Abstract
Abstract. Two plasma instability mechanisms were thought until 2007 to dominate the formation of plasma irregularities in the F region high latitude and polar ionosphere; the gradient-drift driven instability, and the velocity-shear driven instability. The former mechanism was accepted as accounting for plasma structuring in polar cap patches, the latter for plasma structuring in polar cap sun aligned arcs. Recent work has established the need to replace this view of the past two decades with a new patch plasma structuring process (not a new mechanism), whereby shear-driven instabilities first rapidly structure the entering plasma, after which gradient drift instabilities build on these large "seed" irregularities. Correct modeling of cusp and early polar cap patch structuring will not be accomplished without allowing for this compound process. This compound process explains several previously unexplained characteristics of cusp and early polar cap patch irregularities. Here we introduce additional data, coincident in time and space, to extend that work to smaller irregularity scale sizes and relate it to the structured cusp current system.
Highlights
The plasma in the polar cap ionosphere is highly structured, and the nature of this structure and the phenomena leading to its structuring has been the focus of much research for the past few decades (Basu and Valladares, 1999)
We have reviewed how this has led to a new framework for interpreting cusp plasma and polar cap plasma structuring
We describe not a new cusp and polar cap plasma structuring mechanism, but a new process whereby known mechanisms apply and interact to produce new physical consequences
Summary
The plasma in the polar cap ionosphere is highly structured, and the nature of this structure and the phenomena leading to its structuring has been the focus of much research for the past few decades (Basu and Valladares, 1999). For the past twenty years this has led to active studies of what has come to be known as polar cap patches (Crowley, 1996) and polar cap arcs (Valladares and Carlson, 1991). The most intense structuring and scintillation occurs in polar cap patches. Their structuring has been a subject of intensive study (Basu and Valladares, 1999). Our primary focus in this work is to discuss the processes that structure the plasma in polar cap patches
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