共查询到20条相似文献，搜索用时 46 毫秒
1.
Wavelength shifts converted to velocities between solar lines observed at disc center and laboratory wavelengths of Fei, Feii, Tii, Nii, and Fei lines in the near infrared are plotted as a function of the logarithm of their solar equivalent width in milliångstroms. The need for wavelengths based on the wavelength standards is stressed. A comparison of photographic Fei solar wavelength is shown to agree, on the average, with Fourier Transform Spectrometer solar wavelengths within less than 0.5 milliångstroms. Using Balthasar's limb effect tables we convert the disc center velocities to limb velocities and find, though the scatter is large, that there is little evidence for a super-gravitational red shift. 相似文献
2.
Below the scale of supergranules we find that cellular flows are present in the solar photosphere at two distinct size scales, approximately 2 Mm and 4 Mm, with distinct characteristic times. Simultaneously present in the flow is a non-cellular component, with turbulent scaling properties and containing 30% of the flow energy. These results are obtained by means of wavelet spectral analysis and modeling of vertical photospheric motions in a 2-hour sequence of 120 SOHO/MDI, high-resolution, Doppler images near disk center. The wavelets permit detection of specific local flow patterns corresponding to convection cells. 相似文献
3.
Sequences of line-of-sight (LOS) magnetograms recorded by the Michelson Doppler Imager are used to quantitatively characterize photospheric magnetic structure and evolution in three active regions that rotated across the Sun??s disk during the Whole Heliosphere Interval (WHI), in an attempt to relate the photospheric magnetic properties of these active regions to flares and coronal mass ejections (CMEs). Several approaches are used in our analysis, on scales ranging from whole active regions, to magnetic features, to supergranular scales, and, finally, to individual pixels. We calculated several parameterizations of magnetic structure and evolution that have previously been associated with flare and CME activity, including total unsigned magnetic flux, magnetic flux near polarity-inversion lines, amount of canceled flux, the ??proxy Poynting flux,?? and helicity flux. To catalog flare events, we used flare lists derived from both GOES and RHESSI observations. By most such measures, AR 10988 should have been the most flare- and CME-productive active region, and AR 10989 the least. Observations, however, were not consistent with this expectation: ARs 10988 and 10989 produced similar numbers of flares, and AR 10989 also produced a few CMEs. These results highlight present limitations of statistics-based flare and CME forecasting tools that rely upon line-of-sight photospheric magnetic data alone. 相似文献
4.
Hathaway D.H. Beck J.G. Bogart R.S. Bachmann K.T. Khatri G. Petitto J.M. Han S. Raymond J. 《Solar physics》2000,193(1-2):299-312
Spectra of the cellular photospheric flows are determined from observations acquired by the MDI instrument on the SOHO spacecraft. Spherical harmonic spectra are obtained from the full-disk observations. Fourier spectra are obtained from the high-resolution observations. The p-mode oscillation signal and instrumental artifacts are reduced by temporal filtering of the Doppler data. The resulting spectra give power (kinetic energy) per wave number for effective spherical harmonic degrees from 1 to over 3000. Significant power is found at all wavenumbers, including the small wavenumbers representative of giant cells. The time evolution of the spectral coefficients indicates that these small wavenumber components rotate at the solar rotation rate and thus represent a component of the photospheric cellular flows. The spectra show distinct peaks representing granules and supergranules but no distinct features at wavenumbers representative of mesogranules or giant cells. The observed cellular patterns and spectra are well represented by a model that includes two distinct modes – granules and supergranules. 相似文献
5.
A. W. Fullerton 《Astrophysics and Space Science》1994,221(1-2):105-114
The characteristics of the line profile variations observed in optical transitions of O-type stars are reviewed. For a few well-observed stars, there is compelling evidence that the variations are due to photospheric velocity fields from one or more modes of nonradial pulsation. However, the origin of the line profile variations observed in most O stars is not yet established. To date, there is little empirical evidence to suggest that the variability in optical absorption lines of O stars is causally linked to the stellar wind variability commonly observed in their UV resonance lines. 相似文献
6.
