1. M. P. Baldwin is at Northwest Research Associates, Bellevue, WA 98009, USA.
2. M. Dameris is at the Institut für Physik der Atmosphäre, Oberpfaffenhofen, 82234 Wessling, Germany.
3. T. G. Shepherd is in the Department of Physics, University of Toronto, Toronto, M5S 1A7 Canada.