dynamo region. Thus, discharging currents flow via electric field-aligned currents (Birkeland currents) along Lm within the ionospheric dynamo region. The field-aligned currents flow into the ionosphere on the morning side and out of the ionosphere on the evening side. The variability of the solar wind flux determines the magnetospheric activity, generally expressed by the degree of geomagnetic activity observed on the ground. Polar Magnetosphere The electric convection field in the near Earth polar region can be simulated by eq.() with the exponent q = - 1/2. At the separatrix at Lm ,Φc is continuous. However, a field reversal takes place accompanied by field-aligned currents, both in agreement with the observations. The electric field reversal at Lm clearly indicates a reversal of the plasma drift within the inner and the polar magnetosphere. In a more sophisticated model, the auroral oval between about 15° and 20°colatitude (again simulated by a coaxial auroral zone), as a transition zone between the field reversal, has been taken into account. The ionospheric dynamo region between about 100 to 200 km altitude is a region where ions and electrons have different mobility. Thus the plasma becomes electrically conducting. Due to the geomagnetic field, two kinds of electric currents exist: Pedersen currents parallel to E, and Hall currents orthogonal to E and B. Moreover, a significant enhancement of the electric conductivity within the aurora area depending on geomagnetic activity exists which influences the parameter τco in eq.() The electric convection field drives strong electric currents within the polar dynamo regions (e.g. DP1 and DP2) which can be simulated by the model. Manifestations of upper atmospheric electric currents are the corresponding magnetic variations on the ground. Unfortunately, this connection is unique only for horizontally flowing current systems. E.g., the vertically flowing field-aligned currents have almost no magnetic effect on the ground. The model allows to separate the contributions of both kinds of electric currents. The polar magnetic disturbances DP2 are mainly Hall currents. The auroral electrojets (DP1) with magnitudes of the order of several hundreds of kA flowing within the aurora zones consist of Hall currents and Pedersen currents. Dissipation of the Pedersen currents produces Joule heating which is transferred to the neutral gas of the thermosphere thus generating thermospheric and ionospheric disturbances. Longer-lasting magnetospheric disturbances of the order of several hours to days can develop into global-scale thermospheric and ionospheric storms (e.g.,). During major magnetospheric disturbances, large amounts