Observations of Ionospheric Very-Low-Frequency Radio Noise
A summary is presented of the AC electric and magnetic fields observed in the ionosphere by the Javelin 8.45 UI sounding rocket launched from Wallops Island, Virginia, on 21 September 1967. The electric dipole and magnetic loop antenna systems and the VLF (30 Hz–70 kHz) receivers are described. Data on the spectral characteristics, the noise amplitude, and the wave field geometry for two types of noise are summarized. A high frequency electromagnetic noiseband occurred between 7 kHz and 30 kHz throughout the flight. Marked spectral changes with altitude, a large ratio of electric to magnetic field amplitude and a field geometry which indicates that the noise is propagating perpendicular to the geomagnetic field were observed. It is argued that the lower cutoff frequency may be the lower hybrid resonance frequency. Precession modulated intense noise bursts were observed on the electric antennas only. This electrostatic noise occurred below 1 kHz in frequency and below 500 km in altitude both upgoing and downgoing. From the spectral shape, the phase of the noise amplitude with respect to the component of velocity perpendicular to the geomagnetic field and the relative electric field amplitudes, it appears that this noise may be caused by a turbulent wake of the payload.