scholarly journals Helically decomposed turbulence

2017 ◽  
Vol 812 ◽  
pp. 752-770 ◽  
Author(s):  
Alexandros Alexakis
Keyword(s):  
Total Energy ◽  
Numerical Simulations ◽  
Energy Flux ◽  
Large Scale ◽  
Inertial Range ◽  
Inverse Cascade ◽  
New Directions ◽  
Total Energy Flux

A decomposition of the energy and helicity fluxes is used to analyse turbulent hydrodynamic flows. The decomposition is based on the projection of the flow to a helical basis. This allows the roles of interactions among modes of different helicities to be investigated separately. The proposed formalism is applied to large-scale numerical simulations of non-helical and helical flows, where the decomposed fluxes are explicitly calculated. It is shown that the total energy flux can be split into three fluxes that independently remain constant in the inertial range. One of these fluxes which corresponds to the interactions of fields with the same helicity is negative, implying the presence of an inverse cascade that is ‘hidden’ inside the forward cascade. Similarly to the energy flux, it is also shown that the helicity flux can be decomposed into two fluxes that remain constant in the inertial range. Implications of these results as well as possible new directions for investigations are discussed.

scholarly journals Diagnostics of Non-thermal Particles in Solar Chromospheric Flares

2004 ◽  
Vol 219 ◽  
pp. 171-175
Author(s):  
C. Fang ◽  
Z. Xu ◽  
M. D. Ding
Keyword(s):  
Total Energy ◽  
Energy Flux ◽  
Atmospheric Condition ◽  
Particle Beam ◽  
Profile Measurement ◽  
Solar Chromosphere ◽  
Line Profiles ◽  
Total Energy Flux ◽  
Hydrogen Lines ◽  
Semi Empirical

Particle beam bombardment on the solar chromosphere produces non-thermal ionization and excitation. The effect on hydrogen lines is investigated by using non-LTE theory and semi-empirical flare models. It has been found that in the case of electron bombardment, the Hα line is widely broadened and enhanced. Significant enhancements at the wings of Lyα and Lyβ lines are also predicted. In the case of proton bombardment, less strong broadening and less central reversal are expected. We found that the total energy flux of the particle beam and the atmospheric condition give much influence on the line profiles, which, however, are less sensitive to the power index. Based on the Hα line profile measurement, a method to deduce the total energy flux of the particle beam is proposed.

Strong MHD helical turbulence and the nonlinear dynamo effect

1976 ◽  
Vol 77 (2) ◽  
pp. 321-354 ◽  
Author(s):  
A. Pouquet ◽  
U. Frisch ◽  
J. Léorat
Keyword(s):  
Large Scale ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Power Laws ◽  
Inertial Range ◽  
Small Scale ◽  
Mhd Turbulence ◽  
Inverse Cascade ◽  
Small Scales ◽  
Dynamo Effect

To understand the turbulent generation of large-scale magnetic fields and to advance beyond purely kinematic approaches to the dynamo effect like that introduced by Steenbeck, Krause & Radler (1966)’ a new nonlinear theory is developed for three-dimensional, homogeneous, isotropic, incompressible MHD turbulence with helicity, i.e. not statistically invariant under plane reflexions. For this, techniques introduced for ordinary turbulence in recent years by Kraichnan (1971 a)’ Orszag (1970, 1976) and others are generalized to MHD; in particular we make use of the eddy-damped quasi-normal Markovian approximation. The resulting closed equations for the evolution of the kinetic and magnetic energy and helicity spectra are studied both theoretically and numerically in situations with high Reynolds number and unit magnetic Prandtl number.Interactions between widely separated scales are much more important than for non-magnetic turbulence. Large-scale magnetic energy brings to equipartition small-scale kinetic and magnetic excitation (energy or helicity) by the ‘Alfvén effect’; the small-scale ‘residual’ helicity, which is the difference between a purely kinetic and a purely magnetic helical term, induces growth of large-scale magnetic energy and helicity by the ‘helicity effect’. In the absence of helicity an inertial range occurs with a cascade of energy to small scales; to lowest order it is a −3/2 power law with equipartition of kinetic and magnetic energy spectra as in Kraichnan (1965) but there are −2 corrections (and possibly higher ones) leading to a slight excess of magnetic energy. When kinetic energy is continuously injected, an initial seed of magnetic field will grow to approximate equipartition, at least in the small scales. If in addition kinetic helicity is injected, an inverse cascade of magnetic helicity is obtained leading to the appearance of magnetic energy and helicity in ever-increasing scales (in fact, limited by the size of the system). This inverse cascade, predicted by Frischet al.(1975), results from a competition between the helicity and Alféh effects and yields an inertial range with approximately — 1 and — 2 power laws for magnetic energy and helicity. When kinetic helicity is injected at the scale linjand the rate$\tilde{\epsilon}^V$(per unit mass), the time of build-up of magnetic energy with scaleL[Gt ] linjis$t \approx L(|\tilde{\epsilon}^V|l^2_{\rm inj})^{-1/3}.$

scholarly journals Direct Evidence of an Oceanic Inverse Kinetic Energy Cascade from Satellite Altimetry

2005 ◽  
Vol 35 (9) ◽  
pp. 1650-1666 ◽  
Author(s):  
Robert B. Scott ◽  
Faming Wang
Keyword(s):  
Kinetic Energy ◽  
Energy Flux ◽  
Direct Evidence ◽  
Inertial Range ◽  
Turbulence Theory ◽  
Kinetic Energy Density ◽  
Geostrophic Flow ◽  
Inverse Cascade ◽  
Barotropic Mode ◽  
Geostrophic Turbulence

