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1.
Phase-correlation statistics comparing acoustic radiation coming out of a particular point on the solar photosphere with acoustic radiation going into it show considerably reduced sound travel times through the subphotospheres of active regions. We have now applied techniques in phase-sensitive seismic holography to data from the Solar Oscillations Investigation – Michelson Doppler Imager (SOI-MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft to obtain high resolution phase-correlation maps of a large, complex active region and the `acoustic moat' which surrounds it. We report the following new results: First, the reduced sound travel-time perturbations in sunspots, acoustic moats, and isolated plages increase approximately in proportion to the logarithm of the surface magnetic flux density, for flux densities above 10 G. This is consistent with an interpretation of the travel-time anomalies, observed with holographic and other local-helioseismic procedures, as caused by acoustic Wilson-like depressions in photospheres of magnetic regions. Second, we find that, compared with isolated plages, the acoustic moats have an additional sound travel-time reduction on the order of 3–5 s which may be explained by a thermal excess due to the blockage of convective transport by the sunspot photosphere. Third, the combined effect of the Wilson depression in plages, acoustic moats, and sunspots may explain the observed variation of global p-mode frequencies with the solar cycle. Fourth, we find that active regions, including sunspots, acoustic moats, and plages, significantly reflect p modes above the acoustic cut-off frequency, where the surface of the quiet Sun acts as a nearly perfect absorber of incident acoustic radiation. 相似文献
2.
Using the boundary element method (BEM) for constant-, force-free fields, the vector magnetic field distributions in the chromosphere of a flare-productive active region. AR 6659 in June 1991, are obtained by extrapolating from the observed vector magnetograms at the photosphere. The calculated transverse magnetic fields skew highly from the photosphere to the chromosphere in the following positive polarity sunspot whereas they skew only slightly in the main preceding sunspot. This suggests that more abundant energy was stored in the former area causing flares. Those results demostrate the validity of the BEM solution and the associations between the force-free magnetic field and the structure of the AR 6659 region. It shows that the features of the active region can be revealed by the constant- force-free magnetic field approximation. 相似文献
3.
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
4.
Axel Koch 《Solar physics》1984,93(1):53-72
The rotational velocity of the Sun is determined by sunspot tracings and by spectroscopic measurements of the photospheric plasma using the non-Zeeman-split line Fe i 5576 and absolute iodine reference. Stationary line shifts as limb-effect and longperiodical shifts introduced by supergranulation are discussed. The dependence on solar activity as Ca+ emissivity and magnetic fields is investigated including line asymmetries. The results are: (a) The non active photospheric regions rotate with 1995 ± 30 m s-1. Solar active regions yield a 60 m s-1 higher value. (b) In quiet regions the absolute limb shift varies between 170 m s-1 at the line core and 310 m s-1 at I/I
cont 0.8 (C-shape); thus the limb shift is mainly due to entire line shifts. (c) In solar active regions (close to spots) asymmetries are widely reduced in line cores; this effect cannot be associated with a variation of the limb effect due to a large scatter of Doppler shifts near spots. (d) A reduced limb shift of 50 m s-1 is found in network boundaries and is mainly due to a small scale downflow. (e) Observations with a smaller influence of stray light yield symmetric profiles in umbrae. (f) Differences between umbral rotation rates from tracer and spectroscopic measurements do not exceed 20 m s-1, when considering straylight. The rotational velocity from umbrae exceeds that from the photosphere by 30–60 m s-1. Some individual spots yield nearly the same rotation rate as the photosphere. 相似文献
5.
