title: Electron gyroharmonic effects in ionization and electron acceleration during high-frequency pumping in the ionosphere.
abstract: Optical emissions and incoherent scatter radar data obtained during high-frequency electromagnetic pumping of the ionospheric plasma from the ground give data on electron energization in an energy range from 2 to 100 eV. Optical emissions at 4278 A from N2+ that require electrons with energies above the 18 eV ionization energy give the first images ever of pump-induced ionization of the thermosphere. The intensity at 4278 A is asymmetric around the ionospheric electron gyroharmonic, being stronger above the gyroresonance. This contrasts with emissions at 6300 A from O(1D) and of electron temperature enhancements, which have minima at the gyroharmonic but have no apparent asymmetry. This direct evidence of pump-induced ionization contradicts previous indirect evidence, which indicated that ionization is most efficiently produced when the pump frequency was below the gyroharmonic.
authors.affiliation: Department of Physics and Technology, University of Tromsø, Tromsø, Norway.
authors.forename: B
authors.initials: B
authors.lastname: Gustavsson
authors.forename: T B
authors.initials: TB
authors.lastname: Leyser
authors.forename: M
authors.initials: M
authors.lastname: Kosch
authors.forename: M T
authors.initials: MT
authors.lastname: Rietveld
authors.forename: A
authors.initials: A
authors.lastname: Steen
authors.forename: B U E
authors.initials: BU
authors.lastname: Brändström
authors.forename: T
authors.initials: T
authors.lastname: Aso