共查询到20条相似文献，搜索用时 15 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.
M. N. Izakov 《Solar System Research》2012,46(4):278-290
Vertical profiles of the turbulence parameters calculated for the planet-averaged conditions from the experimental data on the turbulent fluctuations of temperature and wind velocity are presented. Improved formulas accounting for the difference between the atmospheric gas on Venus and an ideal one, and the large difference in its thermal capacity at different altitudes, are used. The commonly used formula for the potential temperature describing the atmospheres of the Earth and Mars is inapplicable to the atmosphere of Venus. It has been shown that the opinion on the absence of turbulence in the atmosphere of Venus is based on overestimated values of the dynamic Richardson number obtained from the smoothed profiles of wind velocity, while its actual values are below unity due to the large wind velocity gradients produced by buoyancy waves. To improve the global circulation models of the atmosphere of Venus, it is necessary to use the currently available turbulence parameters calculated from experimental data. 相似文献
3.
《Planetary and Space Science》2007,55(6):755-769
A new ULF wave index, characterizing the turbulent level of the geomagnetic field, has been calculated and applied to the analysis of relativistic electron enhancements during space weather events in March–May 1994 and September 1999. This global wave index has been produced from the INTERMAGNET, MACCS, CPMN, and Greenland dense magnetometer arrays in the northern hemisphere. A similar ULF wave index has been calculated using magnetometer data from geostationary (GOES) and interplanetary (Wind, ACE) satellites. During the periods analyzed several magnetic storms occurred, and several significant increases of relativistic electron flux up to 2–3 orders of magnitude were detected by geostationary monitors. However, these electron enhancements were not directly related to the intensity of magnetic storms. Instead, they correlated well with intervals of elevated ULF wave index, caused by the occurrence of intense Pc5 pulsations in the magnetosphere. This comparison confirmed earlier results showing the importance of magnetospheric ULF turbulence in energizing relativistic electrons. In addition to relativistic electron energization, a wide range of space physics and geophysics studies will benefit from the introduction of the ULF wave index. The ULF index database is freely available via anonymous FTP for all interested researchers for further validation and statistical studies. 相似文献
4.
A thermal regime of the troposphere of Venus is mainly determined by the greenhouse effect. A closeness of the real temperature gradient to the adiabatic one indicates that turbulent heat fluxes are also essential. Additional problems arise as only about 11% of the solar radiation absorbed by the planet reaches the surface, and most of it is taken up in the clouds at altitudes of 60–70 km. The present study summarizes experimental data on atmospheric parameters related to turbulence and estimates turbulent fluxes and turbulence characteristics. These data confirm the author's hypothesis of an anomalous downward turbulent heat flux in the free atmosphere. A normal upward turbulent heat flux exists in the planetary boundary layer. 相似文献
5.
We present a new experimental platform for studies of turbulence and turbulent mixing in accelerating and rotating fluids.
The technology is based on the ultra-high performance optical holographic digital data storage. The state-of-the-art electro-mechanical,
electronic, and laser components allow for realization of turbulent flows with high Reynolds number (>107) in a relatively small form-factor, and quantification of their properties with extremely high spatio-temporal resolutions
and high data acquisition rates. The technology can be applied for investigation of a large variety of hydrodynamic problems
including the fundamental properties of non-Kolmogorov turbulence and turbulent mixing in accelerating, rotating and multiphase
flows, magneto-hydrodynamics, and laboratory astrophysics. Unique experimental and metrological capabilities enable the studies
of spatial and temporal properties of the transports of momentum, angular momentum, and energy and the identification of scalings,
invariants, and statistical properties of these complex turbulent flows. 相似文献
6.
