Abstract
We analyze conditions for excitation of ULF waves in the ionospheric Alfven resonator (IAR), taking into account the altitude-inhomogeneous profile of the magnetospheric convection velocity. This profile is formed as a result of interaction of the convective flow with the neutral atmosphere at altitudes 90–150 km. ULF waves comprise oblique Alfven waves, trapped into the IAR, and ionospheric drift waves, which are in resonance with them. These waves together form strongly anisotropic, closed current loops, whose scale along the magnetic field greatly exceeds their transverse scale, i.e., lz ≫ l⊥, and can be considered Alfven vortices. Within the framework of the proposed model of the ionosphere, we study the instability threshold and the amplitude growth rate of the Alfven vortices as functions of different parameters (wave vector k22A5, angle between the wave vector and the convection velocity, ratio of the Alfven-wave and Pedersen conductivities, etc.). Some estimates are given in application to the observed small-scale field-aligned currents in the auroral ionosphere.
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