Braided Structures Observed in Flare-Associated Hα Filaments

1979 ◽  
Vol 44 ◽  
pp. 272-274
Author(s):  
V. Gaizauskas
Keyword(s):  
Fine Structure ◽  
Magnetic Fields ◽  
Spatial Data ◽  
Active Regions ◽  
Solar Observatory ◽  
Pass Band ◽  
Ottawa River ◽  
Doppler Shifts ◽  
Quantitative Measurements ◽  
Full Resolution

The motions of flare-associated filaments and prominences produce such large Doppler shifts that the morphology of these active phenomena cannot be studied without filtergrams taken in rapid succession at a number of wavelengths across the Hα line. It is therefore standard practice at the Ottawa River Solar Observatory (ORSO) to photograph single active regions through a Zeiss filter while the pass-band (0.25A) of the filter is stepped continously back and forth across the Hα line. A typical scan consists of 17 steps in the range Hα ± 1.4A and is completed in 42 seconds. Important by-products result from this procedure, especially when the seeing allows the full resolution (0.7 arc-sec) of the 25 cm objective of the ORSO photoheliograph to be realized. First, filtergrams taken outside the core of Hα (Δλ≥ 0.9A) reveal the bright photospheric network (Vrabec, 1971; Dunn and Zirker, 1973; Dravins, 1974) which is, within the resolution capabilities of this instrument, co-spatial with strong magnetic fields near photospheric levels. In active regions the photospheric network is enhanced in brightness and becomes plainly visible as an aggregation of interlocking cells of various sizes. These data supplement magnetograms which are still needed to identify polarities and to furnish quantitative measurements of magnetic flux. Second, the visibility of the multi-threaded fine structure of filaments is usually much improved at wavelengths displaced from the centre of Hα. Thus a single instrument can provide the spatial data for investigating the relationship between the fine structure of filaments and highly localized concentrations of strong photospheric magnetic fields.

scholarly journals Magnetic Fields Measured with the 10830 Å HeI Line

1971 ◽  
Vol 43 ◽  
pp. 279-288 ◽  
Author(s):  
J. Harvey ◽  
D. Hall
Keyword(s):  
Fine Structure ◽  
Magnetic Fields ◽  
Near Infrared ◽  
Active Regions ◽  
Field Measurements ◽  
Spectral Lines ◽  
Magnetic Field Measurements ◽  
Infrared Spectral ◽  
Polarity Reversals ◽  
Absorption Features

Several advantages of near infrared spectral lines for magnetic field measurements are listed. In particular, the 10830 Å multiplet of HeI is well suited for observations of chromospheric magnetic fields.New photoelectric spectroheliograms made with the 10830 Å line reveal a large amount of filamentary fine structure in active regions. This fine structure has important consequences on the interpretation of 10830 Å magnetograms. Except for an association of 10830 Å disk filaments with polarity reversals there is little correlation between absorption features and the 10830 Å longitudinal field. Comparisons of chromospheric and photospheric observations show that the chromospheric field is spatially more diffuse and weaker than the photospheric field.

scholarly journals Of Tilt and Twist

2005 ◽  
Vol 13 ◽  
pp. 135-135
Author(s):  
Zachary A. Holder ◽  
Richard C. Canfield ◽  
Rebecca A. McMullen ◽  
Robert F. Howard ◽  
Alexei A. Pevtsov
Keyword(s):  
Active Region ◽  
Magnetic Fields ◽  
Active Regions ◽  
Solar Observatory ◽  
Flux Tubes ◽  
Vector Magnetograms ◽  
Full Disk

AbstractUsing Mees Solar Observatory active-region vector magnetograms and Mt. Wilson Observatory full-disk longitudinal magnetograms, we measure both the twist and tilt of the magnetic fields of 368 active regions. This dataset clearly shows two well-known phenomena, Joy’s law and the hemispheric helicity rule, as well as a lesser-known twist-tilt relationship, which is the point of this work. Those regions that closely follow Joy’s law show no twist-tilt relationship, which is a predicted consequence of convective buffeting of initially untwisted and unwrithed flux tubes through the Σ effect. Those regions that strongly depart from Joy’s law show significantly larger than average twist and a very strong twist-tilt relationship. These properties suggest that the twist-tilt relationship in these regions is due to kinking of flux tubes that are highly twisted but not strongly writhed.

scholarly journals The formation, structure and changes in filaments in active regions

1968 ◽  
Vol 35 ◽  
pp. 267-279 ◽  
Author(s):  
Sara F. Smith
Keyword(s):  
Fine Structure ◽  
Image Quality ◽  
Large Scale ◽  
Active Regions ◽  
Solar Observatory ◽  
Granular Structure ◽  
Solar Granulation ◽  
Good Image Quality ◽  
Good Image

During periods of good image quality the large-scale films of the Lockheed Solar Observatory obtained during 1966 and 1967 have proven to be especially useful for studying filaments and their relationship to the Hα fine structure observed in active regions. Structures with dimensions on the order of 1 sec of arc can frequently be resolved, as illustrated in Figure 1. The ‘solar vortices’ are clearly resolved into numerous individual fibrils. Bright Hα plage is resolved into a fine granular structure resembling the solar granulation. Filaments are usually seen as irregular dense collections of material which are occasionally resolved into finer striations which run parallel to the path of the filaments.

