Comparing the ionosphere F2-layer response to geomagnetic storms at midand low latitudes

We study the ionosphere response to two strong storms on 17-19 Aug 2003 and 22-23 Jan 2004. The data from ionospheric stations in Irkutsk (52.5°N, 104°E) and in Hainan (19.5°N, 109°E) were used. Analysis of the A/ 0F2 relative deviation variations showed the following. The negative disturbances were observed at mid-latitudes (Irkutsk) in the summer ionosphere. The positive disturbances were observed in the winter ionosphere during the storm main phase while the negative disturbances were observed during the recovery phase. Whereas the disturbances were positive for all the considered cases at low latitudes (Hainan). To analyze the mechanisms for disturbance formation, we used the NRLMSISE-00 empirical models for the neutral atmosphere and the HWM07 models for thermospheric wind. At midlatidudes, main factors determining the A/ 0F2 variation during the storms were shown to be probably the following: equatorward disturbed thermospheric wind transporting the atmosphere disturbed composition; atomic oxygen concentration increase; internal gravity wave passage. At low latitudes, the effects associated with variations of neutral composition are small compared with the effects of electric fields and thermospheric winds.