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  • 1
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    Potential contribution of MDI to understanding large-scale structures in the corona (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: In relation to the understanding of the structure and dynamics of the solar atmosphere which requires realistic coronal magnetic field models, a horizontal current-current sheet (HCCS) coronal model was developed. The model includes large-scale, low altitude, horizontal currents and the effect of thin current sheets in the streamer belt of the field above cusp-type neutral points. The effect of the streamer current sheet on the field below the cusp points is accounted for. In order to suggest what can be anticipated from Michelson Doppler imager (MDI) photospheric magnetic field data calculations of the coronal magnetic field using low spatial resolution data, are presented, and results from the calculations of solar eclipses are compared with solar eclipse images.
    Keywords: SOLAR PHYSICS
    Type: NASA-CR-200367 , NAS 1.26:200367 , ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 509-514
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  • 2
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    Hot spots and active longitudes: Organization of solar activity as a probe of the interior (1995)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: In order to investigate how solar activity is organized in longitude, major solar flares, large sunspot groups, and large scale photospheric magnetic field strengths were analyzed. The results of these analyses are reported. The following results are discussed: hot spots, initially recognized as areas of high concentration of major flares, are the preferred locations for the emergence of big sunspot groups; double hot spots appear in pairs that rotate at the same rate separated by about 180 deg in longitude, whereas, single hot spots have no such companions; the northern and southern hemispheres behave differently in organizing solar activity in longitude; the lifetime of hot spots range from one to several solar cycles; a hot spot is not always active throughout its lifetime, but goes through dormant periods; and hot spots with different rotational periods coexist in the same hemisphere during the same solar cycle.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 113-118
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  • 3
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    The effect of coronal mass ejections on the structure of the heliospheric current sheet (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The existence of a stable heliospheric current sheet (HCS) structure near solar cycle maximum was questioned since the recognition that coronal mass ejections (CME's) occur in coronal helmet streamers. Evidence is presented suggesting that pre-existing helmet streamers disrupted or blown out by CME's reform in a time interval much shorter than the life time of the HCS, and that the concept of the HCS has a meaning at any time of thesolar cycle. It appears that the HCS, the current layer that separates adjacent interplanetary magnetic field regions with opposite magnetic polarity, exists throughout the solar cycle, though not always as a thin disk-like sheet. The sheet may be thickened by embedded magnetic ropes formed by CME's, especially near sunspot maximum. The HCS may be used as timing mark in identifying or predicting CME's in the interplanetary medium.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 3rd SOHO Workshop on Solar Dynamic Phenomena and Solar Wind Consequences; p 321-324
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  • 4
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    The solar oscillations investigation: Michelson Doppler imager (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Solar Oscillations Investigation (SOI) developed the Michelson Doppler Imager (MDI) to investigate the properties of the solar interior using the tools of helioseismology and of the photosphere and corona using more conventional techniques. The fundamental goal is to understand the Sun by determining its structure and observing its dynamics. The basic observables, velocity, intensity, and magnetic field, are computed on board from up to twenty 1024 by 1024 filtergrams made each minute. Subsequent analysis will extend the region to be explored downward into the solar interior and upward into the corona. While the instrument is dedicated to producing an uninterrupted series of helioseismology data, several magnetograms will be made each day and special eight hour campaigns are being developed to address specific scientific questions, some in coordination with other SOHO (Solar and Heliospheric Observatory) instruments.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of the First SOHO Workshop: Coronal Streamers, Coronal Loops, and Coronal and Solar Wind Composition; p 9-12
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  • 5
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    The detection of global convective wave flows on the sun (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Global convective flows in the solar convection zone have been predicted by theoretical interpretations of the global-scale ordering of magnetic fields and activity centers and by theoretical analyses of rotating convection zones. Direct evidence of these flows in the photosphere has not previously been found despite several long-term efforts. The signatures of such flows have now been detected by analyzing the daily series of low-resolution Dopplergrams obtained at the Wilcox Solar Observatory at Stanford University. The signatures are patterns of alternating east and west flows with amplitudes on the order of 25 m/s and longitudinal extent of about 30 degrees. The patterns move across the disc at approximately the solar rotation rate and have lifetimes of at least several rotations. Boundaries of the fast and slow flows are often associated with large magnetic active regions.
