共查询到20条相似文献，搜索用时 31 毫秒
1.
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
2.
George L. Withbroe 《Solar physics》2006,235(1-2):369-386
An analysis of spatially-resolved measurements of the intensity of the photospheric continuum by the Michelson Doppler Imager
(MDI) on the SOHO spacecraft indicates that these data can be used to study variations of the Total Solar Irradiance (TSI).
Since the techniques employed depend upon ratios of intensities measured by MDI, they are independent of the absolute photometric
calibration of the instrument. The results suggest that, while it is possible to account for short-term (weeks to months)
variation in TSI by variations in the irradiance contributions of regions with enhanced magnetic fields (larger than ten G
as measured by MDI), the longer-term variations are influenced significantly by variations in the brightness of the quiet
Sun, defined here as regions with magnetic field magnitudes smaller than ten G. The latter regions cover a substantial fraction
of the solar surface, ranging from approximately 90% of the Sun near solar minimum to 70% near solar maximum. The results
provide evidence that a substantial fraction, 50% or more, of the longer term (≥one year) variation in TSI is due to changes
in the brightness of the quiet Sun. 相似文献
3.
George L. Withbroe 《Solar physics》2009,257(1):71-81
The daily images and magnetograms acquired by MDI are a rich source of information about the contributions of different types
of solar regions to variations in the total solar irradiance (TSI). These data have been used to determine the temporal variation
of the MDI irradiance, the mean intensity of the solar disk in the continuum at 676.8 nm. The short-term (days to weeks) variations
of the MDI irradiance and TSI are in excellent agreement with rms differences of 0.011%. This indicates that MDI irradiance
is an excellent proxy for short-term variations of TSI from the competing irradiance contributions of regions causing irradiance
increases, such as plages and bright network, and regions causing irradiance decreases, such as sunspots. However, the long-term
or solar cycle variation of the MDI proxy and TSI differ over the 11-year period studied. The results indicate that the primary
sources of the long-term (several months or more) variations in TSI are regions with magnetic fields between about 80 and
600 G. The results also suggest that the difference in the long-term variations of the MDI proxy and TSI is due to a component
of TSI associated with sectors of the solar spectrum where the contrast in intensity between plages and the quiet Sun is enhanced
(e.g., the UV) compared to the MDI proxy. This is evidence that the long-term variation of TSI is due primarily to solar cycle
variations of the irradiance from these portions of solar spectrum, a finding consistent with modeling calculations indicating
that approximately 60% of the change in TSI between solar minimum and maximum is produced by the UV part of the spectrum shortward
of 400 nm (Solanki and Krivova, Space Sci. Rev. 125, 53, 2006). 相似文献
4.
Photospheric (Fei 5324.19 Å line) and chromospheric (H line) magnetic fields in quiet-Sun regions have been observed in the solar disk center by using the vector video magnetograph at Huairou Solar Observing Station of Beijing Astronomical Observatory. Observational results show that the quiet-Sun magnetic elements in the solar photosphere and chromosphere present similar magnetic structures. Photospheric and chromospheric magnetograms show corresponding time variations. This suggests that the magnetic fields in quiet-Sun regions present different 3-D magnetic configurations compared to those in solar active regions. 相似文献
5.
It has been suggested that slope fluctuations on the scale of pixel dimensions could be determined by statistical photoclinometry. A closer study of the surface of Phobos reveals variations in the scattering properties of single particles and micro-structures formed by the particles. In the present context, the photoclinometric method of brightness moments is extended to account for these variations by allowing statistical fluctuations in the phase function of the assumed Lommel-Seeliger scattering law. The mean slope on the investigated regions of Phobos has been found to vary from approximately 12 degrees on a 61m scale to approximately 7 degrees on a 216-272m scale. On the same scales, a value of the order of 2% has been obtained for the standard deviation of the scattering phase function. Hints of a fractal-like scale-invariance have been noticed in the covariance function of brightness. 相似文献
6.
Milan Minarovjech Milan Rybanský Vojtech Ru&#x;in 《Journal of Astrophysics and Astronomy》2000,21(3-4):197-200
We present an analysis of short time-scale intensity variations in the coronal green line as obtained with high time resolution
observations. The observed data can be divided into two groups. The first one shows periodic intensity variations with a period
of 5 min. the second one does not show any significant intensity variations. We studied the relation between regions of coronal
intensity oscillations and the shape of white-light coronal structures. We found that the coronal green-line oscillations
occur mainly in regions where open white-light coronal structures are located. 相似文献
7.
