Journal cover Journal topic
Annales Geophysicae Sun, Earth, planets, and planetary systems An interactive open-access journal of the European Geosciences Union
Ann. Geophys., 26, 2435-2447, 2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.
11 Aug 2008
An optical study of multiple NEIAL events driven by low energy electron precipitation
J. M. Sullivan1, M. Lockwood1,2, B. S. Lanchester1, E. P. Kontar3, N. Ivchenko4, H. Dahlgren4, and D. K. Whiter1 1School of Physics and Astronomy, University of Southampton, UK
2Rutherford Appleton Laboratory, Didcot, Oxfordshire, UK
3Department of Physics and Astronomy, University of Glasgow, UK
4Space and Plasma Physics, School of Electrical Engineering, KTH, Stockholm, Sweden
Abstract. Optical data are compared with EISCAT radar observations of multiple Naturally Enhanced Ion-Acoustic Line (NEIAL) events in the dayside cusp. This study uses narrow field of view cameras to observe small-scale, short-lived auroral features. Using multiple-wavelength optical observations, a direct link between NEIAL occurrences and low energy (about 100 eV) optical emissions is shown. This is consistent with the Langmuir wave decay interpretation of NEIALs being driven by streams of low-energy electrons. Modelling work connected with this study shows that, for the measured ionospheric conditions and precipitation characteristics, growth of unstable Langmuir (electron plasma) waves can occur, which decay into ion-acoustic wave modes. The link with low energy optical emissions shown here, will enable future studies of the shape, extent, lifetime, grouping and motions of NEIALs.

Citation: Sullivan, J. M., Lockwood, M., Lanchester, B. S., Kontar, E. P., Ivchenko, N., Dahlgren, H., and Whiter, D. K.: An optical study of multiple NEIAL events driven by low energy electron precipitation, Ann. Geophys., 26, 2435-2447,, 2008.
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