In this paper we study the longitudinal distribution of solar magnetic regions, using the synoptic magnetic maps from Kitt Peak National Observatory, the active region data from Solar Geophysical Data and the Hobservations from Prairie View Solar Observatory. The clusters of activity were identified by comparing the positions of sunspot groups between successive Carrington rotations. We have found that a large percentage of active regions was involved in the clustering process (40–50%, if we only take into account clusters with a minimum lifetime of 4 rotations). The nests followed the differential rotation of the solar surface, within an intrinsic spread. A remarkable feature of sunspot nests detected in our study is their high degree of complexity, with a large number of nests being organized in diverging, converging, or parallel structures. Of the flares which occurred during the time interval of interest, the great majority originated from the sunspot nests; the distribution of the flares between these nests was not uniform, revealing active and quiet nests. A high flaring rate was recorded at the intersection points of diverging or converging nests, suggesting that these points represent violent interactions of magnetic fluxes. The complexes were in continuous interaction, which impacts their properties and future evolution. The behavior of the nests indicate that they are maintained by repeated injection of magnetic flux rather than by the evolution of the surface magnetic fields. 相似文献
6.
Broad band pinhole photometer intensity observations of 15 large sunspots covering the spectral region 0.387–2.35 m are presented. The data are based on measurements on approximately 500 days during the period June, 1967 to December, 1979.We have found real and significant intensity differences between large sunspots. These differences may be explained by a systematic variation in the umbral temperature throughout the solar cycle. A connection between umbra intensity and heliographic latitude is discussed.No center-limb variation in the umbra/photosphere intensity ratio is detected. We have searched for possible connections between umbra intensity and a number of other sunspot parameters, like the spot size, without detecting any significant correlation. We conclude that the umbra/photosphere intensity ratio seems to be a unique function of epoch for large sunspots. 相似文献
7.
A time series of velocity oscillations is observed in the vicinity of NOAA region 5395 with the Kitt Peak vacuum telescope for 6.8 hours on 1989 March 10 as part of a program to study the interaction of solar p-mode oscillations with solar active regions. The data is transformed in a cylindrical coordinate system centered on the visible sunspot, then Hankel- and Fourier-transformed to produce the power spectra of in- and outgoing acoustic waves. It is observed that a maximum of nearly 70% of the power of incident high-degree modes is absorbed by this unusually large sunspot group. The absorptive properties of this active region are compared with those of more typical regions studied previously.A major flare occurred within this region during the observing sequence, providing a rare opportunity to test the hypothesis that flares may excite acoustic waves in the photosphere. A comparison is made of the amount of outgoing p-mode power in equal 200 min time intervals before and after the time of the flare. No significant difference in outgoing acoustic waves is observed within a one-sigma error of about 5% averaged over the interval. A search for acoustic pulses emanating from the flare is made by filtering the data and performing appropriate inverse transforms. No such pulses were detected to a level of about 20% of the background power.NAS-NRC Resident Research Associate. 相似文献
8.
An analysis of the local sources (LS) structure of the S-component of solar radio emission confirms the presence of a core component which is characterized by strong circular polarization and a steep growing spectrum at shorter centimeter wavelengths. These details coincide in position with the sunspots' umbra and their height above the photosphere does not generally exceed about 2000 km. Gyroresonance emission of thermal electrons of the corona is generally accepted as being responsible for this type of emission. The spectral and polarization observations of LS made with RATAN-600 using high resolution in the wavelength range 2.0–4.0 cm, allow us to measure the maximum magnetic fields of the corresponding sunspots at the height of the chromosphere-corona transition region (CCTR). This method is based on determining the short wavelength limit of gyroresonance emission of the LS and relating it to the third harmonic of gyrofrequency.An analysis of a large number of sunspots and their LS (core component) has shown a good correlation between radio magnetic fields near the CCTR and optical photospheric ones. The magnetic field in CCTR above a sunspot is found only 10 to 20% lower than in the photosphere. The resulting gradient of the field strength is not less than 0.25 G km–1. This result seems to contradict the lower values of magnetic fields generally found above sunspots using the chromospheric H line. Some possible ways of overcoming this difficulty are proposed. 相似文献
9.
