scholarly journals Near-inertial dissipation due to stratified flow over abyssal topography

2021 ◽  
Author(s):  
Varvara E. Zemskova ◽  
Nicolas Grisouard
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Large Scale ◽  
Stratified Flow ◽  
Ocean Bottom ◽  
Numerical Work ◽  
Resonant Wave ◽  
Dissipation Rates ◽  
Lee Wave ◽  
Radiative Regime

AbstractLinear theory for steady stratified flow over topography sets the range for topographic wavenumbers over which freely propagating internal waves are generated, and the radiation and breaking of these waves contribute to energy dissipation away from the ocean bottom. However, previous numerical work demonstrated that dissipation rates can be enhanced by flow over large scale topographies with wavenumbers outside of the lee wave radiative range. We conduct idealized 3D numerical simulations of steady stratified flow over 1D topography in a rotating domain and quantify vertical distribution of kinetic energy dissipation. We vary two parameters: the first determines whether the topographic obstacle is within the lee wave radiative range and the second, proportional to the topographic height, measures the degree of flow non-linearity. For certain combinations of topographic width and height, breaking occurs in pulses every inertial period, such that kinetic energy dissipation develops inertial periodicity. In these simulations, kinetic energy dissipation rates are also enhanced in the interior of the domain. In the radiative regime the inertial motions arise due to resonant wave-wave interactions. In the small wavenumber non-radiative regime, instabilities downstream of the obstacle can facilitate the generation and propagation of non-linearly forced inertial motions, especially as topographic height increase. In our simulations, dissipation rates for tall and wide non-radiative topography are comparable to those of radiative topography, even away from the bottom, which is relevant to the ocean where the topographic spectrum is such that wider abyssal hills also tend to be taller.

scholarly journals Near-inertial dissipation due to stratified flow over abyssal topography

2021 ◽  
Author(s):  
Varvara Zemskova ◽  
Nicolas Grisouard
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Numerical Simulations ◽  
Linear Theory ◽  
Internal Waves ◽  
Wave Breaking ◽  
Large Scale ◽  
Stratified Flow ◽  
Dissipation Rates ◽  
Flow Over Topography

<p>Linear theory for steady stratified flow over topography sets the range for topographic wavenumbers over which freely propagating internal waves are generated, whose radiation and breaking contribute to energy dissipation in the interior. Previous work demonstrated that dissipation rates can be enhanced over large-scale topographies with wavenumbers outside of such radiative range. We conduct idealized rotating 3D numerical simulations of steady stratified flow over 1D topography and quantify kinetic energy dissipation. We vary topographic width, which determines whether the obstacle is within the radiative range, and height, which measures the degree of flow non-linearity. Simulations with certain width and height combinations develop periodicity in wave breaking and energy dissipation, which is enhanced in the domain interior. Dissipation rates for tall and wide non-radiative topography are comparable to those of radiative topography, even away from the bottom, which is important for the ocean where wider hills also tend to be taller. </p>

scholarly journals Turbulence kinetic energy dissipation rates estimated from concurrent UAV and MU radar measurements

2018 ◽  
Vol 70 (1) ◽  
Author(s):  
Hubert Luce ◽  
Lakshmi Kantha ◽  
Hiroyuki Hashiguchi ◽  
Dale Lawrence ◽  
Abhiram Doddi
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulence Kinetic Energy ◽  
Mu Radar ◽  
Dissipation Rates ◽  
Radar Measurements

scholarly journals Diffusional and accretional growth of water drops in a rising adiabatic parcel: effects of the turbulent collision kernel

2009 ◽  
Vol 9 (7) ◽  
pp. 2335-2353 ◽  
Author(s):  
W. W. Grabowski ◽  
L.-P. Wang
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Collision Kernel ◽  
Small Scale ◽  
Large Set ◽  
Initiation Time ◽  
Cloud Droplets ◽  
Dissipation Rates ◽  
Speedup Factor

