Counterstreaming electrons in small interplanetary magnetic flux ropes

Abstract

Small interplanetary magnetic flux ropes (SIMFRs) are commonly observed by spacecraft at 1 AU, and their origin still remains disputed. We investigated the counterstreaming suprathermal electron (CSE) signatures of 106 SIMFRs measured by Wind during 1995–2005. We found that 79 (75%) of the 106 flux ropes contain CSEs, and the percentages of counterstreaming vary from 8% to 98%, with a mean value of 51%. CSEs are often observed in magnetic clouds (MCs), and this indicates these MCs are still attached to the Sun at both ends. CSEs are also related to heliospheric current sheets (HCSs) and the Earth's bow shock. We divided the SIMFRs into two categories: The first category is far from HCSs, and the second category is in the vicinity of HCSs. The first category has 57 SIMFRs, and only 7 of 57 ropes have no CSEs. This ratio is similar to that of MCs. The second category has 49 SIMFRs; however, 20 of the 49 events have no CSEs. This ratio is larger than that of MCs. These two categories have different origins. One category originates from the solar corona, and most ropes are still connected to the Sun at both ends. The other category is formed near HCSs in the interplanetary space.

A multispacecraft study of a small flux rope entrained by rolling back magnetic field lines

“…If it had been formed through magnetic reconnection within the HCS, then the rolling back magnetic field lines in the leading side that contain the HCS would disappear after the reconnection process or at least would not show up in the leading side of the SFR. This also suggests that, at least, some SFRs in the vicinity of HCSs may not be formed at the HCSs in the interplanetary space, which is different from the conclusion suggested by Feng et al [].…”

“…The large‐scale MCs, which have been thoroughly studied, are associated with strong solar eruptions and drive major space weather events [e.g., Lawrance et al , ; Liu et al , ]. The origins of SFRs and their contributions to the slow solar wind have attracted much attention in recent years [ Moldwin et al , ; Kilpua et al , ; Rouillard et al , ; Feng et al , ; Yu et al , , ].…”

The Distributions of Iron Average Charge States in Small Flux Ropes in Interplanetary Space: Clues to Their Twisted Structures

“…Large‐scale flux ropes or magnetic clouds (MCs), which are considered to be a subset of interplanetary coronal mass ejections (ICMEs), usually have a timescale of 1 day (e.g., Burlaga et al, ; Jian et al, ; Shen et al, ; Tian et al, ). However, small‐scale flux ropes (SFRs), which have been first reported by Moldwin et al (, ), primarily have a limited duration of no more than 12 hr (e.g., Cartwright & Moldwin, ; Feng et al, ). Similar to large‐scale MCs, SFRs can also be well fitted with the Lundquist flux rope model (Lundquist, ).…”

“…MCs are of great interest due to their associations with strong solar eruptions and potentially immense geoeffectiveness (e.g., H. Hu et al, ; Wang, Zhang, et al, ). SFRs contribute mainly to slow solar wind, and their source regions and formation mechanisms are still under discussion (e.g., Feng et al, , ; Janvier et al, , ; Kilpua et al, ; Tian et al, ; Yu et al, , ; Zheng & Hu, ).…”

“…Different from MCs that originate from the solar corona, SFRs are believed to have two source regions: the solar corona and the interplanetary medium (e.g., Cartwright & Moldwin, ; Feng et al, ; Janvier et al, ; Moldwin et al, ; Rouillard et al, ; Tian et al, ; Yu et al, , ). SFRs originating in the solar corona can be classified into two categories.…”