Abstract. Observations of traveling ionospheric disturbances (TIDs) associated with atmospheric gravity waves (AGWs) generated by the moving solar terminator have been made with the Millstone Hill incoherent scatter radar. Three experiments near 1995 fall equinox measured the AGW/TID velocity and direction of motion. Spectral and cross-correlation analysis of the ionospheric density observations indicates that STgenerated AGWs/TIDs were observed during each experiment, with the more-pronounced eect occurring at sunrise. The strongest oscillations in the ionospheric parameters have periods of 1.5 to 2 hours. The group and phase velocities have been determined and show that the disturbances propagate in the horizontal plane perpendicular to the terminator with the group velocity of 300±400 m s A1 that corresponds to the ST speed at ionospheric heights. The high horizontal group velocity seems to contradict the accepted theory of AGW/TID propagation and indicates a need for additional investigation.

Abstract. In late March and early April of 1995, an experimental campaign involving the modification of the F2 ionospheric layer took place in Russia and Ukraine. HF pulsed and CW Doppler radar observations of field-aligned irregularities within the region over the Sura heater were made with the UTR-2 radio telescope serving as the receiver. In this paper, some preliminary results of our bistatic radar observations of the modified region are presented. These results include measurements of the drift, evolution, and decay of inhomogeneities and turbulence contained within the modified region and evidence of interactions between the ionospheric plasma, Alfv•n waves, and free geomagnetic pulsations.

Bistatic HF radar scatter from magnetic field‐aligned irregularities created by the Sura heater near Nizhny Novgorod, Russia, has been detected and analyzed at the UTR 2 decametric radio telescope near Kharkov, Ukraine. The decay phase of the irregularities exhibits two decay time constants in general. The shorter time constant, which is only sometimes seen, is consistent with classical diffusive dissipation theory for small‐scale, field‐aligned waves. The longer time constant, which is almost always present, is much too long to be accounted for by diffusion. It is more likely associated with the decay of large‐ and intermediate‐scale plasma turbulence. Three‐wave nonlinear interaction with turbulent modes is shown to be capable of generating the field‐aligned irregularities.

A single digisonde, used as a receiver for ionospheric high frequency signals from broadcast stations, was able to determine the wave characteristics of traveling ionospheric disturbances (TIDs) using frequency shift and arrival angle measurements. During a measurement campaign, aimed at recovering large‐scale wave‐like processes in the upper atmosphere, in March 2001 at the MIT Haystack Observatory (Millstone Hill, MA), a Digisonde Portable Sounder (DPS) made simultaneous observations with the incoherent scatter radar (ISR). The DPS was upgraded to include the frequency and angular sounding (FAS) technique previously developed at the Institute of Radio Astronomy in Kharkov, Ukraine, for TID diagnostics. The DPS with four spaced receive antennas received the radio signals at 3.33 MHz and 7.335 MHz from Radio CHU of the Canadian Time Service (Ottawa, Ontario). The FAS technique recovered the basic parameters of TIDs, i.e., amplitude, speed, and the direction of the propagation vector by modeling the ionosphere as a perfectly reflecting surface. For three days during the campaign the Millstone Hill ISR monitored the ionospheric midpoint using a triangulation mode to identify the direction of motion and speed of the wave‐like ionospheric disturbances. Comparison of the results from the two diagnostic techniques showed good agreement. The wave directions were within 10 to 15 degrees, and speed and wavelength were within 10 to 12%.