Origin and structures of solar eruptions I: Magnetic flux rope

Abstract

Coronal mass ejections (CMEs) and solar flares are the large-scale and most energetic eruptive phenomena in our solar system and able to release a large quantity of plasma and magnetic flux from the solar atmosphere into the solar wind. When these highspeed magnetized plasmas along with the energetic particles arrive at the Earth, they may interact with the magnetosphere and ionosphere, and seriously affect the safety of human high-tech activities in outer space. The travel time of a CME to 1 AU is about 1-3 days, while energetic particles from the eruptions arrive even earlier. An efficient forecast of these phenomena therefore requires a clear detection of CMEs/flares at the stage as early as possible. To estimate the possibility of an eruption leading to a CME/flare, we need to elucidate some fundamental but elusive processes including in particular the origin and structures of CMEs/flares. Understanding these processes can not only improve the prediction of the occurrence of CMEs/flares and their effects on geospace and the heliosphere but also help understand the mass ejections and flares on other solar-type stars. The main purpose of this review is to address the origin and early structures of CMEs/flares, from multi-wavelength observational perspective. First of all, we start with the ongoing debate of whether the pre-eruptive configuration, i.e., a helical magnetic flux rope (MFR), of CMEs/flares exists before the eruption and then emphatically introduce observational manifestations of the MFR. Secondly, we elaborate on the possible formation mechanisms of the MFR through distinct ways. Thirdly, we discuss the initiation of the MFR and associated dynamics during its evolution toward the CME/flare. Finally, we come to some conclusions and put forward some prospects in the future.

A Study of Pre-flare Solar Coronal Magnetic Fields: Magnetic Flux Ropes

“…Indeed, the relevance of MFRs with solar flares and eruptions has also been extensively evidenced from both observations and coronal magnetic field reconstructions. For instance, X-ray and EUV sigmoid, filament, EUV hot channel, and coronal cavity are invoked as indirect observations of coronal MFRs (e.g., see a recent review paper by Cheng et al 2017). Using nonlinear force-free field (NLFFF) extrapolations from vector magnetograms, which is a basic tool for unraveling the 3D information of solar coronal magnetic field, MFRs were identified frequently (e.g., see another recent review by Guo et al 2017).…”

Unambiguous Evidence of Filament Splitting-induced Partial Eruptions

“…The pre-eruptive configuration of CMEs/flares is often believed to be a magnetic flux rope (MFR), which may contain a filament/prominence (Kuperus & Raadu 1974;van Tend & Kuperus 1978;van Ballegooijen & Martens 1989;Mackay et al 2010;Schmieder et al 2013;Cheng et al 2017). In this system, filament material is preferentially collected in the magnetic dips of the MFR, which provide an upward Lorenz force that naturally balances gravity (Low & Hundhausen 1995;Gibson et al 2004;Gibson & Fan 2006a).…”

How Many Twists Do Solar Coronal Jets Release?

“…It has also been sug-gested that kink instability could be associated with small-scale (nano) flares [e.g., Browning et al, 2008]. Meanwhile, plenty of literature is available to present abundant evidence in theories, numerical simulations and observations on how the eruptions of filaments and CMEs are related to kink-unstable magnetic flux ropes [e.g., Rust and Kumar, 1996;Kliem et al, 2004;Török and Kliem, 2005;Williams et al, 2005;Guo et al, 2010;Kumar et al, 2012;Liu et al, 2016c;Cheng et al, 2017;Vemareddy et al, 2017]. Recently, Wang et al [2016] has further identified the magnetic twist inside post-eruption flux ropes in the heliosphere from analyzing 115 magnetic clouds observed at 1 AU.…”