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

Abstract

We present a small flux rope (SFR) with smooth magnetic field rotations entrained by rolling back magnetic field lines around 1 AU. Such SFRs have only been seldom reported in the literature. This SFR was adjacent to a heliospheric plasma sheet (HPS), which is defined as a high plasma beta region in the vicinity of a heliospheric current sheet. Even though the SFR and HPS have different plasma beta, they possess similar plasma signatures (such as temperature, density, and bulk speed), density ratio of alpha particle‐to‐proton (Nα/Np), and heavy ion ionization states, which imply that they may have a similar origin in the corona. The composition and the configuration of the rolling back magnetic field lines suggested that the SFR originated from the streamer belt through interchange reconnection. The origin processes of the SFR are presented here. Combining the observations of STEREO and ACE, the SFR was shown to have an axis tilted to the ecliptic plane and the radius may vary with different spatial positions. In this study, we suggest that interchange reconnection can play an important role for the origin of, at least, some SFRs and slow solar wind.

Unusually low density regions in the compressed slow wind: Solar wind transients of small coronal hole origin

“…As suggested in the introduction, most small transients occur in slow solar wind, and they have some characteristics (e.g., enhanced magnetic field strength, low plasma beta, Alfvén Mach number) based on statistical studies (Yu et al 2014(Yu et al , 2016. Furthermore, the above statistical results clearly show that the signatures of small transients vary greatly (as shown by the large error bars in (Janvier et al 2014;Huang et al 2017).…”

“…The HCS is defined as a sustained change in signs of the magnetic field; it is accepted as a separation for the different polarity of the interplanetary magnetic field (Crooker et al 2004;Liu et al 2014) when it is consistent with TSB, which is defined as the change in direction of PADs (Kahler et al 1996;Foullon et al 2009). When the magnetic field lines roll back, HCS is separated from TSB (Owens et al 2013;Huang et al 2017). Thus, the low density region solar wind does not depend on the streamer belt structure or on HCS.…”

“…Another study by Wang et al (2019) traced most of these Alfvénic solar winds back to active regions. Small transients are common in the solar wind (Yu et al 2016), and a subset of them are small flux ropes that show twisted magnetic structures (Moldwin et al 2000;Huang et al 2017). In general, small transients have short duration, decreased magnetic field variability, and low proton temperature and/or proton beta (Kilpua et al 2009).…”

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

“…Rouillard et al (, ) confirmed this result by tracing several SFRs back to their source regions. But whether they are released through interchange reconnection processes (Huang et al, ; Wang et al, ) or pinched off by the intrinsic instability‐driven magnetic reconnection processes (Chen et al, ) still needs further investigation. The other category may be related to X‐ray jets that arise from the photosphere (Janvier et al, ).…”

“…By utilizing STEREO A data, Yu et al () investigated the Q <Fe> variations in small transients, an extended range of SFRs, and they demonstrated that Q <Fe> only increases in less than 5% of small transients. Moreover, Huang et al () traced a SFR, which is entrained by rolling back magnetic field lines, back to its source region in the cusp of the streamer belt with the support of N α / N p and heavy ion compositions. SFRs are more influenced than MCs by ambient solar wind due to their small sizes (Feng & Wang, ; Janvier et al, ), but the Q <Fe> variations, which are frozen‐in within several solar radii, can be used to exclude propagation effects and provide evolutionary properties on the conditions at the origin (Huang et al, ; Lepri et al, ; von Steiger et al, ).…”