A great geomagnetic storm occurred on July 15/16, 2000 with a minimum value of about -300 nT in Dst index. Collecting digisonde data from ionospheric stations at Chungli, Wuhan, Kokubunji and Anyang, the ionospheric responses at the low latitudes near longitude 120(E during this storm are analyzed in this paper. There was a strong negative phase storm at low latitudes on July 16. The G-condition in the ionograms was clearly seen on the early first day after the commencement of geomagnetic storm. Those were considered to be caused by the storm-induced increase in the concentration ratios of neutral molecular O2 or N2 to atom O. On July 17 and some days thereafter, a positive phase storm appeared. In addition, anomalous equatorial ionization anomaly (EIA) inhibitions and developments were observed on July 16 and 17. There were also prominent nighttime enhancements in foF2 during these days, and the diurnal variation of foF2 was less clear than before.
