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1.
It is shown that the parameters of the solar-wind magnetic field are determined by regions in coronal holes at distances of
1.1–1.4 solar radii, where the field lines are radial at low heights. Expanding further in a narrow nozzle or funnel, the
field lines become radial throughout the unipolar region at 2.5 solar radii. Hence, the traditional approach of comparing
the characteristics of the interplanetary field at the Earth’s orbit and at the corresponding helio-projection point on the
Sun is not quite correct. It gives good results for the signs and sector structure of the field; however, the magnitude of
the field is formed in a more extensive area. Taking this into account, we can correlate the field values on the Sun with
the interplanetary magnetic field (IMF), and thus explain the absence of weak fields in the vicinity of the IMF neutral line
(the two-peaked nature of the distribution). 相似文献
2.
Evidence that the distribution of the abundances of admixtures with low first-ionization potentials (FIP < 10 eV) in the lower solar corona could be associated with the typology of the largescale magnetic field is presented. Solar observations show an enhancement in the abundances of elements with low FIPs compared to elements with high FIPs (>10 eV) in active regions and closed magnetic configurations in the lower corona. Observations with the ULYSSES spacecraft and at the Stanford Solar Observatory have revealed strong correlations between the manifestation of the FIP effect in the solar wind, the strength of the open magnetic flux (without regard to sign), and the ratio of the large-scale toroidal and poloidal magnetic fields at the solar surface. Analyses of observations of the Sun as a star show that the enhancement of the abundances of admixtures with low FIPs in the corona compared to their abundances in the photosphere (the FIP effect) is closely related to the solar-activity cycle and also with variations in the topology of the large-scale magnetic field. A possible mechanism for the relationship between the FIP effect and the spectral type of a star is discussed in the framework of solar–stellar analogies. 相似文献
3.
Eruptions of material from lower to upper layers of the solar atmosphere can be divided into two classes. The first class of eruptions maintain their (usually loop-like) shapes as they increase in size (eruptive prominences), or display a sudden expansion of fairly shapeless clumps of plasma in all directions (flare sprays). The second class refers to narrow, collimated flows of plasma on various scales (spicules, surges, jets). It is obvious that the magnetic configurations in which these phenomena develop differ: for the first class they form closed structures that confine the plasma, and in the second class open structures directing flows of plasma in a particular direction, as a rule, upward. At the same time, the mechanisms initiating eruptions of both classes could be similar, or even practically identical. This mechanism could be instability of twisted magnetic tubes (flux ropes), leading to different consequences under different conditions. It is shown that the results of eruptive instability are determined by the ratio of the scales of the magnetic flux rope and the confining coronal field, and also by the configuration of the ambient magnetic field in the corona. Observations of both types of eruptions are analyzed, the conditions for their develoment are examined, and phenomenological models are proposed. 相似文献
4.
New results from electrophotometric scanning of the solar disk in the HeI λ 10830 Å and Hα lines are presented. The intensity at the center of the HeI λ 10830.30 Å line is 1–3% higher in the regions of coronal holes than in quiescent regions; this is accompanied by a decrease in the size and contrast of the chromospheric network compared to the network in quiescent regions. Our observations in the HeI line revealed chains of “dark points” surrounding coronal holes. The Hα±0.5 observations show increased velocities of ascent near the dark points compared to the velocities inside coronal holes and in quiescent regions. It is proposed that the intensification and acceleration of the flows of solar plasma from the dark points are due to reconnection of the magnetic fields of the bipolar chromospheric network and the predominantly unipolar magnetic field inside the coronal holes. Our observations suggest that the same reconnection process takes place near the temperature minimum, in the presence of certain conditions at the boundary between coronal holes and bipolar active regions. The reconnection process produces plasma flows from the chromosphere to the corona, which are sufficient to form prominences. 相似文献
5.
