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Astron. Astrophys. 357, 1105-1114 (2000)

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Temporal dynamics of Joule heating and DC-electric field acceleration in single flare loop

V.V. Zaitsev 1, S. Urpo 2 and A.V. Stepanov 3

1 Institute of Applied Physics, Ulyanova 46, N. Novgorod 603600, Russia
2 Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland
3 Central Astronomical Observatory at Pulkovo, St. Petersburg 196140, Russia

Received 7 February 2000 / Accepted 14 March 2000


Pulsating and explosive time profiles of mm-wave solar bursts observed at Metsähovi are examined in terms of the energy release in a single current-carrying loop. We suppose that the electric current in the loop is driven by photospheric convective flows. The flare occurs due to flute instability provoking the penetration of partially ionized plasma from the chromosphere or prominence into the current channel of a loop and increasing the loop resistance by many orders of magnitude. The feedback of deviation of the loop magnetic field on the energy release rate is taken into account. Joule plasma heating due to current dissipation and electron acceleration in DC electric field are considered. Both processes act simultaneously and are driven by one parameter, the penetration depth of partially ionized plasma into the current-carrying loop. Two regimes of energy release are studied: (i) Pulsating energy release in current-carrying loops with negative radial gradient of gas pressure; (ii) Explosive plus pulsating energy release in a loop with positive radial gradient of gas pressure. One can explain the various time behaviours of the flares, for example, several quasi-periodic pulses, and pulsations with increasing amplitude at pre-flash phase followed by explosive enhancement of the emission at flash phase. The possibility of powerful flare in current-carrying magnetic loop with plasma beta [FORMULA] is discussed.

Key words: acceleration of particles – plasmas – Sun: activity – Sun: chromosphere – Sun: flares – Sun: radio radiation

Send offprint requests to: A.V. Stepanov (stepanov@gao.spb.ru)

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© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000