【作者】 朱爱琴；

【导师】 黄际英； 张北辰；

【作者基本信息】 西安电子科技大学 ， 无线电物理， 2008， 硕士

【摘要】 极区电离层强烈地受到极区对流电场、极光粒子沉降和场向电流等的影响。通过这些驱动过程,来自太阳风和磁层的能量沉积在极区电离层中,直接改变极区电离层的状态;或通过与中性大气的耦合,改变全球中性大气风场和中性大气成份,影响到全球电离层。而电离层与远距离通讯、导航等人类活动紧密相关。开展极区电离层研究具有重要的科学意义和潜在的应用价值。人们已经观测到丰富的极区电离层物理现象。对这些物理现象的解释,比如极隙区软电子沉降电离在TOI结构形成中的贡献大小、等离子体云块的形成机制、暴时极区电离层受不同磁层驱动过程影响的相对大小,以及中性大气变化在其中所起的作用等,都是未能完全解决的问题。空间等离子体受地球磁场的控制和影响。由于南北两极磁场位形的相似性,两极电离层的不同表现,可能通过相同的物理机制加以解释。由于太阳风与磁层相互作用的南北极不对称性,在极区电离层中的踪迹所表现出来的差异可能为我们弄清电离层中的基本物理过程提供帮助。本文以中山站数字式电离层测高仪数据为基础,联合分析与中山站具有相同地磁纬度并构成地磁共轭的Svalbard站,和与中山站具有相同地理纬度,几乎位于同一磁经度子午面的Tromso站测高仪探测数据,结合数值模拟和理论分析,研究了极区冬季F层电离层气候学特征的形成机理,分别考虑了极光粒子沉降和对流电场对极区电离层的影响。对不同地磁活动条件下南极中山站电离层变化特性进行了初步统计分析。论文的主要研究结果如下:1、光致电离、极区对流电场和极光沉降粒子电离共同作用的不同使得中山站和Tromso站foF2日变化形态上出现差异。中山站通常处于极隙区纬度,其foF2日变化主峰靠近磁中午,主要是日侧等离子体与极区对流相互作用的结果,此时日侧极隙区软电子沉降也会对foF2产生影响。Tromso站在日侧通常处于亚极光区纬度,由于日侧等离子体与极区对流相互作用较弱,foF2日变化主峰在地方时中午形成,此时F层电子浓度主要由太阳天顶角决定。2、中山站与Tromso站F层电离层均受到极光沉降粒子电离的影响。由于中山站地磁纬度较高,该站F层受极光带电离作用主要分别发生在MLT晨侧和傍晚侧,在MLT子夜附近处于极盖区,电子浓度较低。Tromso站地磁纬度相当于夜侧极光带中心位置,因而在MLT子夜前后受到极光沉降粒子电离的作用明显。极光沉降粒子电离在太阳活动低年对中山站foF2日变化形态影响显著。3、中山站与Tromso站foF2随太阳活动的增强而整体变大。中山站在太阳活动高年随太阳辐射流量F10.7的增大,极区背景foF2增大,造成foF2日变化次峰不明显。4、Svalbard站与中山站虽然地磁纬度相当,但由于地磁极偏离地理极方向相反,南极TOI结构的形成与北极相差约12小时。因此与南极中山站不同,Svalbard站foF2日变化主峰不出现在磁中午附近,但此时光致电离较弱,极隙区软电子电离作用相对明显。5、不同AE条件下中山站foF2日变化特性存在较大差别。AE指数大的情况下中山站foF2月中值日变化峰值比AE指数小的情况下的偏小,中山站“磁中午异常”现象明显。更多还原

【Abstract】 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.更多还原