行星际扰动和地磁活动对GEO相对论电子影响

利用1988—2010年小时平均的GOES卫星数据,对地球同步轨道(GEO)相对论电子变化进行了统计分析,研究了相对论电子通量(Fe)增强事件的发展过程,探讨了利于相对论电子通量增强的太阳风和地磁活动条件.主要结论如下:(1)GEO相对论电子通量即使是峰值,也具有明显的地方时特性,最大电子通量出现在磁正午时.午/夜电子通量比率随着太阳风速度(Vsw)增加而增大;在Dst-50nT时相对论电子具有规则的地方时变化.在太阳活动下降相,电子通量与各参数的相关性较好,与其相关性最好的Vsw、Kp指数以及三次根号下的太阳风密度(N)分别出现在电子通量前39~57h、57~80h和12~24h.(2)强(日平均电子通量峰值Femax≥104 pfu)相对论电子事件,在距离太阳活动谷年前两年左右和春秋分期间发生率最高,较弱(104Femax≥103 pfu)事件无此特点;大部分强相对论电子事件中,电子通量在磁暴主相开始增加,较弱事件中则在恢复相开始回升.(3)太阳风密度变化对相对论电子事件的发展具有重要指示作用.电子通量在太阳风密度极大值后0~1天达到极小值,太阳风密度极小值后0~2天达到极大值.(4)90%以上相对论电子事件是在磁暴及高速太阳风的条件下发生的,与其伴随的行星际参数和地磁活动指数极值满足以下条件:Vswmax516km/s,Dstmin-31nT,Nmin2.8cm-3,Nmax14.1cm-3,Bzmin-2.9nT,AEmax698nT.(5)磁暴过程中,Dstmin后日平均电子通量大于103 pfu的发生概率为53%左右,强/弱相对论电子事件占总数比例分别为36%/64%左右,磁暴强度对其无影响.磁暴过程中的Vsw、N和AE指数大小对于能否引起相对论电子增强起着指示作用.

Effect of interplanetary disturbances and geomagnetic activities on relativistic electrons at geosynchronous orbit

Using hourly averaged data of >2 MeV electron fluxes measured with GOES 7/9/10/11 satellites during 1988-2010, this paper investigates statistically the conditions of solar wind and geomagnetic activities during relativistic electrons flux (F_e) enhancements, and describes the dependence of relativistic electrons at geosynchronous orbit (GEO) on local time and magnetic storms. The results are as follows: (1) The local time dependence of GEO relativistic electrons is influenced by solar wind and geomagnetic activities. The noon/midnight electron flux ratio grows with higher solar wind velocity (V_sw). On conditions of the Dstindex above -50 nT, relativistic electrons show regular variation with local time, while during storms with Dst<-50 nT, the maximum electrons flux may not measured at local noon. During the declining phase of a solar cycle relativistic electron fluxes approaching maximum, the solar wind velocity,Kp index and the cube root of solar wind density (N) show better correlations with electron fluxes after 39~57 h, 57~80 h and 12~24 h, respectively.(2) Before about two years of solar minimum and near the equinoxes, occurrence frequencies of intense relativistic electron flux enhancement events, in which the daily maximum relativistic electron flux F_emax≥ 10⁴ pfu, increase, while weaker events with 10⁴>F_emax≥10³ pfu exhibit no such solar cycle and seasonal dependences. For most intense events, relativistic electron fluxes begin to increase during main phases of magnetic storms, while for weaker events, relativistic electron fluxes tend to increase during recovery phases. (3) The solar wind density shows as a good indicator of subsequent relativistic electron activities. For most electron flux enhancement events, relativistic electron flux decreases to its minimum after 0~1 days of the maximum solar wind density, N_max, while approaching the maximum after 0~2 days of the minimum solar wind density, N_min. (4) Above 90% of relativistic electron events occurred on conditions of high wind solar velocities and geomagnetic disturbances, which are as follows: V_swmax>516 km/s,Dst_min <-31 nT,N_min <2.8 cm^-3,N_max14.1 cm^-3,B_zmin<-2.9 nT,AE_max >698 nT. (5) For all magnetic storms, occurrence probability of daily maximum electron flux above 10³ pfu after Dst_min, is about 53%, the percent of intense, weak events being 36%, 64%, respectively, which is hardly affected by intensities of storms. During storms, solar wind velocity, density, and the AE index are important indicators for subsequent relativistic electron activities.