NUMERICAL STUDY FOR THE SEMI-ANNUAL VARIATION OF ELECTRIC FIELDS AT THE MID-AND LOW-LATITUDES
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摘要: 利用一个中低纬电离层电场理论模式,模拟太阳活动低年、地磁活动平静情况下,中低纬地区电离层电场全年的变化情况。结果显示,单独计算南、北半球（去耦合）得到电离层电场具有明显的周年变化特征,且两个半球电场的相位相差半年左右。而同时计算南、北半球（计及耦合）时,电场则是以半年变化为主,且这种半年变化的幅度和相位随地方时和地磁纬度有变化。提出一个南、北半球耦合电路的简单物理模型给予解释。电路模型初步计算发现,即使两个半球电离层电场分别具有周年变化,只要它们变化的幅度相当,相位相差半年左右,由于跨越南北半球磁力线的耦合效果,耦合的电离层电场会产生明显的半年变化分量。由于缺少连续的电离层电场观测资料,将模拟结果与Richmond基于非相干散射雷达数据建立的经验模式（ISR Model）相比较,结果符合较好。Abstract: With a theoretical model of ionospheric electric fields, the yearly variation of ionospheric electric fields at mid- and low-latitudes under the condition of low solar and quiet geomagnetic activities were studied. The main results are as follows: when the ionospheric electric fields are calculated individually in the northern or southern hemisphere without including the influence of the other hemisphere （uncoupled）, the electric fields in both hemispheres vary in an obvious annual pattern with an anti-phase; when the electric field was calculated simultaneously in both hemispheres with the influence of the other hemispheres （coupled） included, the electric field varies in a predominant semi-annual pattern. Moreover, quite good consistency was found between the behaviors of semi-annual variation calculated by our theoretical electric field model and an empirical model of Richmond. A simple circuit with the coupling between the northern and southern hemispheres was introduced to interpret the semi-annual variation of electric field. Results from the circuit model reveal that the coupled electric field would show a pronounced semi-annual variation due to the ’coupling effect’ along the magnetic field lines between two hemispheres, whereas the uncoupled electric field have an annual variation in respective hemisphere.
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