A dynamo theory of solar flares

Kan, J. R.; Akasofu, S.‐I.; Lee, L. C.

doi:10.1007/bf00157454

Cited by 66 publications

(18 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…This becomes clear in treating it as an equivalent electric circuit. The electric circuit approach has been applied to the different problems of solar and stellar physics including flares (e.g., Alfvén & Carlqvist 1967;Spicer 1976;Kan et al 1983;Melrose & McClymont 1987;Melrose 1991;Zaitsev & Stepanov 1992;Zaitsev et al 1998) (Miller et al 1994). In our case an appropriate loop (a source of accelerated particles) may be the compact emerging magnetic flux EL shown in Fig. 1b.…”

Section: Rlc-oscillations Of Emerging Magnetic Loop (El)mentioning

confidence: 99%

Solar type IV burst spectral fine structures

Zlotnik

Зайцев

Auraß

et al. 2003

A&A

View full text Add to dashboard Cite

Abstract.We discuss a source model for the origin of solar type IV burst fine structures (FS) using the data of an event in AR 7792 on 25 October 1994. After giving a comprehensive observational treatment of FS (Paper I), here we repeat the main observed facts to construct a simplified radio source model. It consists of two interacting loops (named LS1 and EL) with one spatial order of magnitude scale difference (turning heights 70 and 7 Mm). We consider the implications of this model for physical mechanisms of broad band pulsations (BBP) and zebra patterns (ZP). Our analysis leads to the conclusion that meter wave BBP and ZP originate from a common magnetic source structure -a large asymmetric coronal loop. It is shown that the BBP result from periodically repeated injections of fast electrons into the asymmetric magnetic trap. The excitation of plasma waves is due to the stream instability when these electrons are propagating along the loop. We demonstrate that a two percent quasi-periodic modulation of a magnetic field component in EL is sufficient for it to act as a periodic electron accelerator. The ZP is due to a plasma wave instability at the levels of double plasma resonance (DPR) in an inhomogeneous source distributed along the loop axis of LS1. The DPR frequencies appear at those height levels where the upper hybrid frequency is equal to a harmonic of the gyrofrequency. Two Appendices review theoretical details needed to understand the given ZP interpretation. The gyrofrequency as a function of height was derived from a force-free extrapolated field line that passes the coronal radio source. After knowing the loop turning height and the magnetic field strength we identified for a fixed observing time the harmonic number of each zebra stripe. The comparison of the calculated DPR levels with the observed zebra stripe peak frequencies yields a density law for the ZP source volume. It turns out that this is a barometric law with a temperature near 106 K. We demonstrate that the drift of the whole ZP to higher frequencies can be explained as a signature of magnetic field decrease and/or plasma cooling in the ZP source. The time delay between BBP and ZP was found to be due to the higher fast particle threshold of the DPR versus the beam instability. The present analysis confirms the double plasma resonance model for the ZP fine structure, and underlines the significance of force-free extrapolated photospheric fields for coronal magnetic field modelling.

show abstract

Section: Rlc-oscillations Of Emerging Magnetic Loop (El)mentioning

confidence: 99%

Solar type IV burst spectral fine structures

Zlotnik

Зайцев

Auraß

et al. 2003

A&A

View full text Add to dashboard Cite

show abstract

“…This fact indicates that magnetic shear must be increased above some critical level before and during flare onset. A dynamo process associated with motions of photospheric gas may be needed (Kan et al, 1983;Akasofu, 1984). In fact, a rapid rotation of one of the sunspots in the pair was observed during a recent typical flare (Fig.…”

Section: Solar Flaresmentioning

confidence: 99%

The choice of the concept of magnetic field lines or of electric current lines: Alfvén medal lecture

Akasofu

2011

Ann. Geophys.

Self Cite

View full text Add to dashboard Cite

Abstract.In 1967, at the Birkeland Symposium in Sandefjord, Norway, Professor Hannes Alfvén stated that the second approach (in solving unsolved problems by the standard MHD theory) to cosmic electrodynamics is to "thaw" the "frozen-in" magnetic field lines. "We can illustrate essential properties of the electromagnetic state of space either by depicting the magnetic field lines or by depicting electric current lines," he said. There has been much progress in space physics since the Birkeland Symposium more than 40 years ago, but unfortunately our scientific community has not really succeeded in thawing the frozen-in field lines. Instead, it has pursued magnetic reconnection, a concept that Alfvén had been critical of. It is shown here that we have to study many unsolved problems and problems thought to be solved in terms of both the magnetic field line concept and the current system concept. In taking Alfvén's approach, we must consider the whole system, including the power supply (dynamo process) and its transmission and distribution (electric currents) and observed phenomena (power dissipation processes). Such a consideration can provide physical insight into many of our unsolved problems and problems thought to be solved. In this paper, we consider substorm onset processes, the substorm current system, sunspots, solar flares, coronal mass ejections, the interplanetary current sheet, and the magnetic field configuration of the heliosphere in terms of the current system concept. In particular, it is shown that a study of the current system is essential in substorm studies, more than changes of the magnetic field configuration in the magnetotail.

show abstract

“…It is becoming widely accepted that coronal heating is due to the dissipation of either AC or DC currents in coronal loops [SO, 511. One model of a flare is that it is a nonlinear response to a steady change in the input power, with the idea being that if the dissipation rate has to adjust too rapidly or too far, then it can only do so through an explosive change in configuration [52]. However, these ideas remain speculative: at present bulk energization is simply not adequately understood.…”

Section: Acceleration Mechanismsmentioning

confidence: 99%

Solar Radio Bursts with Special Regard to Particle Acceleration and Mass Ejection

Melrose

Dulk

1987

Phys. Scr.

View full text Add to dashboard Cite

Radio data on solar radio bursts imply that acceleration occurs in more than the traditional two phases. Short timescale phenomena, called spike bursts, may be the most direct signatures of acceleration, but they are inadequately understood for firm conclusions to be drawn. Data on events in the solar wind provide direct evidence on particle accelerations. It is suggested that phenomena may be classified according to the type of acceleration involved, with four types being identified: bulk energization, stochastic acceleration, diffusive shock acceleration and shock drift acceleration.

show abstract

A dynamo theory of solar flares

Cited by 66 publications

References 20 publications

Solar type IV burst spectral fine structures

Solar type IV burst spectral fine structures

The choice of the concept of magnetic field lines or of electric current lines: Alfvén medal lecture

Solar Radio Bursts with Special Regard to Particle Acceleration and Mass Ejection

Contact Info

Product

Resources

About