Electron pitch angle variations recorded at the high magnetic latitude boundary layer by the NUADU instrument on the TC-2 spacecraft

The NUADU (NeUtral Atom Detector Unit) experiment aboard TC-2 recorded, with high temporal and spatial resolution, 4π solid angle images of electrons (∼50-125 keV) spiraling around geomagnetic field lines at high northern magnetic latitudes (L > 10), during its in-orbit commissioning phase (September 2004). The ambient magnetic field, as well as electrons in other energy ranges, were simultaneously measured by the TC-2 magnetometer (FGM), the plasma electron and current experiment (PEACE), the low energy ion detector (LEID) and the high energy electron detector (HEED). The NUADU data showed that up-flowing electron beams could form "ring-like" and "dumbbell-type" pitch angle distributions (PADs) in the region sampled. Changes in these pitch angle distributions due to transient magnetic variations are suggested to have been associated with electron acceleration along the geomagnetic field lines. A nested magnetic bottle configuration that formed due to the propagation towards the Earth of a magnetic pulse, is proposed to have been associated with this process.