We investigate the association of high-speed solar wind with coronal holes during the Skylab mission by: (1) direct comparison of solar wind and coronal X-ray data; (2) comparison of nearequatorial coronal hole area with maximum solar wind velocity in the associated streams; and (3) examination of the correlation between solar and interplanetary magnetic polarities. We find that all large near-equatorial coronal holes seen during the Skylab period were associated with high-velocity solar wind streams observed at 1 AU.
We propose that the coronal source longitude and latitude of solar wind plasma can be estimated within ~ i0 ~ Previous writers have argued that the solar wind in the ecliptic should originate near the equator and that a quasi-radial hypervelocity (QRH) approximation (constant radial flow) is valid beyond the magnetohydrodynamic critical points. We demonstrate that an extension of the QRH approximation (as if the solar wind flowed radially with constant velocity from the center of the Sun) yields a proper estimate of the high coronal source location at the 'release zone' where the solar wind makes its transition to radial interplanetary flow. This 'extrapolated' QRH (or EQRH) approximation succeeds because the two main corrections to this source estimate, coronal corotation and interplanetary acceleration, tend to cancel (the former correcting the source location eastward, the latter westward). Although this 'ideal spiral' approximation was first suggested by Snyder and Neugebauer (1966), only recently has it been demonstrated that it relates a wide range of interplanetary plasma, magnetic field and energetic particle data to observed coronal magnetic structure. We estimate quantitatively the error in the EQRH approximation by comparison with steady-state streamlines predicted by azimuthally independent and dependent theoretical solutions to the steady-state plasma equations. We find the error in both cases ~< 10 ~ in longitude and therefore suggest that the EQRH approximation offers the means to relate observed solar 'initial conditions' in the 'release zone' directly to interplanetary measurements. If, in addition, the EQRH approximation also leads to agreement with low coronal structure, then there should be a straightforward correspondence to otherwise unobservable high coronal structure.
This atlas shows the boundary locations of the coronal holes observed in soft X-rays (2-32, 44-54 A) by the AS & E X-ray spectrographic telescope on Skylab. The data are presented as tracings of the boundaries as they appeared when the holes were near central meridian.
We present revised values of temperature and density for the flare loops of 29 July 1973 and compare the revised parameters with those obtained aboard the SMM for the two-ribbon flare of 21 May 1980. The 21 May flare occurred in a developed sunspot group; the 29 July event was a spotless two-ribbon flare. We find that the loops in the spotless flare extended higher (by a factor of 1.4-2.2), were less dense (by a factor of 5 or more in the first hour of development), were generally hotter, and the whole loop system decayed much slower than in the spotted flare (i.e. staying at higher temperature for a longer time). We also align the hot X-ray loops of the 29 July flare with the bright H~ ribbons and show that the Hc~ emission is brightest at the places where the spatial density of the hot elementary loops is enhanced.
Skylab S-054 data have been used to examine the flux from X-ray bright points with -90 s time resolution. There is evidence of a steady heating input, similar to one reported for active region loops. Also observed are impulsive brightenings of bright points and rapid decays which are consistent with a sudden turn-off of the steady heating.
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