Earth Planets Space, Vol. 58 (No. 9), pp. 1183-1191, 2006
S. Nozawa1, Y. Ogawa1, A. Brekke2, T. Tsuda1, C. M. Hall2, H. Miyaoka3, J. Kurihara4, T. Abe4, and R. Fujii1
1Solar-Terrestrial Environment Laboratory, Nagoya University, Japan
2Faculty of Science, University of Tromsø, Norway
3National Institute Polar Research, Japan
4Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Japan
(Received January 16, 2006; Revised May 2, 2006; Accepted May 15, 2006; Online published September 29, 2006)
This paper aims at describing the ionospheric conditions during the DELTA (Dynamics and Energetics of the Lower Thermosphere in Aurora) campaign period based on EISCAT radar observations conducted at Tromsø (69.6°N, 19.2°E). We conducted EISCAT UHF radar observations on December 5 and from December 8 to December 13, 2004 with a beam-scanning mode for a total of 74 hours. Except for December 8 during a 2 hr interval operation, we operated the EISCAT UHF radar for 12 hour intervals everyday to make it possible to derive semidiurnal tidal amplitudes and phases in the lower thermosphere. Observed electron densities and derived electric fields by the EISCAT UHF radar indicate that magnetospheric activity was high during the period from December 5 to 13 except for the night of December 13. Derived semidiurnal amplitudes during December 9-12, 2004 exhibited a day to day variation at and below 110 km, while the corresponding phase was relatively stable over the four days except for the zonal component on December 12. Neutral and electron temperatures measured by the DELTA rocket were compared with neutral/ion and electron temperatures from the EISCAT UHF radar observations. Comparison of neutral/ion temperatures show some agreement, while poor agreements were found for the electron temperature. Possible causes of the discrepancy are discussed.
Key words: EISCAT, Tromsø, day-to-day variability, semidiurnal tide, neutral temperature, electron temperature.