A reexamination of a filament oscillation event on 2013 March 15

Abstract

The key element in the research of solar activities is the coronal magnetic field, which is however difficult to measure directly. Filament (or prominence) oscillations offer a new approach to derive important information of the coronal magnetic field, which is called prominence seismology. However, it is vital to determine the oscillation mode before applying the prominence seismology since for a given magnetic structure of a filament, the two different modes of oscillation, namely, the longitudinal and transverse, have different eigen frequencies. In low-resolution observations, it is hard to distinguish the oscillation mode since both modes of oscillations are associated with lateral displacements, and the subtle difference between the two modes becomes unresolvable. On 2013 March 15, there is a filament oscillation event with a period of ∼63 minutes and a decay timescale of ∼105 minutes, which was explained in the literature to be a transverse oscillation or a mixture of both transversal and longitudinal components with the same period. With the analysis of the high-resolution SDO/AIA data, we reexamine the filament oscillation event, and argue that this event is a longitudinal oscillation. We tentatively propose a new method on how to identify the oscillation mode when the observational resolution is not so high. A numerical simulation is also provided in order to match the observations, which leads to the ratio between the depth and the width of the magnetic dip being 0.1.