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ARE THE FAINT STRUCTURES AHEAD OF SOLAR CORONAL MASS EJECTIONS REAL SIGNATURES OF DRIVEN SHOCKS?

2014; IOP Publishing; Volume: 796; Issue: 1 Linguagem: Inglês

10.1088/2041-8205/796/1/l16

2041-8213

Jae‐Ok Lee, Yong‐Jae Moon, Jin‐Yi Lee, Kyoung‐Sun Lee, Sujin Kim, Kangjin Lee,

Stellar, planetary, and galactic studies

Recently, several studies have assumed that the faint structures ahead of coronal mass ejections (CMEs) are caused by CME-driven shocks. In this study, we have conducted a statistical investigation to determine whether or not the appearance of such faint structures depends on CME speeds. For this purpose, we use 127 Solar and Heliospheric Observatory/Large Angle Spectroscopic COronagraph (LASCO) front-side halo (partial and full) CMEs near the limb from 1997 to 2011. We classify these CMEs into two groups by visual inspection of CMEs in the LASCO–C2 field of view: Group 1 has the faint structure ahead of a CME and Group 2 does not have such a structure. We find the following results. (1) Eighty-seven CMEs belong to Group 1 and 40 CMEs belong to Group 2. (2) Group 1 events have much higher speeds (average = 1230 km s−1 and median = 1199 km s−1) than Group 2 events (average = 598 km s−1 and median = 518 km s−1). (3) The fraction of CMEs with faint structures strongly depends on CME speeds (V): 0.93 (50/54) for fast CMEs with V ⩾ 1000 km s−1, 0.65 (34/52) for intermediate CMEs with 500 km s−1 ⩽ V < 1000 km s−1, and 0.14 (3/21) for slow CMEs with V < 500 km s−1. We also find that the fraction of CMEs with deca–hecto metric type II radio bursts is consistent with the above tendency. Our results indicate that the observed faint structures ahead of fast CMEs are most likely an enhanced density manifestation of CME-driven shocks.