It is well known that the occurrence rate of earthquakes and the avalanches of a sandhill against their magnitude also show power law-like distributions, and these phenomena can now be understood in terms of self-organized criticality (Bak et al., 1987). Lu and Hamilton (1991) proposed that the coronal magnetic field is in a self-organized critical state, and solar flare represents the avalanche of many small reconnection events, which is analogous to the avalanche in the sandpile model. They successfully explained the observed power-law distribution of the occurrence rate of flares. Although there is a big gap between the avalanche model for a group of events and the magnetohydrodynamic model focused on an individual event, the avalanche model is still useful for understanding the process of energy release in the system of the solar atmosphere. If you want to know the recent development of the avalanche model, see the review by Charbonneau et al. (2001).
There have also been proposed several models for flares where magnetic reconnection is not assumed. One of them is found at the Alfvén’s current disruption model (Alfvén and Carlqvist, 1967). The other models are proposed by Akasofu (1984), Uchida and Shibata (1988), Melrose (1997), and so on. Many of these models assume energy release inside a flaring loop, thus they are not consistent with those observations provided by Yohkoh, such as loop-top hard X-ray source and plasmoid ejection above a soft X-ray loop.
|LDE flares||impulsive flares||microflares|
|hot cusp loop||yes1||?||?|
|HXR loop-top source||no||yes6||?|
|size (L)||time scale (t)||energy||associated ejection|
|microflares||0.5 – 4||60 – 600||1026 – 1029||jet/surge|
|impulsive flares||1 – 10||60 – 3 × 103||1029 – 1032||X-ray/H|
|LDE flares||10 – 40||3 × 103 – 105||1030 – 1032||X-ray/H|
|large scale||30 – 100||104 – 2 × 105||1029 – 1032||X-ray/H|
|arcade formation||filament eruption|
|microflares||100||1010||3000||5||12 – 120|
|impulsive flares||100||1010||3000||10||6 – 300|
|LDE flares||30||2 × 109||2000||90||30 – 103|
|large scale||10||3 × 108||1500||400||25 – 500|
|mass ejections||mass ejections|
|giant arcades||H filament||CMEs|
|LDE flares||H filament||X-ray plasmoid|
|impulsive flares||H sprays||X-ray plasmoid|
|transient brightenings (microflares)||H surges||X-ray jets|
|EUV microflares||surges/spicules||EUV jets|
|facular points||spicules||(Alfvén waves)|
Living Rev. Solar Phys. 8, (2011), 6
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