A statistical study of large-scale traveling ionospheric disturbances observed by GPS TEC during major magnetic storms over the years 2003-2005

In this paper, we plot two-dimensional total electron content (TEC) perturbation maps and investigate the statistical characteristics of large-scale traveling ionospheric disturbances (LSTIDs) during major magnetic storms from 2003 to 2005. The TEC data were obtained from more than 600 GPS receivers in North America within the geographical latitudes of 25 degrees N-55 degrees N. We found a total of 135 cases of LSTIDs, with amplitudes of up to 3.5 TECU and a maximum front width of similar to 4000 km. The mean value of periods, horizontal velocities, and azimuths are 1.8 h, 300 m/s, and 187 degrees (7 degrees west of south), respectively. The mean velocity is obviously slower than that observed at lower latitudes such as Japan. Of all the 135 LSTID events, 35 cases (26%) occurred in the nighttime with their possible source within the region of North America, according to the variation of magnetic H component observed in this region. In addition, the occurrence of LSTIDs peaks at 1200 LT and at 1900 LT. It is also pointed out that the UT dependence of the occurrence of auroral geomagnetic disturbances plays a major role in the forming of UT and LT dependence of the occurrence of LSTIDs observed at midlatitudes.