Global ionospheric TEC variations during January 10, 1997 storm

The ionospheric storm evolution process was monitored during the January 10, 1997 magnetic cloud event, through measurements of the ionospheric total electron content (TEC) from 150 GPS stations. The first significant response of the ionospheric TEC to the geomagnetic storm was at 0300 UT as an auroral/subauroral enhancement around the Alaskan evening sector. This enhancement then extended to both noon and midnight. Around 0900 UT, the enhancement at noon broke from the subauroral band and moved to lower latitudes. This dayside northern hemisphere enhancement also corresponded to a conjugate geomagnetic latitude enhancement in the southern hemisphere and lasted about 5 hours. At 1500 UT a large middle latitude enhancement appeared over Mexico and the southern US, and persisted until 2200 UT. The enhancement was probably caused by the equatorward neutral wind which pushed the plasma up. On the basis of this assumption, the kinetic energy of the neutral wind which caused the middle latitude enhancement is estimated as similar to 4.1x10(9) Joules. This is about 0.03% of solar wind energy impinging on the magnetosphere and about 3% of the energy deposited on polar cap ionosphere. After 2000 UT, a negative phase gradually became stronger (especially in the southern hemisphere), although the northern subauroral enhancement persisted one more day. The entire ionosphere gradually recovered to normal on January 12. Thus, large middle latitude enhancement, equatorward motion of the dayside enhancement (probably related to a TID), the persistence of the subauroral enhancement, and the conjugate features at both hemispheres are the main characteristics of this storm.