Multi-wavelength analysis of downflows along an off-limb loop like structure

An EIT shutterless campaign was conducted on 11 July 2001 and provided 120 high-cadence (68s) 30.4 nm images of the north-eastern quarter of the Sun. Systematic intensity variations are seen which appear to propagate along an off-limb half loop structure. In this paper we study the nature of these intensity variations by confronting the EIT observations with simultaneous Hα images from Big Bear Solar Observatory. The two image sets are carefully co-registred by means of a new technique designed to compare data of two different instruments, and later overplotted in order to visualize and compare the behaviour of the propagating disturbances in both data sets. Since the same intensity variations are seen in the EIT 30.4 nm and in the Hα images, we confirm the interpretation of De Groof et al. (2004) that we are observing downflows of relatively cool plasma. The origin of the downflows is explained by numerical simulations of catastrophic cooling in a coronal loop which is heated predominantly at its footpoints.status: publishe