Small Interplanetary Magnetic Flux Rope

TL;DR

Small interplanetary magnetic flux ropes (SIMFRs) are small, often slow-moving structures near 1 AU, with diverse origins and properties, potentially linked to small CMEs and different formation mechanisms in the solar corona or interplanetary space.

Contribution

This paper reviews the properties, origins, and observational features of SIMFRs, highlighting their similarities to magnetic clouds and discussing their possible dual origins.

Findings

SIMFRs are mostly observed in slow solar wind.

Many SIMFRs show abnormal heavy ion compositions.

Some SIMFRs are confirmed to be interplanetary counterparts of CMEs.

Abstract

Small interplanetary magnetic flux ropes (SIMFRs) are often detected by space satellites in the interplanetary space near 1 AU. These ropes can be fitted by a cylindrically symmetric magnetic model. The durations of SIMFRsare usually <12 h, and the diameters of SIMFRsare <0.20 AU and show power law distribution. Most SIMFRs are observed in the typically slow solar wind (<500 km/s), and only several events are observed with high speed (>700 km/s). Some SIMFRs demonstrate abnormal heavy ion compositions, such as abnormally high He abundance, abnormally high average iron ionization, and enhanced O7+ abundance. These SIMFRs originate from remarkablyhot coronal origins. Approximately 74.5% SIMFRs exhibit counterstreamingsuprathermal electron signatures. Given their flux rope configuration, SIMFRs are potentially more effective for substorms. SIMFRs and magnetic clouds havemany similar observational properties but also show some different observations.These similar properties may indicate that SIMFRs are the interplanetary counterparts of small coronal mass ejections. Some direct bodies of evidence have confirmed that several SIMFRs areinterplanetary counterparts of CMEs. However, their different properties may imply that some SIMFRs haveinterplanetary origins. Therefore, one of the main aims of future research on SIMFRs is to determine whether SIMFRs originate from two different sources, that is, some events are formed in the solar coronal atmosphere, whereas others originate from the interplanetary space. Finally, in this study, we offer some prospects that shouldbe addressed in the future.