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Coronal Mass Ejections: Models and Their Observational Basis (P.F. Chen. 2011.Living Rev. Solar Phys.). 张英智 2011.05.05 中国科学院空间科学与应用研究中心 空间天气学国家重点实验室. 1. Observational Features 2. Theoretical Models 3. Debates 4. Summary. Contents. Morphology and mass Angular width Occurrence rate
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Coronal Mass Ejections: Models and Their Observational Basis (P.F. Chen. 2011.Living Rev. Solar Phys.) 张英智 2011.05.05 中国科学院空间科学与应用研究中心 空间天气学国家重点实验室
1. Observational Features 2. Theoretical Models 3. Debates 4. Summary Contents
Morphology and mass Angular width Occurrence rate Velocity and energy Association with flares and filament eruptions 1. Observational Features
Narrow CMEs : the angular width less than 10 degree Normal CMEs : the others Observational Features
2.1 Basic principles the typical energy density of possible energy sources is shown in Table 1 (Forbes, 2000). 2 .Theoretical Models Except some slow CMEs which might be accelerated by the ambient solar wind, it is well established that many CMEs are due to the rapid release of magnetic energy in the corona.
The essential feature that can distinguish them is that narrow CMEs show an elongated jet-like shape, whereas normal CMEs present a closed (or convex-outward) loop. 2.2 Global picture
It is always interesting for researchers to know what kind of structures have the potential to erupt as a CME. For narrow CMEs, the progenitor is the open magnetic field, usually the coronal hole. For normal CMEs, the progenitor should be a strongly twisted or sheared magnetic structure, which has stored a lot of nonpotential energy. 2.3 Progenitor
Regarding the CME progenitor, i.e., the strongly sheared and /or twisted core field restrained by the overlying envelop field, two issues are worthy to be clarified by future MHD numerical simulations: (1) The helical flux rope– twisted field lines winding many times. (2) The SXR sigmoids– SXR signature
1. Tether-cutting or flux cancellation mechanism 2. Shearing motions. 3. Magnetic breakout model 4. Emerging flux triggering mechanism 5. Flux injection triggering mechanism 6. Instability and catastrophe-related triggering mechanisms 7. Hybrid mechanisms 8. Other mechanisms 2.4 Triggering mechanisms
2.4.5 Instability and catastrophe-related triggering mechanisms
Mass drainage or Sympathetic effect or Solar wind 2.4.7 Other mechanisms
Is magnetic reconnection necessary? Should fast and slow CMEs be attributed to different models? Nature and the driving source of “EIT waves” What is the nature of CMEs? Are halo CMEs special? 3. Debates
Morphologically, CMEs can be distinguished as narrow (jet-like) and normal (loop-like) CMEs. The physics of narrow CMEs is quite clear, i.e., they correspond to the outflow as emerging flux or a coronal loop reconnects with the open magnetic field. 4. Summary
(1) Classification: velocity (slow and fast) evolution (impulsive and gradual) (2) Progenitors: The pre-CME structure might be strongly sheared or weakly twisted magnetic field that is restrained by less-sheared envelope field, and flux rope is not necessarily required in the progenitor. (3) Triggering mechanisms: It is generally believed that magnetic free energy has been stored in the CME progenitors, and the triggering process, which can be ideal or resistive, does not supply much energy to the eruptions. Summary – normal CMEs
(4) Eruption: current sheet is formed below the core and then reconnection is excited in the current sheet. (5) Nature of the CME frontal loop? (6) Is magnetic reconnection necessary? Finally, some comments for the future research: (1) In order to understand and predict the CME initiation, the internal cause, e.g., the magnetic nonpotentiality, and external cause, e.g., the emerging flux , should be considered together. (2) Little attention was paid to the nature of the CME frontal loop, which is not fully understood yet. (3) It might be of great importance to predict how much energy and magnetic helicity can be released from a source region if it erupts as a CME. Summary – normal CMEs
