南极中山站的f_0F2特征

本文利用电离层数字测高仪 (DPS - 4)所测的f0 F2和从美国NOAA和DMSP卫星观测估算的半球功率指数和午夜极光区赤道侧边界纬度等资料 ,考察中山站电离层的极区特征。结果表明 ,冬季中山站电离层内的电离生成主要取决于从磁层沉降的粒子。在太阳活动和地磁变化宁静环境下 ,磁正午极隙区内的软粒子是最主要的电离源 ,它能使f0 F2达全天的最大值 ;上、下午各有数小时处于极光带内时 ,高能粒子的电离作用也很重要 ;夜间进入极盖区后 ,电子密度则很低。夏季太阳辐射电离效应使f0 F2值比冬季增加 1- 1 .5MHz,而其日变化的最大值时间也提前了 1- 2hr。发生很大扰动时 ,极隙区和极光带的位置均向低纬方向移动。若中山站日间也处于极盖区内时 ,电子密度会大幅度下降 ,并常接收不到电离层回波的信号。在中等扰动环境下情况更加复杂。由于高纬电离层对流速度很高 ,离子 /中性分子间的碰撞复合系数就很大。热层中性大气全球经向环流对高纬电离层电子密度的增加无显著作用。磁暴期间中午从极隙区向南的等离子体对流对中山站f0 F2的增高也无明显影响。

THE FEATURES OF f_0F2 AT ZHONGSHAN STATION OF ANTARCTICA

The data of f 0 F2, measured by a Digisonde Portable Sounder (DPS 4) at Zhongshan Station of Antarctica in 1995, the hemispheric power index and the midnight equatorward boundary of the aurora, estimated by observations of American NOAA and DMSP satellites are used to examine features of the polar ionosphere. The results show that the major source of electron and ion production at Zhongshan Station is almost completely dependent on particles precipitated from the magnetosphere. Under a quiet environment of the solar activity and geomagnetic variation, the soft particles in the cleft are the controlling source of ionospheric ionization at dipole magnetic noon. The ionized effect of energy particles is also important during several hours both in the morning and afternoon when the station lies in the auroral region. The electron density is much lower at night in the polar cap areas. The ionization action of solar EUV radiation in summer makes the monthly median of f 0 F2 1—1.5hr MHz larger than that in winter, and the time of the peak of the f 0 F2 diurnal variation in summer is 1—2hr earlier than in winter. During a strong disturbance period, the cleft and auroral regions move toward lower latitudes. The electron density will decrease a lot and the ionospheric echo may often not be received when the station is located at the polar cap area. The situation is more complex under a moderate disturbed environment. Since at high latitudes the magnetospheric convection velocity can become very large and the recombination coefficient of the colliding ion and neutral is highly increased, global meridional thermospheric circulation has not led a remarkable intension of electron density in the high latitude ionospheres. During disturbed periods the southward plasma flux carried by convection has not noticeable effect to increase f 0 F2 at Zhongshan Station too.