We present observations of radio induced optical emissions from a HAARP experiment with simultaneous transmission in X and O-mode. The additional transmission of X-mode with a frequency 700 kHz higher than the O-mode, reduces the enhancement of the 6300 A emission. This suggests that the wave-plasma process that energizes the electrons, which excites oxygen to the O(D-1) state, is closely connected to the excitation of upper-hybrid waves, whose onset and initial growth are reduced by additional X-mode pumping. Citation: Gustavsson, B., R. Newsome, T. B. Leyser, M. J. Kosch, L. Norin, M. McCarrick, T. Pedersen, and B. J. Watkins (2009), First observations of X-mode suppression of O-mode HF enhancements at 6300 angstrom, Geophys. Res. Lett., 36, L20102, doi:10.1029/2009GL039421.
2009. Vol. 36, L20102- p.