Ignition of MHD shocks associated with solar flares |
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| Authors: | B Vr?nak V Ru?djak P Zlobec H Aurass |
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| Institution: | (1) Faculty of Geodesy, Hvar Observatory, 41000 Zagreb, Croatia;(2) Trieste Astronomical Observatory, 34131 Trieste, Italy;(3) Astrophysikalisches Institut Potsdam, D-14552 Tremsdorf, Germany |
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| Abstract: | We have selected single frequency recordings of 28  high-frequency type II bursts characterized by a starting frequency greater than 237 MHz to estimate as accurately as possible the launch-time of the flare-associated MHD shocks. We established the time associations between metric type II burst onsets and the time characteristics of the microwave and X-ray fluxes of the associated flares. The associated flares were impulsive events with rise times most often about 1 min in the hard X-ray range and 1–2 min in the microwave wavelength range. The majority of the type II bursts from our sample started about 1 min after the maximum of the microwave burst. Launch times of MHD shocks producing type II bursts were obtained using the 10 × Saito coronal model and shock velocities estimated from burst characteristics at different frequencies. Back-extrapolations of type II recordings indicate that MHD shocks are launched in the time interval prior to the maximum of the first peak in the associated microwave burst, most probably at the beginning of the rapid increase of the microwave burst. |
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