[1] Univ Turku, Dept Phys & Astron, Vesilinnantie 5, Turku 20014, Finland
[2] Armagh Observ & Planetarium, Coll Hill, Armagh BT61 9DG, North Ireland
[3] Univ Western Ontario, Dept Phys & Astron, 1151 Richmond St North, London, ON N6A 3K7, Canada
[4] Leibniz Inst Sonnenphys KIS, Schoneckstr 6, Freibirg, Germany
[5] Univ Svizzera Italiana, IRSOL Ist Ric Solari Aldo e Cele Dacco, Fac Informat, Via Patocci 57, Locarno, Switzerland
[6] Univ Svizzera Italiana, Euler Inst, Fac Informat, Via Santa 1, CH-6962 Lugano, Switzerland