共查询到20条相似文献，搜索用时 50 毫秒
1.
随着观测的时间分辨率和空间分辨率的提高,近年来已发现和仔细研究了很多小尺度的太阳活动现象.它们的物理过程同复杂激烈的爆发现象有许多共同之处,因而可以为研究有复杂结构的激烈爆发现象(如耀斑和日冕物质抛射等)提供重要线索;同时,它们对太阳大气的加热可能有重要贡献,因而对理解太阳大气的加热机制有重要意义.太阳小尺度活动现象可... 相似文献
2.
H. Q. Zhang 《Astrophysics and Space Science》2006,305(3):211-224
We discuss the study of solar magnetic fields based on the photospheric vector magnetograms of solar active regions which were obtained at Huairou Solar Observing Station near Beijing in the period of 22nd and 23th solar cycles. The measurements of the chromospheric magnetic field and the spatial configuration of the field at the lower solar atmosphere inferred by the distribution of the solar photospheric and chromospheric magnetic field. After the analysis on the formation process of delta configuration in some super active regions based on the photospheric vector magnetogram observations, some results are obtained: (1) The analysis of magnetic writhe of whole active regions cannot be limited in the strong field of sunspots, because the contribution of the fraction of decayed magnetic field is non-negligible. (2) The magnetic model of kink magnetic ropes, proposed to be generated in the subatmosphere, is not consistent with the evolution of large-scale twisted photospheric transverse magnetic field and the relationship with magnetic shear in some delta active regions completely. (3) The proposition is that the large-scale delta active regions are formed from contribution by highly sheared non-potential magnetic flux bundles generated in the subatmosphere. We present some results of a study of the magnetic helicity. We also compare these results with other data sets obtained by magnetographs (or Stokes polarimeters) at different observatories, and analyze the basic chirality of the magnetic field in the solar atmosphere. 相似文献
3.
M. N. Pasechnik 《Kinematics and Physics of Celestial Bodies》2016,32(2):55-69
Results of the analysis of spectral observations of two Ellerman bombs in the Hα line are presented. These bombs (EB-1 and EB-2) appeared and evolved in the active region NOAA 11024 in the emerging magnetic flux area. The spectral data of a high temporal and spatial resolution were obtained with the French–Italian solar telescope THEMIS (Tenerife Island, Spain; THEMIS stands for Télescope Héliographique pour l’Etude du Magnétisme et des Instabilités Solaires) on July 4, 2009. The Hα-line profiles obtained for different periods of the Ellerman bombs (EBs) evolution were asymmetrical, demonstrating the emission excess in the long-wavelength wing. The intensity variations in the line wings indicate both the gradual and pulsed release of energy in the course of EBs. Temporal variations in the line-of-sight velocities V los of the chromospheric material at a level of the Hα-core formation showed two periods in the velocity enhancement, containing several individual peaks. The maximum line-of-sight velocity of the material was–9 and 8 km/s toward and from the observer, respectively. Rapid upward and downward plasma streams (where V los reaches–80 and 50 km/s, respectively) were sometimes observed. The Ellerman bombs were accompanied by small chromospheric ejections (surges) lasting for 0.5–1.5 min. A fine structure of EBs was found in the Hα-line spectra obtained during 4 min, when the intensity in the line wings sharply increased. The peculiarities of variations in the intensity of the Hα-line wings and the line-of-sight velocity of the chromospheric material suggest that two investigated EBs appeared and evolved as a physically connected pair. Our results support the model wherein the magnetic reconnection in the lower atmospheric layers is considered as a triggering mechanism for the EB formation. 相似文献
4.
In this paper we present the observational results of chromospheric and photospheric magnetograms in active regions obtained at the Huairou Solar Observing Station of the Beijing Astronomical Observatory. Simultaneous observations of the chromospheric and photospheric magnetic fields enable us to construct a possible configuration of the magnetic field in the solar atmosphere. The chromospheric magnetic field shows more diffusion than the photospheric magnetic field and consists of fibril-like features. We also discuss the possible configuration of the magnetic shear in highly sheared active regions. 相似文献
5.
