Using more than 350 ionospheric images reconstructed tomographically, studies on the motion of the anomaly crest and its geophysical implications are carried out. On an average day, the crest forms at 09:00 LT and, in the next two hours, moves poleward with a speed of about 1¿ per hour as it intensifies. This poleward motion is slowed as the crest reaches its highest latitude where it stays for several hours until early afternoon. Thereafter, the crest starts to weaken as it recedes with a speed of about 0.5¿ per hour equatorward. During 12:00 -- 14:00 LT, the crest latitude is found to correlate with the fountain strength and the total number of electrons in a cross sectional plane at the observational longitude of the whole equatorial ionosphere. ¿ 2001 American Geophysical Union