scholarly journals The connection of fine-structure photospheric features in active regions with magnetic fields

1968 ◽  
Vol 35 ◽  
pp. 201-201
Author(s):  
N. V. Steshenko
Keyword(s):  
Magnetic Field ◽  
Fine Structure ◽  
High Resolution ◽  
Magnetic Fields ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Active Regions ◽  
Transverse Magnetic ◽  
List Type ◽  
The Magnetic Field

1.The fine structure of the proton sunspot group of July 4–8, 1966 was studied on the basis of high-resolution heliograms. The comparison of the orientation between penumbral filaments and the transverse magnetic fields (observed by A.B. Severny and T.T. Tsap) shows that the direction of the filaments coincides in general with that of the magnetic field.2.Measurements of the magnetic fields of smallest pores (1·5″-2″) showed that the pores are always connected with strong magnetic field (in average 1400 gauss), which is localized at the same small area as the pore.3.Magnetic fields of faculae are concentrated in small elements with the dimension not exceeding 1·5″-3″. Magnetic-field strength H|| of about 45% of facular granules is within the limits of photographic measuring errors (approximately 25 gauss). For a quarter of all facular granules the strength H|| is from 25–50 gauss; about 30% of facular granules have H|| > 50 gauss, and sometimes there appear faculae with field strength of about 200 gauss. The magnetic-field strength of facular granules, which are found directly above spots, is 10–20 times less than the field strength of spots. This field is 80–210 gauss only.4.All observational data mentioned above show that the appearance of the fine-structure features in active regions is directly connected with the fine structure of magnetic field of different strength and different orientation. The study of high-resolution heliograms gives additional information about the fine structure of the magnetic field.

scholarly journals On the manifestation in the Sun-as-a-star magnetic field measurements of the quiet and active regions

2010 ◽  
Vol 6 (S273) ◽  
pp. 56-60 ◽  
Author(s):  
Mikhail Demidov
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Active Regions ◽  
Field Measurements ◽  
Solar Observatory ◽  
Spectral Lines ◽  
The Sun ◽  
Time Data ◽  
Full Disk

AbstractThe best way to test the stellar magnetic field mapping codes is to apply them, with some changes, to the Sun, where high-precision disk-integrated and disk-resolved observations are available for a long time. Data sets of the full-disk magnetograms and the solar mean magnetic fields (SMMF) measurements are provided, for example, by the J.M.Wilcox Solar observatory (WSO) and by the Sayan Solar observatory (SSO). In the second case the measurements in the Stokes-meter mode simultaneously in many spectral lines are available. This study is devoted to analysis of the SSO quasi-simultaneous full-disk magnetograms and SMMF measurements. Changes of the SMMF signal with rotation of the surface large-scale magnetic fields are demonstrated. Besides, by deleting of selected pixels with active regions (AR) from the maps their contribution to the integrated SMMF signal is evaluated. It is shown that in some cases the role of AR can be rather significant.

scholarly journals Helicity Generation and Signature in Solar Atmosphere

2005 ◽  
Vol 13 ◽  
pp. 89-93 ◽  
Author(s):  
A. A. Pevtsov
Keyword(s):  
Fine Structure ◽  
Magnetic Fields ◽  
Solar Atmosphere ◽  
Active Regions ◽  
Turbulent Convection ◽  
Coronal Loops ◽  
The Sun ◽  
Solar Magnetic Fields ◽  
And Topology ◽  
Current Helicity

AbstractTo fully understand the origin, evolution and topology of solar magnetic fields, one should comprehend their magnetic helicity. Observationally, non-zero helicity reveals itself in the patterns of electric currents inside active regions, superpenumbral sunspot whirls, the shape of coronal loops and the fine structure of chromospheric filaments. Some patterns may bear information about deep sub-photospheric processes (e.g., dynamo, turbulent convection). Others may originate at or near the photosphere. This presentation reviews the observations of magnetic and current helicity on the Sun, discusses the possible mechanisms of helicity generation, and compares them with the observations.

scholarly journals Summary-Introduction

1960 ◽  
Vol 12 ◽  
pp. 403-415
Author(s):  
A. B. Severny
Keyword(s):  
Magnetic Fields ◽  
Active Regions ◽  
Magnetic Activity ◽  
Velocity Fields ◽  
Spectral Lines ◽  
The Sun ◽  
Line Profiles ◽  
Doppler Shifts ◽  
State Of Affairs ◽  
Image Position

Speaking on localized velocity fields on the Sun, we mean the velocity fields in active regions on the disk. The experimental data used to picture these fields are based mainly on 1) the observations of Doppler shifts of spectral lines, 2) the form (asymmetry) of line profiles, 3) moving picture process in monochromatic, mainly Hα and H or K, light. However the big skin-time of solar plasma makes these data insufficient to get an adequate and complete idea about the motions in active regions, and we must also take into account the available observational data about magnetic fields in these regions. Somewhere the state of affairs permits one to disregard the possible influence of magnetic fields on the picture of velocity fields But these occasions are comparatively rare, because the main source of solar activity is closely, but in a not quite recognized way, connected with magnetic activity of the Sun. This is why we should in our talk consider as closely as possible both subjects—the motions in active regions and their magnetic fields. The best illustrations of the necessity of such a mode of consideration are the velocity fields in sunspots.

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

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