共查询到20条相似文献，搜索用时 31 毫秒
1.
M. N. Izakov 《Solar System Research》2005,39(1):33-44
Based on spaceborne experimental data, characteristics of turbulence are calculated for the Venusian troposphere under conditions corresponding to the planet-averaged flux of solar radiation, which is equal to its value at a solar zenith angle of 66°. Additionally, given experimental data on radiation fluxes and their numerical calculations, turbulence characteristics were calculated for a solar zenith angle of 45°. The turbulence pattern is significantly different for small and large solar zenith angles. At large solar zenith angles, there exist an anomalous downward turbulent heat flux above 7–10 km and a normal upward flux at lower heights. At small zenith angles, the turbulent flux is normal throughout the entire troposphere. The dissipation of turbulent energy contributes significantly to the atmospheric heating in a wide range of altitudes. The spectrum of the time and space scales of dissipative processes in the troposphere is very wide and changes with height.Translated from Astronomicheskii Vestnik, Vol. 39, No. 1, 2005, pp. 38–50.Original Russian Text Copyright © 2005 by Izakov. 相似文献
2.
V. V. Pipin 《Astronomy Letters》2001,27(3):171-175
We investigate the influence of turbulence anisotropy and rotation on the diffusion of a low-concentration passive scalar in a turbulent medium. Using the renormalization the diffusion tensor over the spectrum of turbulent fluctuations, we show that enhanced horizontal mixing reduces the vertical diffusion transport of a passive scalar. Allowance for rotation results in two effects, which have not been noted previously: (1) under the influence of Coriolis forces, horizontal turbulence also produces a vertical diffusion flux, with the horizontal and vertical diffusions being of the same order of magnitude for rapidly rotating stars and (2) in the case of rapid rotation, all diffusion fluxes of a passive scalar decrease in inverse proportion to the square root of the Coriolis number. 相似文献
3.
We have developed three types of mathematical models to describe the mechanisms of plasma heating in the corona by intense heat fluxes from a super-hot (T e ? 108 K) reconnecting current layer in connection with the problem of energy transport in solar flares. We show that the heat fluxes calculated within the framework of self-similar solutions using Fourier’s classical law exceed considerably the real energy fluxes known from present-day multi-wavelength observations of flares. This is because the conditions for the applicability of ordinary heat conduction due to Coulomb collisions of thermal plasma electrons are violated. Introducing anomalous heat conduction due to the interaction of thermal runaway electrons with ion-acoustic turbulence does not give a simple solution of the problem, because it produces unstable temperature profiles. Themodels incorporating the effect of collisional heat flux relaxation describe better the heat transport in flares than Fourier’s law and anomalous heat conduction. 相似文献
4.
S.J. Weidenschilling 《Icarus》2006,181(2):572-586
In the absence of global turbulence, solid particles in the solar nebula tend to settle into a thin layer in the central plane. Shear between this layer and pressure-supported gas produces localized turbulence in the midplane; the thickness of the particle layer is determined by balance between settling and turbulent diffusion. A numerical model is described, which allows computation of the vertical structure of a layer of particles of arbitrary size, with self-consistent distributions of particle density, turbulent velocity, and radial fluxes of particles and gas. Effects of varying particle size and the abundances of solids and gas are evaluated. If the surface density of solids is increased by an order of magnitude over nominal solar abundance, the peak density within a layer of small particles can approach the critical value needed for gravitational instability. However, depletion of the nebular gas is much less effective for raising the density of such a layer to the critical value, due to decreased coupling of particles to the gas as the density of the gas decreases. The variation of radial particle flux with surface density of the particle layer is not consistent with secular instability of the layer driven by gas drag. 相似文献
5.
An attempt is made to construct a phenomenological model of turbulence as a self-organization process in an open system. The representation of a turbulized continuum in the form of a thermodynamic complex consisting of two subsystems—the subsystem of averaged motion and the subsystem of turbulent chaos, which is considered, in turn, as a conglomerate of vortex structures of different space–time scales—made it possible to obtain, by methods of nonequilibrium thermodynamics, the defining relationships for the turbulent fluxes and forces that describe most comprehensively the transport and structurization processes in such a continuum. Using two interpretations of the Kolmogorov parameter (as a quantity that describes the rate of dissipation of energy into heat and as the rate of transfer of turbulent energy in the eddy cascade), the defining relationships were found for this quantity, thereby making the thermodynamic approach self-sufficient. An introduction into the model of internal parameters of the medium, which characterize the excitation of macroscopic degrees of freedom, made it possible to describe thermodynamically the Kolmogorov cascade process and to obtain a variety of kinetic equations (of the Fokker–Planck type in the configuration space) for the functions of distribution of small-scale turbulence characteristics, including the unsteady kinetic equation for the distribution of probability of dissipation of turbulent energy. As an example, a detailed derivation of such relationships is given for the case of stationary turbulence, when a tendency toward local isotropy is observed. In view of the wide occurrence of this phenomenon in nature, one might expect that the developed approach to the problem of modeling strong turbulence will find its use in astrophysical and geophysical applications. 相似文献
6.
