-
[show abstract]
[hide abstract]
ABSTRACT: 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.
Solar Physics 04/2012; 250(1):31-51. · 2.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: High cadence high spatial resolution observations in H-alpha with the Swedish
1-m Solar Telescope on La Palma have revealed the existence of small-scale
highly dynamic bright blobs. A fast wavelength tuning spectro-polarimeter
provides spectral information of these structures. The blobs slide along thin
magnetic threads at speeds in the range from 45 km/s to 111 km/s. The blobs
have a slight elongated shape and their lengths increase by a factor of 3 from
close to 1/2 arcsec when they first appear till they disappear 1-2 min later.
The brightest blobs show the highest speed. The widths of the H-alpha line
emission of the blobs correspond to non-thermal velocities in the plasma less
than 10 km/s which imply that they are not the result of shock driven heating.
The dynamic character of the bright blobs is similar to what can be expected
from an MHD fast mode pulse.
01/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: From recent high-resolution observations obtained with the Swedish 1 m Solar Telescope in La Palma, we detect swaying motions of individual filament threads in the plane of the sky. The oscillatory characters of these motions are comparable with oscillatory Doppler signals obtained from corresponding filament threads. Simultaneous recordings of motions in the line of sight and in the plane of the sky give information about the orientation of the oscillatory plane. These oscillations are interpreted in the context of the magnetohydrodynamic (MHD) theory. Kink MHD waves supported by the thread body are proposed as an explanation of the observed thread oscillations. On the basis of this interpretation and by means of seismological arguments, we give an estimation of the thread Alfvén speed and magnetic field strength by means of seismological arguments.
The Astrophysical Journal 09/2009; 704(1):870. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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 – 2km s−1) waves propagating along a number of threads with an average phase velocity of 12km s−1 and a wavelength of4″. The oscillatory period of individual threads vary from 3 to 9minutes. Temporal variation of the
Doppler velocities averaged over a small area containing a number of individual threads shows a short-period (3.6minutes)
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.
Solar Physics 10/2007; 246(1):65-72. · 2.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Solar prominences are sheets of relatively cool and dense gas embedded in the surrounding hotter corona. An erupting prominence can inject a mass of up to 10
Nature 12/1998; 396(6710):440-441. · 36.28 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Although it is generally accepted that quiescent filaments have strong
horizontal axial magnetic field (Leroy,1984) the field configuration in
the legs (``barbs'' or ``feet'') is controversial. Previous observations
indicate both rising and falling Doppler motions in such appendages, at
speeds less than ``free-fall'' (Dunn,1960; Yi et al,1991; Zirker et al,
1994). Such observations could be consistent with the presence of
horizontal magnetic fields that are slowly drifting up and down carrying
plasma with them. However the H alpha fine-structure strongly suggests
the presence of vertical or highly inclined magnetic field lines.
Without vector field observations it is difficult to choose between
these alternatives. In an attempt to clarify the issue, H alpha
observations of a quiescent filament were made during its passage across
the disk, from 12 to 20 April, 1993 at the Big Bear Observatory.
Remarkable high-speed flows (of order 20 km/s ) were seen along the
axial "spine" of the filament. Substantially slower motions were
detected in the barbs. The paradox of non-free-fall motions in the
predominantly vertically directed threads of barbs, will be discussed
briefly. Bommier,V., Landi Degli'Innocenti,E., Leroy, J-L., and
Sahal-Brechot, S.: 1994, Solar Phys. 154,231 Dunn, R.B.,1960, Ph D
Thesis, Harvard University Engvold,O.: 1976,Solar Phys.49,283.
Leroy,J-L. Bommier,V. nd Sahal Brechot,S.:1984, Astronomy and
Astrophysics, 131,33. Yi,Z.,Engvold,O. and Keil,S.L.: 1991, Solar Phys.
132,63. Zirker,J.B.,Engvold,O.and Yi,Z. 1994, Solar Phys. 150,81.
11/1997; 29:1402.
-
[show abstract]
[hide abstract]
ABSTRACT: High resolution H alpha and magnetograms 0 2 arc sec of an active region
were obtained in alternating time series at 42 sec cadences using the
Swedish 1-m Solar Telescope on 2004 August 21 The 79 times 52 arcsec
field of view was centered at N11 W5 The H alpha filtergrams reveal an
active region filament and surges consisting of thread-like structures
which have widths similar to the widths of chromospheric fibrils both
recorded down to the resolution limit in the best images All observed
structures in the active region are highly dynamic The flow speeds in
some active filament threads 25 km s -1 are higher than typical speeds
in quiescent filament threads Fibrils show counterstreaming strongly
resembling the counterstreaming threads in filaments The transverse
speeds of mass within fibrils are comparable to the typical speeds of
mass flows in quiescent filament threads sim 10 km s -1 Streaming along
the threads of surges extending more than 10 arc sec is higher in speed
sim 20 km s -1 than in the filament and fibrils and appears to flow over
the chromospheric fibrils Small surges near one end of the filament
appear to flow into the filament thereby mass seems to be added to the
filament Blue shifts seen in the H alpha Dopplergrams confirm the
outward mass motion of the surges However in at least one case we also
see simultaneous red shifts from the same site in the opposite direction
toward the chromosphere We suggest that the site between these two
opposite motions identifies the place where magnetic
36:3193.
-
[show abstract]
[hide abstract]
ABSTRACT: High resolution Hα images and magnetograms (0.2 arc s) of an active region were obtained in alternating time series at 42 s cadences using the Swedish 1-m Solar Telescope on 2004 August 21. The Hα filtergrams reveal an active region filament and surges consisting of thread-like structures which have widths similar to the widths of chromospheric fibrils, both recorded down to the resolution limit in the best images. All observed structures in the active region appear highly dynamic. Fibrils show counterstreaming strongly resembling the counterstreaming threads in filaments.Streaming, along the threads of surges extending more than 10 arc s, is higher in speed (∼20 km s−1) than in the filament and fibrils and appears to flow independently over and above the chromospheric fibrils. Blue shifts seen in the Hα Dopplergrams confirm the outward mass motion of the surges. However, in at least one case, we also see simultaneous downflows from the same site but in the opposite direction and downward toward the chromosphere. We suggest that the site between these two outward and downward flows identifies the place where magnetic reconnection could occur and thereby cause of the surge. This appears to imply that the reconnection site is in the high chromosphere or low corona.
Advances in Space Research.
