Dynamics and anisotropy of traveling ionospheric disturbances as deduced from transionospheric sounding data

This paper presents the diurnal and seasonal statistics for the dynamics and anisotropy of medium-scale traveling ionospheric disturbances (MS TIDs) in comparison with the dynamics of small-scale irregularities (SSIs), using data from an annual run of ETS 2 radio signal polarization, angle-of-arrival, and scintillation measurements at 136 MHz in Irkutsk, Russia (52 degrees N, 104 degrees E). In daytime, phase interference patterns have the form of traveling waves with the mean propagation direction psi equal to 160 degrees and rms of 68 degrees, and phase velocity of 133 +/- 62 m/s. The mean value of psi increases in a clockwise direction from southeastward to southward and opposite to the calculated direction of the neutral wind, with the spread not exceeding 10 degrees-30 degrees. This result is in agreement with the hypothesis of neutral wind-induced filtering of atmospheric gravity waves (AGW) and MS TIDs caused by them. It was found that at night, MS TIDs are characterized by a strong anisotropy; the direction of elongation (modulo 180 degrees) is, on average, 25 degrees less than for SSIs. This difference can be explained by assuming that medium-scale phase disturbances detected at eight are caused by magnetic-field-aligned irregularities located in the plasmasphere.