ICES Journal of Marine Science 72, n. 6 (4 febbraio 2015): 1961–70. http://dx.doi.org/10.1093/icesjms/fsv006.
Testo completoAbstract (sommario):
Abstract Since publication, the Sverdrup hypothesis, that phytoplankton are uniformly distributed within the ocean mixed layer and bloom once the ocean warms and stratifies in spring, has been the conventional explanation of subpolar phytoplankton spring bloom initiation. Recent studies have sought to differentiate between the actively mixing section of the upper ocean and the uniform-density mixed layer, arguing, as Sverdrup implied, that decreases in active mixing drive the spring bloom. In this study, we use in situ data to investigate the characteristics and depth of active mixing in both buoyancy- and wind-driven regimes and explore the idea that the shift from buoyancy-driven to wind-driven mixing in the late winter or early spring creates the conditions necessary for blooms to begin. We identify the bloom initiation based on net rates of biomass accumulation and relate changes in the depth of active mixing to changes in biomass depth profiles. These analyses support the idea that decreases in the depth of active mixing, a result of the transition from buoyancy-driven to wind-driven mixing, control the timing of the spring bloom.
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Dinniman, Michael S., John M. Klinck, Eileen E. Hofmann e Walker O. Smith. "Effects of Projected Changes in Wind, Atmospheric Temperature, and Freshwater Inflow on the Ross Sea". Journal of Climate 31, n. 4 (febbraio 2018): 1619–35. http://dx.doi.org/10.1175/jcli-d-17-0351.1.
Testo completoAbstract (sommario):
A 5-km horizontal resolution regional ocean–sea ice–ice shelf model of the Ross Sea is used to examine the effects of changes in wind strength, air temperature, and increased meltwater input on the formation of high-salinity shelf water (HSSW), on-shelf transport and vertical mixing of Circumpolar Deep Water (CDW) and its transformation into modified CDW (MCDW), and basal melt of the Ross Ice Shelf (RIS). A 20% increase in wind speed, with no other atmospheric changes, reduced summer sea ice minimum area by 20%, opposite the observed trend of the past three decades. Increased winds with spatially uniform, reduced atmospheric temperatures increased summer sea ice concentrations, on-shelf transport of CDW, vertical mixing of MCDW, HSSW volume, and (albeit small) RIS basal melt. Winds and atmospheric temperatures from the SRES A1B scenario forcing of the MPI ECHAM5 model decreased on-shelf transport of CDW and vertical mixing of MCDW for 2046–61 and 2085–2100 relative to the end of the twentieth century. The RIS basal melt increased slightly by 2046–61 (9%) and 2085–2100 (13%). Advection of lower-salinity water onto the continental shelf did not significantly affect sea ice extent for the 2046–61 or 2085–2100 simulations. However, freshening reduces on-shelf transport of CDW, vertical mixing of MCDW, and the volume of HSSW produced. The reduced vertical mixing of MCDW, while partially balanced by the reduced on-shelf transport of CDW, enhances the RIS basal melt rate relative to the twentieth-century simulation for 2046–61 (13%) and 2085–2100 (17%).
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Synodinou, B. M. "Estimating the contamination resulting from hypothetical nuclear accidents during nuclear emergency exercises". HNPS Proceedings 10 (5 dicembre 2019): 194. http://dx.doi.org/10.12681/hnps.2189.
Testo completoAbstract (sommario):
An assessment of the radiological contamination of Europe, following radioactive pollutant releases and using prognostic meteorological data is presented. A modified and simplified version of SHEAR code, a Lagrangian long-range transport and dispersion model, taking into account the wind shear effect, is used. This is possible by applying the diurnal differences in vertical mixing to the winds in the vertical layer used to calculate advection. In its present version the code takes account of dry deposition processes and different mixing heights for day and night conditions. Prognostic temperature and u, ν wind parameters every 6 hours for a total of 72, are provided by the National Meteorological Service of Greece in two levels 0 and 850 mb of pressure. The wind field is then calculated in both heights. This field forms an input to the SHEAR code. Plume direction and radioactive pollutant concentration have been calculated for hypothetical releases postulated during a recent ΝΕΑ/OECD exercise. The results of this study indicated that the code predicted well direction and concentration of the plume, in agreement with the predictions by other programs. Since the code in this version uses surface winds, at most, which are much weaker than the higher altitude winds used by other codes, the results of the plume spread are smaller in the present study. We believe that taking into account the surface winds during an eventual accident produces more realistic results. If predictions in more heights are available mixing heights would be calculated with greater accuracy, with consequent improvement of the results.
