HIGH-RESOLUTION OBSERVATIONS OF A LARGE FAN-SHAPED SURGE

Abstract

ABSTRACT We present high-resolution observations of a large fan-shaped surge, which was observed on 2013 June 5 with the current largest solar telescope, the 1.6 m New Solar Telescope (NST), at the Big Bear Solar Observatory. The observations are made at TiO, Hα, and 10830 Å wavebands with a spatial resolution better than 0 .″ 1 and a full-run cadence of ∼30 s. The fan-shaped surge consists of many small-scale threads with a typical width of 100 km and a length of up to 200 Mm at the maximum. The threads come from material ejections, which start with a velocity of several km s−1, and then accelerate up to 60–80 km s−1 over six to seven minutes with an acceleration of up to 0.2–0.3 km s−2. The threads can be observed in the Hα band and in SDO/AIA 171 Å images as absorbed objects, implying that they are cool material ejections. The surge is ejected along open magnetic field lines in the extrapolated non-linear force-free field, which might actually be a part of a large-scale magnetic loop stretching back to the solar surface. After 10–20 minutes, the ejections gradually decay and the surge eventually vanishes. The total lifetime is about 35 minutes. The Hα brightening at the root of the fan-shaped surge implies that there is heating in the chromosphere, which could be produced by low-atmosphere interchange magnetic reconnection. Our observation provides evidence of the reconnection model for the fan-shaped surges, which was proposed by Jiang et al.