Small‐scale field‐aligned currents observed by the Akebono (EXOS‐D) satellite

The EXOS‐D fluxgate magnetometer data obtained at 3000–10000 km altitude have shown that small‐scale field‐aligned currents always exist in large‐scale region 1, region 2, cusp and polar cap current systems. Assuming that these small‐scale field‐aligned currents have current sheet structure, the width of current sheet is estimated to be 5–20 km at ionospheric altitude. By comparing the magnetometer data with charged particle and high frequency plasma wave data simultaneously obtained from EXOS‐D, it is found that small‐scale currents have one‐to‐one correspondence with localized electron precipitation events characterized by flux enhancement over a wide energy range from 10 eV to several keV and broadband electrostatic bursts occasionally extending above local plasma frequencies or electron cyclotron frequencies.