ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-26-2871-2008 On a new process for cusp irregularity production Carlson H. C. 1 2 Oksavik K. 3 Moen J. 1 Department of Physics, University of Oslo, Oslo, Norway Utah State University, CASS, Logan, UT, USA Arctic Geophysics, The University Centre in Svalbard, Longyearbyen, Norway 23 09 2008 26 9 2871 2885 Copyright: © 2008 H. C. Carlson et al. 2008 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/26/2871/2008/angeo-26-2871-2008.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/26/2871/2008/angeo-26-2871-2008.pdf

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.

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