Karl-Ludwig Klein

Coronal electron acceleration and relativistic proton production during the 14 July 2000 flare and CME

The large solar flare of 14 July 2000 10 UT occurred in an active region near the central meridian. It was accompanied by the eruption of a lament and a rapid halo-type coronal mass ejection (CME). Large particle fluxes were detected up to relativistic energies at 1 AU. In this paper accelerated particles and plasma structures in the corona are traced using radio, X-ray, EUV and visible light observations, together with neutron monitor measurements of relativistic protons at 1 AU. Both the bulk of the radio emission at decimetric and longer waves and the escape of suprathermal electrons and relativistic protons from the Sun were delayed by 10{20 min with respect to the hard X-ray emission. Despite the delay and the association with a flare near the central meridian the neutron monitor time prole was impulsive. We show that the escape of the relativistic protons occurred in time coincident both with a coronal shock wave, which may be the bow shock of the CME, and with radio sources which trace electron acceleration and magnetic eld reconguration in the western hemisphere. Three observations support the idea that the relativistic protons were accelerated during this reconguration, at heights between 0.1 and 1 R above the photosphere, and not in the flaring active region or at the bow shock of the CME: (i) the rise of the neutron monitor count rates is simultaneous with the brightening of a new continuum radio source; (ii) the duration of the continuum emission is similar to the rise time of the neutron monitor count rates; (iii) the radio source is close to the Earth-connected interplanetary magnetic eld line.

The Origin of Solar Energetic Particle Events: Coronal Acceleration versus Shock Wave Acceleration

We review evidence that led to the view that acceleration at shock waves driven by coronal mass ejections (CMEs) is responsible for large particle events detected at 1 AU. It appears that even if the CME bow shock acceleration is a possible model for the origin of rather low energy ions, it faces difficulties on account of the production of ions far above 1 MeV: (i) although shock waves have been demonstrated to accelerate ions to energies of some MeV nucl−1 in the interplanetary medium, their ability to achieve relativistic energies in the solar environment is unproven; (ii) SEP events producing particle enhancements at energies ≥100 MeV are also accompanied by flares; those accompanied only by fast CMEs have no proton signatures above 50 MeV. We emphasize detailed studies of individual high energy particle events which provide strong evidence that time-extended particle acceleration which occurs in the corona after the impulsive flare contributes to particle fluxes in space. It appears thus that the CME bow shock scenario has been overvalued and that long lasting coronal energy release processes have to be taken into account when searching for the origin of high energy SEP events.

The high energy solar corona: waves, eruptions, particles

Introduction: The High-energy Corona - Waves, Eruptions, Particles.- Introduction: The High-energy Corona - Waves, Eruptions, Particles.- Particle Acceleration During Flares.- Magnetic Complexity, Fragmentation, Particle Acceleration and Radio Emission from the Sun.- Review of Selected RHESSI Solar Results.- RHESSI Results - Time for a Rethink?.- Small Scale Energy Release and the Acceleration and Transport of Energetic Particles.- Large-scale Disturbances.- Large-scale Waves and Shocks in the Solar Corona.- Energetic Particles Related with Coronal and Interplanetary Shocks.- Particle Acceleration at the Earths Bow Shock.- On the Existence of Non-maxwellian Velocity Distribution Functions in the Corona and their Consequences for the Solar Wind Acceleration.- Recent Research: Large-scale Disturbances, their Origin and Consequences.- Plasma of the Solar Corona.- Quasi-periodic Pulsations as a Diagnostic Tool for Coronal Plasma Parameters.- Pulsating Solar Radio Emission.

Acceleration of Relativistic Protons During the 20 January 2005 Flare and CME

The origin of relativistic solar protons during large flare/CME events has not been uniquely identified so far. We perform a detailed comparative analysis of the time profiles of relativistic protons detected by the worldwide network of neutron monitors at Earth with electromagnetic signatures of particle acceleration in the solar corona during the large particle event of 20 January 2005. The intensity – time profile of the relativistic protons derived from the neutron monitor data indicates two successive peaks. We show that microwave, hard X-ray, and γ-ray emissions display several episodes of particle acceleration within the impulsive flare phase. The first relativistic protons detected at Earth are accelerated together with relativistic electrons and with protons that produce pion-decay γ rays during the second episode. The second peak in the relativistic proton profile at Earth is accompanied by new signatures of particle acceleration in the corona within ≈1R⊙ above the photosphere, revealed by hard X-ray and microwave emissions of low intensity and by the renewed radio emission of electron beams and of a coronal shock wave. We discuss the observations in terms of different scenarios of particle acceleration in the corona.

Metric Radio Emission Associated with X-Ray Plasmoid Ejections

In this paper we report the first detection of metric/decimetric radio emission associated with two soft X-ray plasmoid ejecta events that occurred during two limb flares observed by the Yohkoh SXT. In the first event a loop started to rise slowly (~10 km s-1) before the beginning of the hard X-ray impulsive phase of the flare. At about the onset of the impulsive flare, there was acceleration of the ejecta, resulting in a speed of 130 km s-1 and finally to ~200 km s-1. The associated radio emission was observed with the Nancay radioheliograph (NRH) in the frequency range of 230-450 MHz. It was an unpolarized continuum that lasted 8-10 minutes. The 410 MHz source was located close to the height where the plasmoid was last identified in the SXT images. In the second event an eruption resulted in the expansion of a large-scale, looplike feature and the development of two plasmoid ejecta which moved in different directions. The speed of the ejecta was 60-100 km s-1. In this event, the associated radio emission was a long-lasting (about 2 hr) continuum observed from 450 to 164 MHz. The onset of the low-frequency emission was delayed with respect to the onset of the high-frequency emission. In both cases the radio sources were located above the soft X-ray ejecta in the general direction of the prolongation of the ejecta movement. In both cases the radio emission comes from nonthermal electrons which are accelerated in close relationship with the propagation of the X-ray plasmoid: as the plasmoid reaches higher altitudes, it interacts with increasingly more extended magnetic field lines and new coronal sites of production of nonthermal electrons are created.

Vertical Dynamics of the Energy Release Process in a Simple two-Ribbon Flare

AbstractObservations of the quiescent filament eruption and the spotless two-ribbon flare of 12 September 2000 are presented. A simple flare morphology, large spatial scales, and a suitable viewing angle provide insight into characteristics of the energy release process which is attributed to the reconnection process in the current sheet formed below the eruptive filament. The flare ribbons appeared and started to expand laterally while the filament was still recognizable, enabling simultaneous measurements of the ribbon separation w and the height of the lower edge of the filament, h. The ratio w/h estimated for the expanding portions of ribbons indicates that the width-to-length ratio of the current sheet at the onset of the fast reconnection ranges between

Release timescales of solar energetic particles in the low corona

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Long-duration non thermal energy release in flares and outside flares

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