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1.
In the quasilinear theory of magnetospheric radial diffusion caused by fluctuating electrostatic (E) or magnetic (B) fields, the diffusion coefficientD LLis proportional to the spectral density of E or B at the particle drift frequency 3/2. Since 3 varies withL at fixedM andJ (adiabatic invariants), the drift resonance =3 can be maintained only transiently, and therefore is not perfectly sharp. Its bandwidth * is approximately (16D LL /L 23)1/33. In magnetospheric radial diffusion caused mainly by electrostatic fluctuations, the value of *3 typically exceeds 0.4 for particle energiesE40 keV. However, the numerical value ofD LLis correctly given (within 1% in all cases) by quasilinear theory because the spectrum of E is rather flat at resonance frequencies for which the bandwidth is an appreciable fraction of 3. (Numerical conclusions are based on a quasilinear model forD LLused successfully by Cornwall in 1972.)  相似文献   

2.
A model is presented for the generation and evolution of bump-in-tail driven Langmuir waves in the solar wind during type III emission, which removes a number of apparent inconsistencies between theory and observations. It is argued that there must be localized enhancements of f b /v by a factor of 102 over the measured average values. Growth rates and energy densities of Langmuir waves are, therefore, considerably enhanced, permitting growth to overcome linear scattering losses, and also allowing nonlinear decay into ion-acoustic waves, in line with observations. Estimates are made of the probability distribution p(E), of wave field strengths E, based on linear and nonlinear wave-packet evolution, yielding p(E) E –a, 3. This helps explain why very high values of E are rarely found in the measured spiky wave turbulence.  相似文献   

3.
The problem to compute the magnetic field above the chromosphere using data of the vector = B t/Bt that gives the projected field direction can be solved with different approximations. The field of direction vectors is, however, not the only field accessible to observations. The Stokes parameters, which are components of the radiation tensor, can be measured at each point of the image plane. The directions of the eigenvectors of the radiation tensor define two mutually orthogonal systems of integral curves in the image plane. These families of curves have singular points, which are generally of different type than those of the vector field. When the morphology of H chromospheric fibrils are used to infer the topology of the magnetic field, a similar problem is met, suggesting that singular points should also be present there.  相似文献   

4.
The evolution of the current sheet in the electric current direction (in the guiding magnetic field direction) is studied numerically in the 3-D particle-in-cell model with two current sheets and periodic boundary conditions. In the regime with (where v D and are the electric current drift and electron thermal velocities, respectively) the current sheets are unstable owing to the Buneman and kink instabilities and become strongly fragmented. During their evolution, in addition to an increase of the energy of the electric field component in the guiding magnetic field direction, the energies of the electric field components in the perpendicular direction are even more enhanced. In the current sheet the anomalous resistivity (η anom/η C∼7×105, where η C is the classical resistivity) is generated and thus the magnetic field dissipates. Most of the dissipated magnetic energy is transformed into the electron kinetic energy in the direction of the electric current. The associated electric field accelerates the electrons from the tail of the distribution function.  相似文献   

5.
Energy accumulation in a current sheet (CS) can occur during the injection of a fast plasma jet in a perpendicular magnetic field. A similar situation can occur in the solar corona when a flux of plasma appears under a magnetic arch. The flare can be produced at the CS disruption. The CS creation during plasma jet interaction with the magnetic field is demonstrated by numerical MHD simulation. The choice of dimensionless parameters Re, Rem,, II, which are suitable for simulation of coronal phenomena, is discussed. When jet injection ceases, the CS evolution produces an unstable state and fast magnetic energy dissipation is observed.  相似文献   

6.
The time evolution of the velocity dispersion as a function of radius, called v-profiles, of threeN-body simulations of Wielen are presented in units ofr/R G (whereR G is the gravitational or virial radius) and discussed as a function of mass sample. The evolution of the radial and tangential components of the velocity dispersion is discussed, and each v-profile is fitted to a simple power law in the halo (0.15r/R G2.0). Several structural features appear at late time intervals: (a) an upturn in the radial component of v which occurs in a decreasing shell (closer to the core) in time, (b) the v-profile of the massive particles mimics that of the total sample, since equipartition of kinetic energy does not obtain, and (c) a local minimum atr0.3–0.5R G appears in one model which coincides with the local minimum in the number density profiles and possibly with feature (a).The line-of-sight v-profile, called LS-profile, of each model as a function of time and mass sample are also presented and discussed. They contain the same structural features as the v-profiles. Projection factors at small radii are also discussed. The LS-profiles of the models can be compared with the observed velocity dispersion profiles of clusters of galaxies in Struble (1979a).  相似文献   

