A statistical study on ionospheric disturbances at middle and low latitude caused by super magnetic storms

Using ionospheric data near 120°E in the northern hemisphere during 72 super magnetic storms between 1957 and 2005, we studied the statistical characteristics of the ionospheric disturbances. The results showed that, the morphology varies with the onset season and local time of the storms. In winter, the negative disturbances are limited at middle latitude mostly, while the positive disturbances prevail at low latitude, with a separatrix between Manzhouli and Beijing. When the onset time of the storms is restrained in local afternoon at middle latitude, the resulted ionospheric disturbances last longer. At low latitude the super magnetic storm occurred at night can cause negative ionospheric disturbances with whose duration time are much longer. In summer, the negative disturbances can reach to lower latitude, and the events occurred in local afternoon can caused more intense ionospheric disturbances. The duration time is much longer for the events corresponding to the magnetic storms occurred before midnight. In equinoxes, the disturbances are mostly negative, though the intense and the duration time depend much on the local time distribution of the commence time. Preliminary analysis showed that the statistic results achieved above are much related with storm-time therm-ospheric circulations.