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Zhai, Xiaoming, Helen L. Johnson, David P. Marshall e Carl Wunsch. "On the Wind Power Input to the Ocean General Circulation". Journal of Physical Oceanography 42, n. 8 (1 agosto 2012): 1357–65. http://dx.doi.org/10.1175/jpo-d-12-09.1.
Testo completoAbstract (sommario):
Abstract The wind power input to the ocean general circulation is usually calculated from the time-averaged wind products. Here, this wind power input is reexamined using available observations, focusing on the role of the synoptically varying wind. Power input to the ocean general circulation is found to increase by over 70% when 6-hourly winds are used instead of monthly winds. Much of the increase occurs in the storm-track regions of the Southern Ocean, Gulf Stream, and Kuroshio Extension. This result holds irrespective of whether the ocean surface velocity is accounted for in the wind stress calculation. Depending on the fate of the high-frequency wind power input, the power input to the ocean general circulation relevant to deep-ocean mixing may be less than previously thought. This study emphasizes the difficulty of choosing appropriate forcing for ocean-only models.
29
Rainville, Luc, Craig Lee e Rebecca Woodgate. "Impact of Wind-Driven Mixing in the Arctic Ocean". Oceanography 24, n. 3 (1 settembre 2011): 136–45. http://dx.doi.org/10.5670/oceanog.2011.65.
Testo completo
30
Huber, Anita, Gregory N. Ivey, Geoff Wake e Carolyn E. Oldham. "Near-Surface Wind-Induced Mixing in a Mine Lake". Journal of Hydraulic Engineering 134, n. 10 (ottobre 2008): 1464–72. http://dx.doi.org/10.1061/(asce)0733-9429(2008)134:10(1464).
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31
Munk, Walter, e Carl Wunsch. "Abyssal recipes II: energetics of tidal and wind mixing". Deep Sea Research Part I: Oceanographic Research Papers 45, n. 12 (dicembre 1998): 1977–2010. http://dx.doi.org/10.1016/s0967-0637(98)00070-3.
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32
Skyllingstad, Eric D., W. D. Smyth e G. B. Crawford. "Resonant Wind-Driven Mixing in the Ocean Boundary Layer". Journal of Physical Oceanography 30, n. 8 (agosto 2000): 1866–90. http://dx.doi.org/10.1175/1520-0485(2000)030<1866:rwdmit>2.0.co;2.
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MICHIOKU, Kohji, Gouzou TSUJIMOTO e Hitoshi MIYAMOTO. "Flow and Mixing Properties in wind-Induced Density Currents". PROCEEDINGS OF HYDRAULIC ENGINEERING 37 (1993): 293–98. http://dx.doi.org/10.2208/prohe.37.293.
Testo completo
34
Findikakis, Angelos N., e Adrian W. K. Law. "Wind Mixing in Temperature Simulations for Lakes and Reservoirs". Journal of Environmental Engineering 125, n. 5 (maggio 1999): 420–28. http://dx.doi.org/10.1061/(asce)0733-9372(1999)125:5(420).
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35
Watanabe, Michio, e Toshiyuki Hibiya. "Energetics of wind-induced turbulent mixing in the ocean". Journal of Oceanography 64, n. 1 (febbraio 2008): 131–40. http://dx.doi.org/10.1007/s10872-008-0010-8.
Testo completo
36
Perlin, Natalie, Simon P. de Szoeke, Dudley B. Chelton, Roger M. Samelson, Eric D. Skyllingstad e Larry W. O’Neill. "Modeling the Atmospheric Boundary Layer Wind Response to Mesoscale Sea Surface Temperature Perturbations". Monthly Weather Review 142, n. 11 (24 ottobre 2014): 4284–307. http://dx.doi.org/10.1175/mwr-d-13-00332.1.
