Statistical analysis of the energy spectra of shock accelerations of solar energetic particles:ACE observations
Solar Energetic Particles(SEPs)significantly affect terrestrial space environment.Diffusive Shock Acceleration(DSA)of SEPs is the process in which particles are scattered in the upstream and downstream regions of the shock and cross the shock multiple times to gain energy.In this work,we use the data of energetic particles of 47.0 keV～4.80 MeV measured by Advanced Composition Explorer(ACE)spacecraft at 1AU,to investigate the ion acceleration process of 76 interplanetary shocks at 1 AU from 1998 to 2014.Among the selected 60 quasi-perpendicular(16 quasi-parallel)shock events,about 88.33％(81.25％)and 48.33％(43.75％)of the events display significant increases of ion fluxes(JD/JA)for the energy channels 47.0 keV and 4.8 MeV,respectively,where JD and JA represent the ion fluxes in the downstream region of the shocks and in the ambient solar wind,respectively.Among the shock parameters considered,both JD/JA(JD)are most correlated with the magnetic field compression ratio rB.Through statistical analysis,we quantify the possible factors affecting the energy spectra of high-energy ions.The results show that among all the shock parameters and plasma parameters,the correlation between shock compression ratio r and downstream energy spectrum index sE,d is the weakest,which is in sharp contrast with the energy spectrum index results predicted by classical DSA.The correlation between upstream solar wind velocity Vsw and downstream ion energy spectrum index sE,d is the strongest,and the variation of sE,d with upstream solar wind speed Vsw is similar to an inverse proportional function.The decline rate is large at the beginning and then becomes small.In addition,combining the analysis of other possible factors,we can show that the energy spectrum of shock-accelerated ions is the result of the coupled effects of multiple factors,rather than relying on one single factor.
Acceleration of particlesShock waveSolar energetic particlesSpace plasma
NETL
NSTL
万方数据
