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  • 1
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    Average photospheric poloidal and toroidal magnetic field components near solar minimum (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Average (over longitude and time) photospheric magnetic field components are derived from 3-min Stanford magnetograms made near the solar minimum of cycle 21. The average magnetograph signal is found to behave as the projection of a vector for measurements made across the disk. The poloidal field exhibits the familiar dipolar structure near the poles, with a measured signal in the line Fe I 5250 A of about 1 G. At low latitudes the poloidal field has the polarity of the poles, but is of reduced magnitude (about 0.1 G). A net photospheric toroidal field with a broad latitudinal extent is found. The polarity of the toroidal field is opposite in the northern and southern hemispheres and has the same sense as subsurface flux tubes giving rise to active regions of solar cycle 21. These observations are used to discuss large-scale electric currents crossing the photosphere and angular momentum loss to the solar wind.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 61; Mar. 197
    Format: text
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  • 2
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    An investigation of the 1.9 A feature in solar-flare X-ray spectra (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The 1.9 A feature, observed in the X-ray spectra of three solar flares with the Columbia University and Lockheed Palo Alto Research Laboratory spectrometers on the OSO 8 satellite, is shown to be due to a blend of 1s-2p transitions in a range of Fe ions. In the temperature range 9-16 x -10 to the 6th K, the feature has a mean wavelength of 1.900 + or - 0.009 A and is 0.04 A wider than a single line, indicating that the main contributors are Fe XIX-Fe XXII. Most of the emission originates from the dielectronic recombination process, and when inner-shell excitation is included together with normal collisional excitation, the observed intensity of the feature can be accounted for adequately. For these events, if the electron density is below approximately 10 to the 12th/cu cm, deviations from ionization equilibrium will be significant for ions more highly ionized than Fe XXI.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 231
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  • 3
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    H-alpha macrospicules - Identification with EUV macrospicules and with flares in X-ray bright points (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The paper presents observational evidence that two newly observed transient solar phenomena, EUV macrospicules and X-ray bright-point flares, are closely related. Time-lapse H-alpha filtergram observations of the limb in quiet regions show small surgelike eruptions called H-alpha macrospicules. From the similarity of H-alpha macrospicules and EUV macrospicules, and from comparison of simultaneous H-alpha and He II 304 A observations, we conclude that H-alpha macrospicules are EUV macrospicules viewed in H-alpha, although most EUV macrospicules are too faint in H-alpha to appear on H-alpha filtergrams of normal exposure. From comparison of simultaneous X-ray and H-alpha observations of flares in X-ray bright points situated on the limb, we show that flares in X-ray bright points often produce H-alpha macrospicules.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 218
    Format: text
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  • 4
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    Variations in plasma characteristics near D sheets in the solar wind (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A strong interplanetary shock was detected by the Pioneer 8 magnetometer, plasma probe, and wave instrument at 0048 UT, on June 11, 1968. During the rest of this day the interplanetary medium was highly disturbed as seven well-defined current layers or D sheets, as well as a number of other localized interaction regions, swept past the spacecraft. The local plasma characteristics that were best correlated with passage of the D sheets appeared to involve changes in the suprathermal electron population. Changes in the 400-Hz wave levels were also detected near the discontinuities during periods when the local ion plasma frequency was near 400 Hz, but the limited measurement capability of the Pioneer 8 wave instrument does not allow an unambiguous identification of the wave-particle interactions associated with these measurements.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research; 81; Nov. 1
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  • 5
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    Comparison of H alpha synoptic charts with the large-scale solar magnetic field as observed at Stanford (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Two methods of observing the neutral line of the large-scale photospheric magnetic field are compared: (1) neutral line positions inferred from H alpha photographs and (2) observations of the photospheric magnetic field made with low spatial resolution (3 arc min.) and high sensitivity using the Stanford magnetograph. The comparison is found to be very favorable.
    Keywords: SOLAR PHYSICS
    Type: NASA-CR-154125 , SU-IPR-700
    Format: application/pdf
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  • 6
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    The solar XUV spectrum of He II (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: OSO-7 observations of the first five Lyman lines and the Lyman continuum of He II are given for the quiet sun, a coronal hole, prominences, filaments, and the flare of August 7, 1972. These data are calibrated and given in specific intensity units together with color and brightness temperatures for the He II continuum. It is found that He II is overionized in all features except the flare and that the continuum is formed at temperatures near 14,000 K. The He II-He III ionization equilibrium appears to be dominated by photoionizations and radiative recombinations. Schematic calculations for realistic chromosphere and transition-region models can account for the observed intensities of Ly-beta through Ly-epsilon, the Lyman continuum, and its color temperature. To account for the intensity of Ly-alpha, either an implausible 100-km plateau at temperatures near 80,000 K is needed or, more likely, the diffusion-enhanced collisional excitation should be incorporated into the models.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; 203; Jan. 15
    Format: text
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  • 7
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    Relation of the observed far ultraviolet solar irradiance to the solar magnetic sector structure (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 45; Nov. 197
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  • 8
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    The strength of the sun's polar fields (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The magnetic field strength within the polar caps of the sun is an important parameter for both the solar activity cycle and for our understanding of the interplanetary magnetic field. Measurements of the line-of-sight component of the magnetic field generally yield 0.1 to 0.2 mT near times of sunspot minimum. This paper reports measurements of the polar fields made at the Stanford Solar Observatory using the Fe I line at 525.02 nm. It is found that the average flux density poleward of 55 deg latitude is about 0.6 mT peaking to more than 1 mT at the pole and decreasing to 0.2 mT at the polar cap boundary. The total open flux through either polar cap thus becomes about 3 x 10 to the 14th Wb. It is also shown that observed magnetic field strengths vary as the line-of-sight component of nearly radial fields.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 58; July 197
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  • 9
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    The mean magnetic field of the sun - Observations at Stanford (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A solar telescope has been built to study the organization and evolution of large-scale solar magnetic fields and velocities. The observations are made using a Babcock-type magnetograph connected to a 22.9-m vertical Littrow spectrograph. Sun-as-a-star integrated-light measurements of the mean solar magnetic field have been made daily since May 1975. The typical mean-field magnitude has been about 0.15 G, with a typical measurement error of less than 0.05 G. The mean-field polarity pattern is essentially identical to the interplanetary-magnetic-field sector structure (seen near earth with a four-day lag). The differences in the observed structures can be understood in terms of a 'warped current sheet' model.
    Keywords: SOLAR PHYSICS
    Type: AD-A086395 , Solar Physics; 54; Oct. 197
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  • 10
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    The mean magnetic field of the sun: Observations at Stanford (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A solar telescope was built at Stanford University to study the organization and evolution of large-scale solar magnetic fields and velocities. The observations are made using a Babcock-type magnetograph which is connected to a 22.9 m vertical Littrow spectrograph. Sun-as-a-star integrated light measurements of the mean solar magnetic field were made daily since May 1975. The typical mean field magnitude is about 0.15 gauss with typical measurement error less than 0.05 gauss. The mean field polarity pattern is essentially identical to the interplanetary magnetic field sector structure (seen near the earth with a 4 day lag). The differences in the observed structures can be understood in terms of a warped current sheet model.
    Keywords: SOLAR PHYSICS
    Type: NASA-CR-153255 , SU-IPR-682
    Format: application/pdf
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