Solar flare signatures of the ionospheric GPS total electron content

6 [1] In this study, ionospheric solar flare effects on the total electron content (TEC) and 7 associated time rate of change (rTEC) derived from ground-based global positioning 8 system (GPS) receivers in the midday region are examined. The occurrence times and 9 locations of 11 solar flares are isolated from the 1–8 Å X-ray radiations of the 10 geosynchronous operational environmental satellite (GOES) and the SOHO Extreme 11 Ultraviolet Imaging Telescope (EIT) images, respectively, while the TEC and rTEC are 12 obtained from the international GPS services (IGS). Results show that the maximum value 13 of the TEC increase solely depends on the flare class, while the maximum value of 14 the rTEC increase is related to not only the flare class but also the time rate of change 15 in flare radiations. A statistical analysis further demonstrates that the two maximum values 16 are inversely proportional to the cosine of the great circle angle between the center and 17 flare locations on the solar disc.