On cool coronal loops

Analytical model calculations and physical arguments are used to examine cool equilibria in coronal loops. Static loop model assumptions include a one-dimensional energy equation, a constant cross-sectional area, and a loop symmetric top. It is shown, in contradiction to Hood and Priest (1979) results, that cool loop maximum height has a minimal dependence on the heating mechanism and the radiation losses, and does not depend on constants of proportionality. In addition, thermal catastrophe occurs not only as a result of loop length variations, but also as a result of heating or pressure variations. It is also concluded that for a given heating mechanism, thermal catastrophe occurs at only one loop length.