We investigate further the interpretation of dark magnetic faculae observed in previous imaging of the solar photosphere at 1.63 m. We show that their contrast at 1.63 m increases with magnetic flux beyond a threshold value of 2 × 1018 Mx and blends smoothly with the contrast vs flux relation measured at this wavelength for larger structures of sunspot size. Not all facular structures that are bright in Ca K are dark at 1.63 m, apparently because their magnetic flux is not large enough. After correction for blurring, the contrast of the dark faculae observed near the disc center at 1.63 m is approximately 4%. But our observations at 1.23 m, which probe slightly higher photospheric levels, do not show these dark faculae. These results indicate that magnetic flux tubes of diameter as small as 500 km significantly inhibit convective heat flow to the photosphere, much as do sunspot flux tubes of much larger diameter. They also suggest that, in even smaller flux tubes, the inhibition becomes rapidly less significant. Finally, we show that the sunspot-size dependence of umbral infrared contrast versus wavelength that we observe can probably be explained in terms of instrumental blurring. Observations with lower scattered light will be required to determine whether a real decrease of contrast with diameter also plays a role. 相似文献
10.
We use five-day helioseimic data from the Taiwan Oscillation Network to study the flow around a sunspot, NOAA 7887. The p-mode oscillations in an annular region centered at the sunspot are decomposed into the modes propagating toward and away from the sunspot. We find that the frequency of an outgoing mode is greater than that of the corresponding incoming mode. This indicates that the plasma is flowing outward from the sunspot. The outflow velocity is estimated to be about 40–80 m s-1. 相似文献
11.
Five days of coordinated observation were carried out from 24–29 September, 1987 at Big Bear and Huairou Solar Observatories. Longitudinal magnetic fields of an p sunspot active region were observed almost continuously by the two observatories. In addition, vector magnetic fields, photospheric and chromospheric Doppler velocity fields of the active region were also observed at Huairou Solar Observatory. We studied the evolution of magnetic fields and mass motions of the active region and obtained the following results: (1) There are two kinds of Moving Magnetic Features (MMFs). (a) MMFs with the same magnetic polarity as the center sunspot. These MMFs carry net flux from the spot, move through the moat, and accumulate at the moat's outer boundary. (b) MMFs in pairs of mixed polarity. These MMFs are not responsible for the decay of the spot since they do not carry away the net flux. MMFs in category (b) move faster than those of (a). (2) The speed of the mixed polarity MMFs is larger than the outflow measured by photospheric Dopplergrams. The uni-polar MMFs are moving at about the same speed as the Doppler outflow. (3) The chromospheric velocity is in approximately the opposite direction from the photospheric velocity. The photospheric Doppler flow is outward; chromospheric flow is inward. We also found evidence that downward flow appears in the photospheric umbra; in the chromosphere there is an upflow. 相似文献
12.
In this paper we present the results of a sunspot rotation study using Abastumani Astrophysical Observatory photoheliogram data for 324 sunspots. The rotation amplitudes vary in theinebreak 2–64° range (with maximum at 12–14°), and the periods around 0–20 days (with maximum atinebreak 4–6 days). It could be concluded that sunspot rotations are rather inhomogeneous and asymmetric, but several types of sunspots are distinguished by their rotational parameters.During solar activity maximum, sunspot average rotation periods and amplitudes slightly increase. This can be affected by the increase of sunspot magnetic flux tube depth. So we can suppose that sunspot formation during solar activity is connected to a rise of magnetic tubes from deeper layers of the solar photosphere, strengthening the processes within the tube and causing variations in rotation.There is a linear relation between tilt-angle oscillation periods and amplitudes, showing higher amplitudes for large periods. The variations of those periods and especially amplitudes have a periodical shape for all types of sunspots and correlate well with the solar activity maxima with a phase delay of about 1–2 years. 相似文献
13.
