Štěpán Štverák, Institute of Atmospheric Physics CAS, Praha 4, Czech Republic; Astronomical Institute CAS, Prague, Czech Republic, Pavel M. Travnicek, University of California Berkeley, Space Sciences Laboratory, Berkeley, CA, United States, Ondrej Sebek, Institute of Atmospheric Physics CAS, Prague, Czech Republic and David Hercik, Technische Universität Braunschweig, Braunschweig, Germany; Institute of Atmosperic Physics CAS, Prague, Czech Republic