共查询到20条相似文献，搜索用时 328 毫秒
1.
J. Klačka 《Earth, Moon, and Planets》1994,64(1):95-98
The problem of the stability of the zodiacal cloud is scrutinized. The central idea of the paper sticks in the theoretical treatment of the action of the solar electromagnetic radiation on small interplanetary dust particles (IDPs). It is suggested that the virtual problem of the (in-)stability of the zodiacal cloud originated from the physically incorrect application of the Poynting-Robertson effect on IDPs. Real particles are not of spherical shape and so the braking acceleration is not proportional to -v/c. Depending on the shape (and other optical properties) of the particle, also spiralling outward from the Sun may occur. 相似文献
2.
Solar Physics - The ionization and excitation equilibrium of C and O for the electron κ-distribution in the solar corona is studied. The change of the distribution shape changes the... 相似文献
3.
The inverse scattering problem for reconstruction of the structure of reflecting potential from the observed frequency dependence of the phase shift of reflected acoustic waves is considered. The linearized formulation of the ill-posed inverse problem is used, which is solved using a perturbation technique. The potential perturbation of the standard model as a combination of five B-splines leads to a constructive solution of the discrepancy problem between the observational and theoretical frequencies of the 5-min oscillations. The discrepancy is reduced by an order of magnitude. The corresponding change of the shape of the reflecting potential is interpreted as a requirement of a general increase of convection efficiency in the standard solar model. In this way, the agreement of the oscillation frequencies of high degree is also improved. 相似文献
4.
G. Thuillier J. Claudel D. Djafer M. Haberreiter N. Mein S. M. L. Melo W. Schmutz A. Shapiro C. I. Short S. Sofia 《Solar physics》2011,268(1):125-149
In this paper we compare observed, empirical, and modelled solar limb profiles and discuss their potential use to derive physical
properties of the solar atmosphere. The PHOENIX, SolMod3D, and COSI radiative transfer codes as well as VAL-C models are used
to calculate the solar limb shape under different assumptions. The main properties of each model are shown. The predicted
limb shape as a function of wavelength for different features on the solar disk, such as quiet Sun, sunspots, and faculae,
is investigated. These models provide overall consistent limb shapes with some discrepancies that are discussed here in terms
of differences in solar atmosphere models, opacities, and the algorithms used to derive the solar limb profile. Our analysis
confirms that the most common property of all models is limb shapes that are much steeper than what is observed, or predicted
by the available empirical models. Furthermore, we have investigated the role of the Fraunhofer lines within the spectral
domain used for the solar limb measurements. Our results show that the presence of the Fraunhofer lines significantly displaces
the limb inflection point from its position estimated assuming only the photospheric continuum. The PICARD satellite, launched
on 15 June 2010, will provide measurements of the limb shape at several wavelengths. This work shows that the precision of
these measurements allows for discrimination among the available models. 相似文献
5.
《天文和天体物理学研究(英文版)》2021,(7)
Solar flare prediction plays an important role in understanding and forecasting space weather.The main goal of the Helioseismic and Magnetic Imager(HMI), one of the instruments on NASA's Solar Dynamics Observatory, is to study the origin of solar variability and characterize the Sun's magnetic activity.HMI provides continuous full-disk observations of the solar vector magnetic field with high cadence data that lead to reliable predictive capability; yet, solar flare prediction effort utilizing these data is still limited. In this paper, we present a machine-learning-as-a-service(MLaa S) framework, called Deep Sun,for predicting solar flares on the web based on HMI's data products. Specifically, we construct training data by utilizing the physical parameters provided by the Space-weather HMI Active Region Patch(SHARP)and categorize solar flares into four classes, namely B, C, M and X, according to the X-ray flare catalogs available at the National Centers for Environmental Information(NCEI). Thus, the solar flare prediction problem at hand is essentially a multi-class(i.e., four-class) classification problem. The Deep Sun system employs several machine learning algorithms to tackle this multi-class prediction problem and provides an application programming interface(API) for remote programming users. To our knowledge, Deep Sun is the first MLaa S tool capable of predicting solar flares through the internet. 相似文献
6.
The problem of whether the solar dynamo is quasi-periodic or chaotic is addressed by examining 1500 years of sunspot, geomagnetic and auroral activity cycles. We find sub-harmonics of the fundamental solar cycle period during the years preceding the Maunder minimum and loss of phase of the subharmonic on emergence from it. These phenomena are indicative of chaos. They indicate that the solar dynamo is chaotic and is operating in a region close to the transition between period doubling and chaos. Since Maunder type minima reoccur irregularly for millennia, it appears that the Sun remains close to this transition to and from chaos. We postulate this as a universal characteristic of solar type stars caused by feedback in the dynamo number. 相似文献
7.
