Magnetospheric electric convection field
The impact of the solar wind onto the magnetosphere generates an electric field within the inner magnetosphere - the convection
field-. Its general direction is from dawn to dusk. The co-rotating thermal plasma within
the inner magnetosphere drifts orthogonal to that field and to the geomagnetic field Bo. The generation process is not yet completely understood. One possibility is viscous interaction between solar wind and the boundary layer of the magnetosphere (magnetopause). Another process may be magnetic reconnection. Finally, a hydromagnetic dynamo process in the polar regions of the inner magnetosphere may be possible. Direct measurements via satellites have given a fairly good picture of the structure of that field. A number of models of that field exists.
Figure 1: Equipotential lines of electric convection field within the equatorial plane of the magnetosphere (left), and superposition of the convection field with the co-rotation field (right) during magnetically quiet conditions
Ionospheric dynamo region
In the height region between about 85 and 200 km altitude on Earth, the ionospheric plasma is electrically conducting. Atmospheric tidal winds due to differential solar heating or due to gravitational lunar forcing move the ionospheric plasma against the geomagnetic field lines thus generating electric fields and currents just like a dynamo coil moving against magnetic field lines. That region is therefore called ionospheric dynamo region.
The magnetic manifestation of these electric currents on the ground can be observed during magnetospheric quiet conditions. They are called Sq-variations and L-variations (L=lunar) of the geomagnetic field.
Additional electric currents are generated by the varying magnetospheric electric convection field. These are the DP1-currents and the polar DP2-currents.
Finally, a polar-ring current has been derived from the observations which depends on the polarity of the interplanetary magnetic field. These geomagnetic variations belong to the so-called external part of the geomagnetic field. Their amplitudes reach at most about 1% of the main internal geomagnetic field Bo.
Figure 1. Streamlines of equivalent ionospheric Sq current during equinox (1957 - 1969) at 12 UT separated into primary (a) and secondary (b) part. Between two streamlines flow 20 kA.
Figure 2. Blockdiagram illustrating coupling between the horizontal wind U and pressure p via the Ampere force jx Bo, and the Lorentz force Ux Bo. Here j is the electric current density, Bo the geomagnetic field, h the equivalent depth, σ the electric conductivity, and E the electric polarization field. In a self-consistent treatment of the coupled system, gate B must be closed. In conventional dynamo theories, gate B is open.