Strong Range Spread-F Characteristics Observed in Hainan During Intense Storm

The response of equatorial ionosphere during geomagnetic storms is one of the important issues related to space weather studies and how they affect the occurrence characteristics of equatorial spread-F is one of the prominent research fields. In this study, the Strong range Spread-F （SSF） data from DPS-4 digisonde during the five strong storms （Dst 〈 -100nT） period in 2004 in Hainan （19.4°N, 109.1°E, MLat. 9.0°N） China are used to investigate the effects of geomagnetic storms on SSF. The results show that there are three storms, the minimum Dst of which lied in the period 2200-0200 LT and SSF occurred during the main or earlier recovery phase of these storms, the role of directly penetrated electric field of magnetosphere maybe the only important factor for occurrence of SSF. The other two storms whose minimum Dst lied in the dayside also trigger SSF during the night of recovery phase of one storm and initial phase of another super intense storm. The SSC of the later super storm led to penetrated electric field towards to lower latitude/equator of ionosphere which triggered SSF. During the storms, SSF occurred only before midnight or started midnight and continued after midnight. The comparisons between the results of Dabas et al. and ours also discussed.