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Abstract.Comparisons of modeled and measured responses of the ionosphere to the passage of atmospheric gravity waves are made for data recorded by an ionosonde located at Almaty (76 • 55 E, 43 • 15 N) from June 2000 until May 2001. Temporal variations of the altitude (hmF) and electron content (NmF) of the F-layer peak are used for comparisons. A significant part of the observations showed well-defined wave structures on the hmF, NmF and other parameter variations observed throughout the entire nights. Both the modeling study and measurements showed that, as the F-layer is lifted by the positive surge in gravity wave, the electron content at the F-layer peak decreases, with the slab thickness being increased as well. Subsequently, the opposite happens as hmF falls below its equilibrium value. Some discrepancy between the model and experimental results related to the phase difference between hmF and NmF variations is revealed.

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This study reports observations of the response of the mid-latitude ionospheric F-layer to the passage of the atmospheric gravity wave (AGW) produced by the July 2004 geomagnetic storm, using data from the ground ionosonde located at Alma-Ata (43.25 0 N, 76.92 0 E). Ionograms were recorded every 5 min. They were analysed for temporal variations of virtual heights of specific frequencies (the virtual heights of a constant electron density), critical frequencies of the Flayer (f o , x F) and height profiles of the electron density (N(h)-profiles). The temporal behaviour of all F-layer parameters such as the altitude of its peak (h m F), the electron density at the peak (NmF) and the half thickness of the layer (∆hF) revealed well-defined wave structures throughout the entire night of 24-25 July 2004. A comprehensive understanding of the relationship between phases of various parameters of the F-layer is established. It is shown that the relationship between phases of h m F, NmF and ∆hF variations is determined by the value of the wave front tilt. As a rule, the certain phase of ∆hF precedes that of h m F, and NmF anticorrelates with ∆hF. Last result contrast with previous investigations, which have frequently assumed a negative correlation between NmF and h m F.A small amplitude of NmF variations compared with N(t) at certain altitudes may be largely explained in terms of the height gradient of AGW amplitudes.