1. Centro de Rádio Astronomia e Astrofísica Mackenzie, Escola de Engenharia, Universidade Presbiteriana Mackenzie , 01302-907, São Paulo , Brazil
2. SUPA School of Physics and Astronomy, University of Glasgow , Glasgow G12 8QQ , UK
3. Rosseland Centre for Solar Physics, University of Oslo , PO Box 1029 Blindern, NO-0315 Oslo , Norway