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  • 1
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    A case for submergence of magnetic flux in a solar active region (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: In NOAA Active Region 2372 (April 1980), 4 x 10 to the 20th maxwells of magnetic flux concentrated in an area 30 arcsec across disappeared overnight. Vector magnetograms show that all components of the magnetic field weakened together. If the field had weakened through diffusion or fluid flow, 90 percent of the original flux would still have been detected by the magnetograph within a suitably enlarged area. In fact there was a threefold decrease in detected flux. Evidently, magnetic field was removed from the photosphere. Since the disappearing flux was located in a region of low magnetic shear and low activity in H-alpha and Ly-alpha, it is unlikely that the field dissipated through reconnection. It is argued that the most likely possibility is that flux submerged. The observations suggest that even during the growth phase of active regions, submergence is a strong process comparable in magnitude to emergence.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 287; 404-411
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  • 2
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    Heating the sun's lower transition region with fine-scale electric currents (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Analytical and observational data are presented to show that the lower transition zone, a 100 km thick region at 10,000-200,000 K between the solar chromosphere and corona, is heated by local electric currents. The study was spurred by correlations between the enhanced atmospheric heating and magnetospheric flux in the chromospheric network and active regions. Field aligned current heated flux loops are asserted to mainly reside in and make up most of the transition region. It is shown that thermal conduction from the sides of hot gas columns generated by the current dissipation is the source of the observed temperature distribution in the transition regions.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 285; 359-367
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  • 3
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    Observation of the impulse phase of a simple flare (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The paper presents a broad range of complementary observations (SMM and ground-based) of the onset and impulsive phase of the fairly large (1B, M1.2) but simple two-ribbon flare which occurred at 19:15 UT on November 1, 1980 in the northern part of the active region Boulder No. AR2776. It is found that the overall magnetic field configuration in which the flare occurred was a fairly simple, closed arch containing nonpotential substructure; the flare occurred spontaneously within the arch (it was not triggered by emerging magnetic flux). The two major spikes of the impulsive energy release are examined, and the three immediate products of this energy release are discussed.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 90; 41-62
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  • 4
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    Evidence for a poleward meridional flow on the sun (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Two subsets of all polar zone filaments, designated polemost filament and polar filament bands, are defined for observational study of their behavior, which is compared with the evolution of the polar magnetic field over Howard and LaBonte's (1981) activity cycle. The magnetic data show that the polar magnetic fields are built up and maintained by the episodic arrival of discrete f-polarity regions originating in active region latitudes and subsequently drifting to the poles. F-polarity regions are carried poleward by a meridional flow, rather than by diffusion. It is noted that the mean latitude of the polemost filaments tracks the boundary of the polar field cap, and undergoes an equatorward dip during each arrival of additional polar field, and that the polar filament bands track the boundary latitudes of the unipolar regions, drifting poleward with the regions at about 10 m/sec.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 79; Aug. 198
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  • 5
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    The role of magnetic field shear in solar flares (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Observational results and their physical implications on magnetic field shear in relation to flares are presented. The observed character of magnetic shear and its involvement in the buildup and release of flare energy are reviewed. It is pointed out that the magnetic field in active regions can become sheared by several processes, including shear flow in the photosphere, flux emergence, magnetic reconnection, and flux submergence. Modeling studies of the buildup of stored magnetic energy by shearing are reported which show ample energy storage for flares. Observational evidence is presented that flares are triggered when the field shear reaches a critical degree, in qualitative agreement with some theoretical analyses of sheared force-free fields. Finally, a scenario is outlined for the class of flares resulting from large-scale magnetic shear; the overall instability driving the energy release results from positive feedback between reconnection and eruption of the sheared field.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 4; 7, 19
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  • 6
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    X-ray and H-alpha observations of a filament-disappearance flare - An empirical analysis of the magnetic field configuration (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: On August, 29, 1973, a flare event occurred that involved the disappearance of a filament near central meridian. The event, well-observed in X-rays on Skylab and in H-alpha, was a four-ribbon flare involving both new and old magnetic inversion lines which were roughly parallel. The H-alpha, X-ray, and magnetic field data are used to deduce the magnetic polarities of the H-alpha brightening at the footpoints of the brightest X-ray loops. It is suggested that the event involved a reconnection of magnetic field lines rather than a brightening in place of preexisting loops. The simultaneity of the H-alpha brightening onsets in the four ribbons and the apparent lack of an eruption of the filament are consistent with this interpretation.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 70; Apr. 198
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  • 7
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    Dynamic phenomena in the visible layers of sunspots (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The empirical properties of the various dynamic phenomena are reviewed and interrelated, with emphasis placed on recent observational results. On the basis of the observations, it is proposed that umbral dots and penumbral grains are essentially the same phenomenon and that the observational goal of highest priority with respect to both the origin of the periodic phenomena and the problem of the missing heat flux is to better determine the nature of these elementary bright features. The dynamic phenomena discussed are features or events that display spectral evidence for mass motion or that change appreciably in brightness or position on time scales less than approximately one hour. It is also concluded that nonoscillatory convection in umbral dots may well contribute strongly to umbral turbulence as presently observed.
    Keywords: SOLAR PHYSICS
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  • 8
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    A continuum bright point at the penumbral edge (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A small continuum bright point, observed at the outer edge of the penumbra of a small spot in a large complex spot group, is related to an occurrence beneath the suns's surface. The characteristics of the point appear to be unique, and the name 'penumbra-periphery bright point' is proposed.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 67; Aug. 198
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  • 9
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    The thermal X-ray flare plasma (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Following a review of current observational and theoretical knowledge of the approximately 10 to the 7th K plasma emitting the thermal soft X-ray bursts accompanying every H alpha solar flare, the fundamental physical problem of the plasma, namely the formation and evolution of the observed X-ray arches, is examined. Extensive Skylab observations of the thermal X-ray plasmas in two large flares, a large subflare and several compact subflares are analyzed to determine plasma physical properties, deduce the dominant physical processes governing the plasma and compare large and small flare characteristics. Results indicate the density of the thermal X-ray plasma to be higher than previously thought (from 10 to the 10th to 10 to the 12th/cu cm for large to small flares), cooling to occur radiatively as much as conductively, heating to continue into the decay phase of large flares, and the mass of the thermal X-ray plasma to be supplied primarily through chromospheric evaporation. Implications of the results for the basic flare mechanism are indicated.
    Keywords: SOLAR PHYSICS
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  • 10
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    Remote flare brightenings and type III reverse slope bursts (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Observations are presented on two large (H-alpha class 2) flares that each produced an extensive chain of discrete H-alpha brightenings spanning 370,000-470,000 km in length in remote quiet regions more than 100,000 km from the main flare site. A large group of Type III RS bursts was also observed accompanying each flare. The onset of about half the remote H-alpha emission patches were nearly simultaneous with the RS bursts. One flare was observed in hard X-rays, and it is noted that the RS bursts occurred during hard X-ray spikes. For the other flare, soft X-ray filtergrams indicate coronal loops connecting from the main flare site to the remote H-alpha brightenings. Observations indicate that the RS burst electrons were generated in the flares, and it is proposed that the remote H-alpha brightenings were initiated by direct heating of the chromosphere by RS burst electrons traveling in closed magnetic loops connecting the flare site to the remote patches. It is also suggested that after onset, the brightenings were heated by thermal conduction by slower thermal electrons.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 77; Apr. 198
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