Effects of the 4–20 April 2006 major geomagnetic storms on GPS ionospheric scintillations at Guilin

The effects of the 4-20 April 2006 geomagnetic storms on GPS ionospheric scintillations are studied using GPS scintillation data recorded at Guilin, a low-latitude station in China. Three major geomagnetic storms (Dst < -80 nT) occurred consecutively during the period of 4-20 April 2006. The results show that ionospheric scintillations were triggered by the first storm but inhibited by the latter two storms. The maximum dDst/dt determined local time, that was different for each analyzed storm, is proposed to be the cause of this different response of ionospheric scintillations to the magnetic storms. For station Guilin, the maximum dDst/dt determined local time is close to post-sunset for the first storm but at the noon sector for the latter two storms, which leads to the phenomena presented in this paper. Furthermore, TEC depletions and rapid ROT fluctuations occurred at the same time when enhanced scintillations were triggered by the first storm, which implies the co-existence of large and small-scale ionospheric irregularities over Guilin.