This publication provides an overview of magnetic fields in the solar atmosphere with the focus lying on the corona. The solar magnetic field couples the solar interior with the visible surface of the Sun and with its atmosphere. It is also responsible for all solar activity in its numerous manifestations. Thus, dynamic phenomena such as coronal mass ejections and flares are magnetically driven. In addition, the field also plays a crucial role in heating the solar chromosphere and corona as well as in accelerating the solar wind. Our main emphasis is the magnetic field in the upper solar atmosphere so that photospheric and chromospheric magnetic structures are mainly discussed where relevant for higher solar layers. Also, the discussion of the solar atmosphere and activity is limited to those topics of direct relevance to the magnetic field. After giving a brief overview about the solar magnetic field in general and its global structure, we discuss in more detail the magnetic field in active regions, the quiet Sun and coronal holes. 相似文献
6.
A simple geometric model is proposed to explain the recently reported effect of the prolateness of the solar chromosphere. We assume that a specific dynamical part of the solar atmosphere above the 2 Mm level, being a mixture of moving up and down jets of chromospheric matter with the coronal plasma between them, is responsible for the solar prolateness. Due to the dynamic nature of this layer, the magnetic field is considered to play a very important role in the density distribution with the height, guiding the mass flows along the field lines. The difference of the magnetic field topology in the polar and the equatorial regions leads to different heights of the chromospheric limb. Calculations show a satisfactory coincidence with observations when the mean separation between opposite polarity concentrations is about 9 Mm. The possible observational signature of this network in low photospheric and chromospheric layers is discussed. 相似文献
7.
We study the propagation of a train of acoustic shocks guided by diverging magnetic fields through a static model of the solar chromospheric network and transition region. Our results show that for initial flux densities of the order 106 ergs cm–2 s–1 in the lower chromosphere, the local efficiency of acoustic transmission into the corona can be much higher than calculated for a plane parallel atmosphere. Thus acoustic energy will tend to be deposited at higher chromospheric levels in diverging magnetic fields, and magnetic guiding may well influence the temperature profile of the network and plages. But the total flux that can be transmitted into the corona along such diverging fields is severely limited, since the magnetic elements occupy a small fractional area of the photosphere, and the transmission efficiency is a rapidly decreasing function of initial acoustic flux density. We conclude that diverging magnetic fields and a varying ratio of specific heats are not likely to allow high frequency shocks to dissipate high enough in a static atmosphere, to contribute significantly to the coronal energy balance. This result strengthens the view that acoustic waves do not heat the solar corona. However, the conclusion may be sensitive to the influence of observed mass motions, such as spicules. 相似文献
8.
In a highly dynamic environment with sources and sinks of energy, flux tubes do not in general obey local conservation laws,
nor do the ensembles of flux tubes that exhibit collective phenomena. We use the approach of energetically open dissipative
systems to study nonlinear waves in flux tubes and their role in the dynamics of the overlying atmosphere. We present results
of theoretical and observational studies of the properties of moving magnetic features (MMFs) around sunspots and the response
of the overlying atmosphere to various types of MMFs. We show that all types of MMFs, often having conflicting properties,
can be described on a unified basis by employing the model of shocks and solitons propagating along the penumbral filaments
co-aligned with Evershed flows. The model is also consistent with the response of the upper atmosphere to individual MMFs,
which depends on their type. For example, soliton-type bipolar MMFs mainly participate in the formation of a moat and do not
carry much energy into the upper atmosphere, whereas shock-like MMFs, with the appearance of single-polarity features, are
often associated with chromospheric jets and microflares. 相似文献
9.
S. D. Bouwer 《Solar physics》1992,142(2):365-389
Using a dynamic power spectral analysis technique, the time-varying nature of solar periodicities is investigated for background X-ray flux, 10.7 cm flux, several indices to UV chromospheric flux, total solar irradiance, projected sunspot areas, and a sunspot blocking function. Many prior studies by a host of authors have differed over a wide range on solar periodicities. This investigation was designed to help resolve the differences by examining how periodicities change over time, and how the power spectra of solar data depend on the layer of the solar atmosphere. Using contour diagrams that show the percent of total power over time for periods ranging from 8 to 400 days, the transitory nature of solar periodicities is demonstrated, including periods at 12–14, 26–28, 51–52, and approximately 154 days. Results indicate that indices related to strong magnetic fields show the greatest variation in the number of periodicities, seldom persist for more than three solar rotations, and are highly variable in their frequency and amplitude. Periodicities found in the chromospheric indices are fewer, persist for up to 8–12 solar rotations, and are more stable in their frequency and amplitude. An additional result, found in all indices to varying degrees and related to the combined effects of solar rotation and active region evolution, is the fashion in which periodicities vary from about 20 to 36 days. I conclude that the solar data examined here are both quasi-periodic and quasistationary, with chromospheric indices showing the longest intervals of stationarity, and data representing strong magnetic fields showing the least stationarity. These results may have important implications to the results of linear statistical analysis techniques that assume stationarity, and in the interpretation of time series studies of solar variability. 相似文献
10.
