Ionospheric oscillations with a quasi-period of ∼6 hr during intense magnetic storms

It is found for the first time that quasi-periodic enhancements in the ion density with a period of SIM;6 hr occur nearly simultaneously at 0630, 0830, and 0930 local time in the dawn sector during the storm main phase with southward interplanetary magnetic field (IMF).

The quasi-periodic density enhancements extend from the southern subauroral latitudes to the northern subauroral latitudes. In the dusk sector, the topside ion density during the storm main phase is increased at middle latitudes for SIM;12 hr but shows decrease or relatively small increase over the magnetic equator, indicating that penetration electric fields dominate the ion density redistribution. Similar quasi-periodic enhancements in the topside ion density are also observed in the dawn sector during other intense magnetic storms.