On an anomalous polarization of the corona

At present data exist showing that in some regions of the corona the polarization degree has been found to be higher than the maximum possible value determined by Thomson scattering. Besides this, there exist regions where the direction of the prevailing vibration of the E-vector does not coincide with the tangential one. This may be caused by the velocity of scattered electrons. The theory of polarization taking the velocity into account is given, and the above-mentioned data are discussed. The direction of polarization turns out to be the sensitive detector of fact electrons (for energy of 5 keV, the deviation angle 10°).Very important data about accelerated electrons on the Sun may be received from precise measurements of the corona polarization.     

Equilibrium and stability of force-free magnetic field

Force-free magnetic fields (f.f.f) are considered as the first approximation of magnetic hydrodynamic equations in the case when the energy of the field exceeds the thermal energy of the medium. Such a relation of energies takes place in the upper atmosphere of the Sun in active regions.The consequence of the virial theorem obtained shows that for any solution of the corresponding non-linear system of equations only two cases are possible: either the total energy of the field is given by a divergent integral, or in some regions the force-free character of field is destroyed. This permits the conclusion that it is impossible to build f.f. current systems everywhere, and therefore boundary problems for this type of fields are of the same importance as for harmonic fields.Integral relations are obtained which are the necessary conditions for the solution of boundary problems. According to the classical principle of Thompson the harmonic fields are always stable, while f.f.f. may be stable or unstable.It is shown that: (1) arbitrary f.f.f. are stable to small changes of boundary conditions; (2) among f.f.f. the hydrodynamically stable configurations exist.The hydrodynamic stability condition restricts the size of force-free currents in such configurations.     

On stereoimages of some structures in the solar atmosphere

Three-dimensional structures in the solar chromosphere and corona are considered. It is demonstrated that two photoheliograms separated by ～1 day can be used (using computer-graphics methods) to construct a stereo image of the Sun. The algorithm for this is presented and carried out for H_α images of the total disk. A bulge in the equatorial region resulting from the differential rotation of the Sun can be seen in the stereo image. Structures called Whitney pleats in catastrophe theory are observed in the solar corona. Such structures are encountered in prominences. The well-known helmets (or streamers) are pleats of heliospheric plasma sheets. Isophotes for such a sheet and the degree of polarization of the radiation in the pleat are calculated and compared with observational data.