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  • 1
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    Observations of the longitudinal magnetic field in the transition region and photosphere of a sunspot (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The Ultraviolet Spectrometer and Polarimeter on the Solar Maximum Mission spacraft has observed for the first time the longitudinal component of the magnetic field by means of the Zeeman effect in the transition region above a sunspot. The data presented here were obtained on three days in one sunspot, have spatial resolutions of 10 arcsec and 3 arcsec, and yield maximum field strengths greater than 1000 G above the umbrae in the spot. The method of analysis, including a line-width calibration feature used during some of the observations, is described in some detail in an appendix; the line width is required for the determination of the longitudinal magnetic field from the observed circular polarization. The transition region data for one day are compared with photospheric magnetograms from the Marshall Space Flight Center. Vertical gradients of the magnetic field are compared from the two sets of data; the maximum gradients of 0.41 to 0.62 G/km occur above the umbra and agree with or are smaller than values observed previously in the photosphere and low chromosphere.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 81; Dec. 198
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
    Electronic Resource
    Electronic Resource
    The spiral configuration of sunspot magnetic fields (1977)
    Springer
    Solar physics 53 (1977), S. 3-13 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Distributions of circularly and linearly polarized intensities are computed using an analytical magnetic field model for an isolated sunspot, and these intensity distributions are compared with observed intensities in all Stokes parameters in the λ 5250 line measured with the Marshall Space Flight Center's vector magnetograph. The qualitative agreement between measured and calculated linearly polarized intensity distributions is discussed with regard to implications as to the configuration of the transverse magnetic field of the isolated sunspot.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02260205
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    A quantitative study relating observed shear in photospheric magnetic fields to repeated flaring (1984)
    Springer
    Solar physics 91 (1984), S. 115-126 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper we present a quantitative evaluation of the shear in the magnetic field along the neutral line in an active region during an epoch of flare activity. We define shear as the angular difference in the photosphere between the potential magnetic field, which fits the boundary conditions imposed by the observed line-of-sight field, and the observed magnetic field. For the active region studied, this angular difference (shear) is non-uniform along the neutral line with maxima occurring at the locations of repeated flare onsets. We suggest that continued magnetic evolution causes the field's maximum shear to exceed a critical value of shear, resulting in a flare around the site of maximum shear. Evidently, the field at the site of the flare must relax to a state of shear somewhat below the critical value (but still far from potential), with subsequent evolution returning the field to the critical threshold. We draw this inference because several flares occurred at sites of maximum photospheric shear which were persistent in location.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00213618
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Observations of the longitudinal magnetic field in the transition region and photosphere of a sunspot (1982)
    Springer
    Solar physics 81 (1982), S. 231-244 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Ultraviolet Spectrometer and Polarimeter on the Solar Maximum Mission spacecraft has observed for the first time the longitudinal component of the magnetic field by means of the Zeeman effect in the transition region above a sunspot. The data presented here were obtained on three days in one sunspot, have spatial resolutions of 10 arc sec and 3 arc sec, and yield maximum field strengths greater than 1000 G above the umbrae in the spot. The method of analysis, including a line-width calibration feature used during some of the observations, is described in some detail in an appendix; the line width is required for the determination of the longitudinal magnetic field from the observed circular polarization. The transition region data for one day are compared with photospheric magnetograms from the Marshall Space Flight Center. Vertical gradients of the magnetic field are computed from the two sets of data; the maximum gradients of 0.41 to 0.62 G km−1 occur above the umbra and agree with or are smaller than values observed previously in the photosphere and low chromosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00151299
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Interpretation of vector magnetograph data including magneto-optic effects (1983)
    Springer
    Solar physics 88 (1983), S. 51-64 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper, the presence of Faraday rotation in measurements of the orientation of a sunspot's transverse magnetic field is investigated. Using observations obtained with the Marshall Space Flight Center's (MSFC) vector magnetograph, the derived vector magnetic field of a simple, symmetric sunspot is used to calculate the degree of Faraday rotation in the azimuth of the transverse field as a function of wavelength from analytical expressions for the Stokes parameters. These results are then compared with the observed rotation of the field's azimuth which is derived from observations at different wavelengths within the Fei 5250 Å spectral line. From these comparisons, we find: the observed rotation of the azimuth is simulated to a reasonable degree by the theoretical formulations if the line-formation parameter η o is varied over the sunspot; these variations in η o are substantiated by the line-intensity data; for the MSFC system, Faraday rotation can be neglected for field strengths less than 1800 G and field inclinations greater than 45°; to minimize the effects of Faraday rotation in sunspot umbrae, MSFC magnetograph measurements must be made in the far wings of the Zeeman-sensitive spectral line.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00196176
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Vertical gradients of sunspot magnetic fields (1983)
    Springer