Small-scale explosive events or microflares occur throughout the chromospheric network of the Sun. They are seen as sudden bursts of highly Doppler-shifted spectral lines of ions formed at temperatures in the range 2×104–5×105 K. They tend to occur near regions of cancelling photospheric magnetic fields and are thought to be directly associated with magnetic field reconnection. Recent observations have revealed that they have a bi-directional jet structure reminiscent of Petschek reconnection. In this paper compressible MHD simulations of the evolution of a current sheet to a steady Petschek, jet-like configuration are computed using the Versatile Advection Code. We obtain velocity profiles that can be compared with recent ultraviolet line-profile observations. By choosing initial conditions representative of magnetic loops in the solar corona and chromosphere, it is possible to explain the fact that jets flowing outward into the corona are more extended and appear before jets flowing towards the chromosphere. This model can reproduce the high Doppler-shifted components of the line profiles, but the brightening at low velocities, near the center of the bi-directional jet, cannot be explained by this simple MHD model. 相似文献
11.
I. P. Turova 《Astronomy Letters》2014,40(2-3):145-160
The oscillatory processes in the relatively quiet solar atmosphere, at the base of an extensive coronal hole, have been investigated. The properties of the oscillations in a number of parameters related mainly to the Ca II line intensity have been analyzed in areas belonging to various chromospheric network structures (cells, networks, flocculi, etc.). The goal of this study was to reveal peculiarities of the oscillatory process in the spatial areas located (in projection) at the center of a coronal hole, near its boundary, and at a bright coronal point at various heights of the solar atmosphere (from the photosphere to the middle chromosphere). In most structural elements, the low- and high-frequency components of the spectrum have been found to increase and decrease, respectively, with height. The oscillatory power of the low-frequency oscillations is at a maximum in the areas bordering the bright magnetic network elements. The power of the three-minute, five-minute, and low-frequency oscillations decreases at the centers of the bright chromospheric network. The phase relations point to the propagation of waves mainly at the boundaries of the bright chromospheric network and intermediate (in brightness) network elements. In two of the three investigated regions, the power of the five-minute oscillations (2.4–4.0 mHz) in cells is higher than that of the three-minute ones (5.2–6.8 mHz) at the investigated levels of the quiet solar atmosphere. 相似文献
12.
Hardi Peter L. Abbo V. Andretta F. Auchère A. Bemporad F. Berrilli V. Bommier A. Braukhane R. Casini W. Curdt J. Davila H. Dittus S. Fineschi A. Fludra A. Gandorfer D. Griffin B. Inhester A. Lagg E. Landi Degl’Innocenti V. Maiwald R. Manso Sainz V. Martínez Pillet S. Matthews D. Moses S. Parenti A. Pietarila D. Quantius N. -E. Raouafi J. Raymond P. Rochus O. Romberg M. Schlotterer U. Schühle S. Solanki D. Spadaro L. Teriaca S. Tomczyk J. Trujillo Bueno J. -C. Vial 《Experimental Astronomy》2012,33(2-3):271-303
The magnetic field plays a pivotal role in many fields of Astrophysics. This is especially true for the physics of the solar atmosphere. Measuring the magnetic field in the upper solar atmosphere is crucial to understand the nature of the underlying physical processes that drive the violent dynamics of the solar corona—that can also affect life on Earth. SolmeX, a fully equipped solar space observatory for remote-sensing observations, will provide the first comprehensive measurements of the strength and direction of the magnetic field in the upper solar atmosphere. The mission consists of two spacecraft, one carrying the instruments, and another one in formation flight at a distance of about 200 m carrying the occulter to provide an artificial total solar eclipse. This will ensure high-quality coronagraphic observations above the solar limb. SolmeX integrates two spectro-polarimetric coronagraphs for off-limb observations, one in the EUV and one in the IR, and three instruments for observations on the disk. The latter comprises one imaging polarimeter in the EUV for coronal studies, a spectro-polarimeter in the EUV to investigate the low corona, and an imaging spectro-polarimeter in the UV for chromospheric studies. SOHO and other existing missions have investigated the emission of the upper atmosphere in detail (not considering polarization), and as this will be the case also for missions planned for the near future. Therefore it is timely that SolmeX provides the final piece of the observational quest by measuring the magnetic field in the upper atmosphere through polarimetric observations. 相似文献
13.
