Abstract:

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.