N. N. Kondrashova 《Kinematics and Physics of Celestial Bodies》2016,32(2):70-77
Semiempirical models of the photosphere of an Ellerman bomb in the NOAA 11024 active region were obtained using profiles of Stokes parameters I, Q, U, and V of photospheric lines. Spectropolarimetric observations were conducted using the French–Italian THEMIS telescope (Tenerife, Spain). The SIR inversion code [28] was used in the modeling. The models have two components: a magnetic flux tube and nonmagnetic surroundings. The dependences of temperature, magnetic field strength, inclination of the magnetic field vector, and line-of-sight velocity in the tube on the optical depth were obtained. The models demonstrate that the thermodynamic parameters of the Ellerman bomb photosphere differ considerably from those of the quiet photosphere. The temperature in the tube model varied nonmonotonically with height and deviated by up to 700–900 K from its values for the quiet photosphere. Downflows were observed in the lower and the upper photospheric layers. The line-of-sight velocity in the upper layers of the photosphere was as high as 17 km/s. The magnetic field strength in the models varied from 0.1–0.13 T in the lower photospheric layers to 0.04–0.07 T in the upper ones. The physical state of the photosphere did change in the course of observations. 相似文献
14.
The small-scale structure of solar magnetic fields has been studied using simultaneous recordings in the spectral lines Fe i 5250 Å and Fe i 5233 Å, obtained with the Kitt Peak multi-channel magnetograph. We find that more than 90% of the magnetic flux in active regions (excluding the sunspots), observed with a 2.4 by 2.4 aperture, is channelled through narrow filaments. This percentage is even higher in quiet areas. The field lines in a magnetic filament diverge rapidly with height, and part of the flux returns back to the neighbouring photosphere. Therefore the strong fields within a magnetic filament are surrounded by weak fields of the order of a few gauss of the opposite polarity. The field-strength distribution within a filament, including the surrounding opposite-polarity fields, seems to be almost the same for all filaments within a given active or quiet region.The analysis of a scan made during an imp. 2 flare showed that observations during and after the flare would give a fictitious decrease of the magnetic energy in the region by a factor of 2–3 due to line-profile changes during the flare.Visiting Astronomer, Kitt Peak National Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
15.
Joan A. Vorpahl 《Solar physics》1973,28(1):115-122
I examined a moderately active sunspot group, McMath 9735, and found that 15 of 16 flares observed in 1968, October 20–21 occurred near, and were preceded by, at least one of several EFR's (Emerging Flux Regions) in the area. Flares were larger and more numerous when: (1) the EFR appeared close to already existing spots, (2) a large amount of filament reorientation was occurring, and when (3) the EFR was most active, i.e., it was increasing in area and brightness and was accompanied by violent surging and great brightness fluctuations at the feet of the dark fibrils. Only two flares occurred at an inverted EFR, i.e., a leading spot with f polarity, however the largest event (2B) of the 15 quickly spread to this region after starting in a different EFR. A sunspot appeared in the inverted emerging flux region less than three hours after the flares. However this is thought to be merely an indication of the growing EFR and, therefore, a secondary effect. 相似文献
16.
Extrema in Sunspot Cycle Linked to Sun's Motion 总被引：1，自引：0，他引：1
Partitions of 178.8-year intervals between instances of retrograde motion in the Sun's oscillation about the center of mass of the solar system seem to provide synchronization points for the timing of minima and maxima in the 11-year sunspot cycle. In the investigated period 1632–1990, the statistical significance of the relationship goes beyond the level P=0.001. The extrapolation of the observed pattern points to sunspot maxima around 2000.6 and 2011.8. If a further connection with long-range variations in sunspot intensity proves reliable, four to five weak sunspot cycles (R0) are to be expected after cycle 23 with medium strength (R100). 相似文献
17.
Sunspots are strong absorbers of f and p modes. A possible absorption mechanism is direct conversion to slow magnetoacoustic waves. Calculations based on vertical magnetic field models show that this works well for f modes, but is inadequate for p modes. Using a very simple shallow spot model, in which the effects of the magnetic field are accounted for solely by a surface condition, we investigate the possibility that p modes first scatter into f modes inside the spot, which are then more susceptible to conversion to slow modes. We find that the coupling between an incident p mode and the internal f mode is unlikely to be strong enough to account for the observed absorption, but that the incident modes do couple strongly to the acoustic jacket in some cases, leading to a region immediately around the sunspot where a significant fraction of the surface velocity is due to the jacket modes. 相似文献
18.
