We analyze Geotail observations of magnetic field and flow oscillations in the dayside magnetosphere that occurred in direct association with an event of traveling convection vortices observed in the northern high-latitude ionosphere. Geotail was positioned on a magnetic flux tube that mapped very close to the centers of the driving field-aligned currents in the ionosphere. These are the first in situ observations from the source region of such events. The flow signature is seen clearly in the cold, dense plasma population, which the satellite encounters during the event, in addition to a hot magnetospheric (plasma sheet-like) population. This report will present the observations and briefly discuss their implications for our understanding of the traveling convection vortex (TCV) signature. We interpret the event in terms of a boundary wave at the magnetopause. Our analysis suggests that strong gradients in the magnetic field strength or plasma density in the inner magnetosphere should play an important role in this process.