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O. Engvold 《Solar physics》1980,67(2):351-355
Observed H brightness versus size of emission substructures of quiescent prominences are compared with values predicted from thermodynamical models. The measured size of an emission element of a given brightness is substantially less than the theoretical value.Two possible causes for the discrepancy are suggested: (1) The partial filling of a recording aperture, due to the prominence fine structure, may affect the measurements seriously. Caution is therefore urged against using face values of observed brightness vs ratios in model calculations in cases of partly optically thick lines. (2) Changes of individual fine structure elements on a time scale of a few minutes implies that the prominence plasma may be in a non-stationary radiative state. 相似文献
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Observations of two quiescent filaments show oscillatory variations in Doppler shift and central intensity of the He i 10830 Å line.The oscillatory periods range from about 5 to 15 min, with dominant periods of 5, 9, and 16 min. The 5-min period is also detected in the intensity variations, after correction for atmospheric effects. Doppler shifts precede intensity variations by about one period. The possibility that the oscillations are Alfvén waves is discussed.The Doppler signals of the filament form fibril-like structures. The fibrils are all inclined at an angle of about 25° to the long axis of the filament. The magnetic field has a similar orientation relative to the major direction of the filament, and the measured Doppler signals are apparently produced by motions along magnetic flux tubes threading the filament.The measured lifetimes of the small-scale fibrils of quiescent disk filaments are very likely a combined effect of intensity modulations and reshuffling of the structures. 相似文献
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Oddbjørn Engvold 《Solar physics》1976,49(2):283-295
The fine structure of nonspot prominences are studied from H filtergrams. The size of the smallest prominence structures increases with height above the chromosphere. Some prominences contain structures close to 1/2 arc second, which is the spatial resolution in the present data. The effective thickness of many nonspot prominences ranges between 4 × 107 cm and 1.5 × 108 cm. An apparent downward directed motion is observed in the majority of the prominences. No preferred direction of the motion is seen in regions composed of comparatively large diffuse structures. Some bright threads are visible for 1 hr and longer. Bright knots have an average observed lifetime of about 8 min. The process of condensation and subsequent destruction of prominence fine structure appears to take place on a very short time scale compared to the life time of the regions where prominences may exist. The observed H brightness of the prominences in the present data may be accounted for as scattered chromospheric radiation. 相似文献
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High-resolution Hα filtergrams (0.2″) obtained with the Swedish 1-m Solar Telescope resolve numerous very thin, thread-like
structures in solar filaments. The threads are believed to represent thin magnetic flux tubes that must be longer than the
observable threads. We report on evidence for small-amplitude (1 – 2 km s−1) waves propagating along a number of threads with an average phase velocity of 12 km s−1 and a wavelength of 4″. The oscillatory period of individual threads vary from 3 to 9 minutes. Temporal variation of the
Doppler velocities averaged over a small area containing a number of individual threads shows a short-period (3.6 minutes)
wave pattern. These short-period oscillations could possibly represent fast modes in accordance with numerical fibril models
proposed by Díaz et al. (Astron. Astrophys.
379, 1083, 2001). In some cases, it is clear that the propagating waves are moving in the same direction as the mass flows. 相似文献
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Earlier studies of quiescent prominences claim that there is a systematic downward directed motion of the small-scale structure.
Disk observations, on the other hand, have detected mass motions both upwards and downwards. The earlier high-resolution observations
of limb prominences have been re-examined using local cross-correlation techniques for measurements of motion perpendicular
to the line of sight. The new measurements reveal flow speeds and directions that are in good agreement with current Doppler
measurements on the disk. 相似文献
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Solar Physics - A curved filament in a decaying active region (AR&;nbsp;8329) was observed on 9 September 1998 with a combination of several instruments. The main data base is a 4-hour long time... 相似文献
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The utility of very high dispersion spectra (5–11 mm/Å) for the study of line profile and velocity structure in quiescent prominences is demonstrated by observations, taken with the spectregraphic slit positioned normal to the limb in H 6563 Å, He D3 5876 Å, and Ca+K 3933 Å. The emission profiles of both H and the K line often show a central reversal (absorption). Emission structures in the K-line can be complex with details as narrow as 0.04 Å. Frequently this structure consists of two distinct components: a central, strong, rather narrow line, and an often displaced, weak feature of undefined profile appearing as fuzz. It is suggested that this fuzz indicates an exchange of matter between the prominence and the corona.Visiting Astronomer, Institute for Theoretical Astrophysics, Oslo, Norway.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
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The 180-degree ambiguity in magnetic field direction along polarity reversal boundaries can be resolved often and reliably
by the chiral method. The chiral method requires (1) identification of the chirality of at least one solar feature related
to a polarity reversal boundary along which the field direction is sought and (2) knowledge of the polarity of the network
magnetic field on at least one side of the polarity reversal boundary. In the context of the Sun, chirality is an observable
signature of the handedness of the magnetic field of a solar feature. We concentrate on how to determine magnetic field direction
from chirality definitions and illustrate the technique in eight examples. The examples cover the spectrum of polarity boundaries
associated with filament channels and filaments ranging from those connected with active regions to those on the quiet Sun.
The applicability of the chiral method to all categories of filaments supports the view that active region filaments and quiescent
filaments are the extreme ends in a continuous spectrum of filaments.
The chiral method is almost universally applicable because many types of solar features that reveal chirality are now readily
seen in solar images accessible over the World Wide Web; also there are clear differences between left-handed and right-handed
solar structures that can be identified in both high- and low-resolution data although high-resolution images are almost always
preferable. In addition to filaments and filament channels, chirality is identifiable in coronal loop systems, flare loop
systems, sigmoids, some sunspots, and some erupting prominences. Features other than filament channels and filaments can be
used to resolve the 180-degree ambiguity because there is a one-to-one relationship between the chiralities of all features
associated with a given polarity reversal boundary.
Y. Lin is now at the Institute of Theoretical Astrophysics, University of Oslo. 相似文献