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1.
Ioannis Kontogiannis Costis Gontikakis Georgia Tsiropoula Kostas Tziotziou 《Solar physics》2018,293(4):56
We investigate the morphology and temporal variability of a quiet-Sun network region in different solar layers. The emission in several extreme ultraviolet (EUV) spectral lines through both raster and slot time-series, recorded by the EUV Imaging Spectrometer (EIS) on board the Hinode spacecraft is studied along with \(\mbox{H}\upalpha\) observations and high-resolution spectropolarimetric observations of the photospheric magnetic field. The photospheric magnetic field is extrapolated up to the corona, showing a multitude of large- and small-scale structures. We show for the first time that the smallest magnetic structures at both the network and internetwork contribute significantly to the emission in EUV lines, with temperatures ranging from \(8\times 10^{4}~\mbox{K}\) to \(6\times 10^{5}~\mbox{K}\). Two components of transition region emission are present, one associated with small-scale loops that do not reach coronal temperatures, and another component that acts as an interface between coronal and chromospheric plasma. Both components are associated with persistent chromospheric structures. The temporal variability of the EUV intensity at the network region is also associated with chromospheric motions, pointing to a connection between transition region and chromospheric features. Intensity enhancements in the EUV transition region lines are preferentially produced by \(\mbox{H}\upalpha\) upflows. Examination of two individual chromospheric jets shows that their evolution is associated with intensity variations in transition region and coronal temperatures. 相似文献
2.
A. C. deLoach M. J. Hagyard D. Rabin R. L. Moore J. B. Smith Jr. E. A. West E. Tandberg-Hanssen 《Solar physics》1984,91(2):235-242
Distributions of vertical electric current density (J
z) calculated from vector measurements of the photospheric magnetic field are compared with ultraviolet spectroheliograms to investigate whether resistive heating is an important source of enhanced emission in the transition region. The photospheric magnetic fields in Active Region 2372 were measured on 6 and 7 April, 1980 with the MSFC vector magnetograph; ultraviolet wavelength spectroheliograms (L and Nv 1239 Å) were obtained with the UVSP experiment aboard the Solar Maximum Mission satellite. Spatial registration of the J
z (5 arc sec resolution) and UV (3 arc sec resolution) maps indicates that the maximum current density is cospatial with a minor but persistent UV enhancement, but there is little detected current associated with other nearby bright areas. We conclude that although resistive heating may be important in the transition region, the currents responsible for the heating are largely unresolved in our measurements and have no simple correlation with the residual current measured on 5 arc sec scales.National Research Council Resident Research Associate.National Oceanic and Atmospheric Administration Space Environment Laboratory; currently at MSFC/SSL. 相似文献
3.
Solar observations through the atmospheric pass-band centred at 250 GHz have been made in the form of isophote maps. These show chromospheric features which have higher brightness temperatures than the mean disc temperature by up to 10%. Examination of corresponding maps at lower frequencies and also of Caii and H spectroheliograms reveals that the hot areas lie above photospheric active regions, and are regular features of the chromospheric millimetric emission having stable structure and duration of several weeks. Less frequently observed variable enhancements are also described, and linked with the formation of the stable active regions. 相似文献
4.
Takara Nishikawa 《Solar physics》1983,85(1):65-82
EUV spectroheliograms of the quiet Sun obtained with the Harvard experiment on Skylab are analyzed to identify the structure causing the weakening of the EUV line emission due to Lyman continuum absorption. The weakening at the network boundaries can be explained by overlapping of several spicules each of which being wrapped in an EUV emitting sheath. Part of the cell interiors show moderate weakening, this has the shape of a belt surrounding the network boundaries. There are a number of patches showing intense weakening near network boundaries and in cell interiors; the weakening at the points cannot be explained by overlapping of chromospheric structures with an EUV emitting sheath. A possible explanation is that the intense weakening is caused by cool chromospheric clouds or moving blobs over the EUV emitting sources in the cell interiors. Some of the points showing intense weakening are associated with an enhancement of the EUV emission. These points have lifetime shorter than the time interval of 5.5 min between successive observations, which stresses again that the chromosphere-corona transition zone is in a dynamic state. 相似文献
5.
