Upwelling radar backscatter plumes around sunset time associated with equatorial spread F (ESF) are investigated with rapid beam-scanning capability of the Equatorial Atmosphere Radar (EAR). Nonlinear evolution of plumes which could not be understood by single fixed-beam radar observations was observationally studied with the EAR for the first time. The rise velocity of the observed plumes ranging from a few tens to a few hundreds of meters per second is similar to nonlinear evolution of plasma bubbles simulated by the previous numerical studies. Importance of sunset terminator transition should be considered because of its comparable rise velocity. Since the rise velocity of the plumes is highly variable, many factors should contribute to growth of plasma bubbles.