Study On Adiabatic And Non-adiabatic Evolution Of Charged Particles In The Outer Radiation Belt During Storms

Geomagnetic storms are intense disturbances in the Earth’s magnetic field,which can have strong effects on the electromagnetic field and plasma structure in the Earth’s outer space.The radiation belts of the Earth are areas where high-energy and relativistic particles are trapped by the geomagnetic field.Compared with the inner radiation belt,the outer radiation belt is more vulnerable to the influence of geomagnetic storms and shows a highly dynamic evolution process.Enhanced solar wind dynamic pressure(_（99）)can alter the structure of the geomagnetic field,thereby causing adiabatic evolution of the motion and phase space distribution of high-energy electrons in the outer radiation belt.The perturbed geomagnetic environment can also change the distribution and properties of plasma waves in space,thus affecting the non-adiabatic evolution process of high-energy electrons in the outer radiation belt.In this paper,we selected a storm event that meet the conditions based on the geomagnetic indices,solar wind parameters in the Omni database,and observation data by Van Allen Probe.Then,we used the bounce-averaged drift velocity-test particle simulation model to study the evolution of the phase space density（PSD）of high-energy electrons under the time-varying asymmetric geomagnetic field simulated by the International Geomagnetic Reference Field Model（IGRF）and the T96 magnetic field model from December 19 to 20,2015.The simulation results and observations from the Van Allen Probe A both show that the PSD of electrons in the outer radiation belt evolves into different states under different levels of_（99）.In the first stage,the_（99）（～7.94 n Pa）caused a significant increase in electron anisotropy.In the second stage,under the influence of strong_（99）（～22 n Pa）,the PSD of high-energy electrons at all energy levels and pitch angles showed a significant decrease,indicating that magnetopause shadowing effects and outward radial diffusion may play important roles in the second process.To understand the non-adiabatic evolution process of electron PSD in this event,we presented the plasma wave spectrum and diffusion coefficient distribution in this event.The results show that as the sudden increases of_（99）,the plasma waves observed by the satellite changes,and the intensity of the scattering effect of waves on high-energy electrons’pitch angles has changed.The research results can help us further understand the dynamic evolution of the radiation belts during geomagnetic disturbances.