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
6.
Kenneth P. Dere 《Solar physics》1982,75(1-2):189-203
XUV spectroheliograms of 2 active regions are studied. The images are due to lines emitted at temperatures between 8 x 104 K and 2 x 106 K and thus are indicative of transition region and coronal structures. The hot coronal lines are formed solely in loop structures which connect regions of opposite photospheric magnetic polarity but are not observed over sunspots. Transition region lines are emitted in plages overlying regions of intense photospheric magnetic field and in loops or loop-segments connecting such regions. The hot coronal loops are supported hydrostatically while only some of the transition zone loops are. The coronal and transition zone loops are distinctly separated and are not coaxial. A comparison of direct measurements of electron densities using density sensitive line ratios with indirect measurements using emission measures and path lengths shows the existence of fine structures of less than a second of arc in transition region loops. From a similar analysis, hot coronal loops do not have any fine structure below about 2 seconds of arc. 相似文献
7.
G. Cristiani G. Martinez C. H. Mandrini C. G. Giménez De Castro C. W. Da Silva M. G. Rovira P. Kaufmann 《Solar physics》2007,240(2):271-281
Using magnetograms, EUV and Hα images, Owens Valley Solar Array microwave observations, and 212-GHz flux density derived from
the Solar Submillimeter Telescope data, we determine the spatial characteristics of the 1B/M6.9 flare that occurred on November
28, 2001, starting at 16:26 UT in active region (AR) NOAA 9715. This flare is associated with a chromospheric mass ejection
or surge observed at 16:42 UT in the Hα images. We compute the coronal magnetic field under the linear force-free field assumption,
constrained by the photospheric data of the Michelson Doppler Imager and loops observed by the Extreme Ultraviolet Imaging
Telescope. The analysis of the magnetic field connectivity allows us to conclude that magnetic field reconnection between
two different coronal/chromospheric sets of arches was at the origin of the flare and surge, respectively. The optically thick
microwave spectrum at peak time shows a shape compatible with the emission from two different sites. Fitting gyrosynchrotron
emission to the observed spectrum, we derive parameters for each source.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
8.
We study the effect of chromospheric bombardment by an electron beam during solar flares. Using a semi-empirical flare model, we investigate energy balance at temperature minimum level and in the upper photosphere. We show that non-thermal hydrogen ionization (i.e., due to the electrons of the beam) leads to an increase of chromospheric hydrogen continuum emission, H– population, and absorption of photospheric and chromospheric continuum radiation. So, the upper photosphere is radiatively heated by chromospheric continuum radiation produced by the beam. The effect of hydrogen ionization is an enhanced white-light emission both at chromospheric and photospheric level, due to Paschen and H– continua emission, respectively. We then obtain white-light contrasts compatible with observations, obviously showing the link between white-light flares and atmospheric bombardment by electron beams. 相似文献
9.
Detailed comparisons of Culgoora 160 MHz radioheliograms of solar noise storms and Skylab EUV spectroheliograms of coronal loop structures are presented. It is concluded that: (1) there is a close association between changes in large-scale magnetic fields in the corona and the onset or cessation of noise storms; (2) these coronal changes result from the emergence of new magnetic flux at the photospheric level; (3) although new magnetic flux at the photospheric level is often accompanied by an increase in flare activity the latter is not directly responsible for noise storm activity; rather the new magnetic flux diffuses slowly outwards through the corona at rates 1–2 km s–1 and produces noise storms at 160 MHz 1–2 days later; (4) the coronal density above or in large-scale EUV loop systems is sufficiently dense to account for noise storm emission at the fundamental plasma frequency; (5) the scatter in noise storm positions can be accounted for by the appearance and disappearance of individual loops in a system. 相似文献
10.
