Physical Processes of Meso-Scale, Dynamic Auroral Forms
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Physical Processes of Meso-Scale, Dynamic Auroral Forms C. Forsyth1 · V.A. Sergeev2 · M.G. Henderson3 · Y. Nishimura4 · B. Gallardo-Lacourt5,6
Received: 29 April 2019 / Accepted: 28 March 2020 © The Author(s) 2020
Abstract Meso-scale auroral forms, such as poleward boundary intensifications, streamers, omega bands, beads and giant undulations, are manifestations of dynamic processes in the magnetosphere driven, to a large part, by plasma instabilities in the magnetotail. New observations from ground- and space-based instrumentation and theoretical treatments are giving us a clearer view of some of the physical processes behind these auroral forms. However, questions remain as to how some of these observations should be interpreted, given uncertainties in mapping auroral features to locations in the magnetotatil and due to the significant overlap in the results from a variety of models of different plasma instabilities. We provide an overview of recent results in the field and seek to clarify some of the remaining questions with regards to what drives some of the largest and most dynamic auroral forms. Keywords Meso-scale aurora · Poleward boundary intensifications · Auroral streamers · Omega bands · Torches · Auroral beads · Giant undulations · Magnetic mapping · Magnetosphere ionosphere coupling · Plasma instabilities · Magnetotail
Auroral Physics Edited by David Knudsen, Joe Borovsky, Tomas Karlsson, Ryuho Kataoka and Noora Partmies
B C. Forsyth 1
UCL Mullard Space Science Laboratory, Dorking, Surrey, UK
2
St. Petersburg State University, St. Petersburg, Russia
3
Los Alamos National Laboratory, Los Alamos, NM, USA
4
Department of Electrical and Computer Engineering and Center for Space Physics, Boston University, Boston, MA, USA
5
Department of Physics and Astronomy, University of Calgary, Calgary, Canada
6
NASA Goddard Space Flight Center, Greenbelt, MD, USA
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1 Introduction Meso-scale dynamic auroral forms, with scale sizes of 10s to 100s of kilometres, were reported as distinct features in some of the earliest schematic diagrams of the auroral oval. Through combining observations from orbiting and ground-based imagers with in-situ measurements of the magnetosphere and remote sensing observations of the ionosphere, we have begun to understand the physical processes at the source of these auroral forms and, in some cases, the associated acceleration of particles into the ionosphere. This is coupled with a growing body of theoretical and modelling work to help understand the key physical processes that can give rise to localised enhancements of the aurora. However, mapping specific auroral features into a dynamic plasma environment that encompasses millions of cubic kilometres is not straightforward, leaving the coupling of ground and space-based observations open to interpretation. Furthermore, different theoretical and modelling frameworks give overlapping results that fit to various aspects of the observations meaning that the physical processes behind meso-s
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