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°N, 104°E). In daytime, phase interference patterns have the form of traveling waves with the mean propagation direction ψ equal to 160° and rms of 68°, and phase velocity of 133 ± 62 m/s. The mean value of ψ 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°–30°. 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°) is, on average, 25° less than for SSIs. This difference can be explained by assuming that medium-scale phase disturbances detected at night are caused by magnetic-field-aligned irregularities located in the plasmasphere.
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