[1] Max-Planck-Inst. Sonnensystemforsch., Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
[2] Indian Institute of Astrophysics, Koramangala, Bangalore 560034, India
[3] INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
[4] Armagh Observatory, College Hill, Armagh BT61 9DG, United Kingdom
[5] Department of Solar Physics, Royal Observatory of Belgium, Av. Circulaire 3, 1180 Bruxelles, Belgium