Whether Small Flux Ropes and Magnetic Clouds Have the Same Origin: A Statistical Study of Small Flux Ropes in Different Types of Solar Wind

Abstract

Abstract According to the duration and size, magnetic flux ropes can be divided into large-scale flux ropes, namely, magnetic clouds, and small-scale flux ropes (SFRs). Whether SFRs have the same origin as magnetic clouds has been a hot topic for a long time. Based on the SFR database developed by Hu et al. and Chen et al., this paper analyzes the properties of SFRs in different types of solar wind, which are SFRs in interplanetary coronal mass ejections (ICMEs), SFRs in stream interaction regions, and SFRs in background solar wind. On the assumption that SFRs in ICMEs have the same origin as magnetic clouds, we compare the three types of SFRs from several aspects, attempting to shed some light on the dispute, i.e., whether SFRs are homologous to magnetic clouds. The results show that up to 91% of the SFRs are outside ICMEs. Unlike SFRs in ICMEs, SFRs outside ICMEs seldom have large magnetic field strength and apparent expansion signatures. In addition, 36% of the SFRs in ICMEs have enhanced iron charge states. This probability is much higher than the other two types of SFRs. By an automatic method, this paper also find that counterstreaming electrons are more common in SFRs in ICMEs. Considering strong magnetic field, expansion signatures, large iron charge state, and counterstreaming electrons are important indicators of magnetic clouds, we believe that most of the SFRs near Earth have different origins from magnetic clouds.