The strength and hemispheric asymmetry of Equatorial Ionization Anomaly during two geomagnetic storms in 2013 from Global Ionosphere Map and SAMI2

• The strength of the EIA had significant variations after the SSC of two storms in 2013.
• The asymmetry of the EIA had no remarkable changes after the SSC of two storms.
• The two EIA crests moved toward the equator after the SSC of two storms.
• The simulations from SAMI2 and HWM07 show similar results during storm periods.

The variations of the strength and the hemispheric asymmetry of EIA were studied by Global Ionosphere Map (GIM) and SAMI2 during two geomagnetic storm periods in March and June 2013. Compared with the 30-days median TEC, the TEC at the two crests of EIA had small variations while the TEC at the trough had a more remarkable variation for the two storms after the SSC. The TEC difference between the two EIA peaks had an increase or decrease several hours after the SSC, the asymmetry between the two crests of EIA represented by the defined asymmetry index has no obvious variations except several hours after the SSC, and EIA strength represented by the Crest-to-Trough Ratio (CTR) had a remarkable increase one day after the SSC day for March storm and decrease several hours after the SSC for June storm. The variations last several hours, with more than 40% variations compared with the value during the quiet period. The EIA peaks were also found to move toward the equator after the SSC during the two storms. The simulation from SAMI2 and HWM07 also shows that EIA crests would move toward the equator during storm time and EIA strength would decrease, which suggests that the disturbed neutral wind and disturbed electric field may be important factors affecting the EIA during the storm periods.