In this paper, the chromospheric magnetic structures and their relation to the photospheric vector magnetic field in the vicinity of a dark filament in active region 5669 have been demonstrated. Structural variations are shown in chromospheric magnetograms after a solar flare. Filament-like structures in the chromospheric magnetograms occurred after a solar flare. They correspond to the reformation of the chromospheric dark filament, but there is no obvious variation of the photospheric magnetic field. We conclude that (a) some of the obvious changes of the chromospheric magnetic fields occurred after the flare, and (b) a part of these changes is perhaps due to flare brightening in the chromospheric H line.During the reforming process of the dark filament, a part of its chromospheric velocity field shows downward flow, and it later shows upward flow. 相似文献
14.
The direct propagation of acoustic waves, driven harmonically at the solar photosphere, into the three-dimensional solar atmosphere
is examined numerically in the framework of ideal magnetohydrodynamics. It is of particular interest to study the leakage
of 5-minute global solar acoustic oscillations into the upper, gravitationally stratified and magnetised atmosphere, where
the modelled solar atmosphere possesses realistic temperature and density stratification. This work aims to complement and
bring further into the 3D domain our previous efforts (by Erdélyi et al., 2007, Astron. Astrophys. 467, 1299) on the leakage of photospheric motions and running magnetic-field-aligned waves excited by these global oscillations.
The constructed model atmosphere, most suitable perhaps for quiet Sun regions, is a VAL IIIC derivative in which a uniform
magnetic field is embedded. The response of the atmosphere to a range of periodic velocity drivers is numerically investigated
in the hydrodynamic and magnetohydrodynamic approximations. Among others the following results are discussed in detail: i) High-frequency waves are shown to propagate from the lower atmosphere across the transition region, experiencing relatively
low reflection, and transmitting most of their energy into the corona; ii) the thin transition region becomes a wave guide for horizontally propagating surface waves for a wide range of driver periods,
and particularly at those periods that support chromospheric standing waves; iii) the magnetic field acts as a waveguide for both high- and low-frequency waves originating from the photosphere and propagating
through the transition region into the solar corona.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
15.
We analyse data from Hinode spacecraft taken over two 54-minute periods during the emergence of AR 11024. We focus on small-scale portions within the
observed solar active region and discover the appearance of very distinctive small-scale and short-lived dark features in
Ca ii H chromospheric filtergrams and Stokes I images. The features appear in regions with close-to-zero longitudinal magnetic field, and are observed to increase in length
before they eventually disappear. Energy release in the low chromospheric line is detected while the dark features are fading.
Three complete series of these events are detected with remarkably similar properties, i.e. lifetime of ≈ 12 min, maximum length and area of 2 – 4 Mm and 1.6 – 4 Mm2, respectively, and all with associated brightenings. In time series of magnetograms a diverging bipolar configuration is
observed accompanying the appearance of the dark features and the brightenings. The observed phenomena are explained as evidencing
elementary flux emergence in the solar atmosphere, i.e. small-scale arch filament systems rising up from the photosphere to the lower chromosphere with a length scale of a few solar
granules. Brightenings are explained as being the signatures of chromospheric heating triggered by reconnection of the rising
loops (once they have reached chromospheric heights) with pre-existing magnetic fields, as well as being due to reconnection/cancellation
events in U-loop segments of emerging serpentine fields. The characteristic length scale, area and lifetime of these elementary
flux emergence events agree well with those of the serpentine field observed in emerging active regions. We study the temporal
evolution and dynamics of the events and compare them with the emergence of magnetic loops detected in quiet Sun regions and
serpentine flux emergence signatures in active regions. The physical processes of the emergence of granular-scale magnetic
loops seem to be the same in the quiet Sun and active regions. The difference is the reduced chromospheric emission in the
quiet Sun attributed to the fact that loops are emerging in a region of lower ambient magnetic field density, making interactions
and reconnection less likely to occur. Incorporating the novel features of granular-scale flux emergence presented in this
study, we advance the scenario for serpentine flux emergence. 相似文献
16.
We simulate dynamically the downward propagation of the chromospheric condensation, which originates following the chromospheric evaporation during solar flares. Our attention is concentrated on the lower part of the atmosphere. The top of the chromosphere (base of the transition region) is regarded as the top boundary. The condensation is mimicked by assuming an impulsive pressure increase at the top boundary. Using such a method, we compute in detail the evolution process of a condensation. The results show that the condensation can penetrate into the deeper atmosphere, though it becomes very weak at the later phase. Moreover, we also discuss the possibility that the mass motions in the condensation may cause the asymmetries of some spectral lines as observations have indicated. 相似文献
17.
