A new gravity-driven ionospheric current

A new gravity-driven ionospheric current has been identified. The Sun’s ultraviolet radiation ionizes the top of Earth’s atmosphere and thus creates the ionosphere. At the highest altitudes, the ionosphere has few neutral atoms and behaves much like a collisionless space plasma in which the electrons and ions spiral around Earth’s magnetic field lines. At low latitudes, where those lines are almost horizontal, electrons and ions should drift in opposite directions under gravity’s influence, setting up an eastward-flowing electric current that is perpendicular to both the magnetic and gravitational fields. Observational evidence for such a current system has now been found by Stefan Maus (National Oceanic and Atmospheric Administration in Boulder) and Hermann Lühr (Geo-research Center in Potsdam, Germany), using data from Germany’s CHAMP satellite. From the tiny magnetic signature in the data, the geophysicists have determined that the current spans more than 60° of latitude across the equator and, in total, adds up to more than 50 kA. (S. Maus, H. Lühr, Geophys. Res. Lett. 33 , L02812, 2006 http://dx.doi.org/10.1029/2005GL024436 .)