SUN CORONA THICKNESS SERIES

( 1978b) pointed out that two elements are crucial to produce a hot corona, namely, a relatively strong magnetic field coupled with an input of mechanical energy into the field. Concomitantly, it was recognized that magnetic fields are not only acting to confine the plasma in the inner part of the solar atmosphere but they are also playing a fundamental role in coronal heating. The faintest coronal features, with a plasma density one or two orders of magnitude lower than in active regions and characterized by a predominantly open magnetic field, were named coronal holes. X-rays turned out to be principally emitted from coronal loops, regions of closed magnetic field lines overlying zones of enhanced photospheric magnetic field, which were recognized as the basic elements of the solar corona (Vaiana et al.

SUN CORONA THICKNESS SERIES

By the early seventies, after a decade of monitoring the solar emission in the ultraviolet and X electromagnetic domains, the main characteristics of the structure and dynamics of the corona were fairly well established thanks to the Skylab mission, preceded by observations with the Orbiting Solar Observatories and by a series of sub-orbital rocket flights carrying scientific instrumentation. Friedman reports the adventurous account of the first pioneering observations of the solar X-ray sources. The solar corona appeared as a highly inhomogeneous X-ray source with 80% of the emission coming from 5% or less of the area of the solar disk (Blake et al. The X-ray image of the Sun, obtained by the Naval Research Laboratory scientists during a sub-orbital rocket flight on April 19, 1960, in the form of a crude low-resolution photograph, revealed for the first time the hottest layers of the solar atmosphere against the bright disk. These events are characterized by the emission of highly energetic electromagnetic radiation and particle acceleration, frequently associated with huge plasma ejections, inducing transient changes and a reorganization of the structure of the corona. When the level of activity increases, magnetic energy is sporadically released in sudden and powerful reconnection events occurring at coronal heights. Coronal holes and quiescent streamers, reflecting long-lived large-scale patterns, are prevalent in the declining to minimum phase of solar activity when the magnetic field becomes organized according to lower order multipoles. Active regions are dominant in the ascending phase of the solar cycle and at solar maximum when the relatively simple poloidal configuration of the solar magnetic field typically observed at solar minimum is disrupted by the emergence of the toroidal field of the new cycle.

The picture of the solar corona derived from ground-based and space observations is that of a hot inhomogeneous magnetized atmosphere, which is constantly evolving and consisting of features developing on different scales in the various phases of the solar activity cycle.

Sun corona thickness