EXPERIMENTAL-STUDY OF DOUBLE-RESONANCE PARAMETRIC EXCITATIONS IN THE IONOSPHERE

We report the double resonance excitation of two pump waves with frequ encies separated from 5 to several hundred Hz. The cyclotron frequenci es of NO+ and O-2(+) abundant at the bottom of the F layer (similar to 150 km), are within this range. The nonlinear mode coupling takes pla ce at similar to 150 km where the pump frequency matches the plasma fr equency. The experiments show that when the beat frequency is close to the NO+ cyclotron frequency at similar to 30 Hz, the energy transfer from the higher frequency to the lower frequency wave is enhanced thro ugh parametric coupling. When the two pump waves have equal power, dis crete sidebands are symmetrically distributed around the pump frequenc ies. However, a burst of lower-frequency sidebands, lasting for severa l seconds, frequently breaks the symmetry. We attribute this asymmetry to the cascade parametric process. The asymmetric spectra only occur only during O mode experiments.