The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
J. Tonttila - One of the best experts on this subject based on the ideXlab platform.
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TurbulentstructureandscalingoftheInertialSubrangeina stratocumulus-toppedboundarylayerobservedbyaDopplerlidar
2015Co-Authors: J. TonttilaAbstract:The turbulent structure of a stratocumulus-topped marine boundary layer over a 2-day period is observed with a Doppler lidar at Mace Head in Ireland. Using profiles of vertical velocity statistics, the bulk of the mixing is identified as cloud driven. This is supported by the pertinent feature of negative vertical velocity skewness in the sub-cloud layer which extends, on occasion, almost to the surface. Both cou- pled and decoupled turbulence characteristics are observed. The length and timescales related to the cloud-driven mixing are investigated and shown to provide additional information about the structure and the source of the mixing inside the boundary layer. They are also shown to place constraints on the length of the sampling periods used to derive products, such as the turbulent dissipation rate, from lidar measure- ments. For this, the maximum wavelengths that belong to the Inertial Subrange are studied through spectral analysis of the vertical velocity. The maximum wavelength of the iner- tial Subrange in the cloud-driven layer scales relatively well with the corresponding layer depth during pronounced de- coupled structure identified from the vertical velocity skew- ness. However, on many occasions, combining the analysis of the Inertial Subrange and vertical velocity statistics sug- gests higher decoupling height than expected from the skew- ness profiles.Our resultsshowthat investigationofthelength scales related to the Inertial Subrange significantly comple- ments the analysis of the vertical velocity statistics and en- ables a more confident interpretation of complex boundary layer structures using measurements from a Doppler lidar.
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turbulent structure and scaling of the Inertial Subrange in a stratocumulus topped boundary layer observed by a doppler lidar
Atmospheric Chemistry and Physics, 2014Co-Authors: A. Hellsten, J. Tonttila, A. Hirsikko, Hannu Järvinen, Ewan J Oconnor, Colin D Odowd, PETRI RAISANENAbstract:The turbulent structure of a stratocumulus-topped marine boundary layer over a 2-day period is observed with a Doppler lidar at Mace Head in Ireland. Using profiles of vertical velocity statistics, the bulk of the mixing is identified as cloud driven. This is supported by the pertinent feature of negative vertical velocity skewness in the sub-cloud layer which extends, on occasion, almost to the surface. Both cou- pled and decoupled turbulence characteristics are observed. The length and timescales related to the cloud-driven mixing are investigated and shown to provide additional information about the structure and the source of the mixing inside the boundary layer. They are also shown to place constraints on the length of the sampling periods used to derive products, such as the turbulent dissipation rate, from lidar measure- ments. For this, the maximum wavelengths that belong to the Inertial Subrange are studied through spectral analysis of the vertical velocity. The maximum wavelength of the iner- tial Subrange in the cloud-driven layer scales relatively well with the corresponding layer depth during pronounced de- coupled structure identified from the vertical velocity skew- ness. However, on many occasions, combining the analysis of the Inertial Subrange and vertical velocity statistics sug- gests higher decoupling height than expected from the skew- ness profiles. Our results show that investigation of the length scales related to the Inertial Subrange significantly comple- ments the analysis of the vertical velocity statistics and en- ables a more confident interpretation of complex boundary layer structures using measurements from a Doppler lidar.
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Turbulent structure and scaling of the Inertial Subrange in a stratocumulus-topped boundary layer observed by a Doppler lidar
Atmospheric Chemistry and Physics Discussions, 2014Co-Authors: J. Tonttila, A. Hellsten, Chris O'dowd, A. Hirsikko, E. J. O'connor, Hannu Järvinen, PETRI RAISANENAbstract:The turbulent structure of a stratocumulus-topped marine boundary layer over a two-day period is observed with a Doppler lidar at Mace Head in Ireland. Using profiles of vertical velocity statistics, the bulk of the mixing is identified as cloud-driven. This is supported by the pertinent feature of negative vertical velocity skewness in the sub-cloud layer which extends, on occasion, almost to the surface. Both coupled and decoupled turbulence characteristics are observed. The length and time scales related to the cloud driven mixing are investigated, which are shown to provide additional information about the structure and the source of the mixing inside the boundary layer. They are also shown to place constraints on the length of the sampling periods used to derive products, such as the turbulent dissipation rate, from lidar measurements. For this, the upper cut-off wavelength of the Inertial Subrange is studied through spectral analysis of the vertical velocity. The bulk statistical profiles and the scaling of the Inertial Subrange show consistent behaviour as the boundary layer undergoes transitions between a coupled and decoupled stratocumulus layer. The cut-off wavelength of the Inertial Subrange does not appear to scale robustly with the relative depth of the local mixing regime at different altitudes during decoupled periods. Rather, the competition between surface-based and cloud-driven mixed layers suppresses the range of eddy sizes at all heights inside the boundary layer.
