Observations by the Polar satellite of large Poynting flux in the plasma sheet boundary layer at geocentric distances of 4 to 6 RE and between 22 and 3 hrs magnetic local time were correlated with H-bay signatures from ground magnetometer records. We provide evidence that large Poynting fluxes occur during the substorm expansion phase. The Poynting fluxes exceeded 1 ergs/cm2s (125 ergs/cm2s when mapped to 100 km), were dominantly directed toward the ionosphere, and were associated with Alfv¿n waves. These observations demonstrate the importance of Alfv¿n wave power as a means of energy transport from the distant magnetotail to the ionosphere during the most dynamic phase of substorms. ¿ 2000 American Geophysical Union