B. P. Filippov 《Astronomy Reports》2020,64(3):272-279
Solar filaments (prominences), which suddenly and swiftly ascend, i.e., become eruptive, sometimes decelerate and stop at comparatively low altitudes. Causes of failed eruptions generally remain uncertain. The present study analyzes two eruptive phenomena with very similar initial geometries and configurations of external magnetic fields; one of these eruptions evolves in a coronal mass ejection, but the other breaks off shortly after its start. The tension of curved magnetic field lines is the most probable force causing eruptions to stop. Significant external magnetic fields parallel to rope axes located in failed eruption regions can be a decisive factor. Such an effect has been revealed during laboratory experiments on plasma rope dynamics, which likely plays an important role in solar eruptive phenomena. 相似文献
6.
It is shown that the contrast of coronal holes (CH) determines the speed of the solar wind streams to the same extent as their area does. We analyzed more than 400 images obtained in the λ284 Å channel. The time interval under examination covers about 1500 days in the declining phase of cycle 23 (from 2002 to 2006). We considered all coronal holes recorded during that interval in the absence of coronal mass ejections (CME). Comparison was also made with some other parameters of the solar wind (e.g., density, temperature, and magnetic field). A fairly high correlation (0.70–0.89) was obtained with the velocity, especially during the periods of moderate activity, which makes this method useful for everyday forecast. The ratio of CH brightness to the mean brightness of the disk in the λ284 Å channel is about 25%. 相似文献
7.
Analysis of long-term measurements of solar magnetic fields and the flux of UV radiation from the Sun indicates a cause-effect relationship between activity complexs, their residual magnetic fields, and coronal holes. A comparison of the background magnetic fields of the Sun and the evolution of former activity complexes reveals unipolar magnetic regions that form after the decay of these complexes. The latitude and time evolution of unipolar magnetic regions in solar cycles 21–24 is studied. A North-South asymmetry in solar activity is manifest in the distribution of unipolar regions migrating toward higher latitudes. It is shown that, when residual magnetic fields of the opposite polarity reach the polar regions, this leads to a sign change of the polar magnetic field and a decrease in the area of polar coronal holes, or even their complete disappearance. These interactions can explain the triple sign change of the polar magnetic field of the Sun in cycle 21 and the short-term polarity reversals observed in 2010 and 2011. 相似文献
8.
I. M. Chertok V. A. Slemzin S. V. Kuzin V. V. Grechnev O. I. Bugaenko I. A. Zhitnik A. P. Ignat'ev A. A. Pertsov 《Astronomy Reports》2004,48(5):407-417
We analyze large-scale solar activity following the eruption of a very powerful, geoeffective coronal mass ejection in the 23rd solar cycle, observed at 175, 284, and 304 Å on November 4, 2001, using data from the CORONAS-F/SPIRIT telescope. In particular, we have shown that the restructuring of the magnetic field above the eruption center was accompanied by the formation of a multicomponent post-eruptive arcade, which was observed in all three bands over many hours and had an extent of the order of 0.5R⊙. Two kinds of dimmings were observed, i.e., compact dimmings on either side of this arcade and channeled dimmings along some extended features beyond the active region. The intensity in the dimmings decreased by several tens of percent. The enhanced emission observed at the top of the post-eruptive arcade can be due to energy release in the course of magnetic reconnection high in the corona at the relaxation stage of the perturbed magnetic field to a new equilibrium state with a closed configuration. It can also be due to an enhanced emission measure because of the oblique direction of the line of sight crossing both loop tops and footpoint regions. The spatial coincidence of the main dimmings in lines corresponding to different temperatures indicates that a plasma outflow from the transition region and coronal structures with opened field lines are responsible for these dimmings. Variations in the plasma temperature associated with coronal mass ejections probably play an important role for some dimmings, which appear different in different lines. 相似文献
9.
