Comparative Study Of Polar Ionospheric F Layer In Both Hemispheres

The polar ionosphere is strongly influenced by convection electric fields, auroral particle precipitation, and field-aligned electric currents etc. The energy which originates in the solar wind and the magnetosphere deposits in the polar ionosphere, changing the state of the ionosphere, or through coupling between the ionosphere and the thermosphere, changing the neutral winds and compositions globally. This further influences the ionosphere in a global scale. The state of the ionosphere also has great influence on human activities, such as long-distance communication, navigation etc. It is therefore important to study the polar ionosphere in the sense of science and potential technology.There are varies of phenomena which have been reported in the polar ionosphere. However, it is still open questions to understand all of these phenomena, for example, the relative importance of cusp soft electron precipitation in the formation of tongue of ionization (TOI), the mechanism of polar cap patches, the contribution of different driven processes in the polar ionosphere during storm and/or substorm times, and the role of neutral atmosphere in the variation of polar ionosphere.Geospace plasma has been known to be controlled or strongly influenced by the geomagnetic fields. Due to the similarity of geomagnetic field configuration in both hemispheres, it is helpful for the understanding of physical processes through analysis of similarities or dissimilarities in both polar ionospheres.Based on F region critical frequency (foF2) data which has been obtained by DPS-4 at Zhongshan station, comparative analysis has been carried out using foF2 data at Svalbard, which is geomagnetically conjugate with Zhongshan station, and data at Tromso, which is located at the same geographic latitude as Zhongshan in the opposite hemosphere, and in the same geomagnetic meridian plane. Combined with numerical simulation and theoretical analysis, the climatology features of the polar ionosphere during winter times have been studied, with emphasis on the relative contribution of auroral electron precipitation and convection electric fields to the polar ionosphere. Variation of foF2 at Zhongshan station has also been studies for different geomagnetic activities. The main results are as follows:1. The difference in the foF2 diurnal variation between Zhongshan and Tromso stations results from the difference of interaction among sunlit ionization, convection electric fields and aurora particle precipitation. The major peak in the foF2 diurnal variation around magnetic local noon at Zhongshan station is mainly a result of interaction between the sunlit ionization and the horizontal plasma convection on the dayside. Cusp soft electron precipitation also contribute to the enhancement of foF2 at the major peak. Tromso is located at sub-auroral latitude. The interaction between dayside sunlit plasma and the convection is relatively weak, making the major peak in the foF2 diurnal variation at Tromso appear at the time of about its local noon.2. Ionospheres at both Zhongshan and Tromso stations are influenced by aurora precipitation. F region ionization from auroral electrons at Zhongshan station occurs on the morning the evening side in the magnetic local time (MLT) coordinates. Zhongshan station is located in the polar cap at about MLT midnight, resulting in lower F region electron density during the day. Tromso station is located at a lower latitude than Zhongshan station but in the center of auroral oval around midnight sectors. The contribution of aurora electron ionization to the F region plasma is distinct at this time period. Auroral ionization effect is more pronounced in lower solar activity years at both stations.3. foF2 at both Zhongshan and Tromso stations increases generally with higher solar activity. This indicates the importance of sunlit ionization in the overall polar F region ionosphere.4. Zhongshan and Svalbard stations are geomagnetically conjugated. However, due to the opposite deviation of the geomagnetic poles relative to the geomagnetic poles in both hemispheres, the formation of TOI in both hemispheres has a time difference of about 12 hours. This leads to the results that different from Zhongshan station, Svalbard station observes a major peak in the diurnal variation of foF2 not in the magnetic local noon, but at a time around MLT midnight. The contribution of cusp soft electron precipitation to the ionization is more distinct at Svalbard station than at Zhongshan station due to the relative weak sunlit ionization plasma on the dayside at Svalbard station.5. foF2 diurnal variation at Zhongshan station shows great dependence on the geomagnetic activities. With the higher geomagnetic activity, the major peak in the foF2 diurnal variation around MLT noon becomes more distinct.