    Keywords: SOLAR PHYSICS
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  • 6
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    Long-term variability of solar magnetic-fields (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Studies of the variations of the solar magnetic field are reviewed. Consideration is given to the study of 600 Myr-old Australiain varve data showing the 22-yr magnetic cycle and variations with 300-400 yr periods (Williams, 1981 and Bracewell, 1985). Methods of interpreting the organization of large-scale solar field patterns are discussed. Other studies examined include the interpretation of modal structure in the photospheric field by Stenflo et al. (1988), and the study of Sheeley et al. (1987) showing that much of the large-scale surface pattern can be deduced from the measured emerging flux.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 8; 7 19
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  • 7
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    Extending the sun's magnetic field through the three-dimensional heliosphere (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Methods for inferring the interplanetary magnetic field are reviewed. Estimates of the configuration of the field are presented for each phase of the sunspot cycle. The limitations of the methods for predicting it are presented. A contour map of power in the 0.3-0.5 microHz frequency range is presented for various solar latitudes.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 9; 4 19
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  • 8
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    A coronal magnetic field model with horizontal volume and sheet currents (1994)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: When globally mapping the observed photospheric magnetic field into the corona, the interaction of the solar wind and magnetic field has been treated either by imposing source surface boundary conditions that tacitly require volume currents outside the source surface or by limiting the interaction to thin current sheets between oppositely directed field regions. Yet observations and numerical Magnetohydrodynamic (MHD) calculations suggest the presence of non-force-free volume currents throughout the corona as well as thin current sheets in the neighborhoods of the interfaces between closed and open field lines or between oppositely directed open field lines surrounding coronal helmet-streamer structures. This work presents a model including both horizontal volume currents and streamer sheet currents. The present model builds on the magnetostatic equilibria developed by Bogdan and Low and the current-sheet modeling technique developed by Schatten. The calculation uses synoptic charts of the line-of-sight component of the photospheric magnetic field measured at the Wilcox Solar Observatory. Comparison of an MHD model with the calculated model results for the case of a dipole field and comparison of eclipse observations with calculations for CR 1647 (near solar minimum) show that this horizontal current-current-sheet model reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces coro nal helmet structures better than the current-sheet model.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 151; 1; p. 91-105
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  • 9
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    Prediction of the interplanetary magnetic field strength (1995)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A new model of the coronal and interplanetary magnetic field can predict both the interplanetary magnetic field strength and its polarity from measurements of the photospheric magnetic field. The model includes the effects of the large-scale horizontal electric currents flowing in the inner corona, of the warped heliospheric current sheet in the upper corona, and of volume currents flowing in the region where the solar wind plasma totally controls the magnetic field. The model matches the MHD solution for a simple dipole test case better than earlier source surface and current sheet models. The strength and polarity of the radial interplanetary magnetic field component predicted for quiet time samples in each year from 1977 to 1986 agree with observations made near the Earth's orbit better than the hybrid MHD-source surface model (Wang and Sheeley, 1988). The results raise the question of whether coronal holes are the only solar source of the interplantary magnetic field in the solar wind. If some interplanetary flux originates outside coronal holes, the model can match the observed field using the accepted 1.8 saturation correction factor for lambda 5250 A magnetograph observations. Requiring open flux to come exclusively from coronal holes requires and additional factor of two.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A1; p. 19-33
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  • 10
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    Large-scale solar and heliospheric magnetic fields (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The magnetic structure of the extended solar corona varies with the changing photospheric field during the solar cycle. A simple potential model of the corona using solar surface observations from 1976 to the present shows how the large-scale coronal field evolves over more than a solar activity cycle. These predictions match well with large stable structures inferred from measurements of coronal electron density and the IMF, though dynamic changes are poorly modeled. The sun's polar field was about 25 stronger at solar minimum in 1986 than in 1976; the heliospheric current sheet was also flatter. In Cycle 21 the coronal and photospheric large-scale long-lived field patterns rotated every 26.9 days in the northern hemisphere; the southern field rotated every 28 days. Similar periods have been present in the IMF and in the occurrence of solar flares during the last several solar cycles.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 11; 1 19
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