共查询到20条相似文献，搜索用时 15 毫秒
1.
Marian Karlický 《Solar physics》1993,145(1):137-150
Using a 1-D hybrid model of the electron beam bombardment in a flare loop, it is demonstrated that beam electrons, back-scattered in dense layers of the solar atmosphere, are accelerated in the return-current electric field. This effect is shown in two regimes of the electron beam bombardment: (a) with a monoenergetic quasi-steady beam, and (b) with a sequence of 4 pulse beams. It is suggested that the mirroring of electrons at loop magnetic mirrors can amplify this process. The role of such acceleration for the formation of a collisionless return-current, and thus for a decrease of return-current losses, is discussed. 相似文献
2.
Electron beams accelerated during solar flares carry electric currents which should be neutralized by so-called return currents.
Both the electron beam and return current modify the electron distribution function in the solar transition region and low
corona. Thus, they influence the intensities of the spectral lines formed in these layers. Synthetic spectra for the solar
flare atmosphere are computed from model conditions and the possibilities of diagnostics of the return current from the EUV
and X-ray line spectra are discussed. 相似文献
3.
As one of the most violent activities in the solar atmosphere,white-light flares(WLFs)are generally known for their enhanced white-light(or continuum)emission,which primarily originates in the solar lower atmosphere.However,we know little about how white-light emission is produced.In this study,we aim to investigate the response of the continua at 3600?and 4250?and also the Hαand Lyαlines during WLFs modeled using radiative hydrodynamic simulations.We take non-thermal electron beams as the energy source for the WLFs in two different initial atmospheres and vary their parameters.Our results show that the model with non-thermal electron beam heating clearly shows enhancements in the continua at 3600?and 4250?as well as in the Hαand Lyαlines.A larger electron beam flux,a smaller spectral index,or an initial penumbral atmosphere leads to a stronger emission increase at 3600?,4250?and in the Hαline.The Lyαline,however,is more obviously enhanced in a quiet-Sun initial atmosphere with a larger electron beam spectral index.It is also notable that the continua at 3600?and 4250?and the Hαline exhibit a dimming at the start of heating and reach their peak emissions after the peak time of the heating function,while the Lyαline does not show such behaviors.These results can serve as a reference for the analysis of future WLF observations. 相似文献
4.
An estimate is derived of the solar gravitational torque on the thermal atmospheric tide of Venus. The value obtained is compared with the computed torque on the body of the planet itself caused by viscous coupling between it and the superrotating atmosphere. The comparison suggests that the solar thermal torque and the viscous torque are effective in the maintenance of the four-day superrotation of the Venusian atmosphere.UMIST, Department of Physics 相似文献
5.
Radiation is believed to be hostile to the generation of gravity waves by granulation at the base of photosphere where the radiation is effective. A convective overshoot from subphotosphere seems able to penetrate to a height where the solar temperature is minimum and to excite the gravity waves in a stable region there.The response of the solar atmosphere to a Gaussian disturbance characterizing such a convective overshoot is studied in an unbounded isothermal atmosphere. Radiative effects are included, but only in regions which are optically thin. The response is measured in terms of mean vertical kinetic energy density (E
z) and mean vertical external energy flux (Q
z).
E
z and Q
z were calculated for a wide range of frequencies centered at the observed 5-min velocity oscillation period. The computed sharp and broad power spectra at the lower chromosphere and the upper photosphere, respectively, are attributed to the combined effects of space damping and source function. Low-frequency waves (2000 s or longer) are found to be not responsible for depositing energy in the upper solar atmosphere.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
6.
