THE SOLAR-SURFACE BOUNDARY-CONDITIONS OF CORONAL MAGNETIC LOOPS

The dynamical properties of a realistic thermal-structure interface be tween a coronal loop and the chromosphere/photosphere are investigated by numerical simulations using acoustic and Alfvenic excitations. The se properties are relevant to the end conditions seen by coronal MHD p erturbations (e.g., waves or instabilities), in the absence of much sl ower energetics effects. Analytic studies of coronal-loop hydromagneti cs have often made simplifying assumptions about the boundary conditio ns at the loop base in order to make their calculations tractable. How ever, in the presence of a transition region and chromosphere with rap idly varying plasma conditions, it is not clear how valid these heuris tic assumptions are. In this study, we find that the discontinuous flu id-density model approximately represents the reflection/transmission scaling with respect to varying transition-region density and temperat ure (i.e., dynamic impedance) ratios, although it does not quantitativ ely predict the chromospheric response to wave-like coronal activity. This disagreement is partially due to the finite width of the corona-t o-photosphere transition.