极区顶部电离层离子上行的太阳活动依赖性研究

利用第23太阳活动周DMSP F12，F13和F15卫星数据，分别对南北半球极区顶部电离层离子上行的太阳活动依赖性进行了研究.结果表明，南北半球上行事件对太阳活动的响应特征基本一致，即高（低）太阳活动时，离子上行通量以及上行数密度较大（小），但是上行速度及上行发生率较低（高）.以南半球高纬为例，计算得到离子上行通量、数密度、速度及发生率在高低太阳活动条件下的比值分别约为2.26，3.35，0.71，0.51.对离子上行太阳活动依赖性的可能原因进行了分析.不同太阳活动水平下，光致电离及高能粒子沉降的差异会导致电离层离子密度的不同，而电离层离子密度的变化会改变离子elax-elax中性大气之间的碰撞频率，这是影响离子上行发生率的一个重要原因. 

Solar Activity Dependence of Ionosphere Ion Upflow in the Polar Topside

The influence of solar activity on ionosphere ion upflow was studied, over the northern and southern hemispheric polar topside. The observations were obtained from the Defense Meteorological Satellite between 1995 and 2005. Results show that the response characteristics of upflow events on solar activity are roughly consistent for the two hemispheres, that is, ion upflow fluxes and ion densities are generally larger during high solar activity than those during low solar activity, but ion vertical velocities and upflow occurrence rates show an opposite variation trends, i.e., they are higher and more frequently seen under the conditions of low solar activity, respectively. Besides, we further calculated the mean value of upflow parameters in the southern hemisphere. The ratios of them under high and low solar activity conditions are about 2.26, 3.35, 0.71 and 0.51. Furthermore, the results also show that it is the ion densities instead of ion vertical velocities that have profound effect on the upflow fluxes. The causes of such a dependence is briefly analyzed. Under different levels of solar activity, ionosphere ion densities are different because of the variations of ionization rates and ion-neutral collision frequencies. The collision frequency between ion and neutral atmosphere is closely related to the ion density. Therefore, the ion upflow occurrence rate in the polar topside ionosphere depends on the level of solar activity.