Polar Cap Science: Plasma Structuring

Abstract

The polar cap ionosphere is a highly dynamic and structured environment. It is frequently populated with polar cap patches and other mesoscale density structures which, through a number of plasma instability mechanism, can drive the development of smaller-scale structures throughout the region. Here, we discuss the current knowledge of how structured polar cap plasma is and the processes that drive this structuring on a range of scales. We emphasize that much is still unknown about exactly how prevalent small-scale structures are and the factors that drive their formation. Mesoscale structures such as polar cap patches have been studied for decades, but we do not have the ability to predict them accurately, and their impact on the larger geospace system is not well quantified. Continued investment in polar infrastructure is needed to advance many open questions.