Magnetospheric electric convection field
[2] One possibility is viscous interaction between solar wind and the boundary layer of the magnetosphere (magnetopause).
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.
Second, it is assumed that the electric field can be derived from an electrostatic potential Φc.
is the separatrix[13] separating the low latitude magnetosphere with closed geomagnetic field lines at θ ≥ θm from the polar magnetosphere with open magnetic fieldlines (having only one footpoint on Earth), and τ the local time.
Since the electric potential is symmetric with respect to the equator, only the northern hemisphere needs to be considered.
(2) valid at lower latitudes, (θ > θm) and within the inner magnetosphere (r ≤ 10 a) is the Volland-Stern model (see Fig.
The use of an electrostatic field means that this model is valid only for slow temporal variations (of the order of one day or larger).
The assumption of a coaxial magnetic dipole field implies that only global scale structures can be simulated.
This is the so-called electric co-rotation field measured by an observer rotating with the Earth.
Since Φr decreases with distance from the Earth while Φc increases, the configuration of the sum of both potentials has a torus-like inner region of closed equipotential shells, called the plasmasphere, in which ionized particles of thermal energy remain trapped (e.g.,[14]).
Indeed, whistler observations have revealed a plasma density within the plasmasphere several orders of magnitude larger than outside the plasmapause, which is the last closed equipotential shell [15] (see Fig.
(2) has been determined, while the extent of the plasmapause decreasing with geomagnetic activity is simulated by the amplitude Φco The origin of the electric convection field results from the interaction between the solar wind plasma and the geomagnetic field.
This area is connected via the last closed shell parameter Lm with the ionospheric dynamo region.
The electric convection field in the near Earth polar region can be simulated by eq.
However, a field reversal takes place accompanied by field-aligned currents, both in agreement with the observations.
Moreover, a significant enhancement of the electric conductivity within the aurora area depending on geomagnetic activity exists which influences the parameter τco in eq.
Manifestations of upper atmospheric electric currents are the corresponding magnetic variations on the ground.
Longer-lasting magnetospheric disturbances of the order of several hours to days can develop into global-scale thermospheric and ionospheric storms (e.g.,[18]).
