The great magnetic storm of April 6--7, 2000 generated ionospheric disturbances in the west Pacific region. Two ionosondes at Wuhan (30.6¿N, 114.4¿E) and Chung-Li (24.9¿N, 121¿E) observed the ionosphere during this period. The variations of the ionospheric parameters, NmF2 (plasma density of the F-peak), hmF2 (height of the F-peak) and h'F (minimum virtual height of the F-layer), show that a traveling atmospheric disturbance (TAD) affects the ionosphere at middle and low latitudes in this region. The propagation velocities deduced from the time delay of hmF2 and h'F recorded at the two stations are about 655 and 164 m/s, respectively. Furthermore, a method of deriving the vertical phase and group velocities is applied to the sequences of virtual heights at fixed sounding frequencies. The vertical and associated meridional velocities demonstrate that the upward motions of the ionospheric plasma are caused by a TAD.