It is shown that Kantowski–Sachs cosmological models do not exist in Rosen's (1973) bimetric theory of gravitation when the
source of gravitation is either perfect fluid or cosmic string. Hence, the vacuum model is constructed. 相似文献
7.
Jack B. Zirker 《Solar physics》1993,147(1):47-53
We have used the results of a realistic simulation of convection to estimate the power input to coronal loops from the twisting of photospheric magnetic field in intergranular vortices. In this simulation, the vorticity is large (a mean of 0.03 s–1) nearly everywhere in the intergranular lanes, not merely at the corners of three granules. We found the autocorrelation time of vorticity images to be 45 s, but individual vortices last as long as 144 s. Our estimate suggests that field line twisting could supply a substantial fraction, if not all, of the required power to the quiet corona.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. 相似文献
8.
The locations of barbs of quiescent solar filaments are compared with the photospheric/chromospheric network, which thereby serves as a proxy of regions with enhanced concentrations of magnetic flux. The study covers quiet regions, where also the photospheric network as represented by flow converging regions, i.e., supergranular cell boundaries, contain largely weak magnetic fields. It is shown that close to 65% of the observed end points of barbs falls within the network boundaries. The remaining fraction points into the inner areas of the network cells. This confirms earlier findings (Lin et al., Solar Physics, 2004) that quiescent filaments are basically connected with weaker magnetic fields in the photosphere below. 相似文献
9.
In this paper we carry out an analysis of the spatial–temporal line-of-sight velocity variations measured in the chromospheric (H, H) and photospheric (Fei 6569 Å, Fei 4864 Å, Nii 4857 Å) lines at the base of 17 coronal holes. Time series of a duration from 43 to 120 min were recorded with the CCD line-array and the CCD matrix. Rather frequently we observed quasi-stationary upward flows with a measured velocity of up to 1 km s–1 in the photosphere and up to 4–5 km s–1 in the chromosphere (equivalent radial velocity of up to 3 km s–1 and up to 12–15 km s–1 accordingly) near dark points on the chromospheric network boundary inside polar CH. Line-of-sight velocity fluctuation spectra contain meaningful maxima in the low-frequency region clustering around the values 0.4, 0.75, and 1 mHz. Usually, the spatial localization of these maxima mutually coincides and, in our opinion, coincides with the chromospheric network boundary. Acoustic 3- and 5-min oscillations are enhanced in the coronal hole region and reach 1 km s–1 in the photosphere and 3–4 km s–1 in the chromosphere. These oscillations are not localized spatially and are distinguished throughout the entire region observed. 相似文献
10.
The differences between physical conditions in solar faculae and those in sunspots and quiet photosphere (increased temperature and different magnetic field topology) suggest that oscillation characteristics in facula areas may also have different properties. The analysis of 28 time series of simultaneous spectropolarimetric observations in facula photosphere (Fe?i 6569 Å, 8538 Å) and chromosphere (Hα, Ca?ii 8542 Å) yields the following results. The amplitude of five-minute oscillations of line-of-sight (LOS) velocity decreases by 20?–?40% in facula photosphere. There are only some cases revealing the inverse effect. The amplitude of four- to five-minute LOS velocity oscillations increases significantly in the chromosphere above faculae, and power spectra fairly often show pronounced peaks in a frequency range of 1.3?–?2.5 mHz. Evidence of propagating oscillations can be seen from space?–?time diagrams. We have found oscillations of the longitudinal magnetic field (1.5?–?2 mHz and 5.2 mHz) inside faculae. 相似文献
11.