A recent model of solar energetic particle propagation suggests that large fluxes of protons may produce their own turbulence. To verify this theoretical prediction it becomes essential to find out whether these fluxes cause appreciable changes in the interplanetary magnetic field (IMF) fluctuation regime. It is also important to check if the suggested optimum conditions for wave production are consistent with observational evidence. In the present work we perform a study of directional power and magnetic helicity spectra of the IMF fluctuations from a few hours before to a few hours after the maximum flux of 4–13 MeV protons observed on board the two Helios spacecraft during eight solar events. The time evolution of the directional power and helicity spectra show increases which may be associated with the solar energetic proton (SEP) flux in two of the analysed events. In one event, we present a decrease of turbulence and helicity coincident with the maximum flux of SEP may also admit an interpretation in terms of self-generated waves. The existence of solar wind phenomena such as sector boundaries or interplanetary shocks obscure possible signatures of proton self-generated waves in two events. One event with a low level of turbulence previous to the arrival of particles shows no turbulence increase which might be associated with them. The remaining two events show no evidence of particle-generated turbulence, but the conditions on which these were observed do not fulfil some assumptions of the model. 相似文献
7.
In previous publications the author considered how breaking buoyancy waves and the thermal source arising due to different absorption coefficients of solar and atmospheric radiation fluxes contributed to turbulence. In this study, the contribution to turbulence made by the dynamical source arising in consequence of convective instability of large-scale atmospheric motions is examined. Its value is estimated from experimental wind speed data for the atmosphere of Venus. The contributions of the indicated sources of turbulent energy are compared. The rate of dissipation of kinetic energy due to molecular viscosity is demonstrated to be several orders of magnitude less than the rate of dissipation necessary to maintain an invariable superrotation pattern. This is an additional argument for the permanent existence of turbulence in the atmosphere of Venus, which many authors consider doubtful. It is demonstrated why turbulence is present at the atmospheric stratification that seems to be stable. 相似文献
8.
Hannu Savijärvi 《Icarus》2012,221(2):617-623
The daytime convective boundary layer (CBL) of Mars and the transition to it after the cold night is studied on a warm dusty sol at the rover Spirit using temperature profiles from the miniature thermal emission spectrometer (mini-TES) and a 1-D model. The model’s net solar fluxes are linear in z in the CBL while the thermal fluxes decay logarithmically from about 8 m upward, due mainly to the emissivity properties and density of CO2. The induced strong radiative heating of the lower CBL is so well compensated by turbulent cooling (with an elevated maximum in the sensible heat flux H) that the growth of the CBL is uniform by the model, as observed by the mini-TES. Hence the net energy fluxes are linear and the shape of H in the lower CBL can be obtained as a residual. Moisture evolution is also considered although without validation. 相似文献
9.
Based on model calculations, we show that ion-acoustic oscillations can be excited by heat fluxes in a plasma. We discuss the probable effect of ion-acoustic oscillations on the formation of temperature gradients at critical heat fluxes. The local critical heat flux in the transition region of the solar atmosphere is close to the well-known experimental heat flux from the corona into the chromosphere. 相似文献
10.
This paper considers, in the context of modeling the evolution of a protoplanetary cloud, the hydrodynamic aspects of the theory of concurrent processes of mass transfer and coagulation in a two-phase medium in the presence of shear turbulence in a differentially rotating gas–dust disk and of polydisperse solid particles suspended in a carrying flow of solid particles. The defining relations are derived for diffuse fluxes of particles of different sizes in the equations of turbulent diffusion in the gravitational field, which describe the convective transfer, turbulent mixing, and sedimentation of disperse dust grains onto the central plane of the disk, as well as their coagulation growth. A semiempirical method is developed for calculating the coefficients of turbulent viscosity and turbulent diffusion for particles of different kinds. This method takes into account the inverse effects of dust transfer on the turbulence evolution in the disk and the inertial differences between disperse solid particles. To solve rigorously the problem of the mutual influence of the turbulent mixing and coagulation kinetics in forming the gas–dust subdisk, the possible mechanisms of gravitational, turbulent, and electric coagulation in a protoplanetary disk are explored and the parametric method of moments for solving the Smoluchowski integro-differential coagulation equation for the particles' size distribution function is considered. This method takes into account the fact that this distribution belongs to a definite parametric class of distributions. 相似文献
11.