A. A. Nusinov T. V. Kazachevskaya S. N. Kuznetsov I. N. Myagkova B. Yu. Yushkov 《Solar System Research》2006,40(4):282-285
The results of simultaneous measurements of variations of UV radiation (in a band near the hydrogen Lα line, 121.6 nm) and hard X-ray and gamma-ray radiation (50 keV-200 MeV) performed by the VUSS-L and SONG instruments, respectively, onboard the CORONAS-F spacecraft are presented for periods of solar flares. Variations in the Lα ultraviolet radiation during the impulsive phase of a flare are shown to be synchronous with those of hard X-ray radiation. Temporal variations of UV and X-ray fluxes correspond to the progressive heating of higher and higher regions of the solar atmosphere and the energy transfer from the lower layers of the solar atmosphere to the coronal areas of flare regions. The energy of electrons in beams arising during the impulsive phase of flares can be as high as 500 keV. The velocity of the energy propagation from the regions of its release to the upper layers of the solar atmosphere can reach several tens of kilometers per second. 相似文献
8.
Submillimeter lightcurves of Vesta 总被引：1，自引：0，他引：1
Thermal lightcurves of Asteroid Vesta with significant amplitude have been observed at 870 μm (345 GHz) using the MPIfR 19-channel bolometer of the Heinrich–Hertz Submillimeter Telescope. Shape and albedo are not sufficient to explain the magnitude of this variation, which we relate to global variations in thermal inertia and/or other thermophysical parameters. Vesta's lightcurve has been observed over several epochs with the same general shape. However, there are some changes in morphology that may in part be related to viewing geometry and/or asteroid season. Inconsistent night-to-night variations exhibit the inherent difficulties in photometry at this wavelength. We are able to match the observed brightness temperatures with a relatively simple thermal model that integrates beneath the surface and assumes reasonable values of thermal inertia, loss tangent and refractive index, and without having to assume low values of emissivity in the submillimeter. High flux portions of the submillimeter lightcurve are found to correspond to regions with weak mafic bands observed in Hubble Space Telescope images. 相似文献
9.
M. I. Stodilka 《Kinematics and Physics of Celestial Bodies》2012,28(4):162-168
Observations of the Fe I line are used to simulate spatial and temporal pressure variations in the solar photosphere. The local internal gravity waves, which are essentially structures that are quasi-periodic in space (on granular and mesogranular scales) and time and propagate along inclined paths at subsonic velocities, are isolated by appropriate filtering. The phase and group velocities of the wave trains are orthogonal; their z-projections are of the opposite sign. 相似文献
10.
We present in this paper a statistical study aimed at understanding the possible relationship between surface magnetic field
variation and CME initiation. The three samples studied comprise 189 CME-source regions, 46 active regions, and 15 newly emerging
active regions. Both large-scale and small-scale variations of longitudinal magnetic fields of these regions are studied.
To quantitatively study these variations, three physical quantities are calculated: the average total magnetic flux (ATF),
the flux variation rate (FVR), and the normalized flux variation rate (NFVR). Our results show that 60% of the CME-source
regions are found to have magnetic flux increases during 12 hours before CME eruptions and 40% are found to have magnetic
flux decreases. The NFVR of CME-source regions are found to be statistically identical to those of active regions, averaged
over 111 hours, and significantly smaller than those of newly emerging active regions. In addition 91% of the CME-source regions
are found to have small-scale flux emergence, whereas small-scale flux emergences are also easily identified in active regions
during periods with no solar surface activity. Our study suggests that the relationship between flux emergence and CME eruption
is complex and the appearance of flux emergence alone is not unique for the initiation of CME eruption. 相似文献
11.
This paper addresses the fine-scale axisymmetric structure exhibited in Saturn's A and B-rings. We aim to explain both the periodic microstructure on 150-220 m, revealed by the Cassini UVIS and RSS instruments, and the irregular variations in brightness on 1-10 km, reported by the Cassini ISS. We propose that the former structures correspond to the peaks and troughs of the nonlinear wavetrains that form naturally in a viscously overstable disk. The latter variations on longer scales may correspond to modulations and defects in the wavetrains' amplitudes and wavelength. We explore these ideas using a simple hydrodynamical model which captures the correct qualitative behaviour of a disk of inelastically colliding particles, while also permitting us to make progress with analytic and semi-analytic techniques. Specifically, we calculate a family of travelling nonlinear density waves and determine their stability properties. Detailed numerical simulations that confirm our basic results will appear in a following paper. 相似文献
12.