7.
Digitized Mount Wilson sunspot data from 1917 to 1985 are analyzed to examine meridional motion and rotation properties as a function of latitude and distance () from the average latitude of activity (0) in each hemisphere. Latitude dependence similar to previous results is found, but only for spot groups whose areas are decreasing from one day to the next. A previous study of active region magnetic fields, using this technique of motions as a function of the average latitude of activity, had shown meridional motions on average toward 0. In this analysis of spot data some evidence is seen for motion away from 0, with some slight evidence for faster rotation equatorward of 0 and slower motion poleward of 0, similar to the torsional oscillation phenomenon. For reasons that are not clear, both of these effects are significantly more pronounced for sunspot groups whose areas are decreasing.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation.  相似文献   

8.
The structure and dynamics of neutral sheets in the solar wind is examined. The internal magnetic topology of the sheet is argued to be that of thin magnetic tongues greatly distended outward by the expansion inside the sheet. Due to finite conductivity effects, outward flow takes place across field lines but is retarded relative to the ambient solar wind by the reverse J×B force. The sheet thickness as well as the internal transverse magnetic field are found to be proportional to the electrical conductivity to the inverse one third power. Estimating a conductivity appropriate for a current carried largely by the ions perpendicular to the magnetic field, we find sheet dimensions of the order of 500km representative for the inner solar corona. For a radial field of strength 1/2G at 2R , the transverse field there is about 2 × 10–3G and decreases outward rapidly.The energy release in the form of Joulean dissipation inside the sheet is estimated. It is concluded that ohmic heating in current sheets is not a significant source of energy for the overall solar wind expansion, mainly because these structures occupy only a small percentage of the total coronal volume. However, the local energy release through this mechanism is found to be large - in fact, over 7 times that expected to be supplied by thermal conduction. Therefore, ohmic heating is probably a dominant energy source for the dynamical conditions within the sheet itself.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

9.
For the QSO 3C 273 we derive, on the basis of two different theoretical models, expressions for a lower limit to the mass of the QSO, as a function of its distance. We conclude that an appreciable gravitational redshift component is consistent with the observational data only if the QSO mass is at least Galactic in magnitude. The setting of an independent upper limit to the QSO massM1010 M could indicate that the QSO redshift is predominantly cosmological in nature.  相似文献   

10.
The Second Byurakan Survey (SBS) is a well known combined survey, which uses the presence of UV-excess radiation in the continuum, or the presence of emission-lines in the spectra for the identification of active and star-forming galaxies. This paper reports on a comparative study of 77 galaxies identified with UV-excess, and 34 galaxies identified via emission-line techniques in the fields of the SBS. The spectroscopic parameters used for the comparison are the [OII]3727/H and [OIII]5007/H emission-lines ratios, the equivalent widths of [OII]3727, [OIII]5007 and H emission-lines, and the C [OII]-C H index. Spectroscopic parameters as well as new redshifts were determined from the spectra obtained with the 6m telescope of the Special Astrophysical Observatory (Russia). The main results are: 1) Galaxies discovered via UV-excess technique are preferably more active. 2) Galaxies discovered via emission-line technique are preferably high-excitation low-luminosity star-forming galaxies. 3) UV-excess galaxies with faintest UV-excess radiation are likely candidates to be LINER or Sy2 type objects.  相似文献   

11.
Magnetograms in lines originating high in the solar atmosphere show, away from disk center, diffuse fringes of reverse polarity on the limbward side and diffuse centerwards extensions of normal polarity wherever the field is strong. Analysis of a Mg b2 magnetogram reveals that, in active regions (and, hence, wherever the magnetic network is well developed) fields cover associated supergranules completely at heights mostly below 500–600 km (zero height is at 5000 = 1) but possibly up to 700–800 km at great distances (e.g. >104km) from the network. These lie much lower than previously believed, mostly around the solar average temperature minimum. Near plagettes, the low-lying field has been measured out to 6000–7000 km. One consequence is that in active regions and plagettes, the chromosphere-corona transition region probably penetrates below 600 km; another is that potential theory is inapplicable at coronal heights below about 15 000 km.A more accurate analysis requires a specific atmospheric model for magnetic regions. Attention is drawn to the need for studying the consequences for acoustic wave propagation, reflection and dissipation in regions of strong network fields.Visiting Astronomer, Kitt Peak National Observatory.Operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation.  相似文献   

