Coronal phenomena at the release of solar energetic electron events^*

¹ Observatoire de Paris, LESIA-CNRS UMR 8109, 92195 Meudon, France e-mail: ludwig.klein@obspm.fr
² Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450, USA e-mail: krucker@ssl.berkeley.edu

Received: 7 May 2004
Accepted: 9 October 2004

Abstract

We investigate dynamical processes in the solar corona at the release of electrons (~30-500 keV) detected by the Wind/3DP experiment, with the aim to clarify the relationship between coronal acceleration and the escape of electrons to interplanetary space. Energetic electrons and plasma in the corona are traced using radio, EUV and X-ray observations. 40 events were identified where the release time of the electrons could be determined within an uncertainty of a few minutes and occurred during the observing hours of the Nançay Radioheliograph. All were accompanied by decametric-to-kilometric type III bursts (Wind/WAVES), and 30 by metric radio emission in the western hemisphere. The main findings from these 30 events are: (i) Electrons detected at Wind are released at the time of distinct episodes of electron acceleration in the corona signalled by radio emission. The release may occur at the start of the radio event or up to an hour later. (ii) The most conspicuous examples of delayed electron release occur in events associated with complex, long lasting (>10 min, up to seveal hours) radio emission. Radio observations suggest that in these cases the earlier accelerated electrons remain confined in the corona or are injected into flux tubes which are not connected to the spacecraft. (iii) Type II bursts revealing shock waves in the corona accompany about a third of the events. But the shock waves occur in general together with type IV radio signatures due to long lasting acceleration not related to the shock. With a few exceptions these type IV emissions have a clearer timing relationship with the electron release to space than the type II bursts. We conclude that the combination of time-extended acceleration at heights ≲0.5  above the photosphere with the injection of electrons into a variety of closed and open magnetic field structures explains the broad variety of timing shown by the radio observations and the in situ measurements.