There are two parts to this paper. In the first we calculate the hydrodynamic response of the solar atmosphere to the injection of an intense beam of electrons in a numerical simulation of a solar flare. In the second we predict the spectroscopic consequences of the hydrodynamic behaviour calculated in the first part. The hydrodynamics is predicted by solving the equations of conservation of mass, momentum, and energy. The latter is expressed as two temperature equations; one for the electrons and the other for the neutral atoms and positive ions of hydrogen. The equations are solved in one dimension and the geometric form is of a semi-circular loop having its ends in the photosphere. The results show how the loop is filled at supersonic speed with plasma at temperatures characteristic of flares. At the same time a compression wave is predicted to propagate down towards the photosphere. After the heating pulse stops, the plasma that has risen into the loop, starts to decay and return to the condition it was in before the pulse started. In predicting the spectrum that would be emitted by such a plasma calcium was chosen for illustration. The first and main part of this calculation was setting up and solving the time-dependent equations of ionization/recombination. In order to provide a standard for comparison the same ionization and recombination rate coefficients are used to predict the steady-state distribution of populations of ionization stages. This is then compared with the distribution found from the time-dependent solution and shows that there is a negligibly small time lag predicted by the time-dependent result. However the more significant comparisons to make are between the temperatures of the peak abundances of the various ions under the assumptions of steady-state and time-dependent ionization. For the particular circumstances chosen here the temperature differences are predicted to be in the neighbourhood of 10% or less and in view of the overall accuracy of the atomic data are not significant. It would appear therefore that the much simpler assumption of steady-state ionization balance leads to results of acceptable accuracy for the particular case considered. 相似文献
7.
Peter W. Blum 《Planetary and Space Science》1968,16(12):1427-1440
Since 1958 it is known that there exists a response time of the upper atmosphere to changes in solar activity. This response time is best described as the lag between the 27-day variation of solar decimeter flux and the observed density changes of the upper atmosphere. Roemer obtained as a mean observational value for this lag 1.0 ± 0.12 days. Volland's simplified version of the Harris-Priester model of the upper atmosphere is used to calculate the delay which can be expected from theory. Only the effect of solar EUV radiation is taken into account. A possible influence of the corpuscular component of the solar radiation is not included in our estimate.
The calculations are carried out for the Harris-Priester model with solar activity index and a variation of . The resulting delay is 0.6 days. The calculated amplitude of the variations of the diurnal average temperatures during the solar 27-days cycle is in very good agreement with Jacchia's empirical formula. 相似文献
8.
The propagation and dissipation of acoustic waves in the lower solar atmosphere is studied. The level of shock formation is computed for various initial conditions. It is shown that shocks form rather low in the atmosphere and that this result does not depend critically on the assumed initial conditions. 相似文献
9.
V. V. Zharkova 《Solar physics》2008,251(1-2):641-663
In this paper the mechanisms responsible for observational features associated with sunquakes induced by different classes of solar flares are compared. The role of high-energy particle beams via Coulomb and Ohmic heating of the ambient plasma and nonthermal excitation and ionization is explored for different beam parameters at various atmospheric depths. On the one hand, only hard electron beams with high-energy fluxes are found producing extensive nonthermal hydrogen ionization, four orders of magnitude higher than in the quiet atmosphere. This excess ionization leads to the white-light flares associated with the seismic emission appearing simultaneously with hard X-ray emission and, consequently, to a strong increase of Ni-line emission observed as the seismic emission measured with the holographic technique. On the other hand, the ambient plasma hydrodynamic response to heating by such beam electrons forms hydrodynamic shocks just below the transition region, in the upper chromosphere, and they travel with supersonic velocity for up to five minutes before reaching the photosphere. These hydrodynamic responses caused by the beam electrons are maximized in the lower chromosphere for moderate electron beams because of their smaller Ohmic losses in the upper atmosphere compared to those for higher-energy electron beams whose bulk energy is deposited in the transition region. These shocks caused by electron beams can explain the observations of seismic emission by time?–?distance (TD) diagrams and the holographic method in M- and C-class flares, whereas to account for the quakes in X-class flares, high-energy quasi-thermal protons or power-law proton beams either by themselves or blended with electron beams are the most likely agents. Nonthermal ionization and excitation of lower atmospheric levels during the beam injection followed by thermo-conductive heating after the beam is stopped can contribute to the seismic signatures observed with the holographic technique caused by strong nonthermal ionization and back-warming heating occurring in the shock while it loses its energy by optically-thick radiation in the photospheric lines and continua. 相似文献
10.