From the analysis of OSO-4 Lyman-continuum spectroheliograms, differences in the brightness and the color temperature between the poles and the equator have been found. These differences are interpreted as resulting from a lower chromospheric density at the poles than at the equator. Two models, one for the poles and one for the equator, giving temperature and density as a function of height, explain the observations. The poles have a lower density and a smaller temperature gradient than the equator does. The differences begin in the middle chromosphere and increase toward the transition zone. 相似文献
11.
Solar UV emission observed by a filter photometer on Nimbus IV from 1969 to 1973 is examined in an attempt to understand the short term (27 day) and secular variability. Two models are discussed to explain the variations - a calcium plage model and a chromospheric network (faculae and spicule) structure model. Both relate to the remnant magnetic fields of active regions. An association between UV brightenings and the large scale magnetic field has been found consistent with the network model. An increase in UV emittance can be achieved by raising the effective chromospheric temperature closer to a photospheric level. If the Sun's luminosity is constant on these time intervals, the enhanced UV radiation could be partiallly offset by an overall decrease in photospheric temperature as measured by Livingston in visible photospheric profiles. Total solar luminosity may then show less variability, however, the UV to visible luminosity variation may have significant planetary influences. Lockwood and Thompson (1979) report a relation between solar activity and planetary albedos, and Schatten (1979) discussed a long-suspected relationship between solar activity and the Great Red Spot appearance. 相似文献
12.
Zhang Hongqi 《Solar physics》1993,144(2):323-340
In this paper, the formation and the measurement of the H line in chromospheric magnetic fields are discussed. The evolution of the chromospheric magnetic structures and the relation with the photospheric vector magnetic fields and chromospheric velocity fields in the flare producing active region AR 5747 are also demonstrated.The chromospheric magnetic gulfs and islands of opposite polarity relative to the photospheric field are found in the flare-producing region. This probably reflects the complication of the magnetic force lines above the photosphere in the active region. The evolution of the chromospheric magnetic structures in the active region is caused by the emergence of magnetic flux from the sub-atmosphere or the shear motion of photospheric magnetic fields. The filaments separate the opposite polarities of the chromospheric magnetic field, but only roughly those of the photospheric field. The filaments also mark the inversion lines of the chromospheric Doppler velocity field which are caused by the relative motion of the main magnetic poles of opposite polarities in the active region under discussion. 相似文献
13.
V. A. Krat 《Solar physics》1967,1(2):191-203
A new model is proposed for the solar chromosphere, which is assumed to be an instable inhomogeneous formation, consisting of numerous elements (filaments), each with different temperature and density. Fluctuations of the magnetic field may give rise to chromospheric turbulence and may also cause the chromospheric inhomogeneities.The chromosphere is suggested to consist of four discrete groups of filaments: (1) metallic filaments where the conditions for the emission of lines of neutral metals are optimal, (2) hydrogenic elements, with optimum conditions for the emission of the Balmer series of hydrogen, (3) helium filaments, with optimum conditions for the appearence of the neutral helium lines, (4) the subcoronal filaments, representing a transition from chromospheric to coronal formations.The metallic filaments may be further subdivided, first into filaments where the emission arises from scattering of photospheric radiation - these emit lines of neutral metals and of some metallic ions (CaII, SrII, and others), and further into filaments where the emission is farther from LTE conditions; the latter filaments are characterized by a somewhat higher electron temperature and by an electron density at least exceeding that of the other elements by an order of 10. Computations of the optimum conditions for the emission of the neutral helium lines were made with the aid of new tables of Sobolev. The helium filaments in the low chromosphere have lower temperatures and are denser than those in the upper chromosphere; for a part they may also be considered as hydrogen filaments. The derivation of the physical parameters of the subcoronal filaments was based on data on the Heii4686 chromospheric line emission and also on rocket observations of the ultraviolet solar spectrum. In order to evaluate the relative distribution of the various filaments between heights of 0 and 5000 km, data on the radio emission of the Sun at 8 mm are also used. Characteristics of the proposed model of the chromosphere are given in Table III and Figure 1. 相似文献
14.
