A corotation electric field model of the Earth derived from Swarm satellite magnetic field measurements

• Published in: Journal of geophysical research. Space physics 2017-08, Vol.122 (8), p.8733-8754
• Main Author: Maus, Stefan
• Format: Article
• Language: English
• Subjects: Charge density; Conductors; Corotation; corotation electric field; Current carriers; E region; Earth core; Earth magnetosphere; Earth rotation; Electric charge; Electric fields; Geomagnetic field; Geomagnetism; Inertial coordinates; Inertial reference systems; Ionosphere; Lower atmosphere; Magnetic fields; Magnetic measurement; Magnetosphere; Magnetospheres; Plasmasphere; Polar caps; Satellites; Spherical harmonics; Swarm satellite mission
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2017JA024221

Rotation of the Earth in its own geomagnetic field sets up a primary corotation electric field, compensated by a secondary electric field of induced electrical charges. For the geomagnetic field measured by the Swarm constellation of satellites, a derivation of the global corotation electric field inside and outside of the corotation region is provided here, in both inertial and corotating reference frames. The Earth is assumed an electrical conductor, the lower atmosphere an insulator, followed by the corotating ionospheric E region again as a conductor. Outside of the Earth's core, the induced charge is immediately accessible from the spherical harmonic Gauss coefficients of the geomagnetic field. The charge density is positive at high northern and southern latitudes, negative at midlatitudes, and increases strongly toward the Earth's center. Small vertical electric fields of about 0.3 mV/m in the insulating atmospheric gap are caused by the corotation charges located in the ionosphere above and the Earth below. The corotation charges also flow outward into the region of closed magnetic field lines, forcing the plasmasphere to corotate. The electric field of the corotation charges further extends outside of the corotating regions, contributing radial outward electric fields of about 10 mV/m in the northern and southern polar caps. Depending on how the magnetosphere responds to these fields, the Earth may carry a net electric charge. Key Points A complete corotation electric field model has been derived from magnetic measurements of the Swarm satellite mission The equations of the global corotation electric field and secondary corotation charges are given in corotating and inertial coordinates An accurate corotation electric field model is essential for the understanding of plasmasphere underrotation and other phenomena