Auroral electron acceleration by dispersive Alfvén waves – insights from the VISIONS-2 rocket mission

Alfvén waves with small perpendicular scale lengths are dispersive and can carry parallel electric fields. In the Earth's magnetosphere, they capture and accelerate electrons in a resonant process along the magnetic field lines down into the high-latitude ionosphere. These wave-particle interactions are considered to be a significant driver of auroral particle acceleration and as such an important coupling process between the magnetospheric and ionospheric systems. However, studying these waves and their associated auroral precipitations remains challenging due to the short temporal and spatial scales involved. As a result, their role in auroral dynamics continues to be an active area of research.

Here, we present data from one of the VISIONS-2 (Visualizing Ion Outflow via Neutral Atom Sensing-2) sounding rocket launched in December 2018 from Ny-Ålesund, Svalbard, in the active dayside auroral region. Numerous time-energy dispersed structures, indicative of particle acceleration by Alfvén waves, were observed by the top-hat ESA instrument. We present the high-resolution measurements of several of these structures and analyse their time-of-arrival in energy and pitch-angle. We discuss the implications of these observations for understanding the acceleration region.