磁暴期内夜间h’F的突增现象

ON THE NIGHTTIME SUDDEN ENHANCEMENT OF h' F DURING MAGNETIC STORMS

用3个经度链上电离层垂测站资料分析磁暴时夜间h＇F的同时突增现象提出了电动耦合在夜间出现东向电场从而使F层抬升的物理机制同时也解释了突增现象在午夜后更多，且增幅更强的事实．

The simultaneously sudden enhancements of h' F at nighttime during magneticstorms are analyzed by using ionosonde data from stations distributed nearby 3meridian chains. The related physical mechanism is proposed. Generally, the effects ofthe magnetospheric convection and the driving potential across the polar cap (or theregion 1 field-aligned current) during a magnetic storm will lead to a westwardelectric field, but not an eastward one. On the other hand, the shielding effect of theregion 2 field-aligned current may confine the disturbed field within the auroral oveland weaken its influence in lower latitude area. Since the region 1 field--alignedcurrent is usually stronger than the region 2 current the westward electric field cannot be reversed eastward. The turning of the interplanetary magnetic field (IMF) fromsouthward to northward is equivalent to shutting off the driving potential across thepolar cap. If the region 2 field--aligned current strengthens during an IMF turning, theappearance of an eastward field at nighttime is possible, and the drift E×B effectwill lift the F--region obviously. With this mechanism, it is also easy to be understoodwhy the enhancement occurs more frequently and is more intensive in themidnight--dawn sector.