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Sun 26.12.01

Title: The 26 December 2001 Solar Eruptive Event Responsible for GLE63. III. CME, Shock Waves, and Energetic Particles
Author: V.V. Grechnev (1), V.I. Kiselev (1), A.M. Uralov (1), K.-L. Klein (2), A.A. Kochanov (1), ((1) Institute of Solar-Terrestrial Physics SB RAS, Irkutsk, Russia, (2) Observatoire de Paris, Univ. Paris, Observatoire de Meudon, Meudon, France)

The 26 December 2001 moderate solar eruptive event (GOES importance M7.1, microwaves up to 4000 sfu at 9.4 GHz, CME speed 1446 km/s) produced strong fluxes of solar energetic particles (SEPs) and ground-level enhancement of cosmic-ray intensity (GLE63). To find a possible reason for the atypically high proton outcome of this event, we study its multi-wavelength images and dynamic radio spectra, and quantitatively reconcile the findings with each other. An additional eruption probably occurred in the same active region about half an hour before the main eruption, which produced two blast-wave-like shocks during the impulsive phase. Later on, the two shock waves merged around the frontal direction into a single shock, which is traced up to 25 solar radii as a halo ahead of the expanding CME body, in agreement with an interplanetary type II event recorded by Wind/WAVES. The shape and kinematics of the halo indicate that the shock wave was in an intermediate regime between the blast wave and bow shock at these distances. The results show that i) the shock wave appeared during the flare rise and could accelerate particles earlier than usually assumed; ii) the particle event could be amplified by the preceding eruption, which stretched closed structures above the developing CME, facilitating its lift-off and escape of flare-accelerated particles, enabling a higher CME speed and a stronger shock ahead; iii) escape of flare-accelerated particles could be additionally facilitated by reconnection of the flux rope, where they were trapped, with a large coronal hole; iv) a rich seed population was provided by the first eruption for the acceleration by a trailing shock wave.

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