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Ann. Geophys., 25, 1323-1336, 2007
www.ann-geophys.net/25/1323/2007/
© European Geosciences Union 2007
Particle precipitations during NEIAL events: simultaneous ground based observations at Svalbard
J. Lunde1,*, B. Gustavsson1, U. P. Løvhaug1, D. A. Lorentzen2, and Y. Ogawa3
1Department of Physics, University of Tromsø, Tromsø, Norway
2Geophysics Department, University Centre on Svalbard, Longyearbyen, Svalbard
3National Institute of Polar Research, Tokyo, Japan
*now at: Solar Terrestrial Environment Laboratory, Nagoya University, Japan
Abstract. In this paper we present Naturally Enhanced Ion Acoustic Lines (NEIALs)
observed with the EISCAT Svalbard Radar (ESR). For the first time, long
sequences of NEIALs are recorded, with more than 50 events within an hour,
ranging from 6.4 to 140 s in duration. The events took place from
~08:45 to 10:00 UT, 22 January 2004. We combine ESR data with
observations of optical aurora by a meridian scanning photometer at
wavelengths 557.7, 630.0, 427.8, and 844.6 nm, as well as records from a
magnetometer and an imaging riometer. The large numbers of observed NEIALs
together with these additional observations, enable us to characterise the
particle precipitation during the NEIAL events. We find that the intensities
in all optical lines studied must be above a certain level for the NEIALs to
appear. We also find that the soft particle precipitation is associated with
the down-shifted shoulder in the incoherent scatter spectrum, and that
harder precipitation may play a role in the enhancement of the up-shifted
shoulder. The minimum energy flux during NEIAL events found in this study
was ~3.5 mW/m2 and minimum characteristic energy around 50 eV.
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