A thermal catastrophe in a resonantly heated coronal loop

A theory for the thermal stability of hot coronal loops is presented, which is based on the resonant electrodynamic heating theory of Ionson (1982) and the evaporation/condensation scenario of Krall and Antiochos (1980). The theory predicts that gradual changes in the length of a loop or in its magnetic field strength can trigger catastrophic changes in the X-ray visibility of the loop, without the need for a change in the magnetic field topology. A natural explanation is thereby given for the observations of X-ray brightenings in loops and loop evacuations with coronal rain. (Auth.)