Solar coronal loops and coronal heating models

MANDRINI, C.H.

Angra dos Reis, Brasil

Conferencia; Magnetic fields in the Universe: From laboratory and stars to primordial structures; 2004

Universidades de San Pablo, de Pisa y de Wisconsin

Ever since it was realized, some sixty five years ago, that the solar corona is three orders of magnitude hotter than the underlying photosphere, scientists have puzzled over the reason for these extreme conditions. A number of plausible ideas have been put forward, including the dissipation of magnetohydrodynamic (MHD) waves and the dissipation of stressed, current-carrying magnetic fields. Unfortunately, the conversion of magnetic to thermal energy occurs on spatial scales that are far smaller than can be observed directly by present-day solar instruments, and it has been extremely difficult to identify the exact cause of the heating. We will describe two different approaches we have undertaken combining soft X-ray coronal observations and photospheric magnetic observations with other indirect means (e.g. magnetic field extrapolations, quasi-static loop theory), to discriminate between the models that have been so far proposed to explain the coronal heating problem. Both approaches show that models based on the dissipation of stressed, currentcarrying magnetic fields are in better agreement with the observations than models that attribute coronal heating to the dissipation of MHD waves injected at the base of the corona.