On the development of folds in auroral arcs |
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| Institution: | 1. Photogrammetry and Remote Sensing, ETH Zurich, Zurich, Switzerland;2. Instituto de Telecomunicações, Instituto Superior Técnico, Universidade de Lisboa, Portugal;1. Institute of Physics, University of Graz, 8010 Graz, Austria;2. Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH 03824, USA;3. Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA;4. Department of Astronomy, University of Maryland, College Park, MD 20742, USA;5. Max-Planck-Institut für Sonnensystemforschung, 37077 Göttingen, Germany;6. Department of Physics, University of Helsinki, FI-00014 Helsinki, Finland;7. Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030, USA;8. Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA;9. RAL Space, United Kingdom Research and Innovation – Science & Technology Facilities Council, Harwell Campus, Oxfordshire, OX11 0QX, UK;10. Austrian Space Weather Office, GeoSphere Austria, 8020 Graz, Austria;11. Department of Meteorology, University of Reading, Reading RG6 6BB, UK;12. Institute of Atmospheric Physics, 14100 Prague 4, Czech Republic;13. Leibniz-Institut for Astrophysics Potsdam (AIP), 14482 Potsdam, Germany;14. Institute for Space-Earth Environmental Research, Nagoya University, Nagoya 464-8601, Japan;15. Center for Astrophysics and Space Sciences, University of California San Diego, La Jolla, CA 92093, USA;p. Predictive Science Inc., San Diego, CA 92121, USA;q. Radio Astronomy Centre, National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Tamil Nadu 643001, India;r. Arecibo Observatory, University of Central Florida, Arecibo, PR 00612, USA;s. Indian Institute of Astrophysics, Bengaluru 560034, India;t. Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France;u. IRAP, Université Toulouse III — Paul Sabatier, CNRS, CNES, 31028 Toulouse, France;v. Centre for mathematical Plasma Astrophysics (CmPA), KU Leuven, 3001 Leuven, Belgium;w. Solar–Terrestrial Centre of Excellence—SIDC, Royal Observatory of Belgium, 1180 Brussels, Belgium;x. Center for Space Plasma and Aeronomic Research, The University of Alabama in Huntsville, AL 35805, USA;y. CIRES, University of Colorado at Boulder, Boulder, CO 80309, USA;z. Narula Institute of Technology, Kolkata, West Bengal 700109, India;1. Department of Physics, GLA University, Mathura 281406, India;2. Department of Electronics and Communication Engineering, R. B. S. Engineering Technical Campus, Bichpuri, Agra 283105, India;1. Space Science Institute, School of Space and Environment, Beihang University, 100191, Beijing, China;2. Key Laboratory of Space Environment Monitoring and Information Processing, Ministry of Industry and Information Technology, China;3. State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, China;4. RAL_Space, STFC, Chilton, Oxfordshire, OX11 0QX, UK;5. Yunnan Observatory of Chinese Academy of Science, 650216, Yunnan, China;6. Department of Space Physics, Electronic Information School, Wuhan University, 430072, Wuhan, China;7. Sinosteel Tendering Co., LTD, No. 8, Haidian Street, Haidian District, Beijing, China |
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| Abstract: | The development of an auroral arc in the midnight sector, from diffuse to discrete with subsequent large scale folding, is studied with the aid of several ground-based observations, including incoherent scatter radar, and data from a HILAT satellite pass. Ion drift velocities in the F-region, as measured by EISCAT, were consistently eastward throughout and after the whole period of development, whilst the ion temperature showed two large enhancements just prior to the appearance of the main auroral fold. The fold moved eastwards and crossed the EISCAT antenna beam, appearing as a short-lived spike in electron density at altitudes between about 100 km and 400 km. The spike in electron density came progressively later at higher altitudes. The observations are interpreted as the result of enhanced convection in the ionosphere and in the magnetosphere. The auroral arc folding is suggested to be caused by the Kelvin-Helmholtz instability in a velocity shear zone in the magnetosphere. |
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