PETRI RAISANEN - One of the best experts on this subject based on the ideXlab platform.
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turbulent structure and scaling of the Inertial Subrange in a stratocumulus topped boundary layer observed by a doppler lidar
Atmospheric Chemistry and Physics, 2014Co-Authors: A. Hellsten, J. Tonttila, A. Hirsikko, Hannu Järvinen, Ewan J Oconnor, Colin D Odowd, PETRI RAISANENAbstract:The turbulent structure of a stratocumulus-topped marine boundary layer over a 2-day period is observed with a Doppler lidar at Mace Head in Ireland. Using profiles of vertical velocity statistics, the bulk of the mixing is identified as cloud driven. This is supported by the pertinent feature of negative vertical velocity skewness in the sub-cloud layer which extends, on occasion, almost to the surface. Both cou- pled and decoupled turbulence characteristics are observed. The length and timescales related to the cloud-driven mixing are investigated and shown to provide additional information about the structure and the source of the mixing inside the boundary layer. They are also shown to place constraints on the length of the sampling periods used to derive products, such as the turbulent dissipation rate, from lidar measure- ments. For this, the maximum wavelengths that belong to the Inertial Subrange are studied through spectral analysis of the vertical velocity. The maximum wavelength of the iner- tial Subrange in the cloud-driven layer scales relatively well with the corresponding layer depth during pronounced de- coupled structure identified from the vertical velocity skew- ness. However, on many occasions, combining the analysis of the Inertial Subrange and vertical velocity statistics sug- gests higher decoupling height than expected from the skew- ness profiles. Our results show that investigation of the length scales related to the Inertial Subrange significantly comple- ments the analysis of the vertical velocity statistics and en- ables a more confident interpretation of complex boundary layer structures using measurements from a Doppler lidar.
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Turbulent structure and scaling of the Inertial Subrange in a stratocumulus-topped boundary layer observed by a Doppler lidar
Atmospheric Chemistry and Physics Discussions, 2014Co-Authors: J. Tonttila, A. Hellsten, Chris O'dowd, A. Hirsikko, E. J. O'connor, Hannu Järvinen, PETRI RAISANENAbstract:The turbulent structure of a stratocumulus-topped marine boundary layer over a two-day period is observed with a Doppler lidar at Mace Head in Ireland. Using profiles of vertical velocity statistics, the bulk of the mixing is identified as cloud-driven. This is supported by the pertinent feature of negative vertical velocity skewness in the sub-cloud layer which extends, on occasion, almost to the surface. Both coupled and decoupled turbulence characteristics are observed. The length and time scales related to the cloud driven mixing are investigated, which are shown to provide additional information about the structure and the source of the mixing inside the boundary layer. They are also shown to place constraints on the length of the sampling periods used to derive products, such as the turbulent dissipation rate, from lidar measurements. For this, the upper cut-off wavelength of the Inertial Subrange is studied through spectral analysis of the vertical velocity. The bulk statistical profiles and the scaling of the Inertial Subrange show consistent behaviour as the boundary layer undergoes transitions between a coupled and decoupled stratocumulus layer. The cut-off wavelength of the Inertial Subrange does not appear to scale robustly with the relative depth of the local mixing regime at different altitudes during decoupled periods. Rather, the competition between surface-based and cloud-driven mixed layers suppresses the range of eddy sizes at all heights inside the boundary layer.
Jeffrey Robert Chasnov - One of the best experts on this subject based on the ideXlab platform.
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Simulation of the Inertial–conductive Subrange
Physics of Fluids, 1991Co-Authors: Jeffrey Robert ChasnovAbstract:The Inertial–conductive Subrange spectrum of a passive temperature field of a fluid of small Prandtl number is determined by large‐eddy simulation. Results for simulations of both freely decaying and forced turbulence are presented. In the simulations of freely decaying turbulence, a subgrid model is used to simulate a decaying turbulent velocity field with a k−5/3 Inertial Subrange energy spectrum convecting eight different decaying temperature fields with well‐resolved conductive Subranges. In the simulations of forced turbulence, a subgrid model is again used to simulate an Inertial Subrange velocity field; however, the velocity field is now forced at the lowest wave numbers of the simulation, and an external uniform mean temperature gradient is imposed. Statistically stationary velocity and temperature fluctuations are generated. The results of the decaying and forced simulations are in excellent agreement with the Batchelor, Howells, and Townsend (BHT) [J. Fluid Mech. 5, 134 (1959)] k−17/3 spectrum i...
