Ultra‐Fast Measurements of Precipitating Electrons in Earth's Cusp—A Source of Flickering Aurora Near 1 R _<i>E</i>

Abstract We present electron measurements from the Acute Precipitating Electron Spectrometer (APES) that flew on the VISualizing Ion Outflow via Neutral atom imaging during a Substorm‐2 (VISIONS‐2) sounding rocket which launched from Svalbard, Norway into dayside cusp aurora. APES measured the precipitating electron distribution from 200 eV to 16 keV with one millisecond time resolution. These observations show that the electron precipitation associated with the cusp aurora contains highly variable and short‐lived features. These features exhibited distinct energy‐time dispersions, some of which were very short in time (lasting 50 ms or less) while others extended to high energies (10 keV), for short times (100 milliseconds). Time‐of‐flight analyses were completed for eight separate dispersed features and their source altitudes ranged from 1,715 to 6,321 km above Earth's surface. This suggests that electromagnetic wave activity is interacting with the precipitating electrons within 1 of Earth's surface.