Seasonal variations of the ionospheric effects of geomagnetic storms at different latitudes of East Asia

We present the results derived from investigating the ionospheric effects of geomagnetic storm based on analyzing the data obtained at ionospheric stations located at different latitudes in the longitudinal sector of 90-130 degrees E. There are considered geomagnetic storms of different intensities in the period from May, 2003 till March, 2004. During this period 15 storms are selected, which could be separated into different seasons. Our analysis of geomagnetic storms during different seasons suggests the following conclusions. (1) In summer during the initial positive phase of storms the positive disturbance in foF2 with the amplitude of up to 25% is observed at high latitudes. Then the disturbances are negative up to the end of the storm both at high and middle latitudes. The disturbance variations are similar. At low latitudes there are marked both positive and negative disturbances. (2) In winter the daytime disturbances are positive in the beginning of the storm at all stations under investigation. During the early recovery phase they are negative at high and positive at middle latitudes. The night disturbances are positive at high and negative at middle latitudes. At low latitudes the disturbances are positive both in daytime and at night during all storms. The disturbances change their sign near 30 degrees geomagnetic latitude. (3) The equinox ionospheric variations during the storm are similar to those observed in summer: there are observed positive disturbances in the beginning of the storm and negative disturbances during the main and recovery phases both at high and middle latitudes. At low latitudes they are both positive and negative with high amplitudes. (4) In Hainan the intensive oscillations of foF2 are observed during the main phase of every storm. (c) 2006 COSPAR. Published by Elsevier Ltd. All rights reserved.