The evolution of vector photospheric magnetic fields has been studied in concert with photospheric spot motions for a flare-productive active region. Over a three-day period (5-7 April, 1980), sheared photospheric velocity fields inferred from spot motions are compared both with changes in the orientation of transverse magnetic fields and with the flare history of the region. Rapid spot motions and high inferred velocity shear coincide with increased field alignment along the B L = 0 line and with increased flare activity; a later decrease in velocity shear precedes a more relaxed magnetic configuration and decrease in flare activity. Crude energy estimates show that magnetic reconfiguration produced by the relative velocities of the spots could cause storage of ~ 1032 erg day-1, while the flares occurring during this time expended ~< 1031 erg day-1.Maps of vertical current density suggest that parallel (as contrasted with antiparallel) currents flow along the stressed magnetic loops. For the active region, a constant-e, force-free magnetic field (J = eB) at the photosphere is ruled out by the observations.

No abstract

A series of VLA maps at 6 cm wavelength have been generated from observations of a solar active region (NOAA 2363) on 29 and 30 March, 1980. During the same period, X-ray spectroheliograms were acquired for this region in the lines of Ovm, NeIx, MgxL SixxII, Sxv, and Fexxv, with X-rayn Polychromator (XRP) aboard the Solar Maximum Mission (SMM). Intervals of relative quiescence (i.e., when X-ray flares and centimeter wave bursts were not evident) were selected for microwave mapping. The resulting VLA maps have spatial resolution of 4" x 4", and generally show two or more sources whose slowly evolving substructures have spatial scales of 10"-30". These maps were co-registered with He photographs (courtesy of AF/AWS SOON, Holloman and Ramey AFB) to an accuracy of + 8". Similarly, the X-ray spectroheliograms have been co-registered with white light photographs to about the same accuracy. Magnetograms from KPNO and MSFC have also been co-aligned, and the magnetic X-ray, and microwave features compared. In general we have found that (a) the peaks of X-ray and 6 cm emission do not coincide, although (b)the sources in the two wavelength domains tend to overlap. These facts in themselves are evidence for the existence of opacity mechanisms other than thermal bremsstrahlung. In order to quantify this assertion, we have computed differential emission measures to derive densities and temperatures. Using these and calculated force-free magnetic fields from Kitt Peak magnetograms, we present an assessment of the mechanism of gyroresonance absorption at low harmonics of the electron gyrofrequency as the source of opacity responsible for the microwave features. We conclude that large-scale currents must be present in the active region loops to account for the bright 6 cm sources far from sunspots,

A self-consistent magnetohydrodynamic MHD) model of shearing magnetic loops is used to investigate magnetic energy buildup in active region AR 2372 (Boulder number), in the period of 5-7 April, 1980. The magnetic field and sunspot motions in this region, derived using observational data obtained by the Marshall Space Flight Center Solar Observatory, suggest the initial boundary conditions for the model. It is found that the plasma parameters (i.e., density, temperature, and plasma flow velocity) do not change appreciable during the process of energy buildup as the magnetic loops are sheared. Thus, almost all of the added energy is stored in the magnetic field. Furthermore, it is shown that dynamical processes are not important during a slow buildup (i.e., for a shearing velocity less than 1 km s -1). Finally, we conclude that the amount of magnetic energy stored and the location of this stored magnetic energy depend on the initial magnetic field (whether potential of sheared) and the magnitude of the shearing motion.

Time sequences of simultaneous spectra of limb spicules, obtained using the Sacramento Peak Observatory's tower telescope and echelle spectrograph are analyzed. Intensity determinations of Ha and K, H, A8498 and A8542 of calcium are tabulated for three observing heights. Electron densities averaged over the entire visible lifetimes of spicules are =6 x 101~ cm 3 at observing heights of 6000km, while maximum and minimum values were =l.lxl011 cm -3 at 6000km and ~2• 10 TM cm -3 at 10 000 km. Electron temperatures range between 12 000 K and 16 000 K. Profile halfwidths indicate turbulent velocities of 12 to 22 km s -1, and spectral tilts are interpreted as caused by differential velocity fields of =3 kms -1 per 1000km. No large scale spicule expansions or contractions are observed, although possible expulsions or accretions of material are observed. Spicules may be wider in the calcium K and H lines than in Ha.