Research On Characteristics Of Precipitating Particles In The Polar Cap

The polar cap is the region where the Earth's magnetic fields are directly connected with solar wind magnetic fields.The location of polar cap is mainly in the high latitude region around magnetic poles.In this study,the polar cap is defined as the region poleward of 80.We use the high-resolution particle data from DMSP(Defense Meteorological Satellite Program)satellite from year 2004 to 2012 to calculate the physical parameters such as energy flux,number flux and average energy of electrons and ions precipitating in the polar cap,and give statistical results of the particle characteristics in the polar cap.We also utilize the solar wind data and geomagnetic indices from OMNI website to investigate the influence of solar wind magnetic field and geomagnetic field on the precipitating particle characteristics in the polar cap.The study of spatial distribution of particle characteristics in the polar cap shows that the precipitating particles in the polar cap are mainly soft electrons and ions,and the spatial distribution of energy and flux varies with magnetic latitude,as well as with magnetic local time.We find that the particle energy and flux in the polar cap are not smooth,and there are small-scale structures that vary with time.Through numerical simulation of GITM(Global-Ionosphere-Thermosphere Model)upper atmosphere model,we reveal that the effect of soft electrons in polar cap on upper atmosphere heating is quite obvious,and is non-negligible.We verify the conclusions of Gussenhoven and Hardy(1984)claiming the inverse correlation between the flux and energy of electrons,and illustrate that lower-energy electrons have higher flux.However,compared with the conclusion of Gussenhoven and Hardy(1984),the inverse correlation is weaker.Furthermore,the ion data are analyzed to show the less obvious inverse correlation between flux and energy of ions.The study of temporal variation of particle characteristics in the polar cap demonstrates that the particle energy varies with solar cycle obviously,negative correlation with solar activity for electrons,and positive correlation for ions,respectively.We also illustrate that there is clear seasonal variation of particle characteristics in the polar cap,smaller energy in the summer than in the winter,and larger flux in the summer than in the winter.The study of characteristics of precipitating particles under different solar wind conditions shows that the average energy of electrons in the polar cap is not sensitive to IMF(Interplanetary Magnetic Field)and geomagnetic disturbances.This investigation uses nine years of DMSP satellite observational data of precipitating particles(electrons and ions)in the polar cap to analyze the energy flux?number flux ? average energy statistical characteristics.It analyzes the solar wind magnetic field and the earth's magnetic field perturbation influence on particle precipitation;illustrates the non-negligible influence of polar cap particles on the heating of upper atmosphere,and demonstrates their importance in the solar wind energy deposition.The results of this paper are of great significance for understanding the magnetosphere-ionosphere-thermosphere coupling system,and provide a physical basis for the future ionosphere-thermosphere disturbance simulation research.