Testo completoAbstract (sommario):
Abstract The wind speed response to mesoscale SST variability is investigated over the Agulhas Return Current region of the Southern Ocean using the Weather Research and Forecasting (WRF) Model and the U.S. Navy Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) atmospheric model. The SST-induced wind response is assessed from eight simulations with different subgrid-scale vertical mixing parameterizations, validated using Quick Scatterometer (QuikSCAT) winds and satellite-based sea surface temperature (SST) observations on 0.25° grids. The satellite data produce a coupling coefficient of sU = 0.42 m s−1 °C−1 for wind to mesoscale SST perturbations. The eight model configurations produce coupling coefficients varying from 0.31 to 0.56 m s−1 °C−1. Most closely matching QuikSCAT are a WRF simulation with the Grenier–Bretherton–McCaa (GBM) boundary layer mixing scheme (sU = 0.40 m s−1 °C−1), and a COAMPS simulation with a form of Mellor–Yamada parameterization (sU = 0.38 m s−1 °C−1). Model rankings based on coupling coefficients for wind stress, or for curl and divergence of vector winds and wind stress, are similar to that based on sU. In all simulations, the atmospheric potential temperature response to local SST variations decreases gradually with height throughout the boundary layer (0–1.5 km). In contrast, the wind speed response to local SST perturbations decreases rapidly with height to near zero at 150–300 m. The simulated wind speed coupling coefficient is found to correlate well with the height-averaged turbulent eddy viscosity coefficient. The details of the vertical structure of the eddy viscosity depend on both the absolute magnitude of local SST perturbations, and the orientation of the surface wind to the SST gradient.
37
Wolfe, A. Megan, Susan E. Allen, Michal Hodal, Rich Pawlowicz, Brian P. V. Hunt e Desiree Tommasi. "Impact of advection loss due to wind and estuarine circulation on the timing of the spring phytoplankton bloom in a fjord". ICES Journal of Marine Science 73, n. 6 (3 settembre 2015): 1589–609. http://dx.doi.org/10.1093/icesjms/fsv151.
Testo completoAbstract (sommario):
Abstract A coupled biophysical model is used to explore the physical controls involved in the timing of the spring phytoplankton bloom in fjords. Observations from Rivers Inlet, British Columbia, are used to force and evaluate the model. It is found that the interannual variation in timing is due primarily to variations in retention, in particular, to variations in horizontal advection out of the fjord. The two dominant processes are (i) strong outflow winds rapidly advecting the surface layer and thus the phytoplankton population out of the fjord and (ii) losses due to high river flux increasing the estuarine circulation. Both processes delay the timing of spring bloom. Smaller effects on the interannual variation are due to increased wind mixing which deepens the mixing layer and reduces light to phytoplankton, and increased river flow which increases the stratification and decreases the mixing layer depth. Observed interannual variations in cloudiness were small. Strong outflow winds are common in winter along the British Columbia coast, but generally cease after the spring wind transition. Thus, observed interdecadal variations in the spring transition date probably imply strong variations in the timing of spring phytoplankton blooms in British Columbia fjords.
38
Zheng, Xiangyang, Yana Ding, Yandong Xu, Tao Zou, Chunlei Wang e Qianguo Xing. "The Influence of Wind Direction during Storms on Sea Temperature in the Coastal Water of Muping, China". Journal of Marine Science and Engineering 9, n. 7 (27 giugno 2021): 710. http://dx.doi.org/10.3390/jmse9070710.
Testo completoAbstract (sommario):
Sea temperature structures are important for water stratification and marine ecosystems. In the coastal water of Muping, China, stationary measurements of sea temperature captured temporal temperature changes during two summer storm events. The north component of the wind during the two storms was opposite. The temperature responded differently to wind directions in the two storm events. A well-validated numerical ocean model was used to investigate the mechanism of sea temperature variation of the coast of Muping. The model revealed that the southerly and easterly wind was upwelling-favorable in the study area. They generated the shoreward transport of bottom cold water, which induced bottom water cooling, enhanced stratification, and weakened vertical mixing. On the other hand, the northerly and westerly wind was downwelling-favorable and enhanced turbulent mixing. The alongshore upwelling-favorable wind caused more cross-shore transport than cross-shore upwelling-favorable wind, which resulted in stronger bottom cooling. Similarly, alongshore downwelling-favorable wind generated lower temperature than cross-shore wind. A surface cold-water band was formed in the second storm. Although it was formed during upwelling-favorable wind, the temperature balance analysis indicated that vertical mixing and westward horizontal advection were the two dominant processes compared to upwelling.
