Scale-length dependence of the ratio between the magnetic and electric field perturbations in the ionospheric field-aligned current region

There is generally high correlation between the orthogonal magnetic and electric field perturbations on the ionospheric field-aligned current region based on observations by polar orbiting satellites. The ratio between the magnetic and electric field perturbations, ⊿B_z/μ_oE_x, has a scale-length dependence : the ratio ⊿B_z/μ_oE_x decreases with decreasing scale length. B. FORGET et al.(J. Geophys. Res., 96,1843,1991) explained this scale-length dependence using a static model. In this paper, we compare the ratio ⊿B_z/μ_oE_x observed by the DE-2 satellite for various spatial scales with the effective Pedersen conductivity Σ_ calculated by the method of FORGET et al. The results show that in many cases this model can adequately explain the observed scale-length dependence. However, cases exist in which the difference, ⊿B_z/μ_oE_x-Σ_, decreases at about 0.25-1.0s in temporal scales (2-8km in spatial scales). This behavior is explained as being due to Alfven waves.