12.
Nine Orbiter 3 high-resolution photographs were examined at three sites for distributions of boulders around craters 110 m in diameter; three kinds of distributions were noted. Some had boulders inside and far outside (designated), others had boulders only inside or on their ramparts (), and some had no detectable boulders (). Additionally, shapes or morphologies of craters were classified according to their resemblance to one of three Jaffe models (1965); a third classification involved the depth of particulate overlay (Jaffe, 1965). Crater morphologies were classified (A) if they were relatively shallow with sharp, raised rims, (B) if they were rimless and shallow, and (C) if they were relatively deep and had low, broad rims. The data suggested that there were strong relationships between crater types and boulder distributions in which, generally, A-type was related to the-distribution, B-type to-distribution, and C-type to-distribution. Plots of numbers of craters of each crater type and each kind of boulder distribution versus steps of overlay for each site and for the totality of craters considered indicated that neither boulder distribution nor crater type represented orderly progression of age or erosional evolution. The apparent overlays for the A's and C's and for the's and's were similar, implying similar ages or stages of erosion. It is suggested that they represent two kinds of primary craters and that the A's are of impact origin while the C's are of volcanic origin. The B's probably represent later stages of erosion of the C's and possibly of some A's.Now at the University of Maryland.Receipt delayed by postal strike in Great Britain.  相似文献   

13.
The interpretation of the observed-ray burstV/V max statistic in terms of spatial distributions is model-dependent. Detection of-ray bursts requires the counting rate in one or more detectors to exceed a thresholdC lim determined from a time-dependent background rateB(t). The sampling depth of the burst detector is thus time-dependent, and, if burst sources are non-uniform in space, the observedV/V max distribution will be affected byB(t). We demonstrate this effect with a simple geometric distribution of standard candles and argue thatV/V max statistic without information on threshold variations is insufficient for rigorous data analysis. Peak count rates and threshold values must be given separately for all events in order to facilitate a meaningful comparison of observations with theoretical distribution models.  相似文献   

14.
Photospheric motion shears or twists solar magnetic fields to increase magnetic energy in the corona, because this process may change a current-free state of a coronal field to force-free states which carry electric current. This paper analyzes both linear and nonlinear two-dimensional force-free magnetic field models and derives relations of magnetic energy buildup with photospheric velocity field. When realistic data of solar magnetic field (B 0 103 G) and photospheric velocity field (v max 1 km s–1) are used, it is found that 3–4 hours are needed to create an amount of free magnetic energy which is of the order of the current-free field energy. Furthermore, the paper studies situations in which finite magnetic diffusivities in photospheric plasma are introduced. The shearing motion increases coronal magnetic energy, while the photospheric diffusion reduces the energy. The variation of magnetic energy in the coronal region, then, depends on which process dominates.  相似文献   

15.
The decay of a longitudinal plasmon into two neutrinos is studied in the presence of a strong magnetic field. Contrary to the transverse case, for longitudinal plasmons the existence of a new mode, entirely dependent on the magnetic field, greatly enhances the energy loss at high densities. Denoting byQ HandQ 0the neutrino energy losses with and without magnetic field respectively, the situation is as follows: atH1011 G andT109K,Q 0105 Q Hfor <1011g cm–3, WhileQ H1010 Q 0for >1011g cm–3. A second physically interesting feature is the anisotropic character of the energy loss which is highly peaked along the field lines, giving rise to a shorter cooling time in that direction than in any other.  相似文献   

16.
In the deep interior of the giant planets Jupiter and Saturn, ordinary hydrogen and helium are transformed into a conducting metallic liquid at extremely high pressure. It is likely that the giant planets' observed magnetic field is constantly generated in the metallic fluid core by magnetohydrodynamic processes, converting mechanic energy in the form of convection into magnetic energy. The maximum strength of their magnetic fields is likely to be limited by magnetic field instabilities which convert the magnetic energy back into convection. The parameter which governs the occurrence of magnetic instabilities is the Elsasser number, = B 2/2, where B is the field strength, is the electrical conductivity, is the rotation rate and is the density. Since magnetic instability will be very active when exceeds a critical value c 10 (the precise value depending on the magnetic field distribution), this imposes an upper bound on the effective electrical conductivity of the metallic fluid which comprises the bulk of Jupiter's interior and much of Saturn's.Stability calculations including both toroidal (model) and poloidal (observed) components of the magnetic field in a rapidly rotating spherical shell, have been performed. The most stable configuration of the field is when the poloidal component of field is strong and the toroidal field is weak; in this case we obtain an upper bound for electrical conductivity of 3 × 106 S/m; while the most unstable configuration of the field is when the toroidal and poloidal fields are comparable, giving rise to m 3 × 105 S/m. The implications of the results for general dynamo theory are also discussed.  相似文献   