39
Thomson, JD, e JS Godfrey. "Circulation dynamics in the Derwent Estuary". Marine and Freshwater Research 36, n. 6 (1985): 765. http://dx.doi.org/10.1071/mf9850765.
Testo completoAbstract (sommario):
For moderate river discharges the Derwent estuary is strongly stratified in its upstream reaches; however, salt walter is flushed completely as far downstream as Bridgewater, for river discharges greater than about 150 m3 s-1. Salinity returns to normal in this section within about 10-20 days of a rainstorm. The main mixing mechanism appears to be surface stirring by the wind; a semi-empirical formula for wind-driven entrainment velocity gives values a factor of about 1 .5 too small, but this may be due to a number of sources of observational error. Tidal mixing is detectable in the upstream Derwent, but is small compared to wind mixing in terms of induced vertical flows.
40
Liu, X., J. Xu, H. L. Liu, J. Yue e W. Yuan. "Simulations of large winds and wind shears induced by gravity wave breaking in the mesosphere and lower thermosphere (MLT) region". Annales Geophysicae 32, n. 5 (23 maggio 2014): 543–52. http://dx.doi.org/10.5194/angeo-32-543-2014.
Testo completoAbstract (sommario):
Abstract. Using a fully nonlinear two-dimensional (2-D) numerical model, we simulated gravity waves (GWs) breaking and their contributions to the formation of large winds and wind shears in the mesosphere and lower thermosphere (MLT). An eddy diffusion coefficient is used in the 2-D numerical model to parameterize realistic turbulent mixing. Our study shows that the momentum deposited by breaking GWs accelerates the mean wind. The resultant large background wind increases the GW's apparent horizontal phase velocity and decreases the GW's intrinsic frequency and vertical wavelength. Both the accelerated mean wind and the decreased GW vertical wavelength contribute to the enhancement of wind shears. This, in turn, creates a background condition that favors the occurrence of GW instability, breaking, and momentum deposition, as well as mean wind acceleration, which further enhances the wind shears. We find that GWs with longer vertical wavelengths and faster horizontal phase velocity can induce larger winds, but they may not necessarily induce larger wind shears. In addition, the background temperature can affect the time and height of GW breaking, thus causing accelerated mean winds and wind shears.
41
Xu, Mimi, e Haiming Xu. "Atmospheric Responses to Kuroshio SST Front in the East China Sea under Different Prevailing Winds in Winter and Spring". Journal of Climate 28, n. 8 (7 aprile 2015): 3191–211. http://dx.doi.org/10.1175/jcli-d-13-00675.1.
Testo completoAbstract (sommario):
Abstract Atmospheric responses to the Kuroshio SST front in the East China Sea under different prevailing winds are examined using high-resolution observations and numerical modeling. Satellite data reveal a significant in-phase relationship between SST and surface wind speed, indicative of ocean-to-atmosphere influence. The atmospheric response varies according to the relative surface wind direction with respect to the SST front orientation. Under the alongfront condition, low (high) SLP anomalies are found on the warmer (colder) flank of the front, accompanied by surface wind convergence (divergence). Enhanced precipitation and frequent cumulus convection appear over the warm Kuroshio, suggesting an atmospheric response extending into the free troposphere. Under the cross-front condition, when the air blows from cold to warm (warm to cold) SST, divergence (convergence) is located directly over the SST front, and its magnitude is proportional to the downwind SST gradient. Under such prevailing winds, the SST front has little effect on the SLP and precipitation. The Weather Research and Forecasting (WRF) Model is used to investigate the mechanism responsible for the atmospheric adjustment. The results show that under the alongfront condition, large temperature and pressure perturbations in the boundary layer are caused by SST gradients, while stability and turbulent mixing are less affected. By contrast, under the cross-front condition, the perturbations of temperature and pressure are small and shifted downstream, while the SST gradient exerts stronger impact on vertical mixing. The modeling results confirm that the pressure adjustment mechanism contributes more to the atmospheric response under alongfront prevailing winds, while the vertical mixing mechanism dominates the atmospheric adjustment under cross-front winds.
42
Spall, Michael A. "Midlatitude Wind Stress–Sea Surface Temperature Coupling in the Vicinity of Oceanic Fronts". Journal of Climate 20, n. 15 (1 agosto 2007): 3785–801. http://dx.doi.org/10.1175/jcli4234.1.
