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Evidence is given for intense VHF and UHF radar backscatter during equatorial Spread F resulting from irregularities of 1 meter and 36 cm, respectively. The linear theory for high frequency drift waves, generated by the drift-cyclotron and lower-hybrid-drift instabilities, is presented. This linear theory is set forth as a possible explanation for the occurrence of these irregularities below the ion gyroradius. The maximum growth for these instabilities occurs for kr sub e approximately 1, where k is the wavenumber perpendicular to the magnetic field and r sub e is the electron gyroradius. For these instabilities, the growth rate results in growth times than a second. For typical equatorial Spread F ionospheric parameters, the lower-hybrid-drift instability is dominant., WU11

The electromagnetic energy incident on ground-based antennas on Johnston Island as a result of the five high-altitude nuclear bursts of the Fish Bowl series was measured in the frequency regions around 925 Mc, 3000 Mc, and 24,500 Mc by the radiometric techniques described in this report. The data, recorded in terms of antenna temperatures, are directly interpretable as physical temperatures of the thermally radiating regions and allow the deduction of the attenuation encountered by radio-frequency signals passing through the burst regions. The time history of the temperatures of the burst region for the three microwave frequencies of the radiometric measurement presented considerable insight into the physical processes occurring during the high-altitude events. Electron densities and recombination rates have been deduced from the radiometric data.