Van Driel-Gesztelti L. Csepura G. Schmieder B. Malherbe J.-M. Metcalf T. 《Solar physics》1997,172(1-2):151-160
We present a study of the evolution of NOAA AR 7205 in the photosphere and corona, including an analysis of sunspot motions, and show the evolutionary aspects of flare activity using full-disc white-light observations from Debrecen, vector magnetograms from Mees Observatory, Hawaii, and Yohkoh soft X-ray observations. NOAA AR 7205 was born on the disc on 18 June, 1992. During the first 3 days it consisted of intermittent minor spots. A vigorous evolution started on 21 June when, through the emergence and merging (v 100–150 m s-1) of several bipoles, a major bipolar sunspot group was formed. Transverse magnetic fields and currents indicated the presence of shear (clockwise twist) already on 21 June (with 0.015 Mm-1). On 23 June, new flux emerged in the trailing part of the region with the new negative polarity spot situated very close to the big positive polarity trailing spot of the main bipole. The secondary bipole seemed to emerge with high non-potentality (currents). From that time the AR became the site of recurrent flare activity. We find that all 14 flares observed with the Yohkoh satellite occurred between the highly sheared new bipole and the double-headed principal bipole. Currents observed in the active region became stronger and more extended with time. We propose that the currents have been (i) induced by sunspot motions and (ii) increased by non-potential flux emergence leading to the occurrence of energetic flares (X1.8 and X3.9). This observation underlines the importance of flare analysis in the context of active region evolution. 相似文献
19.
The center-to-limb variation of the excess intensity in faculae was obtained for 266 active regions with an accuracy of 10–3. For this observation full-disk images were obtained with a rotating one-dimensional diode array whose rotation axis was set at the disk center, at the wavelength of 5450 Å with a bandpass of 400 Å. From the center-to-limb variation of excess intensity of active regions the excess effective temperature was found to be 6.4 K on the average where the mean longitudinal magnetic field is 65 G as measured by 5233 Å line. In other words the ratio of the excess radiative flux to the total flux was 0.44% on the average for the present measurements of low spatial resolution of 20.The average excess intensity for 60 active regions near the disk center was found to be 4 × 10–4 of the quiet Sun intensity. This very low excess brightness averaged over the whole active region, in contrast to the reported high excess brightness of facular points (diameter 0.2) of 0.4, leads to a hypothesis that the background in between facular points in the active region is darker than the true quiet photosphere by 1%. It is further surmised that the inferred darkness of intra facular points is due to partial compensation for excess total irradiance of facular points. This interpretation is also consistent with previous observations of the contrast of facular points near the limb. 相似文献
20.
We present observations of active region radio emission at 6.16 cm wavelength, obtained with an angular resolution of 3 by 10 arc using the Westerbork Synthesis Radio Telescope (WSRT) during the action interval May 20–27, 1980 of the Solar Maximum Year (SMY). We present maps in both total intensity (I) and circular polarization (V) of three regions (Hale numbers 16850, 16863, and 16864) and provide a detailed comparison of these maps with on- and off-band H pictures and with magnetograms. The strongest sources were associated with neutral lines and soft X-ray arcades. We present evidence that these neutral lines were characterized by having their two opposite polarities close to each other, implying a high magnetic field gradient, and by their association with arch filament systems. The sunspot associated radio sources had a relatively simple structure in region 16850; however for the large spots of regions 16864 and 16863 the emission had a patchy appearance with a tendency of the peaks to lie over the penumbra. In the V maps we observed for the first time two islands, polarized in the sense of the ordinary mode, which were located inside the sunspot associated sources and were associated with intrusions of opposite polarity field into the penumbra. These structures can be accounted for if the electron temperature along the line of sight is not a monotonically increasing function of height, but has a maximum near the second harmonic level. Finally we give a detailed analysis of observations of the inversion of the sense of circular polarization in region 16863. We find that the large scale structure of the magnetic field can be approximated by a dipole with its axis inclined by 11° with respect to the photosphere and with a dipole moment of about 2 × 1031 cgs units; the depolarization line is located at a height of 0.16–0.19 R above the dipole, where the estimated intensity of the magnetic field is 10–20 G. 相似文献