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  • 1
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    Prominence formation in a coronal loop (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A model is presented which depends on the preferential deposition of heating in the legs of a coronal loop and which produces a stable prominence-scale condensation at the loop top. Dynamic stability is attained by the subsequent adjustment of local parallel gravity by a magnetic inversion at the loop (or arcade) apex. A nonlinear numerical simulation of this process, which includes a deep chromosphere, a heating rate with a fixed dissipation length, and full solar gravity is described.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 359; 228-231
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  • 2
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    The nonlinear evolution of magnetized solar filaments (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Thermal instability driven by optically thin radiation is believed to initiate the formation of plasma filaments in the solar corona. The fact that filaments are observed generally to separate regions of opposite, line-of-sight, magnetic polarity in the underlying photosphere suggests that filament formation requires the presence of a highly sheared, local magnetic field. Two-dimensional, nonlinear, magnetohydrodynamic simulations of the local genesis and growth of solar filaments in a force-free, sheared, magnetic field were performed, and the evolution of generic perturbations possessing broad spatial profiles was traced. It was found that simulations of the evolution of initial random-noise perturbations produce filamentary plasma structures that exhibit densities and temperatures characteristic of observed solar filaments. Furthermore, in each of these simulations, the filament axis lies at a finite angle with respect to the local magnetic field, consistent with solar observations.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 353; 297-312
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  • 3
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    MHD simulations of coronal mass ejections - Importance of the driving mechanism (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The importance of the form of the driving mechanism in MHD simulations of coronal mass ejections is investigated. A model simulation problem is devised, and it is found that the use of a simple form for the initial corona, with an upward moving parcel of cold, dense plasma as the driving mechanism, can produce results that are consistent with many of the features observed by coronagraphs. The results imply that the nature of the driving mechanism may play an important role in determining the dynamical evolution of mass ejections.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 4229-423
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  • 4
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    An interplanetary planar magnetic structure oriented at a large (about 80 deg) angle to the Parker spiral (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Magnetic field structures in the solar wind, characterized by a variation of the field vectors within a plane inclined to the ecliptic ('Planar Magnetic Structures', PMSs), were reported recently (Nakagawa et al., 1989). These PMSs have the property that the plane of variation of the field also contains the nominal Parker spiral direction. An observation of a PMS where the direction of the line of intersection of the plane of field variation with the ecliptic plane makes a large (about 80 deg) angle to the Parker spiral direction is presented. Furthermore, the angular variables of the field (1) vary over a restricted range, and (2) are linearly related. The latter property is related to the former. Currently proposed models for the origin of PMS, inasmuch as they require field configurations which retain strict alignment with the Parker spiral direction from formation to observation, are probably incomplete.
    Keywords: SOLAR PHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1025-102
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  • 5
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    Ten Years of Solar Change as Monitored by SBUV and SBUV/2 (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Observations of the Sun by the Solar Backscatter Ultraviolet (SBUV) instrument aboard Nimbus 7 and the SBUV/2 instrument aboard NOAA-9 reveal variations in the solar irradiance from 1978, to 1988. The maximum to minimum solar change estimated from the Heath and Schlesinger Mg index and wavelength scaling factors is about 4 percent from 210 to 260 nm and 8 percent for 180 to 210 nm; direct measurements of the solar change give values of 1 to 3 percent and 5 to 7 percent, respectively, for the same wavelength range. Solar irradiances were high from the start of observations, late in 1978, until 1983, declined until early 1985, remained approximately constant until mid-1987, and then began to rise. Peak-to-peak 27-day rotational modulation amplitudes were as large as 6 percent at solar maximum and 1 to 2 percent at solar minimum. During occasional intervals of the 1979 to 1983 maximum and again during 1988, the dominant rotational modulation period was 13.5 days. Measurements near 200 to 205 nm show the same rotational modulation behavior but cannot be used to track long-term changes in the Sun because of uncertainties in the characterization of long-term instrument sensitivity changes.