Testo completoAbstract (sommario):
Abstract The influences of strong gradients in sea surface temperature on near-surface cross-front winds are explored in a series of idealized numerical modeling experiments. The atmospheric model is the Naval Research Laboratory Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) model, which is fully coupled to the Regional Ocean Modeling System (ROMS) ocean model. A series of idealized, two-dimensional model calculations is carried out in which the wind blows from the warm-to-cold side or the cold-to-warm side of an initially prescribed ocean front. The evolution of the near-surface winds, boundary layer, and thermal structure is described, and the balances in the momentum equation are diagnosed. The changes in surface winds across the front are consistent with previous models and observations, showing a strong positive correlation with the sea surface temperature and boundary layer thickness. The coupling arises mainly as a result of changes in the flux Richardson number across the front, and the strength of the coupling coefficient grows quadratically with the strength of the cross-front geostrophic wind. The acceleration of the winds over warm water results primarily from the rapid change in turbulent mixing and the resulting unbalanced Coriolis force in the vicinity of the front. Much of the loss/gain of momentum perpendicular to the front in the upper and lower boundary layer results from acceleration/deceleration of the flow parallel to the front via the Coriolis term. This mechanism is different from the previously suggested processes of downward mixing of momentum and adjustment to the horizontal pressure gradient, and is active for flows off the equator with sufficiently strong winds. Although the main focus of this work is on the midlatitude, strong wind regime, calculations at low latitudes and with weak winds show that the pressure gradient and turbulent mixing terms dominate the cross-front momentum budget, consistent with previous work.
43
Koseki, Shunya, e Masahiro Watanabe. "Atmospheric Boundary Layer Response to Mesoscale SST Anomalies in the Kuroshio Extension". Journal of Climate 23, n. 10 (15 maggio 2010): 2492–507. http://dx.doi.org/10.1175/2009jcli2915.1.
Testo completoAbstract (sommario):
Abstract The atmospheric boundary layer (ABL) response to mesoscale eddies in sea surface temperature (SST) in the Kuroshio Extension was investigated using a high-resolution (T213L30) atmospheric general circulation model. A control run was performed first by integrating the model for 40 days, driven by the satellite-derived, eddy-resolving SST during January 2006. The spatial pattern of surface wind anomalies—that is, a deviation from large-scale winds—reveals a positive correlation with the spatial pattern of mesoscale SST anomalies. The momentum budget analysis of the anomalous zonal wind was performed to investigate the formation of the ABL response. The most dominant term was the pressure gradient force; the advection term was comparable but in the opposite sense. Vertical mixing acts to weaken the anomalous zonal wind near the surface; however, the downward (upward) vertical turbulent flux anomalies were dominant near the ABL top over the warm (cold) SST anomalies, suggesting that the vertical mixing mechanism is effective. The role of the vertical mixing was further examined by a sensitivity experiment in which the turbulent diffusion coefficient for momentum was spatially smoothed. While the pressure gradient force and the advection terms were almost unchanged in the momentum budgets, the deceleration due to turbulence was enhanced because of the absence of the momentum input from the free atmosphere. The result is a reduction in the amplitude of the surface zonal wind anomalies to approximately half in the sensitivity experiment.
44
Tokinaga, Hiroki, Youichi Tanimoto e Shang-Ping Xie. "SST-Induced Surface Wind Variations over the Brazil–Malvinas Confluence: Satellite and In Situ Observations*". Journal of Climate 18, n. 17 (1 settembre 2005): 3470–82. http://dx.doi.org/10.1175/jcli3485.1.
Testo completoAbstract (sommario):
Abstract The confluence of the Brazil–Malvinas Currents maintains strong sea surface temperature (SST) fronts in the midlatitude southwestern Atlantic year-round. SST effects on near-surface stability and surface wind variations are examined in this region using satellite and in situ datasets. Satellite observations show strong (weak) surface wind speeds over the warm Brazil (cold Malvinas) Current. A novel feature of this study is the construction of a high-resolution surface meteorological dataset that is based on historical ship observations. Analysis of this new in situ dataset reveals an increased (reduced) sea–air temperature difference over the Brazil (Malvinas) Current, indicating destabilization (stabilization) in the atmospheric boundary layer. These results are consistent with the SST-induced vertical mixing mechanism for wind adjustment. The SST effect on the near-surface atmosphere is observed both in the climatology and on interannual time scales in the Brazil–Malvinas confluence. Along a zonal SST front at 49°S northeast of the Malvinas/Falkland Islands, there is a collocated line of surface wind divergence, with moderate convergence to the north. Vertical mixing does not explain this divergence pattern because the prevailing surface winds are westerly, blowing in parallel with the front. An additional mechanism is proposed for boundary layer wind adjustment.
