6. Conclusions

[53]  The results of the studies of disturbances in the midlatitude ionosphere over Kharkov during three geomagnetic storms distinguished by their intensity and occurred under moderate level of solar activity are presented.

[54]  The obtained data showed that intense geomagnetic disturbances (on 25 September 1998 and 29-30 May 2003, Kp approx 8) could be accompanied by phenomena rare for middle latitudes and related to the equatorward shift of the main ionospheric trough, light ion trough, and hot zone to the geomagnetic L shells located within the inner plasmasphere. The disturbances could lead to considerable changes in the structure of the ionospheric F region and thermal and dynamical regimes of the charged and neutral components of the Earth's upper atmosphere.

[55]  The results of observations and modeling of the dynamical processes in the ionosphere showed that a geomagnetic storm of even a modest intensity (on 20-21 March 2003, Kp approx 5) is capable of causing at middle latitudes a strong negative ionospheric storm accompanied by considerable variations in ionospheric parameters. The reversal of the storm phases can be caused by a superposition of two destabilizing factors: electric field pulse and traveling atmospheric disturbance, both factors being generated by magnetospheric substorms.

[56]  The obtained results are used in a study and modeling of disturbed ionosphere (including the processes accompanying the storm phases reversal) in the central Europe region.


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