Ion’s ring current: regularities of the energy density distributions on the main phase of geomagnetic storms

Abstract. Based on the results of measurements near the equatorial plane a fluxes of H+ and O+ ions of the ring current (RC) from the Explorer 45, AMPTE/CCE, and Van Allen Probes (A and B) satellites, a systematic analysis of spatial distributions of the energy density for these ions on the main phase of magnetic storms was carried out. The radial profile of the RC ions energy density is characterized by the maximum (Lm) and by the ratio of the energy densities of the ions and the magnetic field at this maximum (ßm), and at L > Lm this profile is approximated by the function w(L) = w0exp(–L/L0). Quantitative dependences of the parameters Lm, ßm, w0 and L0 on the Dst index, ion energy (E), and magnetic local time (MLT) are obtained; these dependences are different for H+ and O+ ions, as well as for ions of low (E < 60 keV) and higher energies. A strong azimuthal asymmetry of the RC ions with E ~ 1–300 keV at L > Lm was revealed: for H++O+ and O+ ions, L0 increases systematically with the increasing MLT from evening to midnight sector, while for H+ ions L0 decreases; energy density of O+ ions is more uniformly distributed over MLT compared with H+ ions. For O+ ions with E ~ 1–300 keV, ßm ∝ Lm–6; this result this result shows that a deeper penetration of hot plasma into a geomagnetic trap, during strong storms, requires not only a stronger electric field of convection, but also a significant preliminary accumulation and acceleration of ions (especially O+ ions) in the source of the RC. It is shown that the greater |Dst| at the end of the main phase of storms, the smaller the contribution of ions with E < 60 keV and the greater the contribution of higher-energy ions to the RC energy density (the average energy of ions increases); such effect can be associated with increases of the radial diffusion of ions with the increasing the strength of storm and the main phase duration.