Very Low Frequency Radio Transmission

Sudden Ionospheric Disturbances

The receiver is located at Moore Observatory in Brownsboro, Kentucky, where a directional loop antenna is tuned to a very low frequency transmission from a station approximately 1500 kilometers northeast. The receiver amplifies and averages the signal with a time constant of about 15 seconds and its output is recorded four times a minute by a 12-bit analog-to-digital converter under the control of this server running Linux. The graphs are produced every 10 minutes with Grace and converted to jpeg format with ImageMagick.

Each day at 0 hours Coordinated Universal Time the data from the previous day are placed in the data archive, the latest complete plot is saved in the plot archive, and a new record is started.

Each plot should show a signal which varies erratically during the night, but is smooth and steady during the day. The transition at sunrise and sunset is a very distinctive rise and fall pattern. When a flare occurs, the prompt X-ray emission from the Sun modifies the ionosphere and produces a sudden enhancement in the very low frequency 24 kilohertz radio transmission.

Records of this type are kept by several amateur astronomers who coordinate their efforts through the American Association for Variable Star Observers.

A pdf version of the receiver documentation is available here. Additional information is available on request.