本文分析讨论了太阳活动２０、２１周的冕洞及其边界区磁结构的变化。它包括：冕洞区光球磁场强度、磁极性的变化；冕洞面积与高速太阳风风速的关系；冕洞边界周围的环境。重点探讨太阳活动下降、极小相低纬、赤道冕洞区与其边界区磁结构的变化。 相似文献
13.
P.L. Israelevich I.M. Podgorny A.K. Kuzmin N.S. Nikolaeva E.M. Dubinin 《Planetary and Space Science》1988,36(12):1317-1328
Electric and magnetic fields and auroral emissions have been measured by the Intercosmos-Bulgaria-1300 satellite on 10–11 January 1983. The measured distributions of the plasma drift velocity show that viscous convection is diminished in the evening sector under IMF By < 0 and in the morning sector if IMF By > 0. A number of sun-aligned polar cap arcs were observed at the beginning of the period of strongly northward IMF and after a few hours a θ-aurora appeared. The intensity of ionized oxygen emission [O+(2P), 7320 Å] increased significantly reaching up to several kilo-Rayleighs in the polar cap arc. A complicated pattern of convection and field-aligned currents existed in the nightside polar cap which differed from the four-cell model of convection and NBZ field-aligned current system. This pattern was observed during 12 h and could be interpreted as six large scale field-aligned current sheets and three convective vortices inside the polar cap. Sun-aligned polar cap arcs may be located in regions both of sunward and anti-sunward convection. Structures of smaller spatial scale correspond to the boundaries of hot plasma regions related to polar cap arcs. Obviously these structures are due to S-shaped distributions of electric potential. Parallel electric fields in these S-structures provide electron acceleration up to 1 keV at the boundaries of polar cap arcs. The pairs of field-aligned currents correspond to those S-structures: a downward current at the external side of the boundary and an upward current at the internal side of it. 相似文献
14.
Temperature and velocity structures above granules and intergranular lanes were studied on spectrograms covering Caii H and K lines. In agreement with our earlier results, it was confirmed more quantitatively that there appear two kinds of bright continua, one in the outer wings (granular continuum) and the other in the inner wings (temporarily called K0-continuum) of Caii H and K lines, and that these two kinds of bright continua are located more or less in a complementary fashion. Further, it was found that the bright K0-continuum is well associated with higher central residual intensity of absorption lines. These facts suggest that in the upper photosphere of, say, < 0.1, there are high temperature regions in the intergranular lanes. Motions above granular regions are essentially upwards, whereas those of intergranular regions are predominantly downwards, and in the uppermost photosphere the motions become more random. 相似文献
15.
K. V. Krasnobaev 《Astronomy Letters》2001,27(9):568-573
We consider the interaction of an ionization-shock front with isothermal waves in an H I region. Based on a two-front model in the linear approximation, we have detected a significant (approximately by an order of magnitude) periodic amplification of perturbations as they penetrate from the interstellar medium into an H II region. Numerical simulations have revealed that even when the shock-and ionization-front velocities differ and the relative density perturbations in the interstellar medium are ～10?1, the variations in gas parameters near the ionization front are comparable to those observed at the boundaries of H II regions. 相似文献
16.
Observational data on the Ni I 6768 Å line profile variations during the impulsive and post-impulsive phases of the July 18, 2002 while light flare (WLF) in the kernel of WLF emission and in other flare kernels are presented. The line profiles at the sites of intense photospheric motions in active regions are also studied. The effect of the observed Ni I 6768 Å line profile variations on the SOHO/MDI magnetic field measurements is estimated. The following conclusions have been reached. (1) The thermodynamic structure of the photo-spheric layers changes significantly during the flare. As a result, the Ni I line profile changes, particularly at the site of WLF emission. At this time, the line depth decreases significantly, but the line does not show any emission reversal. Subsequently, a relatively slow return to the conditions of an undisturbed photosphere is observed. (2) The technique of SOHO/MDI magnetic field measurements is insensitive to such line variations. Therefore, the detected variations during the flare did not result in any noticeable errors in the MDI longitudinal magnetic field measurements. (3) The line profile is broadened, shifted as a whole, and asymmetric at the sites of active regions where intense photospheric motions appear. In the MDI measurements, such changes in the profile lead to an underestimation of the magnetic field by approximately 10% if the line-of-sight velocity of the photo-spheric ejection is about 1.6 km s?1. 相似文献
17.