    Solar physics 84 (1983), S. 13-31 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper, we describe results of a Solar Maximum Mission (SMM) guest investigation to determine vertical gradients of sunspot magnetic fields for the first time from coordinated observations of photospheric and transition-region fields. Both the photospheric vector field of a sunspot, derived from observations using the NASA Marshall Space Flight Center vector magnetograph, and the line-of-sight component in the transition region, obtained from the SMM Ultraviolet Spectrometer and Polarimeter instrument, are described. From these data, vertical gradients of the line-of-sight magnetic field component are calculated using three methods. (1) The vertical gradient is derived directly from the observations assuming a height difference of 2000 km between the photosphere and transition region. (2) Using the observed transverse photospheric field, the initial gradient (ΔB z/Δz) z = 0 , is calculated from the condition ▽ · B = 0. (3) Using the photospheric line-of-sight component as the boundary condition in a potential-field calculation, the extrapolated potential field at different heights is compared to the observed transition-region field; from these comparisons, an average height difference is derived and used to calculate the average vertical gradient (Δ B z/Δz). Comparisons of gradients derived from these three methods show consistent results for methods (2) and (3). Deviations of the calculated potential transverse field at z = 0 from the observed transverse component are investigated to assess the validity of gradient calculations using method (3). Since the field is shown to be very close to a potential distribution, we conclude that the vertical gradient of B z is lower than values from previous studies and the transition-region field occurs at a height of ≈ 4000–6000 km above the photosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00157439
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Photospheric electric current and transition region brightness within an active region (1984)
    Springer
    Solar physics 91 (1984), S. 235-242 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Distributions of vertical electric current density (J z) calculated from vector measurements of the photospheric magnetic field are compared with ultraviolet spectroheliograms to investigate whether resistive heating is an important source of enhanced emission in the transition region. The photospheric magnetic fields in Active Region 2372 were measured on 6 and 7 April, 1980 with the MSFC vector magnetograph; ultraviolet wavelength spectroheliograms (Lα and Nv 1239 Å) were obtained with the UVSP experiment aboard the Solar Maximum Mission satellite. Spatial registration of the J z (5 arc sec resolution) and UV (3 arc sec resolution) maps indicates that the maximum current density is cospatial with a minor but persistent UV enhancement, but there is little detected current associated with other nearby bright areas. We conclude that although resistive heating may be important in the transition region, the currents responsible for the heating are largely unresolved in our measurements and have no simple correlation with the residual current measured on 5 arc sec scales.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00146296
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  • 8
    Electronic Resource
    Electronic Resource
    A comparison of vector magnetograms from the marshall space flight center and mees solar observatory (1992)
    Springer
    Solar physics 138 (1992), S. 49-68 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We compare completely independent vector magnetic field measurements from two very different polarimetric instruments. The Marshall Space Flight Center's imaging vector magnetograph is based on a birefringent filter, routinely measuring all four Stokes parameters integrated over the filter bandpass (1/8 Å) which is tunable across the Fei λ5250 line in 10 mÅ steps. The Haleakala Stokes Polarimeter of the Mees Solar Observatory (MSO) is based on a spectrometer, routinely measuring all four Stokes parameters of the Fei λ6302.5 line simultaneously and then spatially scanning to build up a vector magnetogram. We obtained active region magnetic field data with both the Marshall Space Flight Center (MSFC) and MSO systems on five days during June 1985. After interpolating the MSFC vector fields onto the more coarse spatial grid of MSO we make a point-by-point comparison of the two vector fields for data obtained on two of these days (June 8 and 9). From this comparison we conclude: (1) the spatially-averaged line-of-sight components agree quite well; (2) although the MSO spatial grid is coarser, the quality of the MSO image is better than that of the MSFC data because of better seeing conditions; (3) the agreement between the transverse magnitudes is affected by the poor image quality of the MSFC data; and (4) if the effects of Faraday rotation caused by including line-center linear polarization in the method of analysis are taken into account, the azimuths show good agreement within the scatter in the data caused by the averaging process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00146196
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    The MSFC vector magnetograph (1982)
    Springer
    Solar physics 80 (1982), S. 33-51 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The NASA/Marshall Space Flight Center's solar vector magnetograph system is described; this sytem allows measurements of all components of the Sun's photospheric magnetic field over a 5 × 5 or 2.0 × 2.0 arc min square field-of-view with an optimum time resolution of ∼ 100 s and an optimum signal-to-noise of ∼ 1600. The basic system components are described, including the optics, detector, digital system and associated electronics. Automatic sequencing and control functions are outlined as well as manual selections of system parameters which afford unique system flexibility. Results of system calibration and performance are presented, including linearity, dynamic range, uniformity, spatial and spectral resolutions, signal-to-noise, electro-optical retardation and polarization calibration. Scientific investigations which utilize the unique characteristics of the instrument are described and typical results are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00153422
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Evolutionary and flare-associated magnetic shear variations observed in a complex, flare-productive active region (1993)
    Springer
    Solar physics 148 (1993), S. 277-299 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Evolution of nonpotential structures in a complex, flare-productive active region NOAA AR 6555 has been studied during the period March 23–26, 1991, using a quantitative description of the degree of magnetic shear at both local and regional scales. Distinct shear evolution in four subareas of AR 6555 is inferred from daily variation of their shear indices. Subareas which showed significant evolution in their overall magnetic structure are found to be most active. Hα flare ribbons mostly formed bordering, andnot within, areas of large shear and expanded over areas of lower shear. Magnetic shear changes are also detected during several flares, including a major X4.7/4B flare. Out of the 14 events for which temporally contiguous magnetograms were available, a decrease, or dip, in area-averaged shear index around flare onset time followed by an increase was observed in eight cases. There were two events with increase, three events with continuous decrease, and one event with no change in the shear index during the flare.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00645091
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