[1] Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA
[2] Univ Colorado, JILA, Boulder, CO 80309 USA
[3] Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80309 USA
[4] KTH Royal Inst Technol, NORDITA, S-10691 Stockholm, Sweden
[5] Stockholm Univ, S-10691 Stockholm, Sweden
[6] Stockholm Univ, AlbaNova Univ Ctr, Dept Astron, Stockholm, Sweden
[7] Ben Gurion Univ Negev, Dept Mech Engn, Beer Sheva, Israel