We analyze stellar occultations by Saturn's rings observed with the Cassini Ultraviolet Imaging Spectrograph and find large variations in the apparent normal optical depth of the B ring with viewing angle. The line-of-sight optical depth is roughly independent of the viewing angle out of the ring plane so that optical depth is independent of the path length of the line-of-sight. This suggests the ring is composed of virtually opaque clumps separated by nearly transparent gaps, with the relative abundance of clumps and gaps controlling the observed optical depth. The observations can be explained with a model of self-gravity wakes like those observed in the A ring. These trailing spiral density enhancements are due to the competing processes of self-gravitational accretion of ring particles and Kepler shear. The B ring wakes are flatter and more closely packed than their neighbors in the A ring, with height-to-width ratios <0.1 for most of the ring. The self-gravity wakes are seen in all regions of the B ring that are not opaque. The observed variation in total B ring optical depth is explained by the amount of relatively empty space between the self-gravity wakes. Wakes are more tightly packed in regions where the apparent normal optical depth is high, and the wakes are more widely spaced in lower optical depth regions. The normal optical depth of the gaps between the wakes is typically less than 0.5 and shows no correlation with position or overall optical depth in the ring. The wake height-to-width ratio varies with the overall optical depth, with flatter, more tightly packed wakes as the overall optical depth increases. The highly flattened profile of the wakes suggests that the self-gravity wakes in Saturn's B ring correspond to a monolayer of the largest particles in the ring. The wakes are canted to the orbital direction in the trailing sense, with a trend of decreasing cant angle with increasing orbital radius in the B ring. We present self-gravity wake properties across the B ring that can be used in radiative transfer modeling of the ring. A high radial resolution (∼10 m) scan of one part of the B ring during a grazing occultation shows a dominant wavelength of 160 m due to structures that have zero cant angle. These structures are seen at the same radial wavelength on both ingress and egress, but the individual peaks and troughs in optical depth do not match between ingress and egress. The structures are therefore not continuous ringlets and may be a manifestation of viscous overstability. 相似文献
18.
The paper considers the relationship between the cyclic variations in the velocity of coronal mass ejections (CME) and the large-scale magnetic field structure (LSMF) in cycles 21??C?23. To characterize a typical size of the LSMF structure, we have used the index of the effective solar multipole (ESMI). The cyclic behavior of the CME occurrence rate and velocity proved to be similar to that of ESMI. The hysteresis observed in variations of the CME maximum velocity is interpreted as a manifestation of different contributions from the two field structures (local and global magnetic fields) in different phases of the 11-year activity cycle. It is suggested that cyclic variations in the maximum velocity of coronal mass ejections are due to different conditions for the formation of the complexes of active regions connected by coronal arch systems, which are the main source of high-velocity CMEs. 相似文献
19.
By using slit observations of solar photospheric lines shifted by 0.4 arcsec, a 2D field on the Sun was scanned to obtain
a 16-minute time series of 2D line-parameter variations. The aim was to investigate in detail the occurrence of turbulence
that can be measured by line-width variations extracted from the line profiles. The continuum-intensity variation served as
a proxy for granular (bright) and intergranular (dark) areas. The results show that turbulence is not limited to the intergranular
space but is also produced by horizontal motions that may become supersonic, leading to turbulence. These motions lead to
brightenings, as predicted by theoretical models. Thus, enhanced line-width variations are found to occur in both bright and
dark areas. A Sobel filter served to detect the areas where strong gradients in the line parameters occur. By applying this
filter to the different line-parameter variations over the 2D field observed, we can determine whether there exists a similarity
of these strong-gradient patterns with other parameters that characterize granular motions such as intensity variations or
velocity fluctuations. 相似文献
20.
P. Ambrož 《Solar physics》2004,224(1-2):61-68
Large-scale magnetic field regions are evolving on a time scale of many weeks and months and are also modified during the
solar activity cycle. The position of the regions are compared in a pair of consecutive synoptic charts and the horizontal
velocity field responsible for their position changes, is inferred. Besides the axially symmetric zonal and meridional drifts,
relating to differential rotation and meridional circulation, also non-axially symmetric velocity structures were observed
during the last three solar activity cycles. Changes of the position and spatial distribution, as well as temporal variations
of the field strength, closely relate to the occurrence and variations of other forms of solar activity such as sunspots,
filaments and prominences and coronal structures. In combination with 11-yr cyclic changes of the large-scale velocity field,
a new global dynamic regime of the convection zone is described. 相似文献