J. J. Podesta 《Solar physics》2005,232(1-2):1-23
The solar convection zone is modeled as a horizontally stratified atmosphere with a constant gravitational field and an adiabatic
temperature gradient (a neutrally stratified polytrope). At equilibrium, the gas pressure and density decreases to zero at
the solar surface so that the solar surface is treated as a free surface which is bounded by vacuum. The evolution of small
amplitude perturbations about the equilibrium state is described by the linearized Euler equations for an inviscid compressible
fluid with an adiabatic equation of state. A sunquake is initiated at time zero by means of an initial perturbation with a
Gaussian velocity profile and the exact solution of the initial value problem is obtained in terms of a Fourier integral.
Comparisons between theory and observations indicate that this highly simplified model is able to predict the propagation
of sunquake waves across the solar surface with an error of approximately 10% or 20%. 相似文献
8.
The shape of the magnetosphere has been calculated self-consistently for inclinations of the Earth's magnetic dipole from perpendicular to the solar wind. Inclination angles of 0–35° have been chosen in steps of 5° and various smooth trends in the surface characteristics with increasing inclination angle noted. The surface points and the complete field at the surface points have been calculated for the entire surfaces. The neutral point region has been given precise study in one degree steps and is found to be tangent to the solar wind velocity and to have a smooth continuous curvature. The inclusion of the Earth's bow shock pressure and other sources of current have not been included at this stage of our program. 相似文献
9.
The measurement of solar oblateness has a rich history extending well back into the past. Until recently, its estimate has been actively disputed, as has its temporal dependence. Recent accurate observations of the solar shape gave cause for doubt, and so far only balloon flights or satellite experiments, such as those onboard SDO, seem to achieve the required sensitivity to measure the expected small deviations from sphericity. A shrinking or an expanding shape is ultimately linked to solar activity (likely not homologously with its change), as gravitational or magnetic fields, which are existing mechanisms for storing energy during a solar cycle, lead to distinct perturbations in the equilibrium solar-structure and changes in the diameter. It follows that a sensitive determination of the solar radius fluctuations might give information about the origin of the solar cycle. In periods of higher activity, the outer photospheric shape seems to become aspheric under the influence of higher-order multipole moments of the Sun, resulting both from the centrifugal force and the core rotation. An accurate determination of the shape of the Sun is thus one of the ways that we have now for peering into its interior, learning empirically about flows and motions there that would otherwise only be guessed at from theoretical considerations, developing more precise inferences, and ultimately building possible alternative gravitational theories. 相似文献
10.
A theoretical model is proposed for the interaction of a plane discontinuity in the solar wind with the magnetosphere. The presence of the bow shock and magnetosheath are taken into account, the calculation being based on the Spreiter et al. (1966) gas-dynamic model for a solar wind Mach Number M = 5. The model proposed predicts the manner in which the shape of the interplanetary discontinuity is distorted in its passage through the magnetosheath; it is found that the point of first impact with the magnetopause makes an angle of 56° with the Sun-Earth line for relatively quiet solar wind conditions. 相似文献
11.
S. Cecchini G. Giacomelli D. Haşegan G. Mandrioli O. Mariş L. Patrizii A. Plaian V. Popa L. Ştefanov V. Văleanu 《Astrophysics and Space Science》2000,273(1-4):35-41
The solar neutrino problem could arise from oscillation of one neutrinotype into a secondtype. Neutrinos would have a mass and there could be the possibility ofradiative neutrino decays. We discuss the search for neutrino decaysduring the 1999 solar eclipse: it involves the emitted visible photons,while neutrinos travel from the Moon to the Earth. The concept and themain characteristics of the NOTTE experiment are presented. 相似文献
12.
Klaus Jockers 《Icarus》1981,47(3):397-411
Photographs of Comet Kohoutek 1973 XII from the period 1974, Jan. 19, 0 UT to Jan. 21, 3 UT, collected from many different observatories and assembled in a unified format, are studied. During this time a large-scale tail disturbance was observed which coincides with the passage of a high-speed solar wind stream and an interplanetary sector boundary. Superimposed on a regular outward motion of tail condensations of a speed less than or about 100 km/sec, a kink moves down the tail with almost solar wind velocity. From the shape of the kink the direction of the solar wind adjacent to the tail is deduced. Of particular interest are tail segments where the solar wind flows across the tail. A waviness on the windward side of the tail is explained by differential acceleration, i.e., dense tail clouds are more massive and therefore less accelerated by the solar wind. On the leeward side tail rays point into the down-wind direction. During the large-scale disturbance the overall plasma density seems to be enhanced. While a tail disconnection does not occur in the event studied it is proposed that the tail disconnection observed in other, more dramatic events is caused by the differential acceleration mechanism combined with changes in the ion source. These are possibly due to enhanced charge exchange of cometary neutrals in the compression region in front of the high speed stream. The problem of tail ray formation near tail condensations is discussed but no solution is offered. 相似文献
13.