A model treating a solar coronal hole as an axially symmetrical magnetic formation that is in equilibrium with the surrounding
medium is proposed. The model is applicable in the lower corona (to heights of the order of several hundreds of Mm), where
the influence of the solar-wind outflow on the state of the system can still be neglected. The magnetic field of the coronal
hole is comprised of a relatively weak open flux that varies with height, which extends into interplanetary space, and a closed
field, whose flux closes at the chromosphere near the coronal hole. Simple analytical formulas are obtained, which demonstrate
for a given equilibrium configuration of the plasma and field the main effect of interest—the lowering of the temperature
and density of the gas in the coronal hole compared to their values in the corona at the same geometric height. In particular,
it is shown that, at heights of several tens of Mm, the temperature and density of the plasma in the coronal hole are roughly
half the corresponding values at the same height in the corona, if the cross-sectional radius of the hole exceeds the scale
height in the corona by roughly a factor of 1.5: R
h
≈ 1.5H(T
0). In the special case when R
h
≈ H(T
0), the plasma temperature in the hole is equal to the coronal temperature, and the darkening of the coronal hole is due only
to an appreciable reduction of the plasma density in the hole, compared to the coronal density. An analogy of the properties
of coronal holes and sunspots is discussed, based on the similarity of the magnetic structures of these formations. In spite
of the fundamental difference in the mechanisms for energy transport in coronal holes and sunspots, the equilibrium distributions
of the plasma parameters in these formations are determined only by the magnetic and gravitational forces, giving rise to
a number of common properties, due to their similar magnetic structures. 相似文献
10.
The large-scale stream structure of the solar wind near the Sun and its evolution during the 11-year solar activity cycle are investigated. The study is based on observations of scattering of the radiation from compact natural radio sources at radial distances R≤14R S (R S is the solar radius). Regular observations were conducted in 1981–1998 on the RT-22 and DKR-1000 radio telescopes of the Russian Academy of Sciences at Pushchino, at λ=1.35 cm and 2.7 m, respectively. The radial dependences of the interplanetary scintillations m(R) and the scattering angle 2?(R) are considered together with the structure of large-scale magnetic fields in the solar corona at R=2.5R S. The entire range of variations in the level of scattering and the associated heliolatitude flow structures in the subsonic solar wind forms over the 11-year solar cycle, as a direct result of the large-scale structure of the evolving magnetic fields at the source of the solar-wind streamlines. 相似文献
11.
A Green’s function solution of Laplace’s equation for the potential magnetic field in an external spherical region is found using the derivative of the potential along a selected direction as a boundary condition. A set of programs applying this solution to construct the potential magnetic-field lines in solar active regions based on the photospheric line-of-sight field component has been developed. The method is tested using some model fields, and the optimal step size is found for realistic conditions. The developed software is applied to four real solar active regions, adopting HMI/SDO magnetograms as the boundary conditions. The potential magnetic field in the chromosphere and corona have been reconstructed for the selected regions. The calculated field lines are compared with flux tubes observed by AIA/SDO in the EUV. This comparison is used as a basis to discuss the applicability of a potential field approximation to the magnetic fields in solar active regions. 相似文献
12.
Comparisons of the brightness distributions of the white corona observed at distances of several solar radii with solar wind velocities derived from interplanetary-scintillation observations, as well as analyses of solar wind data obtained on spacecraft from December 1994 to June 1995, indicate that the fast solar wind can contain plasma with velocities V ≈ 300–450 km/s, approaching those typical for the slow solar wind that flows in the streamer belt and chains of streamers. At the same time, certain other parameters, first and foremost the plasma density N and ratio T/N 0.5 (where T is the temperature), indicate that these two flows differ considerably. The slow solar wind flowing in the streamer belt and chains displays high densities N > 10 ± 2 cm?3 and low T/N 0.5 < 1.7 × 104 K cm3/2 at the Earth’s orbit. The number of slow solar-wind sources observed in chains can be comparable with the number observed in the belt. The fast solar wind flowing from coronal holes always displays low densities N≤ 8 cm?3 and high T/N 0.5 > 1.7 × 104 K cm3/2. These properties probably indicate different origins of the fast and slow solar winds. 相似文献
13.