Photospheric and heliospheric magnetic fields 总被引：1，自引：0，他引：1
The magnetic field in the heliosphere evolves in response to the photospheric field at its base. This evolution, together with the rotation of the Sun, drives space weather through the continually changing conditions of the solar wind and the magnetic field embedded within it. We combine observations and simulations to investigate the sources of the heliospheric field from 1996 to 2001. Our algorithms assimilate SOHO/MDI magnetograms into a flux-dispersal model, showing the evolving field on the full sphere with an unprecedented duration of 5.5 yr and temporal resolution of 6 hr. We demonstrate that acoustic far-side imaging can be successfully used to estimate the location and magnitude of large active regions well before they become visible on the solar disk. The results from our assimilation model, complemented with a potential-field source-surface model for the coronal and inner-heliospheric magnetic fields, match Yohkoh/SXT and KPNO/He?10830 Å coronal hole boundaries quite well. Even subject to the simplification of a uniform, steady solar wind from the source surface outward, our model matches the polarity of the interplanetary magnetic field (IMF) at Earth ～3% of the time during the period 1997–2001 (independent of whether far-side acoustic data are incorporated into the simulation). We find that around cycle maximum, the IMF originates typically in a dozen disjoint regions. Whereas active regions are often ignored as a source for the IMF, the fraction of the IMF that connects to magnetic plage with absolute flux densities exceeding 50 Mx cm?2 increases from ?10% at cycle minimum up to 30–50% at cycle maximum, with even direct connections between sunspots and the heliosphere. For the overall heliospheric field, these fractions are ?1% to 20–30%, respectively. Two case studies based on high-resolution TRACE observations support the direct connection of the IMF to magnetic plage, and even to sunspots. Parallel to the data assimilation, we run a pure simulation in which active regions are injected based on random selection from parent distribution functions derived from solar data. The global properties inferred for the photospheric and heliospheric fields for these two models are in remarkable agreement, confirming earlier studies that no subtle flux-emergence patterns or field-dispersal properties are required of the solar dynamo beyond those that are included in the model in order to understand the large-scale solar and heliospheric fields.
相似文献12.
Small-scale magnetic elements in the quiet photospheric network are believed to play a key role in the energy flow from the solar surface to upper layers of atmosphere. Their intense hydro-magnetic activity includes merging and fragmentation of same polarity fluxes, `total' or partial cancellation of neighboring flux elements of opposite polarity, dynamic appearance and disappearance of compact bipoles, etc. We study the general features of these processes, and show that non-collinearity of flux tubes, sharp stratification of low atmosphere and finite plasma beta lead to several specific effects in the interacting flux tubes that may explain the morphological properties of network magnetic field and also provide a mechanism for the energy build up and release in the nearby chromosphere and transition region. We show that during the collision of flux tubes in the photosphere reconnection occurs regardless of whether the flux tubes are of opposite or of the same polarity. But the dynamics of reconnection products are significantly different and lead to different macroscopic effects that can be observed. 相似文献
13.
Jacques M. Beckers 《Solar physics》1968,5(3):309-322
The large scale (> 5000 km) intensity structure of the photosphere has been examined. The power per frequency unit indicates a continuous increase towards smaller spatial frequency. No excess power exists at wavelengths near the size of the supergranulation (30000 km) or at any other wavelength between 5000 and 100000 km. However, direct measurement of the intensity distribution in 1652 supergranulation cells shows a very small increase of the intensity towards the cell boundary. The amount of this increase is larger near the solar limb. It is probably due to a weak continuum emission associated with the chromospheric network. Any temperature difference arising from the supergranulation convection is obscured by this emission and is probably less than 1 K. 相似文献
14.
本文首次给出了发生在太阳光球磁重联的一个直接的观测证据。 这一磁重联的观测特征是:(1)重联发生在一新浮现磁通量区的一极与极性相反的老磁通量之间;(2)重联前中性线附近磁剪切明显;(3)被重联两极为一对消磁结构,重联发生在稳定的磁通量损失数小时之后;(4)一个级别为C2.9的亚耀斑发生在重联之前。该耀斑以重联区为中心,双带离重联位置2～3万公里,直到耀斑极大相后14分钟,重联仍未发生;(5)重联后,磁对消速率呈增大趋势。 相似文献
15.
