The equilibrium of solar coronal magnetic loops

A method is described for obtaining the temperature and density along a magnetic field line for plasma that is in thermal equilibrium at uniform pressure. One of the main features of the results is that, when the pressure becomes too great or the length of the field line too large, a lack of thermal equilibrium ensues and the plasma cools down to a new equilibrium below 100,000 K. The stretching of a coronal loop may be caused either by the straightforward motion of the photospheric footprints or by the twisting up of a field that remains force-free. It is suggested, therefore, that such an increase in pressure or length is what causes some coronal loops to develop very cool cores. This is proposed as a mechanism for the creation of active region filaments or prominences.