INFLUENCE OF THE FINITE IONOSPHERIC CONDUCTIVITY ON DISPERSIVE, NONRADIATIVE FIELD LINE RESONANCES

The influence of the finite ionospheric conductivity on the structure of dispersive, nonradiative field line resonances (FLRs) is investigat ed for the first four odd harmonics. The results are based on a linear , magnetically incompressible, reduced, two-fluid MHD model. The model includes effects of finite electron inertia (at low altitude) and fin ite electron pressure (at high altitude). The ionosphere is treated as a high-integrated conducting substrate. The results show that even ve ry low ionospheric conductivity (Sigma(P) = 2 mho) is not sufficient t o prevent the formation of a large-amplitude, small-scale, nonradiativ e FLR for the third and higher harmonics when the background transvers e plasma inhomogeneity is strong enough. At the same time, the fundame ntal FLR is strongly affected by a state of low conductivity, and when Sigma(P) = 2 mho, this resonance forms only small-amplitude, relative ly broad electromagnetic disturbance. The difference in conductivities of northern and southern ionospheres does not produce significant asy mmetry in the distribution of electric and magnetic fields along the r esonant held line. The transverse gradient of the background Alfven sp eed plays an important role in structure of the FLR when the ionospher ic conductivity is finite. In cases where the transverse inhomogeneity of the plasma is not strong enough, the low ionospheric conductivity can prevent even higher-harmonic FLRs from contracting to small scales where dispersive effects are important. The application of these resu lts to the formation and temporal evolution of small-scale, active aur oral forms is discussed.