A Statistical Analysis of SITEC Caused by Intense Solar Flares During 1996-2003

In this paper,the SITEC phenomena is investigated which were caused by the X-class X-ray solar flares occurred from 1996 to 2003.The TEC data which obtained from a global GPS network are used to calculate the TEC increment,ΔTEC_f,and the variation rate increment,Δ(dTEC_f/dt),caused by solar flares.It is found that both ΔTEC_f and Δ(dTEC_f/dt) are closely related with the flare's maximal X-ray flux and its location on the solar disc.After eliminating the effect of the maximal X-ray fluxes and the locations on solar disc of different flares,results showed that there is a negative relationship between ΔTEC_f and the distance between the Earth and the Sun.The larger the distance,the smaller is the ΔTEC_f.Another finding is that Δ(dTEC_f/dt) correlates with the duration of the flare.Some characteristics of the flares which cause no obvious SITEC are also found.