A. P. Kropotkin 《Astronomy Reports》2011,55(12):1132-1143
The basis is laid out for a theory relating various phenomena in the solar atmosphere, including localized concentrations
of magnetic field at the bases of coronal magnetic arches, chromospheric spicules, twisted coronal magnetic flux tubes, and
flows of energy carried by Alfvén waves propagating upward into the corona. The structure of photospheric currents localized
in the vicinity of supergranule boundaries and excited by convective motions is studied. These currents exist primarily in
a “dynamo layer” of sharply enhanced transverse conductivity, which forms in the weakly ionized thermal photospheric plasma
located in the solar gravitational field. The motions of the electrons and ions in this layer have appreciably different characters:
the ions are collisionly driven by the flows of neutral atoms, while the electrons drift in the crossed electric and magnetic
fields. The electric field supporting the current arises due to the polarization of the electrons and ions. This field also
gives rise to Alfvén perturbations that propagate upward into the corona, together with their associated longitudinal currents.
The character of this “loading” makes the system of fields and currents uniquely defined. Moreover, the momentum flux carried
by these Alfvén waves should be transferred to the cool chromospheric gas, facilitating the vertical ejection of this gas
in the form of spicules, as was first proposed in 1992 by Haerendel. 相似文献
14.
M. A. Zel’dovich Yu. I. Logachev G. M. Surova K. Kecskemety I. S. Veselovskii 《Astronomy Reports》2016,60(7):687-693
The energy spectra and relative abundances of 3He, 4He, C, O, and Fe ions with energies of ~0.04–2 MeV/nucleon are studied using data from the ULEIS instrument on board the ACE spacecraft obtained during quiescent periods in 2006–2012. During the unique, prolonged minimum between cycles 23 and 24, 35 quiescent periods were distnguished, during which solar-wind flows from near-equatorial coronal holes (CHs) were detected. It is shown that the C/O and Fe/O ratios for suprathermal ions correspond to the relative abundances of the corresponding thermal ions in the fast and slow (Maxwellian) solar wind (SWICS/ACE), while the 4He/O ratio exceeds the corresponding ratio in the solar wind by a factor of two. The intensities of the 3He, 4He, C, O, and Fe suprathermal ions in outflows from CHs grow with the speed of the solar wind. This indicates that, in periods ofminimumsolar activity, suprathermal ions from CHs represent a high-temperature “tail” of the solar wind. An additional flux of suprathermal helium ions may also be contributed by other external sources. 相似文献
15.
Large-scale solar disturbances associated with powerful flares and coronal mass ejections (CMEs) during two passages of a grand system of three active regions in October–November 2003 are analyzed using data obtained with the SOHO/EIT EUV telescope. Dimmings (transient coronal holes) and, to a lesser extent, coronal waves (traveling emitting fronts) are studied using fixed-difference derotated images, in which a correction for the solar rotation is applied and a single heliogram preceding the event is subtracted from all subsequent heliograms. This method allows us to study difference heliograms in both the 195 Å line (with an interval of 12 min) and the various-temperature channels of 171, 195, 284, and 304 Å (with an interval of six hours). Our analysis shows, in particular, that the disturbances associated with CMEs demonstrated a global character and occupied almost the entire southern half of the disk in virtually all eruptive events during the two solar rotations. At the same time, the northern half of the disk, which had a large coronal hole, was only slightly disturbed. The dominant dimmings were observed on the disk as narrow, long features stretched mainly between three main, well-separated regions of the system and as long structures located along lines of solar latitude in the south polar sector. For repetitive events with intervals between them being not so long, the dominant dimmings demonstrated a clear homology in their forms and locations. During the very powerful event of October 28, one homologous global set of dimmings changed to another set. Many dimmings were observed to be identical or very similar in the three coronal channels and the transition-region line. It follows from the analysis that rapidly recovering global structures in the corona and transition region were involved in the eruption of running CMEs and the corresponding reconstruction of the large-scale magnetic fields. 相似文献
16.