K. O. Eschrich 《Astronomische Nachrichten》1978,299(3):137-144
This paper deals with heat transfer and heat production in a gas being in turbulent motion. Our aim is to derive a general equation for the mean temperature which contains coefficients determined by turbulence. This treatment is restricted to weak, homogeneous and stationary turbulence. Especially the heating by density fluctuations is discussed and compared with heating due to internal friction. 相似文献
12.
C. G. Campbell 《Monthly notices of the Royal Astronomical Society》2000,317(3):501-527
A model is presented for an accretion disc with turbulent viscosity and a magnetically influenced wind. The magnetic field is generated by a dynamo in the disc, involving the turbulence and radial shear. Disc-wind solutions are found for which the wind mass flux is sufficient to play a major part in driving an imposed steady inflow, but small enough for most material to be accreted on to the central object. Constraints arise for the magnetic Reynolds and Prandtl numbers in terms of the turbulent Mach number and vertical length-scale of the disc's horizontal magnetic field. It is shown that the imposition of a stellar boundary condition enhances the wind mass flux in the very inner region of the disc and may result in jet formation. 相似文献
13.
Krzysztof Stasiewicz 《Planetary and Space Science》1984,32(3):379-389
On the basis of quasi-linear theory of ion-acoustic turbulence it is shown that the angular and energy distribution of the electron spectra observed in quasi-static inverted-V structures are natural products of electron heating and runaway processes occuring in a region of current-driven turbulence located at h ≈ 1 Re. The power law population J ∞ E?γ, with γ ≈ 1 observed in the energy range ~ 25–1000 eV, is interpreted as a quasi-stationary distribution of suprathermal electrons interacting resonantly with the ion sound waves. This spectrum is generated in the turbulent region and convectively transported earthward along the magnetic field lines. Field-aligned intense electron fluxes with collimation angle < 10° are explained as due to particles escaping from the turbulent region through the runaway cone—a characteristic feature of velocity-space in ion-acoustic turbulence. A complete, new interpretation of the observed electron spectra is given on the basis of the proposed physical acceleration mechanism along with many other implications of this theory. 相似文献
14.
The behaviour of a multi-component anisotropic plasma in a magnetic flux tube is studied in the presence of current-driven electrostatic ion-cyclotron turbulence. The plasma transport is considered in both parallel and perpendicular directions with respect to the given tube. As one of the sources of the parallel electric field, the anomalous resistivityof the plasma caused by the turbulence is taken into account. The acceleration and heating processes of the plasma are simulated numerically. It is found that at the upper boundary of the nightside auroral ionosphere, the resonant wave-particle interactions are most effective in the case of upward field-aligned currents with densities of a few 10—6 A/m2. The occurring anomalous resistivity maycause differences of the electric potential along the magnetic field lines of some kV. Further it is shown that the thickness of the magnetic flux tube and the intensity of the convection strongly influence the turbulent plasma heating. 相似文献
15.
The ultrarelativistic generalized Lorentzian quasi-equilibrium thermodynamic energy distribution is tentatively applied to the energy spectrum of galactic cosmic ray fluxes. It is found that the inferred power law slopes contain a component which evolves with cosmic ray energy in steps of thirds, resembling the sequence of structure functions in fully developed Kolmogorov turbulence. Within the generalized thermodynamics the chemical potential is estimated from the deviation of the fluxes at decreasing energy, presumably throwing light on the cosmic ray acceleration mechanism. A relation between involved turbulent volumina and structure functions is obtained. The conclusions drawn hold only within the realm of applicability of thermodynamics to cosmic ray spectra. 相似文献
16.
Nonlinear processes describing the interaction of neutrinos with collective plasma oscillations and the excitation of plasma turbulence by a large neutrino flux is discussed. The excitation considered is the inverse processes of neutrino emission by plasma waves first considered by Tsytovich (V.N. Tsytovich, Soviet Fiz. Dokl. 9 (1965) 1114). The process is similar to a beam plasma instability considered as inverse Landau damping in which the usual electromagnetic interactions are important. In the neutrino beam relaxation the weak interaction can play a similar role. We emphasize here the possibility of another process namely the interaction of an intense neutrino flux with a strongly turbulent plasma. The turbulence can also be assumed to be due to the shock produced at the early stages of a type II supernova (SN) explosion. The scattering of the neutrinos in the turbulent plasma is shown to be sufficient for transferring momentum and energy from the neutrino flux to the plasma causing the shock to continue moving outward and eventually creating the blow-off of the mantle of the star producing type II SN. 相似文献
17.
