Research On The Radial Evolution Of Ring Current Ions In The Equatorial Region During Geomagnetic Storms

As an important part of the inner magnetosphere of the earth,the ring current enhances during solar storms so as to cause magnetic storms.The evolution process and control mechanism of ring current ions during magnetic storms have been a hot topic in space physics.Among them,interactions between ultra-low frequency(ULF)wave and ring current ion are considered to be the important mechanism to control the evolution of ring current(RC)ions.However,for the interaction of ULF waves and RC ions,it has been seldom reorted that systematic research on the difference in the control efficiency of the evolution of different kinds of ring current ions.Therefore,based on the combination of theoretical analysis and observations of Van Allen satellite in the equatorial ring current region,this paper systematically studies the radial evolution of different species of ring current ions during the magnetic storm in August 23-24,2016.(1)Through in-situ observations of ions and field fluctuations by the Van Allen satellite,it is found that during the magnetic storm the corresponding magnetic moment(?)ranges S of the phase space density enhancements for different kinds of ring current ions meet:S(O~+)>S(He~+)>S(H~+).For the single species,ions with lower magnetic moment values can penetrate deeper L-shells(minimum L?3.6)than those with higher magnetic moment values.As the ions penetrate into the deep inner magnetosphere,the enhancement magnitude of the phase space density decreases gradually.(2)Before the magnetic storm began,the satellite hardly observed obvious signs of ULF fluctuations.Strong ULF fluctuations were observed in the L?3-5range during the main phase of the magnetic storm,with the frequency range of ULF waves concentrated in the?10-50 m Hz.(3)The theoretical calculation of wave-particle resonances based on the observed ULF fluctuation parameters shows that the resonance efficiencies?between ULF waves and three kinds of ring current ions meet:?(O~+)>?(He~+)>?(H~+).The theoretical results are consistent with the observed range characteristics of phase space density enhancement for the different species of RC ions.Therefore,radial transport of ring current ions into the deep inner magnetosphere is caused by the drift-bounce resonance interaction between ions and ULF waves.(4)During the moderate magnetic storm recovery period,the decay rate R for three major ring current ion species is observed to meet:R(O~+)>R(He~+)>R(H~+),i.e.the lifetime of oxygen ions is shorter than that of helium and hydrogen ions during charge exchangeThis paper provides an in-situ observational evidence for the radial evolution of ring current ions controlled by ultra-low frequency wave during magnetic storms.The ion evolution characteristics for different species of the ring current during the magnetic storm revealed in this paper provide an important reference for studying the transport path of ionospheric oxygen ions in the magnetosphere,as well as modeling the ring current.