A. Lazarian 《Astrophysics and Space Science》1994,216(1-2):207-212
The properties of the ISM indicate that it is turbulent. However, the ISM turbulence is radically different from that in incompressible fluids. That is why it is so important to study it through observations. The relevant study still poses a challenging problem. In the present paper recent results based on a statistical approach to the problem are surveyed. Although it was pointed out long ago (see Kaplanet al., 1970) that random 3D motions of the ISM gas result in fluctuations of the observed electromagnetic emission, it is only recently that the problem of recovering statistical properties of the ISM turbulence from the line integrated data was given an adequate mathematical treatment. Here by the example of studying turbulence in HI, it is shown that the inverse problem can be solved uniquely using a realistic model of the ISM. The application of theoretical conclusions to existing data explains some facts which used to be considered inconsistent with turbulent behaviour and reveals unexpected features of the ISM turbulence. 相似文献
7.
A theory is presented for the dynamics of dust particles in an incompressible turbulent fluid. Grain-gas coupling occurs through friction forces that are proportional to the mean grain velocity relative to the gas. This test particle theory is applied to the case of a Kolmogoroff spectrum in a protostellar cloud. The mean turbulence induced grain velocity and the mean turbulent relative velocity of two grains are calculated. Whereas the former should determine the dust scale height, grain-grain collisions are influenced by the latter. For a resonable strength of the turbulence, the mean induced relative velocity of two particles turns out to be at least as large as the corresponding terminal velocity difference during gravitational settling.Paper presented at the Conference on Protostars and Planets, held at the Planetary Science Institute, University of Arizona, Tucson, Arizona, between January 3 and 7, 1978. 相似文献
8.
Collisionless shocks in turbulent space plasmas accelerate particles by the Fermi mechanism to ultrarelativistic energies. The interaction of accelerated particles with the plasma inflow produces extended supersonic MHD flows of multicomponent plasma. We investigate the instabilities of a flow of three-component turbulent plasma with relativistic particles against long-wavelength perturbations with scales larger than the accelerated particle transport mean free path and the initial turbulence scales. The presence of turbulence allows us to formulate the system of single-fluid equations, the equation of motion for the medium as a whole, and the induction equation for the magnetic field with turbulent magnetic and kinematic viscosities. The current of accelerated particles enters into the induction equation with an effective magnetic diffusion coefficient. We have calculated the local growth rates of the perturbations related to the nonresonant long-wavelength instability of the current of accelerated particles for MHD perturbations in the WKB approximation. The amplification of long-wavelength magnetic field perturbations in the flow upstream of the shock front can affect significantly the maximum energies of the particles accelerated by a collisionless shock and can lead to the observed peculiarities of the synchrotron X-ray radiation in supernova remnants. 相似文献
9.
In a previous work by two of us, the main difficulties of the theory of galaxy formation from universal primordial cosmic turbulence were focussed; it was mainly found that the decay of the turbulence was so strong during the plasma era that turbulence should have been almost completely washed out before recombination, unless, and only for low-density universes, unlikely large turbulent velocities were postulated at the largest scale of the turbulence at the end of the radiation era. It was suggested that a possibility to turn around such a difficulty should consist in finding en adequate physical energy source feeding the turbulence during at least the whole plasma phase. The present work is intended to test whether matter-antimatter annihilation theory at the origin of the universe, as it is developed by Omnès and his collaborators, may be considered to yield the required energy source of the turbulence. To this aim, the main results of the work of Stecker and Puget concerning the behaviour of the most important quantities of the matter- antimatter annihilation theory are used, in order to describe the properties of the energy source for the turbulence down to recombination time, and extended to take a somewhat more detailed account of theirz and mean matter density dependences. The energy feeding source thus obtained is then introduced into the general framework of the galaxy formation theory from cosmic turbulence taking account of energy dissipation as developed in our previous works. The results obtained concerning the comparison of the main parameters of galaxies derived from the theory with the experimental data are much more satisfactory than in the previous approach, and show that, inside the errors of the present day values, sufficiently good fits are possible in a range of mean universe densities between 0.4 to 1 times the critical density. 相似文献
10.
