磁层-电离层电动耦合的中纬电离层效应

本文通过对1982年磁扰期间琼中、北京两站地磁X分量变化的分析,证实了磁层-电离层电动耦合对中纬电离层电流的影响.分析发现:磁静、磁扰条件下的平均日变化中,两站X分量变化在白天有反向的趋势.这表明它们分处于与动力效应对应的电离层发电机电流圈中心之南北两侧.在磁暴主相期间,X分量变化形态与之明显不同,两站地磁南北分量有同向变化,且变幅相近,甚至有时北京站△X更大.对环电流能量增长指数R小于—25nT/h的21次事件所作的时序叠加分析（以R最负时为零时）进一步证明,这种同向变化是普遍存在的.两站零时之△X大小相近,相关系数高达0.98.该同向变化与R指数突然变负密切相关. 以上对比表明,与发电机电流造成两站X分量反向变化不同,同向变化是磁层源高纬扰动电流向中低纬直接穿透的结果.本文对动力和电动耦合两种过程的不同进行了初步讨论.

THE EFFECT OF MAGNETOSPHERE-IONOSPHERE COUPLING ON MID-LATITUDE IONOSPHERES

The X-component of ground magnetic data from Beijing （BJ） and Qiongzhong （QZ） sta-tions are used to verify the existence of the effect of magnetosphere-ionosphere electrodynamic coupling on electric currents in mid-latitude ionospheres. The observations indicate that the direction of the average diurnal variations of X（BJ） and X（QZ） during both magnetic quiet and disturbed periods are opposite at day time. It means that these two stations locate at the northside and southside of the electric current focus caused by the ionospheric dynamo.The feature changes completely during the main phase of strong storms. The signs of the variation of these two stations are the same and one can often see that △X（BJ）>△X（QZ）. "Superposed epoch analysis is used for all the 21 events in 1982 in which Dst kept decreasing during the event （each event includes five hours, and the hour at which the ring current inflation rate, R, reaches its extreme negative value is taken as the key hour）. The result of the analysis shows the generality of the phenomena shown in case study. The variations of X（QZ） and X（BJ） are closely related to the decreasing of R and the magnitude of △X（QZ） at key hour is similar to AX（BJ）. The correlation coefficient between △6X（QZ） and△X（BJ） is as high as 0.98.Differing from the average variation of magnetic quiet and disturbed days, the similar response of X（QZ） and X（BJ） to the development of the ring current is a result of the equa-torward penetration of the high-latitude convection electric currents caused by the magnetos-pheric disturbance. The difference between the dynamic and electrodynamic couplings and the related physical processes are discussed as well.