Stuart J. WEIDENSCHILLING 《Meteoritics & planetary science》2010,45(2):276-288
Abstract– In the absence of global turbulence, solid particles in the solar nebula tend to settle toward the midplane, forming a layer with enhanced solids/gas ratio. Shear relative to the surrounding pressure‐supported gas generates turbulence within the layer, inhibiting further settling and preventing gravitational instability. Turbulence and size‐dependent drift velocities cause collisions between particles. Relative velocities between small grains and meter‐sized bodies are typically about 50 m s?1 for isolated particles; however, in a dense particle layer, collective effects alter the motion of the gas near the midplane. Here, we develop a numerical model for the coupled motions of gas and particles of arbitrary size, based on the assumption that turbulent viscosity transfers momentum on the scale of the Ekman length. The vertical distribution of particles is determined by a balance between settling and turbulent diffusion. Self‐consistent distributions of density, turbulent velocities, and radial fluxes of gas and particles of different sizes are determined. Collective effects generate turbulence that increases relative velocities between small particles, but reduce velocities between small grains and bodies of decimeter size or larger by bringing the layer’s motion closer to Keplerian. This effect may alleviate the “meter‐size barrier” to collisional growth of planetesimals. 相似文献
18.
D. Mitra S. Candelaresi P. Chatterjee R. Tavakol A. Brandenburg 《Astronomische Nachrichten》2010,331(1):130-135
We use direct numerical simulations of forced MHD turbulence with a forcing function that produces two different signs of kinetic helicity in the upper and lower parts of the domain. We show that the mean flux of magnetic helicity from the small‐scale field between the two parts of the domain can be described by a Fickian diffusion law with a diffusion coefficient that is approximately independent of the magnetic Reynolds number and about one third of the estimated turbulent magnetic diffusivity. The data suggest that the turbulent diffusive magnetic helicity flux can only be expected to alleviate catastrophic quenching at Reynolds numbers of more than several thousands. We further calculate the magnetic helicity density and its flux in the domain for three different gauges. We consider the Weyl gauge, in which the electrostatic potential vanishes, the pseudo‐Lorenz gauge, where the speed of light is replaced by the sound speed, and the ‘resistive gauge’ in which the Laplacian of the magnetic vector potential acts as a resistive term. We find that, in the statistically steady state, the time‐averaged magnetic helicity density and the magnetic helicity flux are the same in all three gauges (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
19.
C. G. Campbell 《Monthly notices of the Royal Astronomical Society》2003,345(1):123-143
A semi-analytic method is presented for solving for the radial and vertical structures of an accretion disc, with a magnetically channelled wind flowing from its surfaces. Both magnetic and turbulent viscous effects are taken into account, and the essential wind properties are related to the disc structure. The angular momentum removed by the wind plays a major part in driving the inflow through the disc, with photospheric temperatures being sufficient to generate the required wind mass flux. The magnetic field is generated by an αω-dynamo, but the method of solution should have application with other magnetic field sources. Self-consistent disc-wind solutions result, with rms turbulent Mach numbers which are in good agreement with those found in simulations of turbulence generated from magnetic shearing instabilities. 相似文献
20.
Krzysztof Stasiewicz 《Planetary and Space Science》1985,33(6):591-596
The influence of low-frequency electrostatic turbulence on the flux of precipitating magnetospheric electrons is analyzed in the framework of the quasilinear kinetic equation. It is shown that an electron population in a turbulent region, with an electric field parallel to the ambient magnetic field, can be separated into two parts by introducing a pitch angle dependent runaway velocity vr(θ). Lower energy electrons with parallel velocity v∥ < vr are effectively scattered by plasma waves, so that they remain in the main population and are subjected to an anomalous transport equation. A distribution function f ∞ v?4 (or the particle flux vs energy J ∞ E?1) is established in this velocity range. Faster electrons with v∥ ? vr are freely accelerated by a parallel electric field, so that they contribute directly to hot electron fluxes which are observed at ionospheric altitudes. New expressions are derived for the magnetic-field aligned current and the electron energy flux implied by this model. These expressions agree well with empirical relations observed in auroral inverted-V structures. 相似文献