Chapter 5 - The Earth’s Magnetosphere: A Secondary Collisionless Magnetohydrodynamic Generator

Abstract

That the earth and its atmosphere are rotating is communicated along magnetic field lines by electric fields. These electric fields put the plasma in motion so, to first order, the entire inner magnetosphere also rotates with the earth. In the sun’s frame of reference, this is the largest electric field source at latitudes less than about 60°, whereas in the rotating frame, this field vanishes and the processes in Chapter 3 dominate. At higher latitudes corresponding to magnetic field-line crossings at higher altitudes in the equatorial plane (but still below the polar cap), the electric field is determined by the flow field inside the magnetosphere. The flow slows down as it approaches the earth and the mechanical energy is converted to electric energy. This is accompanied by the so-called region 2 field-aligned currents and a variety of electric field generation effects. As particles approach the earth, they become energized and form the outer Van Allen radiation belts. Large ∂B/∂t electric fields can occasionally be generated at the earth’s surface where they endanger electric power systems. Large polarization fields occur in many situations and strong parallel electric fields generate the primary auroral particles. As these energetic particles penetrate deeper into the magnetosphere, they cross electric potential lines, reach 300,000,000K, and fill the outer Van Allen radiation belts. The combination of varying flow fields and plasma gradients creates many localized electric field structures.