CORONAL RAIN AS A MARKER FOR CORONAL HEATING MECHANISMS

Abstract

Reported observations in H-alpha, Ca II H and K or or other chromospheric\nlines of coronal rain trace back to the days of the Skylab mission. Offering a\nhigh contrast in intensity with respect to the background (either bright in\nemission if observed at the limb, or dark in absorption if observed on disk)\nthese cool blobs are often observed falling down from high coronal heights\nabove active regions. A physical explanation for this spectacular phenomenon\nhas been put forward thanks to numerical simulations of loops with footpoint\nconcentrated heating, a heating scenario in which cool condensations naturally\nform in the corona. This effect has been termed 'catastrophic cooling' and is\nthe predominant explanation for coronal rain. In this work we further\ninvestigate the link between this phenomenon and the heating mechanisms acting\nin the corona. We start by analyzing observations of coronal rain at the limb\nin the Ca II H line performed by the SOT instrument on board of the Hinode\nsatellite. We then compare the observations with 1.5-dimensional MHD\nsimulations of loops being heated by small-scale discrete events concentrated\ntowards the footpoints (that could come, for instance, from magnetic\nreconnection events), and by Alfven waves generated at the photosphere. It is\nfound that if a loop is heated predominantly from Alfven waves coronal rain is\ninhibited due to the characteristic uniform heating they produce. Hence coronal\nrain may not only point to the spatial distribution of the heating in coronal\nloops but also to the agent of the heating itself. We thus propose coronal rain\nas a marker for coronal heating mechanisms.\n