B. P. Filippov 《Astronomy Reports》2011,55(6):541-550
Some possibilities for the reconnection of magnetic-field lines of solar filaments that approach when the photospheric polarity
inversion lines change their positions, are discussed. The interaction between filaments depends on their internal properties,
which are determined by the filament chirality, or the sign of the helicity of the filament magnetic field. In quadrupolar
magnetic configurations, filaments with the same chirality can exchange their halves. Filaments with opposite chirality rupture
after the reconnection of the polarity inversion lines, since the two fragments of the different filaments cannot be connected
continuously. The morphology and connectivity of the filaments are analyzed using daily Hα filtergrams obtained over the period of maximum activity of the 23rd solar cycle. Examples of alterations of the filament
connectivity occuring during the evolution of photospheric fields are presented. 相似文献
17.
We present the results of radio sounding observations probing the inner solar wind near the minimum of the solar-activity cycle, using polarized pulses from PSR B0525+21 and PSR B0531+21 received when the lines of sight toward these pulsars were close to the Sun. The observations were obtained in June 2005 and June 2007 on the Large Phased Array of the Lebedev Physical Institute at 111 MHz. An upper limit for the scattering of giant pulses from PSR B0531+21 due to their passage through the turbulent solar-wind plasma is determined. The arrival-time delays for pulses from PSR B0531+21 are used to derive the radial dependence of the mean density of the circumsolar plasma. The resulting density distribution indicates that the acceleration of fast, high-latitude solar-wind outflows continues to heliocentric distances of 5–10R ⊙, where R ⊙ is the solar radius. The mean plasma density at heliocentric distances of about 5R ⊙ is 1.4 × 104 cm?3, substantially lower than at the solar-activity maximum. This is associated with the presence of polar coronal holes. The Faraday rotation measure at heliocentric distances of 6–7R ⊙ is estimated. Deviations of the spatial distribution of the magnetic field from spherical symmetry are comparatively modest in the studied range of heliocentric distances. 相似文献
18.
We analyze calibrated white-light coronal images from the LASCO-C2/SOHO experiment (processing level L1), focusing on quasistationary events without coronal mass ejections or their manifestations in the solar wind. The previous result that the streamer belt forms a set of rays of increased brightness is confirmed. The cross section of the streamer belt is frequently observed as two closely spaced rays differing in brightness. It is difficult to explain this in terms of ordinary bending of the belt. We suggest that the belt is normally a set of pairs of rays with enhanced brightness (or two close rows of rays). The distance between the rays in each pair is comparable to the ray size. The ray brightnesses in any pair can, in general, be different. The magnetic field has opposite directions in the rays forming a pair, so that the neutral line of the radial component of the solar magnetic field probably runs along the strip between the pairs of rays. 相似文献
19.
The magnetic fields of solar active regions are analyzed using a method based on comparing the spatial structures of the reconstructed magnetic field and of the radio emission of the active region. Two approaches are used: comparing the radio size of the active region and the corresponding size calculated using the reconstructed magnetic field, and comparing the radio spectra that are observed and calculated using the reconstructed magnetic field. Overall, the calculated sizes and spectra correspond fairly well to the observational data, making it possible to estimate physical parameters of the emitting region, such as the electron density and temperature. 相似文献
20.
A new type of dimmings, or transient coronal holes (i.e., regions of reduced soft-X-ray and EUV emission), is revealed in analyses of difference solar images obtained with the SOHO EIT ultraviolet telescope at 195 Å. Such features can be observed on the solar disk after halo-type coronal mass ejections (CMEs). If several active regions, filaments, and other structures are present on the disk during a major eruptive event, then strongly anisotropic, channel-shaped (“channeled”) dimmings coexist with relatively compact dimmings adjacent to the eruption center. The channeled dimmings are comparable to the compact dimmings in terms of their contrast; stretch along several narrow, extended features (channels); and can span nearly the entire visible disk. Coronal waves, which appear as fronts of enhanced brightness traveling ahead of the dimmings in some halo CME events, are also anisotropic. We argue that such transient phenomena are closely related to the strong disturbance and restructuring of large-scale magnetic fields involved in CMEs, and the channeled character of the dimmings reflects the complexity of the global solar magnetosphere, in particular, near the solar-activity maximum. 相似文献