This paper examines the relationship between magnetic dipoles in the photosphere and X-ray bright points (XBPs) in the corona, using an XBP special campaign dataset obtained by the Yohkoh SXT and the NSO/Kitt Peak magnetograph. We find that for the cases where a simple dipole exists in the photosphere, the condition that they are separated by a distance less than the interaction distance defined by Longcope1998 is favorable for an XBP to be observed. For the cases where the magnetic topology is more complicated due to the addition of an extra fragment, we find that the geometry of the magnetic fragments is a major factor that determines if an XBP is observed. XBPs are more likely to be formed above magnetic fragments arranged in such a way that photospheric motions giving rise to reconnection between any two fragments will also give rise to reconnection with the remaining fragment. 相似文献
16.
Stodilka M. I. Sukhorukov A. V. Prysiazhnyi A. I. 《Kinematics and Physics of Celestial Bodies》2019,35(5):231-251
Kinematics and Physics of Celestial Bodies - Abstract—From 2D-spectral observation data of a quiet region of the solar disk center in the Fe I λ 557.609 nm line, 3D hydrodynamic models... 相似文献
17.
We propose a mechanism for the formation of a magnetic energy avalanche based on highly dynamic phenomena within the ubiquitous small-scale network magnetic elements in the quiet photosphere. We suggest that this mechanism may provide constant mass and energy supply for the corona and fast wind. Constantly emerging from sub-surface layers, flux tubes collide and reconnect generating magneto-hydrodynamic shocks that experience strong gradient acceleration in the sharply stratified photosphere/chromosphere region. Acoustic and fast magnetosonic branches of these waves lead to heating and/or jet formation due to cumulative effects (Tarbell et al., 1999). The Alfvén waves generated by post-reconnection processes have quite a restricted range of parameters for shock formation, but their frequency, determined by the reconnection rate, may be high enough (0.1–2.5 s–1) to carry the energy into the corona. We also suggest that the primary energy source for the fast wind lies far below the coronal heights, and that the chromosphere and transition region flows and also radiative transient form the base of the fast wind. The continuous supply of emerging magnetic flux tubes provides a permanent energy production process capable of explaining the steady character of the fast wind and its energetics. 相似文献
18.
The source of coronal magnetic energy and helicity lies below the surface of the Sun, probably in the convective zone dynamo. Measurements of magnetic and velocity fields can capture the fluxes of both magnetic energy and helicity crossing the photosphere. We point out the ambiguities which can occur when observations are used to compute these fluxes. In particular, we show that these fluxes should be computed only from the horizontal motions deduced by tracking the photospheric cut of magnetic flux tubes. These horizontal motions include the effect of both the emergence and the shearing motions whatever the magnetic configuration complexity is. We finally analyze the observational difficulties involved in deriving such fluxes, in particular the limitations of the correlation tracking methods. 相似文献
19.
We study photospheric plasma flows in an active region NOAA 8375, by using uninterrupted high-resolution SOHO/MDI observations
(137 intensity images, 44 hours of observations). The active region consists of a stable large spot and many small spots and
pores. Analyzing horizontal flow maps, obtained with local correlation tracking technique, we found a system of stable persistent
plasma flows existing in the active region. The flows start on either side of the sunspot and extend over 100′′ to the east.
Our measurements show that the speed of small sunspots and pores, averaged over 44 hours, was about 100 m s−1, which corresponds to root-mean-square longitudinal drifts of sunspots of 0.67°–0.76° day−1. We conclude that these large-scale flows are due to faster proper motion of the large sunspot relative to the ambient photospheric
plasma. We suggest that the flows may be a good carrier to transport magnetic flux from eroding sunspots into the outer part
of an active region. 相似文献
20.
The photospheric velocity field was observed in an active region which was prolific in moustaches. It is shown that the moustaches occur at the locations where the sign of the line-of-sight velocity changes, and that the extension of the velocity field is large (≈104 km) compared with the dimension of moustaches. 相似文献