Abstract. A large set of rising adiabatic parcel simulations is executed to investigate the combined diffusional and accretional growth of cloud droplets in maritime and continental conditions, and to assess the impact of enhanced droplet collisions due to small-scale cloud turbulence. The microphysical model applies the droplet number density function to represent spectral evolution of cloud and rain/drizzle drops, and various numbers of bins in the numerical implementation, ranging from 40 to 320. Simulations are performed applying two traditional gravitational collection kernels and two kernels representing collisions of cloud droplets in the turbulent environment, with turbulent kinetic energy dissipation rates of 100 and 400 cm2 s−3. The overall result is that the rain initiation time significantly depends on the number of bins used, with earlier initiation of rain when the number of bins is low. This is explained as a combination of the increase of the width of activated droplet spectrum and enhanced numerical spreading of the spectrum during diffusional and collisional growth when the number of model bins is low. Simulations applying around 300 bins seem to produce rain at times which no longer depend on the number of bins, but the activation spectra are unrealistically narrow. These results call for an improved representation of droplet activation in numerical models of the type used in this study. Despite the numerical effects that impact the rain initiation time in different simulations, the turbulent speedup factor, the ratio of the rain initiation time for the turbulent collection kernel and the corresponding time for the gravitational kernel, is approximately independent of aerosol characteristics, parcel vertical velocity, and the number of bins used in the numerical model. The turbulent speedup factor is in the range 0.75–0.85 and 0.60–0.75 for the turbulent kinetic energy dissipation rates of 100 and 400 cm2 s−3, respectively.

scholarly journals Diffusional and accretional growth of water drops in a rising adiabatic parcel: effects of the turbulent collision kernel

2008 ◽  
Vol 8 (4) ◽  
pp. 14717-14763 ◽  
Author(s):  
W. W. Grabowski ◽  
L.-P. Wang
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Collision Kernel ◽  
Small Scale ◽  
Large Set ◽  
Initiation Time ◽  
Cloud Droplets ◽  
Dissipation Rates ◽  
Speedup Factor

Abstract. A large set of rising adiabatic parcel simulations is executed to investigate the combined diffusional and accretional growth of cloud droplets in maritime and continental conditions, and to assess the impact of enhanced droplet collisions due to small-scale cloud turbulence. The microphysical model applies the droplet number density function to represent spectral evolution of cloud and rain/drizzle drops, and various numbers of bins in the numerical implementation, ranging from 40 to 320. Simulations are performed applying two traditional gravitational collection kernels and two kernels representing collisions of cloud droplets in the turbulent environment, with turbulent kinetic energy dissipation rates of 100 and 400 cm2 s−3. The overall result is that the rain initiation time significantly depends on the number of bins used, with earlier initiation of rain when the number of bins is low. This is explained as a combination of the increase of the width of activated droplet spectrum and enhanced numerical spreading of the spectrum during diffusional and collisional growth when the number of model bins is low. Simulations applying around 300 bins seem to produce rain at times which no longer depend on the number of bins, but the activation spectra are unrealistically narrow. These results call for an improved representation of droplet activation in numerical models of the type used in this study. Despite the numerical effects that impact the rain initiation time in different simulations, the turbulent speedup factor, the ratio of the rain initiation time for the turbulent collection kernel and the corresponding time for the gravitational kernel, is approximately independent of aerosol characteristics, parcel vertical velocity, and the number of bins used in the numerical model. The turbulent speedup factor is in the range 0.75–0.85 and 0.60–0.75 for the turbulent kinetic energy dissipation rates of 100 and 400 cm2 s−3, respectively.

Doppler spectral width studies from polar mesospheric summer echoes

2020 ◽  
Author(s):  
Nikoloz Gudadze ◽  
Gunter Stober ◽  
Hubert Luce ◽  
Jorge Luis Chau
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Spectral Width ◽  
Target Area ◽  
Fundamental Parameter ◽  
Dissipation Rates ◽  
Summer Echoes ◽  
Width Measurements ◽  
Fossil Turbulence

<p>Investigation of turbulence in the polar mesopause is essential for a better understanding of dynamical or mixing processes in the region. Polar Mesospheric Summer Echoes (PMSEs), occurring at mesopause altitudes during the summer season, are known to be a result of turbulence-induced fluctuations in the refractive index. The presence of ice particles controls and reduce the free-electron diffusivity in D region plasma, which in turn leads to complex, strong radar echoes at very high frequencies.</p><p>Often, Doppler spectral width of radar measurements are associated with the strength of turbulence in the target area and traditionally used to estimate turbulent kinetic energy dissipation rates, a fundamental parameter of the turbulence processes. Besides the cooling of summer mesopause region induced by GW drag, the turbulence produced by GW breaking contributes to the total energy budget due to release of turbulent kinetic energy to heat. We use PMSE spectral width measurements observed by Middle Atmosphere Alomar Radar System (MAARSY) during summer of 2016 to study their summer temporal mean profiles as well as temporal evolution and connection to the atmospheric turbulence at PMSE altitudes - 80 and 90 km. The current theoretical models suggest that the radar reflectivity should correlate to the strength of the turbulence; however, such a relation is mainly observed for the weaker PMSEs. The mean summer behaviour of estimated turbulent kinetic energy dissipation rates shows an increase from lower altitudes up to 90 km. It should be noticed that spectral width measurements contain additional broadening rather than turbulence, so derived energy dissipation rates are “upper values” than expected from pure turbulence. The results are still slightly lower than those known from climatology obtained from rocket soundings, mostly at altitudes close to the maximum occurrence of PMSE, 86-87 km.</p><p>We discuss a possible consequence of spectral width measurements under strong PMSEs. In such conditions, the strength of the echo does not correlate with the turbulence intensity, and the observed spectral width is weaker. However, the uniform distribution of spectral width values throughout the echo power is expected from the present theoretical understandings. Based on previous studies, strong PMSEs can also be observed during fossil turbulence. The interpretation of connection the spectral with measurements under fossil turbulence with the turbulence energy dissipation rates and the possibility of using PMSEs for the turbulence studies will be discussed.</p>