Magnetic reconnection can take place between two plasma regions with antiparallel magnetic field components. In a time-dependent reconnection event, the plasma outflow region consists of a leading bulge region and a trailing reconnection layer. Magnetohydrodynamic (MHD) discontinuities, including rotational discontinuities, can be formed in both the bulge region and the trailing layer. In this paper, we suggest that the rotational discontinuities observed in the solar wind may be generated by magnetic reconnection associated with microflares in coronal holes. The structure of the reconnection layer is studied by solving the one-dimensional Riemann problem for the evolution of an initial current sheet after the onset of magnetic reconnection as well as carrying out two-dimensional MHD simulations. As the emerging magnetic flux reconnects with ambient open magnetic fields in the coronal hole, rotational discontinuities are generated in the region with open field lines. It is also found that in the solar corona with a low plasma beta ( 0.01), the magnetic energy is converted through magnetic reconnection mostly into the plasma bulk-flow energy. Since more microflares will generate more rotational discontinuities and also supply more energy to the solar wind, it is expected that the number of rotational discontinuities observed in the solar wind would be an increasing function of solar wind speed. The observation rate of rotational discontinuities generated by microflares is estimated to be dN
RD/dt - f/63 000 s (f > 1) at 1 AU. The present mechanism favors the generation of rotational discontinuities with a large shock normal angle. 相似文献
18.
The physical properties of the quiet solar chromosphere–corona transition region are studied. Here the structure of the solar atmosphere is governed by the interaction of magnetic fields above the photosphere. Magnetic fields are concentrated into thin tubes inside which the field strength is great. We have studied how the plasma temperature, density, and velocity distributions change along a magnetic tube with one end in the chromosphere and the other one in the corona, depend on the plasma velocity at the chromospheric boundary of the transition region. Two limiting cases are considered: horizontally and vertically oriented magnetic tubes. For various plasma densities we have determined the ranges of plasma velocities at the chromospheric boundary of the transition region for which no shock waves arise in the transition region. The downward plasma flows at the base of the transition region are shown to be most favorable for the excitation of shock waves in it. For all the considered variants of the transition region we show that the thermal energy transfer along magnetic tubes can be well described in the approximation of classical collisional electron heat conduction up to very high velocities at its base. The calculated extreme ultraviolet (EUV) emission agrees well with the present-day space observations of the Sun. 相似文献
19.
We investigate the thermodynamical and magnetic properties of a “dark‐cored” fibril seen in the chromospheric Ca II IR line at 854.2 nm to determine the physical process behind its appearance. We analyse a time series of spectropolarimetric observations obtained in the Ca II IR line at 854.2 nm and the photospheric Fe I line at 630.25 nm. We simultaneously invert the spectra in both wavelength ranges with the SIR code to obtain the temperature and velocity stratification with height in the solar atmosphere and the magnetic field properties in the photosphere. The structure can be clearly traced in the line‐of‐sight (LOS) velocity and the temperature maps. It connects from a small pore with kG fields to a region with lower field strength. The flow velocity and the temperature indicate that the height of the structure increases with increasing distance from the inner footpoint. The Stokes V signal of 854.2 nm shows a Doppler‐shifted polarization signal with the same displacement as in the intensity profile, indicating that the supersonic flow seen in the LOS velocity is located within magnetized plasma. We conclude that the chromospheric dark‐cored fibril traces a siphon flow along magnetic field lines, driven by the gas pressure difference caused by the higher magnetic field strength at the inner footpoint. We suggest that fast flows guided by the magnetic field lead to the appearance of “dark‐cored” fibrils in intensity images. Although the observations included the determination of the polarization signal in the chromospheric Ca II IR line, the signal could not be analysed quantitatively due to the low S/N. Chromospheric polarimetry will thus require telescopes of larger aperture able to collect a sufficient number of photons for a reliable determination of polarization in deep and only weakly polarized spectral lines (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
20.
Onkar Nath 《Solar physics》1991,136(2):263-268
A model is presented of a solar atmosphere which is heated by the periodic passage of shock waves. The outer atmosphere rotates and is assumed not to affect the strength of the shock waves. This constant shock strength hypothesis is used as the basis of the model of the outer solar atmosphere. From the model it is concluded that the chromospheric temperature rise and flow Mach number are slightly affected by the rotation of the atmosphere. 相似文献