rotating magnetospheric coordinate system into a non-rotating system, τ must be replaced by the longitude -λ. Inner Magnetosphere With the numbers q ~ 2, and Φco and τco increasing with geomagnetic activity (e.g., Φco ~ 17 and 65 kVolt, and τco ~ 0 and 1 h, during geomagnetically quiet and slightly disturbed conditions, respectively), eq.() valid at lower latitudes, (θ > θm) and within the inner magnetosphere (r ≤ 10 a) is the Volland-Stern model (see Fig. 1 a)). 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. The electric field components are derived from as In the presence of the geomagnetic field an electric field is generated in a rotating on frame of reference in order to compensate for the Lorentz force. This is the so-called electric co-rotation field measured by an observer rotating with the Earth. With the simplifying conditions given above its potential is with Φro = 90 kVolt. The thermal plasma within the inner magnetosphere co-rotates with the Earth. In a non-rotating frame of reference, it reacts to the sum of both fields in eq.() and (). 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.,). 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 (see Fig. 1b)). From the shape of the observed plasmapause configuration, the exponent q = 2 in eq.() has been determined, while the extent of the plasmapause decreasing with geomagnetic activity is simulated by the amplitude Φco Origin of Convection Field The origin of the electric convection field results from the interaction between the solar wind plasma and the geomagnetic field. In the polar regions with open magnetic field lines (where the geomagnetic field merges with the interplanetary magnetic field), the solar wind flowing through the polar magnetosphere induces an electric field directed from dawn to dusk. Charge separation takes place at the magnetopause. This area is connected via the last closed shell parameter Lm with the ionospheric