The First Decametre N-burst: Product of Interaction of two CMEs and a Streamer

L. van Driel-Gesztelyi$^{1,2,3}$, P. Demoulin$^2$, K.L. Klein$^2$, C. P. Goff$^1$, J.L. Culhane$^1$, C.H. Mandrini$^4$, S.A. Matthews$^1$, L.K. Harra$^1$

$^1$Mullard Space Science Laboratory, University College London, UK
$^2$LESIA, Observatoire de Paris-Meudon, 5 Place J. Janssen, F-92195 Meudon Cedex, France
$^3$Konkoly Observatory, Budapest, Hungary
$^4$IAFE, CONICET-UBA, Buenos Aires, Argentina

We show that reconnection between the magnetic structures of two CMEs launched about eight hours apart from different parts of the same active region injects electrons into open field lines having a local dip and apex (located at about six solar radii height). This is observed as an N-burst at decametre radio wavelengts. The dipped shape of these field lines is due to large-scale magnetic reconnection between expanding magnetic loops of the first CME and open field lines of a neighbouring streamer. This particular situation explains why this is the first N-burst ever observed at long radio wavelengths.