Medium-scale traveling ionospheric disturbances around the equatorial anomaly crest as detected by the differential Doppler shift method

Abstract

From January 1986 to December 1987, 968 medium-scale traveling ionospheric disturbances (TIDs) incident near the northern equatorial anomaly crest region were detected at Lunping Observatory (25.00°N, 121.17°E geographic; 14.27°N, 191.30°E geomagnetic) by observing the differential Doppler shift of 150 and 400 MHz coherent radio signals transmitted from six polar orbited satellites of the U.S. Navy Navigation Satellite System. By use of these TID data, it has been found that: 1. (1) most of the TIDs detected by the differential Doppler shift method have a peak-to-peak amplitude in the range of 0.2–0.4 Hz, and a wavelength in the range of 100–300km; 2. (2) most of the TIDs are observed during the daytime and early evening period; 3. (3) TIDs appear quite often in geomagnetically calm days or slightly disturbed days; 4. (4) TIDs have occurrence peaks around 29–32°N in summer and equinoxes, and around 23°N in winter.