Experimental results from ionospheric HF pumping experiments in the nightside auroral E region above Troms¿ are reported. We found intriguing evidence that a modification of the ionosphere-magnetosphere coupling, due to the effects of powerful HF waves beamed into an auroral sporadic E layer, can lead to a local intensification of the auroral activity. Summarizing multi-instrument observations during two consecutive nights, one can distinguish the following peculiarities related to this auroral activation: a modification of the auroral arc and its breakup above Troms¿, local changes in the horizontal currents above Troms¿, a burst-like increase of the electron density and temperature, a large increase in the ion temperature in a wide altitude range and in the north-south component of the electric field, distinctive features in dynamic HF radio scatter Doppler spectra, pump-induced electron precipitation, and substorm activation exactly above Troms¿. We discuss the modification of the ionosphere-magnetosphere coupling in terms of the excitation of a turbulent Alfv¿n boundary layer between the base of the ionosphere (~100 km) and the level of sharp increase of the Alfv¿n velocity (at heights up to one Earth radius), and the formation of a local magnetospheric current system. The results suggest that a possible triggering of local auroral activation requires specific geophysical conditions. ¿ 2001 American Geophysical Union