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 Publication Status: Solar Physics 289, 12, 4517-4531 (2014). DOI 10.1007/s11207-014-0604-9 Last Modified: 2014-11-24 07:25

 Radio evidence for breakout reconnection in solar eruptive events Henry Aurass   Submitted: 2013-05-30 03:26 Magnetic reconnection is understood to be fundamental to energy release in solar eruptive events (SEEs). In these events reconnection produces a magnetic flux rope above an arcade of hot flare loops. Breakout reconnection, a secondary reconnection high in the corona between this flux rope and the overlying magnetic field, has been hypothesized. Direct observational evidence for breakout reconnection has been elusive, however. The aim of this study is to establish a plausible interpretation of the combined radio and hard X-ray (HXR) emissions observed during the impulsive phase of the near-limb X3.9-class SEE on 2003 November 03. We study radio spectra (AIP), simultaneous radio images (Nanc{c}ay Multi-frequency Radio Heliograph, NRH), and single-frequency polarimeter data (OAT). The radio emission is nonthermal plasma radiation with a complex structure in frequency and time. Emphasis is on the time interval when the HXR flare loop height was observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) to be at its minimum and an X-ray source was observed above the top of the arcade loops. Two stationary, meter-wavelength sources are observed radially aligned at 0.18 and 0.41Rs above the active region and hard X-ray sources. The lower source is apparently associated with the upper reconnection jet of the flare current sheet (CS), and the upper source is apparently associated with breakout reconnection. Sources observed at lower radio frequencies surround the upper source at the expected locations of the breakout reconnection jets. We believe the upper radio source is the most compelling evidence to date for the onset of breakout reconnection during a SEE. The height stationarity of the breakout sources and their dynamic radio spectrum discriminate them from propagating disturbances. Timing and location arguments reveal for the first time that both the earlier described above the flare loop top'' HXR source and the lower radio source are emission from the upper reconnection jet above the vertical flare CS. Authors: H. Aurass, G. Holman, S. Braune, G. Mann, P. Zlobec Projects:
 Publication Status: Astronomy and Astrophysics 555, A40 (2013) Last Modified: 2013-07-01 07:21

 Radio evidence of break-out reconnection? Henry Aurass   Submitted: 2011-01-24 02:00 We reconsider the Oct. 28, 2003 X17 flare/coronal mass ejection studying the five minutes immediately before the impulsive flare phase (not yet discussed in previous work). To this aim are composed: complementary dynamic radio spectrograms, single frequency polarimeter records, radio images, as well as space-based longitudinal field magnetograms and ultra-violet images. We find widely distributed faint and narrowband meter wave radio sources located outside of active regions but associated with the boundaries of magnetic flux connectivity cells, inferred from the potential extrapolation of the observed photospheric longitudinal field as a model for coronal magnetic field structures. The radio sources occured during the initial decimeter wave effects well-known to be associated with the filament destabilization in the flaring active region (here NOAA 10486). Antiochos et al. (1999, ApJ 510, 485) predict in their break-out model for CME initiation that '' ... huge phenomena ... may be controled by detailed plasma processes that occur in relatively tiny regions''. They suggest that the expected faint energy release '' ... on long field lines far away from any neutral line ... may be detectable in radio/microwave emission from non-thermal particles ...''. In this paper we describe meter wave sources whose properties correctly coincide with the quoted predictions of the break-out reconnection model of CME initiation. Authors: H. Aurass, G. Mann, P. Zlobec, M. Karlický Projects: None

 Coronal current sheet signatures during the 17 May 2002 CME-flare Henry Aurass   Submitted: 2009-08-20 04:50 The relation between current sheets (CSs) associated with flares, revealed by characteristic radio signatures, and current sheets associated with Coronal Mass Ejections (CMEs), detected in coronal ultra-violet (UV) and white light data, has not been analyzed, yet. We aim at establishing the relationship between CSs associated with a limb flare and CSs associated with the CME which apparently develops after the flare, on the basis of a unique data set, acquired on May 17, 2002, which includes radio and extreme ultra-violet (XUV) observations. Spectral radio diagnostics as well as UV spectroscopic techniques together with white light coronograph imaging and (partly) radio imaging are used to illustrate the relation between the CSs and to infer the physical parameters of the radially aligned features that develop in the aftermath of the CME. During the flare, drifting pulsating structures in dynamic radio spectra, an erupting filament, expanding coronal loops morphologically reminding to the later white light CME and associated with earlier reported hard X-ray source sites, are interpreted in accordance with earlier work and with reference to the common eruptive flare scenario as evidence of flare CSs in the low corona. In the aftermath of the CME, UV spectra allowed us to give an estimate of the CS temperature and density, over the 1.5 - 2.1 Rs interval of heliocentric altitudes. The UV detected CS, however, appears to be only one of many current sheets that exist underneath the erupting flux rope. A type II burst following in time at lower frequencies the CME radio continuum is considered as radio signature of a coronal shock excited at the flank of the CME. The results show that we can build an overall scenario where the CME is interpreted in terms of an erupting arcade crossing the limb of the Sun and connected to underlying structures via multiple CSs. Eventually, the observed limb flare seems to be a consequence of the ongoing CME. Authors: H. Aurass, F. Landini, G. Poletto Projects: None

 The GLE on Oct. 28, 2003 - radio diagnostics of relativistic electron and proton injection Henry Aurass   Submitted: 2006-08-31 03:00 Timing discrepancies between signatures of accelerated particles at the sun and the arrival times of the particles at near-earth detectors are a matter of fundamental interest for space-weather applications. The solar injection times of various components of energetic particles were derived by Klassen et al. (2005) for the October 28, 2003, X-class / gamma-ray flare in NOAA AR10486. This flare occured in connection with a fast halo coronal mass ejection and a neutron monitor-observed ground level event (GLE). We used radio (Astrophysikalisches Institut Potsdam, WIND, Nancay Multifrequency Radio Heliograph), Hα (Observatorium Kanzelhoehe), RHESSI, SOHO (EIT, LASCO, MDI), and TRACE data to study the associated chromospheric and low coronal phenomena. We identify three source sites of accelerated particles in this event. Firstly, there is a source in projection 0.3Rs away from AR10486, which is the site of the reconnection outflow termination, as revealed by a termination shock signature in the dynamic radio spectrum. Secondly, there is the extended current sheet above a giant coronal postflare loop system in the main flare phase. Thirdly, there is a source situated on a magnetic separatrix surface between several magnetic arcades and neighbouring active regions. This source is 0.2Rs away from AR10486 and acts during onset and growth of high energy proton injection in space. It is not clear if this source is related to the acceleration of protons, or if it only confirms that energetic particles penetrate a multistructure magnetic loop system after being previously accelerated near the main HXR- and gamma-ray sources. The result is in favour of energetic particle acceleration in the low corona (<0.5Rs above the photosphere) and in contrast to acceleration of the relativistic particles at remotely propagating shock waves. Authors: H. Aurass, G. Mann, G. Rausche, and A. Warmuth Projects: RHESSI,SoHO-EIT,SoHO-MDI,TRACE