![]() ![]() Plasma, electric current, heat, all flow along channels provided by the lines of force of the magnetic field. Contrary to the photosphere, the magnetic energy density in the chromosphere and the corona is much higher than the energy density of the plasma consequently, as pointed out in the review of Alissandrakis, 2020 on the solar atmospheric structure in this special research topic collection, it is the magnetic field that gives the chromosphere and the corona their highly structured appearance. The structure of the atmospheric layers in particular, is the result of the interaction of the plasma with the magnetic field. The latter affects practically all solar phenomena, in all layers of the solar atmosphere. The sun is made up of plasma and magnetic field. ![]() We close this review with a discussion of the variation of the magnetic field, deduced by radio measurements, from the low corona up to ~ 10 solar radii and with some thoughts about future work. Subsequently we pass to coherent emission mechanisms and present results of measurements from fiber bursts, zebra patterns, and type II burst emission. We proceed by discussing how the inversion of the sense of circular polarization can be used to measure the field above active regions. After a brief presentation of the magneto-ionic theory of wave propagation in cold, collisionless plasmas, we discuss how the magnetic field affects the radio emission produced by incoherent emission mechanisms (free-free, gyroresonance, and gyrosynchrotron processes) and give examples of measurements of magnetic filed parameters in the quiet sun, active regions and radio CMEs. In this review we explore these methods and point out their advantages and limitations. Due to inherent difficulties in measuring magnetic field effects on atoms (Zeeman and Hanle effects) in the corona, radio methods sensitive to electrons are of primary importance in obtaining quantitative information about its magnetic field. The same holds for a variety of solar phenomena that constitute solar activity, from tiny transient brightening to huge Coronal Mass Ejections. The structure of the upper solar atmosphere, on all observable scales, is intimately governed by the magnetic field. Department of Physics, University of Ioannina, Ioannina, Greece. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |