Longitudinal oscillation of intensity fronts in a strand at the edge of an active region

Abstract

The edge of a solar active region (AR) is considered as a possible source region of the slow solar wind. Winebarger et al. (2001) observed outflows from an AR with velocities between 5 and 20 km/s. Recently, Sakao et al. (2007) reported the outflow of X‐ray‐emitting plasma from the edge of an AR. This outflow was inferred from the observation of outward traveling intensity enhancements. However, in Robbrecht et al. (2001), propagation of slow magnetoacoustic waves along the strand was considered as the possible cause for the longitudinal extension of the strand. Whether this phenomenon relates to a slow‐mode wave or the outflow of plasma or a heating process of different parts of the strand is still an open question. Here we try to identify the nature of such a traveling event through studying the longitudinal motions of certain intensity level fronts in the strand. We find that the intensity front is oscillating like a sinusoidal signal along the strand with a period of 11 minutes. This result suggests that the oscillation might be partly related with the 5‐minute p‐mode oscillation in the photosphere. Moreover, we find that such oscillation of intensity‐level fronts can be described by a model in which the strand has periodic extension. Yet, the relation between the extending strand and slow solar wind needs to be further studied.