Magnetospheric resonances at low andmiddle latitudes

摘要

We present results from a numerical study of structure and dynamics of dispersive Alfvén waves in the near-Earth magnetosphere containing proton radiation belt (near L = 1.5 dipole magnetic shell). The interest in this problem is motivated by numerous observations of magnetic oscillations with frequencies in the range of 0.1–4.0 Hz detected on the ground at low and middle latitudes. In a number of studies these oscillations interpreted as shear Alfvén waves standing inside the so-called ionospheric Alfvén resonator. We present results from two-dimensional, time-dependent simulations of the reduced two-fluid MHD model performed in the dipole magnetic field geometry with the realistic parameters of the magnetospheric plasma. These simulations show that these pulsations can be produced by the fundamental mode of the global field line resonator, spanning the entire magnetic field line in the low or middle magnetosphere. Simulations also show that even the waves with the highest considered frequencies (2.44 Hz) are not trapped inside the ionospheric resonator. Therefore, if these waves will be generated by some ionospheric source, then they can reach the equatorial magnetosphere and interact with energetic protons in the proton radiation belt.