engleski

Flare-generated coronal shock on 14 November 2005

Origin of coronal shock waves is still not completely understood. Since the flare impulsive phase and the acceleration phase of a CME are usually well synchronized, it is difficult to give a conclusive answer on the shock wave origin in flare/CME events. We present multiwave-length study of a shock wave associated with the flare event recorded on 14 November 2005. The evolution of the shock wave signature -type II radio burst -is analysed using dynamic spectra recorded by the Green Bank Solar Radio Bursts Spectrometer and Nançay Radioheliograph imaging. The observations of the plasma dynamics in the low and high corona were provided by EIT and LASCO instruments onboard SOHO. The strong type II emission starts at unusually high frequency of 700 MHz. The obtained values for the shock velocity, Alfven velocity and Alfven Mach number are in the range of typical shock parameters. The shock wave was closely associated with the impulsive phase of the compact M3.9 flare in the NOAA AR 10822 (located at S06E60). The short impulsive phase of the flare (4 minutes), suggests that a strong pressure pulse was ignited by the flare. Additionally, RHESSI observations show compact event of a rather high density and high temperature which gives indication of a strong, impulsive increase of pressure in the small flare loop. SOHO/LASCO observations do not show any CME associated with this event. Since the active region is rather close to the limb, the possibility that the corresponding CME is not observed due to the unfavorable geometry is unlikely. We therefore conclude that the shock wave recorded on 14 November 2005 was a blast wave launched by the impulsive energy release in the course of the flare.

coronal shocks; flares; CMEs

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