On the observations and possible interpretations of very long period intensity oscillations of solar coronal loops

A comprehensive analysis of intensity oscillations in the Fe XII line (19.5 nm) observed with EIT/SoHO in solar coronal loops during solar cycle 23 (january 1997-september 2008) was performed. About 450 occurences of oscillations were obtained with periods ranging between 3.4 and 13.6 hours and with durations up to about a hundred hours. Interpratations in term of slow waves or of thermal nonequilibrium were examined. However numerous inconsistencies arise between current theories (in fact mostly expressed in terms of various numerical simulations) and observations. Presently the lack of a direct link between those very long oscillation periods and the characteristic physical parameters of the loops (density, temperature, loop geometry) hampers making progress in this major issue. This situation requires an effort in a specific time analysis of the classical system of equations of the problem: the question is examined from different angles in relation to the data.