A. V. Kolesnichenko 《Solar System Research》2011,45(3):246-263
The problem of the influence of vortex helicity on the synergic structuring of cosmic matter in it, as well as the appearance
of the effect of negative viscosity in three-dimensional gyrotropic turbulence, were studied in the framework of the fundamental
problem of simulating the evolution of a rotating astrophysical nonmagnetic disk—in particular, the accretion disk—surrounding
the Sun at the early stage of its existence. The evolution equations for averaged vorticity and vortex helicity, as well as
rheological relations for the turbulent flow of heat and asymmetrical tensor of the turbulent stress in helical turbulence,
were obtained. The demonstrative dependence of helicity on the rotation velocity, density (temperature) gradients, and turbulent
energy of the disk gas was established. The role of helicity in the appearance of the inverse Richardson-Kolmogorov energy
cascade from small vortices to larger ones and the related process of the generation of the power-consuming macroscale coherent
vortex formations appearing in gyrotropic turbulence at high Reynolds number were discussed. The results of the numerical
experiments confirming the real existence of the inverse energy cascade in helical turbulence were analyzed. It was assumed
that the relatively long-term decay of turbulence in the solar protoplanet cloud can be due to the absence of the reflective
symmetry of the anisotropic field of the turbulent velocities with respect to its equatorial plane. As the concept of the
inverse energy cascade in three-dimensional helical turbulence is more and more reliably confirmed in numerical experiments,
accounting for this effect affecting the structure and dynamics of the astrophysical nonmagnetic disk becomes important during
its simulation. 相似文献
11.
We report on an application of gas-kinetic BGK scheme to the computation of turbulent compressible convection in the stellar interior. After incorporating the Sub-grid Scale (SGS) turbulence model into the BGK scheme, we tested the effects of numerical parameters on the quantitative relationships among the thermodynamic variables, their fluctuations and correlations in a very deep, initially gravity-stratified stellar atmosphere. Comparison indicates that the thermal properties and dynamic properties are dominated by different aspects of numerical models separately. An adjustable Deardorff constant in the SGS model cμ = 0.25 and an amplitude of artificial viscosity in the gas-kinetic BGK scheme C2 = 0 are appropriate for the current study. We also calculated the density-weighted auto-and cross-correlation functions in Xiong's turbulent stellar convection theory based on which the gradient type of models of the non-local transport and the anisotropy of the turbulence were preliminarily studied. No universal relations or con-stant parameters were found for these models. 相似文献
12.
V.I. Shishov 《Astrophysics and Space Science》2001,278(1-2):163-169
Data on interstellar diffraction and refraction scintillation of pulsars are analyzed. Comparison between theory and the observational
data shows that two types of spectra for electron density fluctuations are realized in the interstellar medium: pure power
law and piecewise with a break. The distribution of turbulent plasma in the Galaxy has a three component structure. Component
A is diffuse and it is distributed outside of the spiral arms of the Galaxy. Component BI is cloudy and associated with Galactic
arms. Component BII is extremely nonuniform and associated with HII regions and supernova remnants. The origin of the interstellar
plasma turbulence is considered, and possible sources of turbulent energy are discussed. The contribution of supernova bursts
in the interstellar gas ionization and generation of turbulence are analyzed among other factors.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
Homogeneous anisotropic turbulence simulations are used to determine off-diagonal components of the Reynolds stress tensor and its parameterization in terms of turbulent viscosity and Λ-effect. The turbulence is forced in an anisotropic fashion by enhancing the strength of the forcing in the vertical direction. The Coriolis force is included with a rotation axis inclined relative to the vertical direction. The system studied here is significantly simpler than that of turbulent stratified convection which has often been used to study Reynolds stresses. Certain puzzling features of the results for convection, such as sign changes or highly concentrated latitude distributions, are not present in the simpler system considered here. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
14.
This paper deals with the conception that two-dimensional turbulence is present in a sunspot where the magnetic field is strong. This conception is based upon the incapacity of even a strong magnetic field to influence an arbitrary two-dimensional turbulence, if the magnetic field is parallel to a constant direction and the motion occurs in planes orthogonal to it. It is, moreover, shown that such a two-dimensional turbulence provides for a turbulent decay of the magnetic field. The decay rate possesses nearly the same dependence on the scales as for three-dimensional turbulence. Finally, the turbulent decay is studied by investigating a simple model and comparing the results with those deduced by Bumba from the observed decay of sunspot groups areas. By means of our conception even a good quantitative agreement is stated. 相似文献
15.