45
Ha, Kyung-Ja, Yu-Kyung Hyun, Hyun-Mi Oh, Kyung-Eak Kim e Larry Mahrt. "Evaluation of Boundary Layer Similarity Theory for Stable Conditions in CASES-99". Monthly Weather Review 135, n. 10 (1 ottobre 2007): 3474–83. http://dx.doi.org/10.1175/mwr3488.1.
Testo completoAbstract (sommario):
Abstract The Monin–Obukhov similarity theory and a generalized formulation of the mixing length for the stable boundary layer are evaluated using the Cooperative Atmosphere–Surface Exchange Study-1999 (CASES-99) data. The large-scale wind forcing is classified into weak, intermediate, and strong winds. Although the stability parameter, z/L, is inversely dependent on the mean wind speed, the speed of the large-scale flow includes independent influences on the flux–gradient relationship. The dimensionless mean wind shear is found to obey existing stability functions when z/L is less than unity, particularly for the strong and intermediate wind classes. For weak mean winds and/or strong stability (z/L > 1), this similarity theory breaks down. Deviations from similarity theory are examined in terms of intermittency. A case study of a weak-wind night indicates important modulation of the turbulence flux by mesoscale motions of unknown origin.
46
Jing, Zhao, Lixin Wu e Xiaohui Ma. "Improve the Simulations of Near-Inertial Internal Waves in the Ocean General Circulation Models". Journal of Atmospheric and Oceanic Technology 32, n. 10 (ottobre 2015): 1960–70. http://dx.doi.org/10.1175/jtech-d-15-0046.1.
Testo completoAbstract (sommario):
AbstractThe near-inertial wind work and near-inertial internal waves (NIWs) in the ocean have been extensively studied using ocean general circulation models (OGCMs) forced by 6-hourly winds or wind stress obtained from atmospheric reanalysis data. However, the OGCMs interpolate the reanalysis winds or wind stress linearly onto each time step, which partially filters out the wind stress variance in the near-inertial band. In this study, the influence of the linear interpolation on the near-inertial wind work and NIWs is quantified using an eddy-resolving (°) primitive equation ocean model. In addition, a new interpolation method is proposed—the sinc-function interpolation—that overcomes the shortages of the linear interpolation.It is found that the linear interpolation of 6-hourly winds significantly underestimates the near-inertial wind work and NIWs at the midlatitudes. The underestimation of the near-inertial wind work and near-inertial kinetic energy is proportional to the loss of near-inertial wind stress variance due to the linear interpolation. This further weakens the diapycnal mixing in the ocean due to the reduced near-inertial shear variance. Compared to the linear interpolation, the sinc-function interpolation retains all the wind stress variance in the near-inertial band and yields correct magnitudes for the near-inertial wind work and NIWs at the midlatitudes.
47
Spall, Michael A., e Leif N. Thomas. "Downfront Winds over Buoyant Coastal Plumes". Journal of Physical Oceanography 46, n. 10 (ottobre 2016): 3139–54. http://dx.doi.org/10.1175/jpo-d-16-0042.1.
Testo completoAbstract (sommario):
AbstractDownfront, or downwelling favorable, winds are commonly found over buoyant coastal plumes. It is known that these winds can result in mixing of the plume with the ambient water and that the winds influence the transport, spatial extent, and stability of the plumes. In the present study, the interaction of the Ekman velocity in the surface layer and baroclinic instability supported by the strong horizontal density gradient of the plume is explored with the objective of understanding the potential vorticity and buoyancy budgets. The approach makes use of an idealized numerical model and scaling theory. It is shown that when winds are present the weak stratification resulting from vertical mixing and the strong baroclinicity of the front results in near-zero average potential vorticity q. For weak to moderate winds, the reduction of q by diapycnal mixing is balanced by the generation of q through the geostrophic stress term in the regions of strong horizontal density gradients and stable stratification. However, for very strong winds the wind stress overwhelms the geostrophic stress and leads to a reduction in q, which is balanced by the vertical mixing term. In the absence of winds, the geostrophic stress dominates mixing and the flow rapidly restratifies. Nonlinearity, extremes of relative vorticity and vertical velocity, and mixing are all enhanced by the presence of a coast. Scaling estimates developed for the eddy buoyancy flux, the surface potential vorticity flux, and the diapycnal mixing rate compare well with results diagnosed from a series of numerical model calculations.
