磁暴期离子上行与太阳风及地磁活动水平的统计关系

Statistical relationships between ionospheric ion outflows and solar wind and geomagnetic activity parameters during geomagnetic storms

利用FAST卫星ESA仪器第23太阳活动周上升相(1997—1998年)的观测数据,选取20个磁暴期间能量为4~300 eV的离子上行事件,研究不同磁暴相位电离层上行离子的能通量与太阳风、地磁活动以及电子沉降的统计关系.结果表明:(1)在磁暴初相、主相和恢复相离子上行平均能通量为6.08×10^(7)eV/(cm^(2)·s·sr·eV)、5.75×10^(7)eV/(cm^(2)·s·sr·eV)和3.91×10^(7)eV/(cm^(2)·s·sr·eV),初相期间上行离子能通量最大;(2)上行离子能通量与太阳风动压、行星际磁场B Z分量存在相关关系,相关系数分别为0.47和-0.38;(3)在磁暴初相、主相和恢复相上行离子能通量与Sym-H的相关系数分别为0.74、-0.77和-0.54,与Kp的相关系数分别为0.53、0.75和0.65,整体上离子上行与Sym-H指数的相关性好于Kp指数;(4)在磁暴初相、主相和恢复相上行离子能通量和电子数通量的相关系数分别为0.74、0.52和0.32,表明磁暴期间软电子(<1 keV)沉降可以显著提高电离层离子温度;F区的等离子体摩擦加热和双极电场是离子上行的重要获能机制.本文构建的上行离子能通量与Sym-H和电子数通量的经验关系显著,可用于磁流体模拟研究.

Based on the criteria of choosing ion outflow events,we select 20 ion outflow events within the energy range of 4~300 eV during the magnetic storm,using the data from the FAST/ESA instrument between 1997 and 1998,and explore the relationships between the ionospheric ion outflow and the solar wind,the geomagnetic activity,the precipitating electrons.The results show that:(1)The average ion outflow flux is 6.08×10^(7)eV/(cm^(2)·s·sr·eV),5.75×10^(7)eV/(cm^(2)·s·sr·eV)and 3.91×10^(7)eV/(cm^(2)·s·sr·eV)on the initial phase,the main phase and the recovery phases,respectively.The ion outflow flux reaches the maximum on the initial phase.(2)The correlation coefficients between the ion outflow flux and the solar wind dynamic pressure and the B z component of the interplanetary magnetic field are 0.47 and-0.38,respectively.(3)The correlation coefficients between the upflow flux and the Sym-H index are 0.74,-0.77 and-0.54 on the initial phase,the main phase and the recovery phase,respectively,and the correlation coefficients with Kp are 0.53,0.75 and 0.65,respectively.Overall,the correlations between the ion upflow and the Sym-H index are stronger than Kp.(4)The correlation coefficients between the ion upflow and the electron number flux are 0.74,0.52 and 0.32 on the three phases,respectively.Our conclusions are:1)the soft electron precipitation(<1 keV)contributes significantly to the ion temperature increase and the ion frictional heating;2)the ambipolar electric field is an important energy source for ion outflows.The empirical relationships of the upflowing ions with the Sym-H and the electron number flux are significant in this study,and these empirical models can be used in magnetic fluid simulation studies.