In order to benchmark the three-dimensional calculation of the atmospheric neutrino flux based on the FLUKA Monte Carlo code, muon fluxes in the atmosphere have been computed and compared with data taken by the CAPRICE94 experiment at ground level and at different altitudes in the atmosphere. For this purpose only two additions have been introduced with respect to the neutrino flux calculation: the specific solar modulation corresponding to the period of data taking and the bending of charged particles in the atmosphere. Results are in good agreement with experimental data, although improvements in the model are possible. At this level, however, it is not possible to disentangle the interplay between the primary flux and the interaction model. 相似文献
11.
R. Mäckle 《Solar physics》1969,10(2):348-356
MHD equations including dissipation terms are applied to study the most important irreversible processes occurring in fast hydromagnetic shock waves under the conditions of the outer solar atmosphere. The atmosphere is assumed to be permeated by a nearly horizontal, uniform magnetic field, the magnitude and inclination angle of which being parameters of the analysis. Numerical examples, corresponding to situations which might occur in the upper chromosphere, are computed in order to demonstrate the procedure. 相似文献
12.
动力学阿尔文波是垂直波长接近离子回旋半径或者电子惯性长度的色散阿尔文波.由于波的尺度接近粒子的动力学尺度,动力学阿尔文波在太阳和空间等离子体加热、加速等能化现象中起重要作用.因此,动力学阿尔文波通常被认为是日冕加热的候选者.本研究工作深入、系统地调研了太阳大气中动力学阿尔文波的激发和耗散机制.基于日冕等离子体环境,介绍了几种常见的动力学阿尔文波激发机制:温度各向异性不稳定性、场向电流不稳定性、电子束流不稳定性、密度非均匀不稳定性以及共振模式转换.还介绍了太阳大气中动力学阿尔文波的耗散机制,并讨论了这些耗散机制对黑子加热、冕环加热以及冕羽加热的影响.不仅为认识太阳大气中动力学阿尔文波的驱动机制、动力学演化特征以及波粒相互作用提供合理的理论依据,而且有助于揭示日冕等离子体中能量储存和释放、粒子加热等能化现象的微观物理机制. 相似文献
13.
In this paper we compute the rate of solar EUV heating in the upper atmosphere by photo-dissociation and photo-ionization, taking care to include properly the effects of oblique incidence of solar flux, sphericity of the atmosphere and ellipticity of the Earth's orbit. The time and latitudinal variations of the computed heat function are revealed by numerical Fourier analysis of the heat function into harmonics of the yearly cycle. It is shown that EUV absorption contains a ‘latitude independent’ semi-annual component of heating with the ‘proper phase’ to account for the semi-annual density variations. Further, the annual component of the heat function predicts the existence of ‘summer polar’ density increases in the northern and southern hemispheres. 相似文献
14.
In the last decade, the photospheric solar metallicity as determined from spectroscopy experienced a remarkable downward revision.
Part of this effect can be attributed to an improvement of atomic data and the inclusion of NLTE computations, but also the
use of hydrodynamical model atmospheres seemed to play a role. This “decrease” with time of the metallicity of the solar photosphere
increased the disagreement with the results from helioseismology. With a CO
5
BOLD 3D model of the solar atmosphere, the CIFIST team at the Paris Observatory re-determined the photospheric solar abundances
of several elements, among them C, N, and O. The spectroscopic abundances are obtained by fitting the equivalent width and/or
the profile of observed spectral lines with synthetic spectra computed from the 3D model atmosphere. We conclude that the
effects of granular fluctuations depend on the characteristics of the individual lines, but are found to be relevant only
in a few particular cases. 3D effects are not responsible for the systematic lowering of the solar abundances in recent years.
The solar metallicity resulting from this analysis is Z=0.0153, Z/X=0.0209. 相似文献
15.
