Detection of traveling ionospheric disturbances by medium-frequency Doppler sounding using AM radio transmissions

Nighttime traveling ionosphere disturbances (TIDs) propagating in the lower F region of the ionosphere have been detected by measuring time variations in the Doppler shifts of commercial AM radio broadcast signals. Three receivers, components of the Intercepted Signals for Ionospheric Science (ISIS) Array software radio instrumentation network in the northeastern United States, recorded signals from two radio stations during 11 nights in March–April, 2012. By combining these measurements, TIDs were detected as approximately 40 min periodic variations in the frequencies of the received signals resulting from Doppler shifts produced by the ionosphere. The variations had amplitudes of up to a few tenths of a hertz and were correlated across the array. For one study interval, 0000–0400 UT on 13 April 2012, simultaneous GPS total electron content, Digisonde®, and Super Dual-Auroral Radar Network coherent backscatter radar measurements confirmed the detection of TIDs with the same characteristics. Besides TIDs, the receiver network often detected large (nearly 1 Hz) upward (downward) Doppler shifts of the AM broadcast signals at the dawn (dusk) terminator. These results demonstrate that AM radio signals can be used for detection and monitoring of nighttime TIDs and related effects.