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simulation of the Inertial conductive Subrange
Physics of Fluids, 1991Co-Authors: Jeffrey Robert ChasnovAbstract:The Inertial–conductive Subrange spectrum of a passive temperature field of a fluid of small Prandtl number is determined by large‐eddy simulation. Results for simulations of both freely decaying and forced turbulence are presented. In the simulations of freely decaying turbulence, a subgrid model is used to simulate a decaying turbulent velocity field with a k−5/3 Inertial Subrange energy spectrum convecting eight different decaying temperature fields with well‐resolved conductive Subranges. In the simulations of forced turbulence, a subgrid model is again used to simulate an Inertial Subrange velocity field; however, the velocity field is now forced at the lowest wave numbers of the simulation, and an external uniform mean temperature gradient is imposed. Statistically stationary velocity and temperature fluctuations are generated. The results of the decaying and forced simulations are in excellent agreement with the Batchelor, Howells, and Townsend (BHT) [J. Fluid Mech. 5, 134 (1959)] k−17/3 spectrum i...
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simulation of the kolmogorov Inertial Subrange using an improved subgrid model
Physics of Fluids, 1991Co-Authors: Jeffrey Robert ChasnovAbstract:A subgrid model is developed and applied to a large‐eddy simulation of the Kolmogorov Inertial Subrange. Currently popular subgrid models are derived from models of the turbulent energy equation, resulting in a significant loss of information as a consequence of the statistical averaging performed in going from the Navier–Stokes equation to the energy equation. The subgrid model developed here is based directly on a model of the Navier–Stokes equation. The improved subgrid model contains two terms: an eddy viscosity and a stochastic force. These terms are computed from the EDQNM stochastic model representation of the momentum equation, and from a fully resolved direct numerical simulation. Use of the subgrid model in a forced large‐eddy simulation results in an energy spectrum that exhibits a clear k−5/3 power‐law Subrange with an approximate value Ko=2.1 of the Kolmogorov constant.
Hans Van Haren - One of the best experts on this subject based on the ideXlab platform.
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deep ocean Inertial Subrange small bandwidth coherence and ozmidov frequency separation
arXiv: Atmospheric and Oceanic Physics, 2019Co-Authors: Hans Van HarenAbstract:The Inertial Subrange of turbulence in a density stratified environment is the transition from internal waves to isotropic turbulence, but it is unclear how to interpret its extension to anisotropic stratified turbulence. Knowledge about stratified turbulence is relevant for the dispersal of suspended matter in geophysical flows, such as in most of the ocean. For studying internal-wave-induced ocean-turbulence moored high-resolution temperature (T-)sensors are used. Spectra from observations on episodic quasi-convective internal wave breaking above a steep slope of large seamount Josephine in the Northeast-Atlantic demonstrate an Inertial Subrange that can be separated in two parts: A large-scale part with relatively coherent portions adjacent to less coherent portions, and a small-scale part that is smoothly continuous (to within standard error). The separation is close to the Ozmidov frequency, and coincides with the transition from anisotropic/quasi-deterministic stratified turbulence to isotropic/stochastic Inertial convective motions as inferred from a comparison of vertical and horizontal co-spectra. These observations contrast with T-sensor observations of shear-dominated internal wave breaking in an equally turbulent environment above the slope of a small Mid-Atlantic ridge-crest, which demonstrate a stochastic Inertial Subrange throughout.