48
Wang, Linhui, Huiwang Gao, Jie Shi e Lian Xie. "A Numerical Study on the Impact of High-Frequency Winds on the Peru Upwelling System during 2014–2016". Journal of Marine Science and Engineering 7, n. 5 (25 maggio 2019): 161. http://dx.doi.org/10.3390/jmse7050161.
Testo completoAbstract (sommario):
The contribution of high-frequency wind to the Peruvian upwelling system during 2014–2016 was studied using the Regional Ocean Modeling System (ROMS), forced by four different temporal resolution (six-hourly, daily, weekly, and monthly) wind forcing. A major effect of the high-frequency wind is its warming of the water at all depths along the Peruvian coast. The mechanism for the temperature changes induced by high-frequency wind forcing was analyzed through heat budget analysis, which indicated a three-layer structure. Vertical advection plays a leading role in the warming of the mixed layer (0–25 m), and enhanced vertical mixing balances the warming effect. Analysis suggests that around the depths of 25–60 m, vertical mixing warms the water by bringing heat from the surface to deeper depths. In waters deeper than 60 m, the effect of vertical mixing is negligible. The differences among the oceanic responses in the sensitivity experiments suggest that wind forcing containing variabilities at higher than synoptic frequencies must be included in the atmospheric forcing in order to properly simulate the Peru upwelling system.
49
Shaw, W. J., M. S. Pekour, R. L. Coulter, T. J. Martin e J. T. Walters. "The daytime mixing layer observed by radiosonde, profiler, and lidar during MILAGRO". Atmospheric Chemistry and Physics Discussions 7, n. 5 (19 ottobre 2007): 15025–65. http://dx.doi.org/10.5194/acpd-7-15025-2007.
Testo completoAbstract (sommario):
Abstract. During the MILAGRO campaign centered in the Mexico City area, Pacific Northwest National Laboratory (PNNL) and Argonne National Laboratory (ANL) operated atmospheric profiling systems at Veracruz and at two locations on the Central Mexican Plateau in the region around Mexico City. These systems included radiosondes, wind profilers, a sodar, and an aerosol backscatter lidar. An additional wind profiler was operated by the University of Alabama in Huntsville (UAH) at the Mexican Petroleum Institue (IMP) near the center of Mexico City. Because of the opportunity afforded by collocation of profilers, radiosondes, and a lidar, and because of the importance of boundary layer depth for aerosol properties, we have carried out a comparison of mixing layer depth as determined independently from these three types of measurement systems during the campaign. We have then used results of this comparison and additional measurements to develop a detailed description of the daily structure and evolution of the boundary layer on the Central Mexican Plateau during MILAGRO. Our analysis indicates that the profilers were more consistently successful in establishing the mixing layer depth during the daytime. The boundary layer growth was similar at the three locations, although the mixing layer tended to be slightly deeper in the afternoon in central Mexico City. The sodar showed that convection began about an hour after sunrise. Maximum daily mixing layer depths always reached 2000 m a.g.l. and frequently extended to 4000 m. The rate and variability of mixing layer growth was essentially the same as that observed during the IMADA-AVER campaign in the same season in 1997. This growth did not seem to be related to whether deep convection was reported on a given day. Wind speeds within the boundary layer exhibited a daily low-altitude maximum in the late afternoon with lighter winds aloft, consistent with previous reports of diurnal regional circulations. Norte events, which produced high winds at Veracruz, did not appreciably modulate the winds on the plateau. Finally, despite the typically dry conditions at the surface, radiosonde profiles showed that relative humidity often exceeded 50% in the early morning and in the upper part of the boundary layer. This suggests that aerosol particles would have experienced hygroscopic growth within the boundary layer on many days.
50
MORI, Nobuhito, Takayuki SUZUKI e Naoto KIHARA. "A Study on Air-Sea Mixing due to Wind and Wave under Strong Wind Condition". Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering) 66, n. 1 (2010): 311–15. http://dx.doi.org/10.2208/kaigan.66.311.
Testo completo