Three-dimensional global magnetohydrodynamic simulations are conducted to study the response of the magnetosheath and the magnetosphere to an interplanetary tangential discontinuity (TD), across which the plasma density increases. A fast mode wave and a transmitted TD are generated in the magnetosheath by the interaction between the interplanetary TD and the bow shock. These waves further propagate and disturb the dayside magnetosphere. The fast mode compressional wave propagates downstream out of the dayside region in about 1 minute. The pressure enhancement associated with the transmitted TD later compresses the magnetopause significantly for several minutes. The generation of traveling convection vortices, shear Alfv¿n waves, and the associated field-aligned currents (FACs) in the dayside magnetosphere by these pressure pulses is identified in the simulation. ¿ 2000 American Geophysical Union