First in‐situ observation of night‐time F region currents with the CHAMP satellite

The CHAMP satellite in its polar, low‐Earth orbit (450 km altitude) is a suitable platform for studying F region currents. High precision magnetic field measurements are used to detect and characterize these upper ionospheric currents on the Earth's nightside. A few examples are presented to illustrate the special features of the currents and a statistical study is performed on half a year of data revealing their global distribution. We find a spatial confinement of the currents to the near‐equatorial region bounded by the Appleton anomaly and their appearance in the pre‐midnight sector. The distribution with longitude exhibits high occurrence rates in the Atlantic sector and very few events in the Indian sector. The currents flow generally westward at a height‐integrated current density of several mA/m. Small‐scale fluctuations observed in current intensity are interpreted as an indication for plasma instabilities in the F region. Our analysis indicates that the appearance of F region currents is coupled with the presence of plasma bubbles.