A computer program to convolve numerically any azimuthally symmetric, solar radial brightness distribution with standard antenna patterns of small half power beamwidths has been used to find a solar brightness distribution which is a good fit to the eclipse curve obtained during the 7 March 1970 partial solar eclipse with the NRAO 36-ft antenna at 3.5 mm. This brightness distribution is compared with the brightness distribution at 3.2 mm determined by the Pennsylvania State University Radio Astronomy Observatory group during the same eclipse but observed from Mexico where totality occurred. The two brightness distributions are very similar in shape, showing a double peak near the limb, but differing slightly in the positions of the peaks. 相似文献
14.
15.
The stability of force-free magnetic fields with cylindrical symmetry in the context of solar flares
Ulrich Anzer 《Solar physics》1968,3(2):298-315
The problem of the accumulation and storage of the energy released in solar flares is discussed; it is proposed that convective energy of the photosphere is transformed into magnetic energy of the chromosphere and corona. The consequences of a large ratio of magnetic pressure to gas pressure are investigated. In this case the field must be approximately force-free. The only suitable force-free fields which allow an analytical treatment are those of cylindrical symmetry. The stability of these fields is studied with the energy principle. It is shown that they are always unstable due to kink type instabilities. The shape of the unstable perturbations is described in detail and an upper limit for their amplitude is estimated. The consequences for the proposed mechanism of energy storage are briefly discussed. 相似文献
16.
harold C. Urey 《Astrophysics and Space Science》1972,16(2):311-323
The problem of the accumulation of the Moon is discussed on the assumption that the Moon is a captured object. If it is such, it is highly improbable that it is the only object of this kind present in the early solar system. Evidence indicating that other massive objects were present at that time is presented. Also, it is pointed out that the interior of the Moon must contain normal solar proportions of the elements of intermediate volatility in the lunar interior, if the Moon accumulated in a gas sphere. 相似文献
17.
E. Mysen 《Monthly notices of the Royal Astronomical Society》2007,381(1):301-307
It is demonstrated how globally distributed outgassing activity on a triaxial comet nucleus bridges the gap between the intuitive Sekanina model, used for comet orbit solutions, and the physics of the problem. In this activity and shape limit, it is shown how a recoil force component, which originates from a day-side restricted sublimation process, is necessary to describe the comet's rotational evolution. Modifications of the non-gravitational force cosines are suggested, with a fundamentally different interpretation than before. Applications to asteroid rotation yield that the ability of specular reflection, of solar photons on an asteroid's surface, to change the asteroid's rotation period and equatorial obliquity, is not dependent on the overall shape of the asteroid. 相似文献
18.
Hard X-ray spectra in solar flares provide knowledge of the electron spectrum that results from acceleration and propagation in the solar atmosphere. However, the inference of the electron spectra from solar X-ray spectra is an ill-posed inverse problem. Here, we develop and apply an enhanced regularization algorithm for this process making use of physical constraints on the form of the electron spectrum. The algorithm incorporates various features not heretofore employed in the solar flare context: Generalized Singular Value Decomposition (GSVD) to deal with different orders of constraints; rectangular form of the cross-section matrix to extend the solution energy range; regularization with various forms of the smoothing operator; and preconditioning of the problem. We show by simulations that this technique yields electron spectra with considerably more information and higher quality than previous algorithms. 相似文献
19.
We numerically analyze a magnetohydrodynamic, steady-state model for the interaction of a spherically symmetric solar wind with a three-component local interstellar medium (LISM), which is composed of plasma, hydrogen atoms, and a magnetic field. The magnetic field is assumed to be parallel to the velocity in the LISM. In this case, the model is axisymmetric. We study the effects of magnetic field on the plasma-flow geometry and on the distribution of hydrogen-atom parameters. In particular, we show that the presence of hydrogen atoms does not affect the qualitative change in the shape of the bow shock, the heliopause, and the solar-wind shock with increasing strength of the interstellar magnetic field. The presence of a magnetic field in the LISM can strongly affect the parameters of the energetic hydrogen atoms originated in the solar wind, although its effect on the “hydrogen wall” observed with the GHRS instrument onboard the HST spacecraft (Linsky and Wood 1996) is marginal. 相似文献