Abstract
We present a multi-wavelength study of a solar eruption event on 20 July 2004, comprising observations in Hα, EUV, soft X-rays, and in radio waves with a wide frequency range. The analyzed data show both oscillatory patterns and shock wave signatures during the impulsive phase of the flare. At the same time, large-scale EUV loops located above the active region were observed to contract. Quasi-periodic pulsations with ∼ 10 and ∼ 15 s oscillation periods were detected both in microwave – millimeter waves and in decimeter – meter waves. Our calculations show that MHD oscillations in the large EUV loops – but not likely in the largest contracting loops – could have produced the observed periodicity in radio emission, by triggering periodic magnetic reconnection and accelerating particles. As the plasma emission in decimeter – meter waves traces the accelerated particle beams and the microwave emission shows a typical gyrosynchrotron flux spectrum (emission created by trapped electrons within the flare loop), we find that the particles responsible for the two different types of emission could have been accelerated in the same process. Radio imaging of the pulsed decimetric – metric emission and the shock-generated radio type II burst in the same wavelength range suggest a rather complex scenario for the emission processes and locations. The observed locations cannot be explained by the standard model of flare loops with an erupting plasmoid located above them, driving a shock wave at the CME front.
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Acknowledgements
We thank the research teams of all instruments, both satellite and ground-based, who have made their data available and easily accessible in the web archives. All ETHZ radio spectrometer data are available at http://soleil.i4ds.ch/solarradio/, and we thank Christian Monstein for useful comments and explanations on the ETHZ Phoenix-2 data. The University of Bern radio polarimeters that were located at Bumishus in Switzerland are now at Tuorla Observatory in Finland and part of their data archive is available at the TUBE website at http://tube.utu.fi/unibe-bursts/. The radio monitoring survey at http://secchirh.obspm.fr/ is generated and maintained at the Observatoire de Paris by the LESIA UMR CNRS 8109, in cooperation with the Artemis team, Universities of Athens and Ioannina, and the Naval Research Laboratory. The Green Bank Solar Radio Burst Spectrometer (GBSRBS) is operated by the National Radio Astronomy Observatory, and the Global High Resolution Hα Network is operated by the Space Weather Research Lab, New Jersey Institute of Technology. The GOES SXI data access system is a cooperative effort between NOAA’s Space Weather Prediction Center (SWPC) and National Geophysical Data Center (NGDC). SOHO is a project of international cooperation between ESA and NASA, and TRACE was a NASA Small Explorer (SMEX) mission. The wavelet software was provided by C. Torrence and G. Compo, and it is available at http://atoc.colorado.edu/research/wavelets/.
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Advances in European Solar Physics
Guest Editors: Valery M. Nakariakov, Manolis K. Georgoulis, and Stefaan Poedts
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Kallunki, J., Pohjolainen, S. Radio Pulsating Structures with Coronal Loop Contraction. Sol Phys 280, 491–507 (2012). https://doi.org/10.1007/s11207-012-0003-z
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DOI: https://doi.org/10.1007/s11207-012-0003-z