Introduction

The Earth's plasma sheet plays a key role in the dynamics of the magnetosphere. In the magnetotail it provides the plasma pressure that balances the lobe magnetic field pressure and is the region in which tail reconnection is thought to take place. In the topside ionosphere it provides the source electron population which is accelerated to form the aurora. Most observations of the plasma sheet have been at either low altitude or in the equatorial plane at large radial distances [Eastman et al.(1984),Baumjohann et al.(1989),Winningham et al.(1975),Newell et al.(1996)]. At either the ionosphere or magnetotail, observation of the part of the electron population which is important to the magnetically conjugate region is difficult. In the equatorial plasma sheet, the population which is accelerated to become the aurora is only a degree or two wide. Similarly at the ionosphere, the bulk of the plasma sheet population has been mirrored before it ever reaches the acceleration region.

In the northern hemisphere, Polar crosses the high latitude extension of the plasma sheet at an intermediate point between these two regions. The Hydra experiment resolves, for the first time at these altitudes, the narrow loss cone which is of the order of 5$^\circ$-10$^\circ$. We present observations of the electron plasma sheet at these intermediate altitudes which show distinct regions of electron anisotropy indicative of auroral processes below the spacecraft.