The effects of the great magnetic storm of July 15, 2000 on the equatorial ionosphere have been studied by ground-based and satellite in-situ measurements. A large westward plasma drift in the evening equatorial ionosphere was observed as a result of the ionospheric disturbance dynamo. In that environment, the IMF Bz turned southward and presumably caused penetration of E-fields to low latitudes. This E-field initiated the onset of 250 MHz and L-band scintillations at Ascension Island (15 ¿W) and precipitous TEC decrease at Fortaleza, Brazil (38 ¿W), bounding the narrow longitude region in the South Atlantic. These impulsive ionospheric effects were extremely well correlated with abrupt decreases of SYM-H (1-min resolution Dst). The DMSP in-situ measurements showed the presence of severe ion density biteouts extending over 30¿ latitude in the South Atlantic Magnetic Anomaly region. The ROCSAT-1 satellite measured upward and large southward ion drifts in the same sector. ¿ 2001 American Geophysical Union