Coronal mass ejection associated with the stationary post-flare arch of 21-22 May 1980
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Mccabe, M. K.↗
Engineering topics
Jackson, B. V.
Publications and source records attributed to Jackson, B. V..
Kinematical analysis of flare spray ejecta observed in the corona
Observations in H-alpha, soft X-ray, white light and radio wavelengths are used to track cool and hot material from limb de-occultation to the extent of six solar radii. The kinematics and thermodynamics of the internal material are determined, along with the overall mass and energy budget of the event. It is found that the majority of the mass and energy is linked with the coronal material, but at least 20% of the ejected mass originated as near-surface prominence material, leading to the conclusions that the upper part of the prominence was being heated to coronal temperatures as it rose through the corona. Evidence was found that a moving type IV burst, indicative of strong magnetic fields, was associated with the upper part of the prominence, and the observations are judged to be most consistent with magnetic propulsion models of coronal transients.
Webb, D. F.↗
A comparison of Type III metric radio bursts and global solar potential field models
Evidence of coronal magnetic fields from polarized metric type III radio bursts is compared with (1) global potential field models, (2) direct averages of the observed photospheric magnetic field, and (3) H-alpha synoptic charts. The comparison clearly indicates both that the principal aspects of type III burst radiation are understood and that global potential field models are a significantly more accurate representation of coronal magnetic field structure than either the large-scale photospheric field or H-alpha synoptic charts.
Jackson, B. V.↗
The preflare state
The accumulation, storage and irreversible release of the free energy necessary for a solar flare are discussed on the basis of data obtained from the Apollo Telescope Mount on Skylab and other pertinent sources. Skylab and OSO 7 observations of possible flare precursors and flare evolution are presented, and the evolution of the flare of Sept. 5, 1973, the most completely observed flare of the Skylab program, is described in detail, with account given to magnetic structures and H alpha radiation. Theories of the preflare state are then reviewed, with attention given to the force-free fields and coronal arcades, thermal and magnetic structures and the MHD stability of coronal loops.
Van Hoven, G.↗
Evidence for a peak in the number of isolated Type III bursts prior to large solar flares
Evidence for a broad maximum in the number of isolated metric-wave Type III bursts prior to the large H alpha solar flares observed between May 1973 and February 1974 is reported. The time distribution of isolated Type III bursts within 12.6 h of each of the 111 solar flares of importance 1 or greater recorded during the period is shown to peak approximately 5 h before the time of flare maximum, most markedly in the case of bursts with projected positions near the solar flare position. The examination of H alpha, X-ray and magnetogram data in the vicinity of the flare implies a purely coronal storage and release mechanism for the flare energy. The peak of Type III burst activity is thus suggested as a good indicator of coronal energy input and storage near the time of a large solar flare, although not a reliable flare predictor.
Jackson, B. V.↗
Forerunners - Outer rims of solar coronal transients
The large loop or blob-like transient events viewed in the white-light corona are rimmed by broad regions where the density is slightly enhanced above the pretransient corona. Every one of the Skylab events studied for which sufficiently good Skylab coronagraph coverage is available shows this effect. The upper boundaries of these 'forerunners' blend gradually into the background corona 1-2 solar radii above the transient's leading edges. In any single event, the coronal mass enhancement represented by the forerunner comprises up to 25% of the total excess mass present in the coronagraph's field of view and includes a much larger volume of the corona than previously attributed to the underlying transient. A forerunner without an accompanying transient has not yet been seen. Clearly, forerunners must be reckoned with in any proposed models of discrete outward coronal mass motions, because they indicate the presence of disturbed corona far ahead of the denser portions of the event.
Jackson, B. V.↗
Open magnetic structures on the sun
High-resolution harmonic analysis of the solar magnetic field has been used succesfully to calculate the geometry of open magnetic field lines in the solar corona. Comparison of the loci of open-field-line footpoints with solar X-ray photographs shows that all the coronal holes during two solar rotations are successfully represented, including details of their evolution. Some open magnetic configurations derived in the calculations precede by up to one solar rotation the manifestation of coincident dark areas on the X-ray photographs. The only other areas that contribute open field lines to the corona are separations between active-region loop systems. By varying the radius at which field lines are forced to be open in the calculation, it is possible to reproduce more closely the surface configuration of particular coronal holes. Comparison of the size of X-ray holes with the fraction of the solar surface covered by open field lines leads to the conclusion that a significant part of the area of coronal holes must contain closed magnetic fields. Comparison of open field lines which lie in the equatorial plane of the sun with solar-wind data indicates that eventual high-speed solar-wind streams are associated with those parts of open magnetic structures that diverge the least.
Levine, R. H.↗
Physical properties of a polar coronal hole from 2 to 5 solar radii
Observations with a white-light coronagraph aboard Skylab are used to determine the boundaries of a coronal hole in the northern polar region and the three-dimensional density structure within the hole between heights of 2 and 5 solar radii. The boundary of the hole is found to be essentially axisymmetric about the polar axis, nearly radial from 3 to 6 solar radii, and located near 25 deg latitude at these heights. The radiances arising from the hole are interpreted as resulting from an axisymmetric density distribution whose logarithmic radial gradient is independent of position within the hole and whose magnitude increases with angular distance away from the hole's axis. The velocity distribution within the hole is obtained from the continuity equation by assuming that the particle flux flowing outward in the hole is similar to that measured for high-speed solar-wind streams at 1 AU, and it is shown that the transition from subsonic to supersonic flow occurs between 2.2 and 3 solar radii.
Munro, R. H.↗