This paper studies the effect of a magnetic atmosphere on the global solar acoustic oscillations in a simple Cartesian model.
First, the influence of the ratio of the coronal and the photospheric temperature τ and the strength of the magnetic field
at the base of the corona Bc on the oscillation modes is studied for a convection zone-corona model with a true discontinuity. The ratio τ seems to be
an important parameter. Subsequently, the discontinuity is replaced by an intermediate chromospheric layer of thickness L
and the effect of the thickness on the frequencies of the acoustic waves is studied. In addition, nonuniformity in the magnetic
field, plasma density and temperature in the transition layer gives rise to continuous Alfvén and slow spectra. Modes with
characteristic frequencies lying within the range of the continuum may resonantly couple to Alfvén and/or slow waves. 相似文献
15.
Jana Kašparová Marian KarlickÝ Eduard P. Kontar Richard A. Schwartz Brian R. Dennis 《Solar physics》2005,232(1-2):63-86
A multi-wavelength spatial and temporal analysis of solar high-energy electrons is conducted using the August 20, 2002 flare
of an unusually flat (γ1 = 1.8) hard X-ray spectrum. The flare is studied using RHESSI, Hα, radio, TRACE, and MDI observations with advanced methods
and techniques never previously applied in the solar flare context. A new method to account for X-ray Compton backscattering
in the photosphere (photospheric albedo) has been used to deduce the primary X-ray flare spectra. The mean electron flux distribution
has been analysed using both forward fitting and model-independent inversion methods of spectral analysis. We show that the
contribution of the photospheric albedo to the photon spectrum modifies the calculated mean electron flux distribution, mainly
at energies below ∼100 keV. The positions of the Hα emission and hard X-ray sources with respect to the current-free extrapolation
of the MDI photospheric magnetic field and the characteristics of the radio emission provide evidence of the closed geometry
of the magnetic field structure and the flare process in low altitude magnetic loops. In agreement with the predictions of
some solar flare models, the hard X-ray sources are located on the external edges of the Hα emission and show chromospheric
plasma heated by the non-thermal electrons. The fast changes of Hα intensities are located not only inside the hard X-ray
sources, as expected if they are the signatures of the chromospheric response to the electron bombardment, but also away from
them. 相似文献
16.
Berger T.E. De Pontieu B. Fletcher L. Schrijver C.J. Tarbell T.D. Title A.M. 《Solar physics》1999,190(1-2):409-418
TRACE observations of active regions show a peculiar extreme ultraviolet (EUV) emission over certain plage areas. Termed `moss'
for its spongy, low-lying, appearance, observations and modeling imply that the phenomenon is caused by thermal conduction
from 3–5 MKcoronal loops overlying the plage: moss is the upper transition region emission of hot coronal loops. The spongy
appearance is due to the presence of chromospheric jets or `spicules' interspersed with the EUV emission elements. High cadence
TRACE observations show that the moss EUV elements interact with the chromospheric jets on 10 s time scales. The location
of EUV emission in the moss does not correlate well to the locations of underlying magnetic elements in the chromosphere and
photosphere, implying a complex magnetic topology for coronal loop footpoint regions. We summarize here the key observations
leading to these conclusions and discuss new implications for understanding the structuring of the outer solar atmosphere.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005286503963 相似文献
17.
In this paper, we analyze the relations between photospheric vector magnetic fields, chromospheric longitudinal magnetic fields and velocity fields in a solar active region. Agreements between the photospheric and chromospheric magnetograms can be found in large-scale structures or in the stronger magnetic structures, but differences also can be found in the fine structures or in other places, which reflect the variation of the magnetic force lines from the photosphere to the chromosphere. The chromospheric superpenumbral magnetic field, measured by the Hline, presents a spoke-like structure. It consists of thick magnetic fibrils which are different from photospheric penumbral magnetic fibrils. The outer superpenumbral magnetic field is almost horizontal. The direction of the chromospheric magnetic fibrils is generally parallel to the transverse components of the photospheric vector magnetic fields. The chromospheric material flow is coupled with the magnetic field structure. The structures of the H chromospheric magnetic fibrils in the network are similar to H dark fibrils, and the feet of the magnetic fibrils are located at the photospheric magnetic elements. 相似文献
18.