scholarly journals Deep-sea turbulence evolution observed by multiple closely spaced instruments

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chu-Fang Yang ◽  
Wu-Cheng Chi ◽  
Hans van Haren
Keyword(s):  
Kinetic Energy ◽  
Internal Waves ◽  
Deep Sea ◽  
Large Scale ◽  
Time Derivative ◽  
Deep Ocean ◽  
Energy Dissipation Rate ◽  
Small Scale ◽  
Ocean Bottom ◽  
Seafloor Topography

AbstractTurbulent mixing in the deep ocean is not well understood. The breaking of internal waves on sloped seafloor topography can generate deep-sea turbulence. However, it is difficult to measure turbulence comprehensively due to its multi-scale processes, in addition to flow–flow and flow–topography interactions. Dense, high-resolution spatiotemporal coverage of observations may help shed light on turbulence evolution. Here, we present turbulence observations from four broadband ocean bottom seismometers (OBSs) and a 200-m vertical thermistor string (T-string) in a footprint of 1 × 1 km to characterize turbulence induced by internal waves at a depth of 3000 m on a Pacific continental slope. Correlating the OBS-calculated time derivative of kinetic energy and the T-string-calculated turbulent kinetic energy dissipation rate, we propose that the OBS-detected signals were induced by near-seafloor turbulence. Strong disturbances were detected during a typhoon period, suggesting large-scale inertial waves breaking with upslope transport speeds of 0.2–0.5 m s−1. Disturbances were mostly excited on the downslope side of the array where the internal waves from the Pacific Ocean broke initially and the turbulence oscillated between < 1 km small-scale ridges. Such small-scale topography caused varying turbulence-induced signals due to localized waves breaking. Arrayed OBSs can provide complementary observations to characterize deep-sea turbulence.

Hybrid Eulerian–Lagrangian simulations for polymer–turbulence interactions

2013 ◽  
Vol 717 ◽  
pp. 535-575 ◽  
Author(s):  
Takeshi Watanabe ◽  
Toshiyuki Gotoh
Keyword(s):  
Energy Spectrum ◽  
Energy Dissipation ◽  
Kinetic Energy ◽  
Large Scale ◽  
Isotropic Turbulence ◽  
Polymer Concentration ◽  
Hybrid Approach ◽  
Weissenberg Number ◽  
Polymer Additives ◽  
Kinetic Energy Spectrum

AbstractThe effects of polymer additives on decaying isotropic turbulence are numerically investigated using a hybrid approach consisting of Brownian dynamics simulations for an enormous number of dumbbells (of the order of 10 billion,$O(1{0}^{10} )$) and direct numerical simulations of turbulence making full use of large-scale parallel computations. Reduction of the energy dissipation rate and modification of the kinetic energy spectrum in the dissipation range scale were observed when the reaction term due to the polymer additives was incorporated into the equation of motion for the solvent fluid. An increase in the polymer concentration or Weissenberg number${W}_{i} $yielded significant modifications of the turbulence statistics at small scales, such as a suppression of the local energy dissipation fluctuations. A power-law decay of the kinetic energy spectrum$E(k, t)\sim {k}^{- 4. 7} $was observed in the wavenumber range below the Kolmogorov length scale when${W}_{i} = 25$. The generation of intense vortices was suppressed by the polymer additives, consistent with previous studies using the constitutive equations. The field structures of the trace of the polymer stress depended on the intensity of its fluctuation: sheet-like structures were observed for the intermediate intensity region and filamentary structures were observed for the intense region. The results obtained with few polymers and large replicas could approximate those with many polymers and smaller replicas as far as the large-scale statistics were concerned.

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