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

This paper presents the diurnal and seasonal statistics for the dynamics an d anisotropy of medium-scale traveling ionospheric disturbances (MS TIDs) i n comparison with the dynamics of small-scale irregularities (SSIs), using data from an annual run of ETS 2 radio signal polarization, angle-of-arriva l, and scintillation measurements at 136 MHz in Irkutsk, Russia (52 degrees N, 104 degrees E). In daytime, phase interference patterns have the form o f traveling waves with the mean propagation direction psi equal to 160 degr ees and rms of 68 degrees, and phase velocity of 133 +/- 62 m/s. The mean v alue of psi increases in a clockwise direction from southeastward to southw ard and opposite to the calculated direction of the neutral wind, with the spread not exceeding 10 degrees-30 degrees. This result is in agreement wit h the hypothesis of neutral wind-induced filtering of atmospheric gravity w aves (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 (modu lo 180 degrees) is, on average, 25 degrees less than for SSIs. This differe nce can be explained by assuming that medium-scale phase disturbances detec ted at eight are caused by magnetic-field-aligned irregularities located in the plasmasphere.