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deep ocean Inertial Subrange small bandwidth coherence and ozmidov frequency separation
Physics of Fluids, 2019Co-Authors: Hans Van HarenAbstract:The Inertial Subrange of turbulence in a density stratified environment is the transition from internal waves to isotropic turbulence, but it is unclear how to interpret its extension to anisotropic “stratified” turbulence. Knowledge about stratified turbulence is relevant for the dispersal of suspended matter in geophysical flows, such as in most of the ocean. For studying internal-wave-induced ocean-turbulence, moored high-resolution temperature (T-)sensors are used. Spectra from observations on episodic quasiconvective internal wave breaking above a steep slope of large seamount Josephine in the Northeast-Atlantic demonstrate an Inertial Subrange that can be separated in two parts: A large-scale part with relatively coherent portions adjacent to less coherent portions and a small-scale part that is smoothly continuous (to within standard error). The separation is close to the Ozmidov frequency and coincides with the transition from anisotropic/quasideterministic stratified turbulence to isotropic/stochastic Inertial convective motions as inferred from a comparison of vertical and horizontal cospectra. These observations contrast with T-sensor observations of shear-dominated internal wave breaking in an equally turbulent environment above the slope of a small Mid-Atlantic ridge-crest, which demonstrate a stochastic Inertial Subrange throughout.The Inertial Subrange of turbulence in a density stratified environment is the transition from internal waves to isotropic turbulence, but it is unclear how to interpret its extension to anisotropic “stratified” turbulence. Knowledge about stratified turbulence is relevant for the dispersal of suspended matter in geophysical flows, such as in most of the ocean. For studying internal-wave-induced ocean-turbulence, moored high-resolution temperature (T-)sensors are used. Spectra from observations on episodic quasiconvective internal wave breaking above a steep slope of large seamount Josephine in the Northeast-Atlantic demonstrate an Inertial Subrange that can be separated in two parts: A large-scale part with relatively coherent portions adjacent to less coherent portions and a small-scale part that is smoothly continuous (to within standard error). The separation is close to the Ozmidov frequency and coincides with the transition from anisotropic/quasideterministic stratified turbulence to isotropic/stoch...
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stratified Inertial Subrange inferred from in situ measurements in the bottom boundary layer of the rockall channel
Journal of Physical Oceanography, 2010Co-Authors: Pascale Bouruetaubertot, Hans Van Haren, Pascale M LelongAbstract:Abstract Deep-ocean high-resolution moored temperature data are analyzed with a focus on superbuoyant frequencies. A local Taylor hypothesis based on the horizontal velocity averaged over 2 h is used to infer horizontal wavenumber spectra of temperature variance. The Inertial Subrange extends over fairly low horizontal wavenumbers, typically within 2 × 10−3 and 2 × 10−1 cycles per minute (cpm). It is therefore interpreted as a stratified Inertial Subrange for most of this wavenumber interval, whereas in some cases the convective Inertial Subrange is resolved as well. Kinetic energy dissipation rate ϵ is inferred using theoretical expressions for the stratified Inertial Subrange. A wide range of values within 10−9 and 4 × 10−7 m2 s−3 is obtained for time periods either dominated by semidiurnal tides or by significant subInertial variability. A scaling for ϵ that depends on the potential energy within the inertio-gravity waves (IGW) frequency band PEIGW and the buoyancy frequency N is proposed for these two...
Domenico Anfossi - One of the best experts on this subject based on the ideXlab platform.
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Estimation of the Lagrangian Velocity Structure Function Constant C_0 by Large-Eddy Simulation
Boundary-Layer Meteorology, 2006Co-Authors: Umberto Rizza, Cristina Mangia, Jonas C. Carvalho, Domenico AnfossiAbstract:The Inertial Subrange Kolmogorov constant C _0, which determines the effective turbulent diffusion in velocity space, plays an important role in the Lagrangian modelling of pollutants. A wide range of values of the constant are found in the literature, most of them determined at low Reynolds number and/or under different assumptions. Here we estimate the constant C _0 by tracking an ensemble of Lagrangian particles in a planetary boundary layer simulated with a large-eddy simulation model and analysing the Lagrangian velocity structure function in the Inertial Subrange. The advantage of this technique is that it easily allows Reynolds numbers to be achieved typical of convective turbulent flows. Our estimates of C _0 is C _0=4.3±0.3 consistent with values found in the literature
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Estimation of the Lagrangian Velocity Structure Function Constant C0 by Large-Eddy Simulation
Boundary-Layer Meteorology, 2006Co-Authors: Umberto Rizza, Cristina Mangia, Jonas C. Carvalho, Domenico AnfossiAbstract:The Inertial Subrange Kolmogorov constant C0, which determines the effective tur- bulent diffusion in velocity space, plays an important role in the Lagrangian modelling of pollutants. A wide range of values of the constant are found in the literature, most of them determined at low Reynolds number and/or under different assumptions. Here we estimate the constant C0 by tracking an ensemble of Lagrangian particles in a planetary boundary layer simulated with a large-eddy simulation model and analysing the Lagrangian velocity structure function in the Inertial Subrange. The advantage of this technique is that it easily allows Reynolds numbers to be achieved typical of convective turbulent flows. Our estimates of C0 is C0 = 4.3 ± 0.3 consistent with values found in the literature.