A. V. Kolesnichenko 《Solar System Research》2008,42(5):391-404
A stochastic-thermodynamic approach to the derivation of the generalized fractional Fokker—Planck—Kolmogorov (FFPK) equations
is considered. The equations describe turbulent transfer processes in a subsystem of turbulent chaos on the basis of fractional
dynamics, which takes into account the structure and metric of fractal time. The actual turbulent motion of a fluid is known
to be intermittent, since it demonstrates the properties that are intermediate between the properties of regular and chaotic
motions. On the other hand, the process of the flow turbulization may be non-Markovian because of the multidimensional spatiotemporal
correlations of pulsating parameters; in a physical language, this means that the process has a memory. The introduction of
fractional time derivatives into the FFPK kinetic equations, used to find the probability distribution functions for different
statistical characteristics of structured turbulence, makes it possible to use an unified mathematical formalism in considering
the effects of memory, nonlocality, and time intermittence, with which we usually associate the presence of turbulent bursts
against the background of less intense low-frequency oscillations in the background turbulence. This study is aimed at creating
representative models of space and natural media. It is a development of the synergetic approach to the modeling of structured
turbulence in astrogeophysical systems, which has been developed by the author in a series of papers (Kolesnichenko, 2002–2005). 相似文献
16.
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
17.
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
18.
Dastgeer Shaikh 《Monthly notices of the Royal Astronomical Society》2009,395(4):2292-2298
Non-linear, three-dimensional, time-dependent fluid simulations of whistler wave turbulence are performed to investigate role of whistler waves in solar wind plasma turbulence in which characteristic turbulent fluctuations are characterized typically by the frequency and length-scales that are, respectively, bigger than ion gyrofrequency and smaller than ion gyroradius. The electron inertial length is an intrinsic length-scale in whistler wave turbulence that distinguishably divides the high-frequency solar wind turbulent spectra into scales smaller and bigger than the electron inertial length. Our simulations find that the dispersive whistler modes evolve entirely differently in the two regimes. While the dispersive whistler wave effects are stronger in the large-scale regime, they do not influence the spectral cascades which are describable by a Kolmogorov-like k −7/3 spectrum. By contrast, the small-scale turbulent fluctuations exhibit a Navier–Stokes-like evolution where characteristic turbulent eddies exhibit a typical k −5/3 hydrodynamic turbulent spectrum. By virtue of equipartition between the wave velocity and magnetic fields, we quantify the role of whistler waves in the solar wind plasma fluctuations. 相似文献
19.
C. Hidalgo 《Astrophysics and Space Science》2004,292(1-4):681-690
A view of the mechanisms underlying particle and energy transport in fusion plasmas devices (tokamak and stellarators) is given. The heat and energy transport in fusion plasmas is generally due to turbulent processes. Several driving (plasma gradients) and damping (electric field) mechanisms of turbulence have been investigated. The development of methods to modify and control plasma turbulence by electric field effects has opened a new era on fusion confinement research. Recently, a new approach based on multi-field probability density function statistical analysis has been proposed to describe transport in non-equilibrium systems and to unravel the overall picture connecting transport, gradients and flows in fusion plasmas. 相似文献
20.
The physical processes responsible for transient cosmic-ray decreases have been investigated for two types of interplanetary shock events associated with helium enhancement (He-shocks) and those not associated with helium enhancement (non-He-shocks). The Calgary cosmic-ray neutron monitor data and the interplanetary field data have been subjected to a superposed-epoch Chree analysis. The difference in the profiles of the cosmic-ray intensity have been compared with the interplanetary field data and its variance. It is suggested that the turbulence sheath following the shock front is very effective and of major importance for producing cosmic-ray decreases. A simple model has been proposed to explain the observations which show that a Forbush decrease modulating region consists of a shock front associated with a plasma sheath in which the magnetic field is turbulent and the sheath, in turn, is followed by an ejected plasma cloud having ordered structure and high magnetic field strength. 相似文献