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Ann. Geophys., 26, 1057-1069, 2008
www.ann-geophys.net/26/1057/2008/
© European Geosciences Union 2008
Summer sudden Na number density enhancements measured with the ALOMAR Weber Na Lidar
D. Heinrich1, H. Nesse1, U. Blum1,*, P. Acott2, B. Williams3, and U.-P. Hoppe1
1Norwegian Defence Research Establishment (FFI), 2027 Kjeller, Norway
2Department of Physics, Colorado State University, Fort Collins CO 80523-1875, USA
3NorthWest Research Associates, Colorado Research Associates division, Boulder, CO 80301, USA
*now at: Fraunhofer-Institute for Technological Trend Analysis, Euskirchen, Germany
Abstract. We present summer Na-densities and atmospheric temperatures measured 80 to
110 km above the Arctic Lidar Observatory for Middle Atmosphere Research
(ALOMAR). The Weber Na Lidar is part of ALOMAR, located at 69° N in
Norway, 150 km north of the Arctic Circle. The sun does not set here during
the summer months, and measurements require a narrowband Faraday Anomalous
Dispersion Optical Filter (FADOF).
We discuss an observed sudden enhancement in the Na number density around 22:00 UT
on 1 to 2 June 2006. We compare this observation with previous summer
measurements and find a frequent appearance of Na number density
enhancements near local midnight. We describe the time of appearance, the
altitude distribution, the duration and the strength of these enhancements
and compare them to winter observations. We investigate possible formation
mechanisms and, as others before, we find a strong link between these Na
number density enhancements and sporadic E layers.
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