High-Latitude F-Region Irregularities: A Review and Synthesis

摘要

The most intense, F region irregularities in the high latitude ionosphere appear to be produced by convective plasma processes, and in particular, the fluid E x B (gradient drift) interchange instability. Irregularities are produced by convectively mixing plasma across a mean plasma density gradient. The transport of higher-density plasma into regions of lower density plasma (and vice versa) leads to the development of an irregularity spectrum that extends in scale from about 10 km down to the ion gyroradius. Because irregularities with this range of scales are not independent from larger scale plasma structures that are produced by other means, the characteristics and processes of > 10 km plasma structure are reviewed and related to those of smaller scale irregularities. For the large scale plasma processes, the model includes (1) the formation of 1000 km scale patches in the polar cap from solar-produced plasma that is transported poleward from lower latitudes; (2) the reconfiguration of patches as they convect into the auroral region and become the latitudinally confined but longitudinally extended, plasma-density enhancements near the equatorward auroral boundary; and (3) the production of localized enhancements and depletions along the poleward auroral boundary by soft-particle precipitation and large but localized electric fields. In the model, the most intense, smaller-scale irregularities fields. (jhd)