    Keywords: SOLAR PHYSICS
    Type: Climate Impact of Solar Variability; p 341-348
    Format: application/pdf
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  • 6
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    The systematic radial downflow in the transition region of the quiet sun from limb-to-limb observations of the C IV resonance lines (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: This paper presents absolute velocities of C IV 1548, 1550 nm measured as a function of position along the solar equator, which was free of both active regions and coronal holes, and uniformly representative of the quiet sun. These observations were made with moderate spatial resolution (18 arcsec) using an EUV spectrometer dedicated to measuring absolute wavelengths (velocities) by direct comparison with a platinum spectrum generated on board the sounding rocket. On the assumption that systematic horizontal motions cancel statistically so that the line-of-sight velocities approach zero at the limb, a net radial downflow of 7.5 + or - 1.0 km/sec was found. The assumption was tested using the wavelength reference and found to be valid within the absolute accuracy of the rest wavelengths of the C IV lines.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 358; 693-697
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  • 7
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    Sounding rocket measurement of the absolute solar EUV flux utilizing a silicon photodiode (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A newly developed stable and high quantum efficiency silicon photodiode was used to obtain an accurate measurement of the integrated absolute magnitude of the solar extreme UV photon flux in the spectral region between 50 and 800 A. The adjusted daily 10.7-cm solar radio flux and sunspot number were 168.4 and 121, respectively. The unattenuated absolute value of the solar EUV flux at 1 AU in the specified wavelength region was 6.81 x 10 to the 10th photons/sq cm per s. Based on a nominal probable error of 7 percent for National Institute of Standards and Technology detector efficiency measurements in the 50- to 500-A region (5 percent on longer wavelength measurements between 500 and 1216 A), and based on experimental errors associated with the present rocket instrumentation and analysis, a conservative total error estimate of about 14 percent is assigned to the absolute integral solar flux obtained.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 4291-429
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  • 8
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    The correspondence between small-scale coronal structures and the evolving solar magnetic field (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Solar coronal bright points, first identified in soft X-rays as X-ray Bright Points (XBPs), are compact, short-lived and associated with small bipolar magnetic flux. Coordinated data obtained during recent X-ray sounding rocket flights on August 15 and December 11, 1987 are used to determine the correspondence of XBPs with time-series, ground-based observations of evolving bipolar magnetic structures, He-I dark points, and the network. The results are consistent with the view that coronal bright points are more likely to be associated with the annihilation of preexisting flux than with emerging flux.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 10; 9 19
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  • 9
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    Effects of the driving mechanism in MHD simulations of coronal mass ejections (1990)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Results of time-dependent MHD simulations of mass ejections in the solar coronal are presented. Previous authors have shown that results from simulations using a thermal driving mechanism are consistent with the observations only if an elaborate model of the initial corona is used. The first simulation effort, using a simple model of a plasmoid as the driving mechanism and a simple model of the initial corona, produces results that are also consistent with many observational features, suggesting that the nature of the driving mechanism plays an important role in determining the subsequent evolution of mass ejections. First simulations are based on the assumption that mass ejections are driven by magnetic forces.
    Keywords: SOLAR PHYSICS
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  • 10
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    The Ulysses mission in the high latitude heliosphere (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Ulysses, a joint ESA/NASA mission launched in October 1990, will be the first to explore the high latitude heliosphere. Launch will be from the Shuttle and a Jupiter gravity assist will be used to send the spacecraft first over the southern solar pole approximately three and one half years after launch and then over the northern solar pole one year later. Instruments will be carried to study the solar wind, the heliospheric magnetic field, energetic solar particles, galactic cosmic rays, solar X-rays, cosmic gamma rays, cosmic dust and interstellar neutral helium. The radio signals used to track and transmit spacecraft data will be used also to sound the corona and to search for gravitational waves.
    Keywords: SOLAR PHYSICS
    Type: In: Observatories in earth orbit and beyond (A93-23401 07-89); p. 307-313.
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