Mid-latitude ionosphere observed by ground-based GPS during intense geomagnetic storms in October 2003 and November 2004

Abstract

Ionospheric variabilities can be very important to the qualities and propagation of the radio signals of the global navigation satellite system, which is mostly used in the mid-latitudes. The mid-latitude ionosphere is often considered to be a well-understood and uninteresting stable region of the ionosphere during past few decades. However, it was reported from the large ground-based GPS TEC networks that dramatic changes can occur in the mid-latitude ionosphere especially during geomagnetic storm (Foster, 1993; Tsurutani et al., 2005). During geomagnetic storms, positive and negative phases of ionospheric disturbances are used to describe the increase and decrease of ionospheric electron densities, respectively. We analyze the negative and positive phases of ionospheric storms by using the ground-based GPS TEC data measured in the northeast Asian sector during the intense geomagnetic storms on 29-31 October 2003 and 8-11 November 2004. The positive phase on 8 November 2004 persisted except for dawn, and its maximum value is about 65 TECU, which is almost 3 times greater than the monthly mean TEC values. The positive phase on 10 November 2004 began to occur during the day and lasted for more than 6 hours, and its peak value was about 30 TECU at 23 LT. The other positive storms on 29-31 October 2003 were observed only during daytime and the nighttime TEC was similar or slightly lower than the monthly value. The positive phase on 29-31 October 2003 was significantly weaker than the storms on 8 and 10 November 2004 in which the asymmetric feature of O/N2 ratio from the GUVI/TIMED observation was more distinct. We will also discuss the ionospheric effects on the GPS L1 qualities during intense geomagnetic storms.