Summary: Astronomy & Astrophysics manuscript no. 3826 September 27, 2005
(DOI: will be inserted by hand later)
Repetitive occurrence of explosive events at a coronal hole
J. G. Doyle1, M. D. Popescu1,2 and Y. Taroyan1
Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
Astronomical Institute of the Romanian Academy, RO-040557 Bucharest 28, Romania
Received / accepted
Abstract. SUMER/SoHO data taken at a coronal hole boundary show a repetitive explosive event occurrence rate of around
3 min increasing to over 5 min towards the end of the activity. We suggest that the neighbouring oppositely directed closed
and open field lines at the coronal hole boundary undergo repetitive reconnection seen as a sequence of explosive events.
The repetitive reconnection may be triggered by transverse oscillations of the flux tubes in the closed field line region. These
oscillations periodically separate and bring together the closed and open field lines on the two sides of the coronal hole boundary.
An important indicator favouring the interpretation in terms of a kink mode is the observed increase in the oscillation period.
Key words. Sun: activity: Sun: oscillations Sun: transition region Sun: UV radiation Line: profiles
Explosive events (also called bidirectional jets) are small re-
gions of a few arcseconds size with strong blue- and red-shifted