Craig A. Selcher

Magnetic zenith enhancement of HF radio-induced airglow production at HAARP

[1] Airglow production at various beam positions relative to the magnetic field was investigated as part of an optics campaign at HAARP in February 2002. Strong emissions up to several hundred Rayleigh at 630.0 nm and more than 50 R at 557.7 nm were produced in a small spot approximately 6° in diameter located near the magnetic zenith when the transmitter beam was directed up the magnetic field. This effect was observed hundreds of times over a wide range of frequencies and ionospheric conditions. The spot at HAARP appears on average just equatorward of the nominal magnetic field direction, deflects somewhat toward the beam center when the beam is scanned, and varies slightly in size with transmitter frequency. Red-to-green ratios as low as 3 were observed, with both wavelengths showing significant onset delay. Identifiable enhancements in red-line emission were produced down to 2 MW ERP in a power ramp experiment. INDEX TERMS: 0310 Atmospheric Composition and Structure: Airglow and aurora; 2403 Ionosphere: Active experiments; 2483 Ionosphere: Wave/particle interactions; 2487 Ionosphere: Wave propagation (6934); 2494 Ionosphere: Instruments and techniques. Citation: Pedersen, T. R., M. McCarrick, E. Gerken, C. Selcher, D. Sentman, H. C. Carlson, and A. Gurevich, Magnetic zenith enhancement of HF radio-induced airglow production at HAARP, Geophys. Res. Lett., 30(4), 1169, doi:10.1029/2002GL016096, 2003.

Observations and theory of ion gyro-harmonic structures in the stimulated radiation spectrum during second electron gyro-harmonic heating

Recent observations of Stimulated Electromagnetic Emissions SEE for ionospheric heating near the second electron gyro-harmonic frequency at the HAARP facility are provided. These observations show previously unobserved structures ordered by harmonics of the ion gyro-frequency. An analytical model is presented for three-wave coupling between the pump wave, upper hybrid/electron Bernstein waves, and electrostatic ion cyclotron harmonic waves. It is shown that for pump wave frequencies near the second electron gyro-harmonic, a band of upper hybrid/electron Bernstein waves separated by harmonics of the ion gyro-frequency can be destabilized. A new 2-D computational model using the Particle-In-Cell PIC method is used to more thoroughly investigate the nonlinear processes involved in producing these spectral features and provide results reasonably in line with predictions of the simplified analytical model.

Imaging of ionospheric density structures and plasma drifts using artificial illumination by high-power radio waves

Artificial aurora from energetic electron fluxes may be generated by powerful radio waves beamed into the ionosphere. This radio induced aurora (RIA) provides optical diagnostics for measurements of field aligned irregularities, artificial plasma cavities, and plasma drifts in the E and F layer ionosphere. High-power radio waves coupled with low-light-level optical sensors provide unique measurements of the upper atmosphere.