模式化分析F区电离层赤道异常槽

MODELLING STUDY THE VARIATION OF THE EQUATORIAL ANOMALY IONIZATION TROUGH

利用二维低纬电离层理论时变模式模拟低纬电离层演化，考察影响赤道异常槽位置的物理因素．计算结果显示赤道槽有明显的季节、地方时和经度变化．以１１０°Ｅ为例，北半球夏季期间赤道槽一般在磁倾赤道北侧，最北达３°-３．５°Ｎ，而在北半球冬季期间一般位于磁倾赤道南侧，最南可达４°－５°Ｓ．进一步分析发现，赤道槽季节变化中光化电离率季节改变的影响很小，主要由水平中性风季节变化贡献．计算以８３天为例，白天赤道槽在地理经度１００°Ｅ附近最南，２８５°Ｅ附近最北，与观测特征基本一致．主要是背景大气水平风场的经度差异导致赤道槽位置的经度变化，而非前人认为直接由磁偏角控制的．

An anomalous feature of low latitude ionosphere is the Equtorial Anomaly, and measurements show that the minimum peak density located between two crests of the Equtorial Anomaly, the equatorial anomaly trough (EAT), is not always lo- cated at near the magnetic equator. A two-dimensional theoretical low-latitude ionospheric model is used to simulate the evolution of the EAT and investigate ef fects of some physical factors on the location of the EAT. Each of them is adjusted respectively to study their influences on the EAT. Simulation results show that there are extinct diurnal, seasonal and longitudinal variations of the location of EAT. The EAT situates at the north of the magnetic dip equator at June solstice and shifts to the south at December solstice. It is found that the seasonal variation of the position of EAT is mainly caused by the neutral winds, not by seasonal changes in photoionization productions directly due to the variation of the geomagnetic solar zenith angle. Longitudinally speaking, the EAT lies north near 285°E and south near 100°E, which is basically consistent with previous observations. And its longitudi nal variation is pricipally caused not by the magnetic declination and displacement between the geographical and magnetic equators, but by the longitudinal changes of horizontal neutral wind, which does not support the previous opinion. Only at regions near the 330°E longitudes did the magnetic declination play some larger influence on the EAT location, but it was still much smaller than that of neutral winds. In addition, the displacement between the dip equator and equatorial elec- trojet is not taken into account because the ionospheric model is under the dipole field assumption.