SPECTRAL AND DISPERSION CHARACTERISTICS OF TRAVELING IONOSPHERIC DISTURBANCES AS DEDUCED FROM TRANSIONOSPHERIC SOUNDING DATA

We have developed a statistical method of determining the dispersion a nd spectral properties of travelling ionospheric disturbances (TIDs) b ased on analyzing the power spectra and cross spectra of variations in total electron content (TEC) and angles of arrival. The proposed meth od was used in the analysis of the signal from the ETS-2 satellite at the frequency 136 MHz received near Irkutsk (52-degrees-N, 104-degrees -E). For three seasons of 1990, 10-day-averaged time and spatial spect ra were obtained, as well as phase velocity dispersion, the predominan t propagation direction, the degree of collimation and attenuation of TIDs. Time spectra of daytime variations for periods between 100 and 2 0 min have a power-law form with a power-law slope of 2.5, and for per iods of 10-20 min the slope is 6; at night the slope equals 4 througho ut the entire range of periods considered. With decreasing period, the phase velocity initially increases and then decreases. A change of si gn of the velocity dispersion, and also of the slope of the daytime sp ectra, occurs for periods of the order of 15-20 min. Three-dimensional spatial spectra in the range of TID scales (20-200 km) have a power-l aw character with the power-law slope about 6. During the daytime, TID s with periods of 15-30 min are characterized by a high degree of coll imation and the southeastward direction of motion, independently of th e season.