电离层扰动与磁层耦合

Ionospheric Disturbances and Magnetosphere-Ionosphere Coupling

本文通过两个事例分析表明，磁果期间磁层对流和沉降粒子的增强不仅对祖光区电离层扰动形态有控制作用，而且也会引起继后的中低纬及赤道电离层变化。高纬区低热层大气受热后，F层抬升和中性大气成分变化导致的电子密度正、负扰会向低纬扩展；在E层高度上，扰动发电机对赤道区喷泉效应的抑制使驼峰区扰动更为突出。这些过程均使中低纬电离层foF2和h’mF变化中出现相应材征。地面电离层垂测站链在夜间常能观测到多站几乎同时的h’mF．上升现象。这可能是二区场向电流有极大的增强，或是行星际磁场又转为北向，也可能是此两过程同时作用的结果。

It is shown by two typical samples that the magnetosphere-ionosphere coupling duringa magnetic storm not only takes a control role in ionospheric disturbance in the auroral region, but alsoa main source for successive variations in the mid-and low-latitude ionosphere.At the beginning of the main phase of a strong storm the disturbed energy of the solar wind enters the auroral ionosphere along geomagnetic field line and Penetrates directly into mid-and low-latitude areas. As a result, the eastward equatorial electrojet at daytime intensifies considerablely.In the high latitude the enhancement of magnetospheric convection makes the electron density Nin the auroral F-layer decrease, while the energetic particle precipitation leads to a dramatically increasing of ionization in the E-layer. The combination of these two effects during the main phase ofstrong storms induces the following phenomena in the auroral ionosphere: N' (E-layer) >>N (Flayer), and N (F-layer) decreases with increasing of altitude. The Chapman distribution form of Nin the F-layer disapears entirely. All these proceases occur in the electrodynamic coupling stage of themagnetosphere-ionosphere interaction.At the recover phase of a storm, however, the dynamic coupling dominates as the neutral atmosphere plays an important role. After the lower thermosphere has ben heated, the process, in whichthere is an increasing of N F2 due to the lift of the F-layer and it is followed by a decreasing of N F2caused by the atmosphere with higher ratio of molecule to atom lifting from the lower thermospher,may expand along with the disturbed flow of the neutral atmosphere to the mid-and low-latitudeionosphere.In this stage the ionospheric disturbance dynamo generated by the disturbed thermosPheric circulation drives an anti-Sq electric current system,the flux of which is westward in the low-latitude ionosphere- Since the fountain phenomenon of the equatorial anomaly of N.F2 caused by the eastwardequatorial electrojet is suppressed by the disturbed current, the variation of N in the crest of the equatorial anomaly is much more evident.The simultaneous arising of hmF is often observed in a station chain of ground ionosondes. It ispossible that a significant enhancement of the region 2 field-a1igned current, or the northward turningof IMF, or both of them together, are all responsible for the hmF lift.