We investigate the excitation of magnetoacoustic–gravity waves generated from localized pulses in the gas pressure as well as in the vertical component of velocity. These pulses are initially launched at the top of the solar photosphere, which is permeated by a weak magnetic field. We investigate three different configurations of the background magnetic field lines: horizontal, vertical, and oblique to the gravitational force. We numerically model magnetoacoustic–gravity waves by implementing a realistic (VAL-C) model of the solar temperature. We solve the two-dimensional ideal magnetohydrodynamic equations numerically with the use of the FLASH code to simulate the dynamics of the lower solar atmosphere. The initial pulses result in shocks at higher altitudes. Our numerical simulations reveal that a small-amplitude initial pulse can produce magnetoacoustic–gravity waves, which are later reflected from the transition region due to the large-temperature gradient. The cavities in the lower solar atmosphere are found to have the best conditions to act as a resonator for various oscillations, including their trapping and leakage into the higher atmosphere. Our numerical simulations successfully model the excitation of such wave modes, their reflection and trapping, as well as the associated plasma dynamics. 相似文献
16.
New results of the numerical modeling of the response of the outer atmosphere of the Sun to an impulsive heating are presented.
Features of the general process are considered both for powerful and weak solar flares. For the most powerful flares it is
necessary to take into account the effect of a saturation of the heat flow. Though for the most powerful solar flares the
saturation of a thermal flow is not such large, the influence of this effect is important for cases of powerful flares on
red dwarf stars, strongly limiting the input of the thermal energy downwards. The response of the atmosphere, which consists
of the chromosphere, the transition region and the corona, to weak heating is characterized by creation no one as usually
but two ascending coronal flows. The occurrence of the additional flow at coronal heights is caused by the inhomogeneous initial
heating of the outer atmosphere. Some types of soft X-ray and UV-jets can be associated with such additional flow.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
我们认为存在于太阳高层大气中的一种稳定的物质交换,可以起到冷却日冕和加热色球一日冕过渡区的热机作用。还考虑到来自日冕的热传导和过渡区的辐射损失,计算了太阳过渡区的温度、密度和速度分布。并对物质流通量及速度边值与太阳过渡区厚度之间的关系作了讨论。 相似文献
18.
Onkar Nath 《Astrophysics and Space Science》1989,158(2):183-187
Equations are developed to describe the flow of a rotating atmosphere under force of gravitation heated by an arbitrary distribution of cylindrical shock waves. Solutions are obtained for the outer solar atmosphere with a steady mass motion in which the heat supplied by shock wave is balanced by the convective heat loss due to this motion. It is found that, for very large range of shock strength and frequencies, the temperature profile is similar to that predicted by the constant shock-strength hypothesis. This hypothesis is used as the basis of a model of the outer solar atmosphere starting near the solar atmosphere. 相似文献
19.
Main features of high-frequency wave disturbances (periods ≤5 min), generated by the solar terminator passing through the
Earth atmosphere in a speed-resonance mode, are theoretically investigated. With the troposphere model, formulated in this
paper, and the solar terminator, considered as a wave source, the wave spectral density parameters have been computed. Both
the terminator local speed, relating to the background, and the space-time lag of atmospheric heating are shown to essentially
influence these features. Some possible methods for identification of high-frequency speed-resonant atmospheric waves are
also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
Kunitomo Sakurai 《Astrophysics and Space Science》1974,28(2):375-519
This paper discusses solar cosmic ray phenomena and related topics from the solar physical point of view. Basic physics of the solar atmosphere and solar flare phenomena are, therefore, considered in some detail. Since solar cosmic rays are usually produced by solar flares, we must first understand the processes and mechanism of solar flares, especially the so-called proton flares, in order to understand the acceleration mechanism of solar cosmic rays and their behaviour in both the solar atmosphere and interplanetary space. For this reason, detailed discussion is given on various phenomena associated with solar flares, proton flare characteristics, and the mechanism of solar flares.Since the discovery of solar cosmic rays by Forbush, the interplanetary space has been thought of as medium in which solar cosmic rays propagate. In this paper, the propagation of solar cosmic rays in this space is, therefore, discussed briefly by referring to the observed magnetic properties of this space. Finally, some problems related to the physics of galactic cosmic rays are discussed.Astrophysics and Space Science Review Paper. 相似文献