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It is evident from eclipse photographs that gas-magnetic field interactions are important in determining the structure and dynamical properties of the solar corona and interplanetary medium. Close to the Sun in regions of strong field, the coronal gas can be contained within closed loop structures. However, since the field in these regions decreases outward rapidly, the pressure and inertial forces of the solar wind eventually dominate and distend the field outward into interplanetary space. The complete geometrical and dynamical state is determined by a complex interplay of inertial, pressure, gravitational, and magnetic forces. The present paper is oriented toward the understanding of this interaction. The 'helmet' streamer type configuration with its associated neutral point and sheet currents is of central importance in this problem and is, therefore, considered in some detail.Integration of the relevant partial differential equations is made tractable by an iterative technique consisting of three basic stages, which are described at length. A sample solution obtained by this method is presented and its physical properties discussed.

Three independent observations by rocket, Skylab, and OSO-8 have all indicated the presence of steady downftows of the order of a few kilometers per second in the solar transition region overlying the chromospheric network. Using density estimates at these heights from traditional transition region models, we find that the downward mass fluxes associated with these velocities are comparable with the estimated upward mass flux in spicules, originating in the same regions. Since both observations and theoretical calculations show that the solar wind can accept only a small fraction of the upward spicule flux, we suggest that the downflow represents spicular material returning to the chromosphere after being heated to coronal temperatures. In this context, the differential velocity measurement of Cushman and Rense is interpreted as indicating a difference in downflow speeds rather than a difference in expansion speeds.Moreover, the enthalpy flux associated with the downflow of coronal material into these regions is shown by various estimates to exceed the inward heat flow expected by thermal conduction and it may constitute the dominant energy source for the transition region. Simplified analytical models are used to explore the nature of the transition region overlying the supergranulation boundaries, under the assumption that the thermal structure results from a balance of the downward convection of enthalpy and radiative losses. Models based upon these considerations are shown to be consistent with the observed emission measures.

A model for solar quiescent prominences nested in a ' Figure 8' magnetic field topology is developed. This topology is argued to be the natural consequence of the distention of bipolar regions upward into the corona. If this distention is slow enough so that hydrostatic equilibrium holds approximately along the field lines, the transverse gas pressure forces fall exponentially with height whereas the inward Lorentz forces fall as a power law. At a low height in the corona, the pressure forces cannot balance the Lorentz forces provided the field lines remain tied to the photosphere and an inward collapse with subsequent reconnection at the point of closest approach should occur. Because of initial shear in the magnetic field, the reconnection would produce isolated helices above the point of reconnection since field lines would not interact with themselves but with their neighbors. This resulting topology produces a field above the elevated neutral line which is opposite in polarity to that of the photospheric field as in the current sheet models of Kuperus and Tandberg-Hanssen (1967). Raadu and Kuperus (1973), Raadu (1974), andRaadu (1979) and in agreement with recent observations of Leroy (1982), and Leroy et aL (1983).Assuming the isolated helices formed by reconnection are insulated from coronal thermal conduction and heating, the radiative cooling process and condensation is considered for the temperature range of 104-6000 K. This condensation results in a steady downflow to the bottom of the helices as the temperature scale-height falls, thus forming a dense, cool, prominence at the bottom of the helical configuration resting on the elevated neutral line with the remainder of the helix being essentially evacuated of material. We identify this neutral line at the bottom of the prominence with the sharp lower edge often seen when viewing quiescent prominences side-on and the evacuated helix with the coronal cavity observed around prominences when seen during total eclipses. Downflow speeds associated with the condensation process are calculated for prominence temperatures and yield velocities in the range of the observed downfiows of about 1 km s -1.

Every two-ribbon flare observed during the Skylab period produced an observable coronal transient, provided the flare occurred close enough to the limb. The model presented here treats these two events as a combined process. Transients that occur without flares are believed to involve magnetic fields that are too weak to produce significant chromospheric emission. Adopting the hypothesis that the rising flare loop systems observed during two-ribbon flares are exhibiting magnetic reconnection, a model of a coronal transient is proposed which incorporates this reconnection process as the driving force. When two oppositely directed field lines reconnect a lower loop is created rooted to the solar surface (the flare loop) and an upper disconnected loop is produced which is free to rise. The magnetic flux of these upper loops is proposed as the driver for the transient. The force is produced by the increase in magnetic pressure under the filament and transient.A quantitative model is developed which treats the transient configuration in terms of four distinct parts -the transient itself with its magnetic field and material, the region just below the transient but above the filament, the filament with its magnetic field, and the reconnected flux beneath the filament. Two cases are considered -one in which all the prominence material rises with the transient and one in which the material is allowed to fall out of the transient. The rate of rise of the neutral line during the reconnection process is taken from the observations of the rising X-ray flare loop system during the 29 July, 1973 flare. The MHD equations for the system are reduced to four non-linear ordinary coupled differential equations which are solved using parameters believed to be realistic for solar conditions. The calculated velocity profiles, widths, etc., agree quite well with the observed properties of coronal transients as seen in white light.Since major flares are usually associated with a filament eruption about 10-15 min before the flare and since this model associates the transient with the filament eruption, we suspect that the transient is actually initiated some time before the actual flare itself.

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We examined the sources of magnetic fields in recurrent streams observed by the Imp 8 and Heos spacecraft at 1 AU and by Mariner 10 en route to Mercury between October 31, 1973, and February 9, 1974, during Carrington rotations 1607–1610. Most fields and plasmas at 1 AU were related to coronal holes, and the magnetic field lines were open in those holes. However, some of the magnetic fields and plasmas at 1 AU were related to open field line regions on the sun which were not associated with known coronal holes, indicating that open field lines may be more basic than coronal holes as sources of the solar wind. Magnetic field intensities in five equatorial coronal holes, estimated by projecting the measured interplanetary magnetic fields back to the sun by using the principle of flux conservation, ranged from 2 to 18 G with an average of 9 G. Average measured photospheric magnetic fields along the footprints of the corresponding unipolar fields on circular equatorial arcs at 2.5 RS had a similar range and average, but in two cases the intensities were approximately 3 times higher than the projected intensities. The coronal footprints of the sector boundaries on the source surface at 2.5 RS, determined by a potential field extrapolation of the measured photospheric fields, meandered between −45° and +45° latitude, and their inclination with respect to the solar equator ranged from near 0° at some longitudes to near 90° at others. It is possible that sector boundaries are related to convergence surfaces of the flow near the sun. The high densities observed near sector boundaries between streams might be due in part to the convergence of flows from adjacent coronal holes.

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