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

Abstract

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.