Abstract Sea surface height measurements from satellites reveal the turbulent properties of the South Pacific Ocean surface geostrophic circulation, both supporting and challenging different aspects of geostrophic turbulence theory. A near-universal shape of the spectral kinetic energy flux is found and provides direct evidence of a source of kinetic energy near to or smaller than the deformation radius, consistent with linear instability theory. The spectral kinetic energy flux also reveals a net inverse cascade (i.e., a cascade to larger spatial scale), consistent with two-dimensional turbulence phenomenology. However, stratified geostrophic turbulence theory predicts an inverse cascade for the barotropic mode only; energy in the large-scale baroclinic modes undergoes a direct cascade toward the first-mode deformation scale. Thus if the surface geostrophic flow is predominately the first baroclinic mode, as expected for oceanic stratification profiles, then the observed inverse cascade contradicts geostrophic turbulence theory. The latter interpretation is argued for. Furthermore, and consistent with this interpretation, the inverse cascade arrest scale does not follow the Rhines arrest scale, as one would expect for the barotropic mode. A tentative revision of theory is proposed that would resolve the conflicts; however, further observations and idealized modeling experiments are needed to confirm, or refute, the revision. It is noted that no inertial range was found for the inverse cascade range of the spectrum, implying inertial range scaling, such as the established K−5/3 slope in the spectral kinetic energy density plot, is not applicable to the surface geostrophic flow.

scholarly journals The Total Energy Flux Leaving the Ocean’s Mixed Layer

2016 ◽  
Vol 46 (6) ◽  
pp. 1885-1900 ◽  
Author(s):  
Antonija Rimac ◽  
Jin-Song von Storch ◽  
Carsten Eden
Keyword(s):  
Total Energy ◽  
Wind Stress ◽  
Energy Flux ◽  
Mixed Layer ◽  
General Circulation ◽  
Circulation Model ◽  
Power Input ◽  
Ocean General Circulation Model ◽  
Wind Stress Curl ◽  
Total Energy Flux

AbstractThe total energy flux leaving the ocean’s spatially and seasonally varying mixed layer is estimated using a global ⅝1/10° ocean general circulation model. From the total wind-power input of 3.33 TW into near-inertial waves (0.35 TW), subinertial fluctuations (0.87 TW), and the time-mean circulation (2.11 TW), 0.92 TW leave the mixed layer, with 0.04 TW (11.4%) due to near-inertial motions, 0.07 TW (8.04%) due to subinertial fluctuations, and 0.81 TW (38.4%) due to time-mean motions. Of the 0.81 TW from the time-mean motions, 0.5 TW result from the projection of the horizontal flux onto the sloped bottom of the mixed layer. This projection is negligible for the transient fluxes. The spatial structure of the vertical flux is determined principally by the wind stress curl. The mean and subinertial fluxes leaving the mixed layer are approximately 40%–50% smaller than the respective fluxes across the Ekman layer according to the method proposed by Stern. The fraction related to transient fluctuations tends to decrease with increasing depth of the mixed layer and with increasing strength of wind stress variability.

Internal wave generation by tidal flow over a two-dimensional ridge: energy flux asymmetries induced by a steady surface trapped current

2017 ◽  
Vol 836 ◽  
pp. 192-221 ◽  
Author(s):  
Kevin G. Lamb ◽  
M. Dunphy
Keyword(s):  
Total Energy ◽  
Wave Field ◽  
Energy Flux ◽  
Tidal Flow ◽  
Surface Current ◽  
Equation Model ◽  
Two Dimensional ◽  
Total Energy Flux ◽  
Effects Of Rotation ◽  
Internal Wave Generation

The effects of a surface trapped steady background current on internal waves generated by tidal currents oscillating over a small symmetric ridge are investigated using a two-dimensional primitive equation model. A rigid lid is used with a linearly stratified fluid and the effects of rotation are not considered. We consider uni-directional background currents $\bar{U}(z)\geqslant 0$ confined to a surface layer lying well above the ridge. The current introduces asymmetries in the generated wave field. For sufficiently narrow ridges the upstream energy flux is larger than the downstream flux while the opposite is the case for sufficiently wide ridges. The total energy flux radiating away from the ridge is not significantly affected by the current. Mean second-order currents and pressure fields are shown to make important contributions to the total energy flux. A first-order linear theory, valid for a general stratification and surface current, which accurately predicts the wave field is also developed.

scholarly journals Total energy flux in a marine bioluminescent bacterium

1989 ◽  
Vol 57 (2) ◽  
pp. 161-165 ◽  
Author(s):  
John C. Makemson ◽  
Andrew S. Gordon
Keyword(s):  
Total Energy ◽  
Energy Flux ◽  
Bioluminescent Bacterium ◽  
Total Energy Flux

scholarly journals Kinematics and Energetics of A Solar Jet from NOAA Active Region 12297

2019 ◽  
Vol 14 (1) ◽  
Author(s):  
Reetika Joshi ◽  
Ramesh Chandra
Keyword(s):  
Active Region ◽  
Total Energy ◽  
Energy Flux ◽  
Solar Active Region ◽  
Active Region Noaa ◽  
Solar Dynamics Observatory ◽  
Total Energy Flux ◽  
Region Noaa ◽  
Solar Dynamics ◽  
Noaa Active Region

In this article, we have presented the study of a solar jet on March 14, 2015 recorded from the Atmospheric Imaging Assembly (AIA) onboard Solar Dynamics Observatory (SDO) satellite. The jet was observed from the solar active region NOAA AR 12297. We have discussed the dynamics and calculated the various possible energy contents of the observed jet. The estimated total energy flux liberated during the jet ejection was 2.1 x 107 erg cm-2 s-1 .

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