17.
Longcope  D. W.  Silva  A. V. R. 《Solar physics》1998,179(2):349-377
Observations of the flare on 7 January 1992 are interpreted using a topological model of the magnetic field. The model, developed here, applies a theory of three-dimensional reconnection to the inferred magnetic field configuration for 7 January. In the model field a new bipole ( 1021 Mx) emerges amidst pre-existing active region flux. This emergence gives rise to two current ribbons along the boundaries (separators) separating the distinct, new and old, flux systems. Sudden reconnection across these boundary curves transfers 3 ×1020 Mx of flux from the bipole into the surrounding flux. The model also predicts the simultaneous (sympathetic) flaring of the two current ribbons. This explains the complex two-loop structure noted in previous observations of this flare. We subject the model predictions to comparisons with observations of the flare. The locations of current ribbons in the model correspond closely with those of observed soft X-ray loops. In addition the footpoints and apexes of the ribbons correspond with observed sources of microwave and hard X-ray emission. The magnitude of energy stored by the current ribbons compares favorably to the inferred energy content of accelerated electrons in the flare.  相似文献   

18.
This paper deals with a rather general class of magnetoatmospheres — media for which the restoring forces of buoyancy, compressibility and magnetic tension/pressure are important in sustaining wave motion. The magnetic field has the general form (B 0(z), 0,0) and there is also an aligned shear flow (U 0(z), 0, 0) present. After discussion of the equilibrium and stability of such systems, and certain mathematical properties of a particular system (an isothermal atmosphere with uniform magnetic field, of interest in solar physics), theory is developed which enables expressions to be written down for the mechanical wave energy flux associated with wave motion due to a transient source. These analytic expressions are very general and contain contributions from the continuous and discrete frequency spectra, corresponding respectively to freely propagating and trapped (or surface) waves. These fluxes are evaluated for various ranges of magnetic field, horizontal wavenumber, characteristic source times and frequency, for a simple constant-parameter atmosphere. The source is taken to be a transient fluctuation of the lower boundary, (modelling convective overshoot) which is taken to be located at the level 5000=0.08 in the solar atmosphere. The relative distribution of wave energy flux in the various modes is discussed in the context of solar physics parameters. The possible significance of leaky modes arising from supergranular or other flow, for the local flux balance in the solar chromosphere is outlined.  相似文献   

19.
P. Foukal  S. Hinata 《Solar physics》1991,132(2):307-334
Macroscopic electric fields in the solar atmosphere have received much less attention than magnetic fields, although they must play a role of comparable importance in plasma heating, and in charged particle acceleration and transport. We review various remote sensing techniques that have been developed, whose sensitivity is now 5–10 V cm –1 for measurement of the electric field component transverse to the line-of-sight. Our review of the processes most likely to produce observable fields in the solar atmosphere indicates that quasi-static, macroscopic values of E (the electric field component parallel to the magnetic vector) well above this detection threshold are predicted by the discharge model of flares, by models of return currents associated with flare particle beams, and by models of neutral sheets associated with two-ribbon flares and post-flare loops. In addition, both E and E components may be detectable in time dependent electric fields associated with MHD and plasma waves, and with plasma turbulence. The emission measures and time-scales associated with these electrified plasma volumes are as highly uncertain as our present understanding of the volumes, plasma conditions and processes involved in the liberation of flare energy. Observations of electric field vector intensities, orientations, time-behaviour and spatial distribution at the presently attained electric field sensitivity levels could provide new, direct information of great interest in the electrodynamics of solar magnetic structures.  相似文献   

20.
Solar flares are frequently observed to occur where new magnetic flux is emerging and pressing up against strong active region magnetic fields. Since the solar plasma is highly conducting, current sheets develop at the boundary between the emergent and ambient flux, provided the two magnetic fields are inclined at a non-zero angle to one another.The present paper gives a simple two-dimensional model for the development of such sheets under the assumptions that no reconnection occurs and that the surrounding field remains a potential one. By using complex variable techniques, the position, orientation and shape of a current sheet may be determined, as well as the excess magnetic energy associated with it. Two examples are considered. The first, in which the ambient field is bipolar, may model new flux emergence near the edge of an active region, while the second example assumes a constant ambient field and may approximate the so-called fibril crossings which occur prior to some flares. In each case, the current sheets are curved, and the magnetic energy which is stored in excess of potential is sufficient to supply a solar flare when the sheets are long enough.  相似文献   

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