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
19.
The common observation that where photospheric magnetic fields are strong, the overlying corona is bright is examined quantitatively. White light coronal brightness is employed because it is independent of coronal temperature and is directly related to coronal electron density. Brightness data for the inner corona on 7 March, 1970, taken from isodensitometer traces having a resolution of 10 arc sec, are utilized. The data were obtained from photographs which exhibit distinct chromospheric features 5 arc sec or smaller. These data are quantitatively compared, using cross correlation and scatter plot techniques, with the corresponding photospheric magnetic field data provided by Kitt Peak National Observatory. Cross correlation coefficients are computed between latitudes ±55° at specified heights. In general, a statistically significant positive correlation is found. The correlation decreases with height in the corona. However, a range of values in several parameters remains to be investigated so the physical significance of the presently observed correlation is not yet entirely clear. We expect that refinement of our input parameters will produce a more sensitive correlation and lead to an expression for the relationship of electron density to photospheric magnetic field strength.NAS/NRC Research Associate. 相似文献
20.
Eit Observations of the Extreme Ultraviolet Sun 总被引：3，自引：0，他引：3
D. Moses F. Clette J.-P. Delaboudinière G. E. Artzner M. Bougnet J. Brunaud C. Carabetian A. H. Gabriel J. F. Hochedez F. Millier X. Y. Song B. Au K. P. Dere R. A. Howard R. Kreplin D. J. Michels J. M. Defise C. Jamar P. Rochus J. P. Chauvineau J. P. Marioge R. C. Catura J. R. Lemen L. Shing R. A. Stern J. B. Gurman W. M. Neupert J. Newmark B. Thompson A. Maucherat F. Portier-Fozzani D. Berghmans P. Cugnon E. L. Van Dessel J. R. Gabryl 《Solar physics》1997,175(2):571-599
The Extreme Ultraviolet Imaging Telescope (EIT) on board the SOHO spacecraft has been operational since 2 January 1996. EIT
observes the Sun over a 45 x 45 arc min field of view in four emission line groups: Feix, x, Fexii, Fexv, and Heii. A post-launch
determination of the instrument flatfield, the instrument scattering function, and the instrument aging were necessary for
the reduction and analysis of the data. The observed structures and their evolution in each of the four EUV bandpasses are
characteristic of the peak emission temperature of the line(s) chosen for that bandpass. Reports on the initial results of
a variety of analysis projects demonstrate the range of investigations now underway: EIT provides new observations of the
corona in the temperature range of 1 to 2 MK. Temperature studies of the large-scale coronal features extend previous coronagraph
work with low-noise temperature maps. Temperatures of radial, extended, plume-like structures in both the polar coronal hole
and in a low latitude decaying active region were found to be cooler than the surrounding material. Active region loops were
investigated in detail and found to be isothermal for the low loops but hottest at the loop tops for the large loops.
Variability of solar EUV structures, as observed in the EIT time sequences, is pervasive and leads to a re-evaluation of the
meaning of the term ‘quiet Sun’. Intensity fluctuations in a high cadence sequence of coronal and chromospheric images correspond
to a Kolmogorov turbulence spectrum. This can be interpreted in terms of a mixed stochastic or periodic driving of the transition
region and the base of the corona. No signature of the photospheric and chromospheric waves is found in spatially averaged
power spectra, indicating that these waves do not propagate to the upper atmosphere or are channeled through narrow local
magnetic structures covering a small fraction of the solar surface. Polar coronal hole observing campaigns have identified
an outflow process with the discovery of transient Fexii jets. Coronal mass ejection observing campaigns have identified the
beginning of a CME in an Fexii sequence with a near simultaneous filament eruption (seen in absorption), formation of a coronal
void and the initiation of a bright outward-moving shell as well as the coronal manifestation of a ‘Moreton wave’.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004902913117 相似文献