The ROCSAT-1 observations of vertical ion velocity in low latitudes during the main phase of the storm of 29–30 October 2003 show an occurrence of abnormally large downward plasma drift before dawn and pronounced upward drift after sunset. At the time of the occurrence of the abnormal vertical plasma drifts at the terminators the background ionosphere shows an upward drift during 0800-2000 LT and downward drift during 2000-0800 LT. The global-scale change in the vertical plasma drifts and its coincidence with the onset of dawn-to-dusk interplanetary electric field indicate that the disturbance drifts are associated with the penetration electric field (PE). The nightward PE at the terminators induces an accumulation of positive charges at the terminators; polarization electric fields develop by the charge accumulation; and the addition of the PE and polarization electric field can produce pronounced downward drift before dawn and upward drift after sunset.