HR: 16:30h
AN: SA14A-03    [Abstracts]
TI: Ionospheric climatology deduced from long-term EISCAT UHF radar observations
AU: * Motoba, T
SA14A-03 AF: Graduate School of Environmental Studies, Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya, 464-8601 Japan
AU: Ogawa, Y
SA14A-03 AF: STEL, Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya, 464-8601 Japan
AU: Nozawa, S
SA14A-03 AF: STEL, Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya, 464-8601 Japan
AU: Fujii, R
SA14A-03 AF: STEL, Nagoya Univ., Furo-cho, Chikusa-ku, Nagoya, 464-8601 Japan
AB: Incoherent scatter radar is the most powerful ground-based instrument for the study of various ionospheric processes and can give the vertical profile of basic ionospheric parameters (electron density, electron temperature, and ion temperature). In this paper, we investigate ionospheric climatology and trends in the auroral zone using all available CP1 data taken by the EISCAT UHF radar at Tromsoe (69.6N, 19.2E) between 1984 and 2004. First, we present various variations of these parameters including diurnal, seasonal and altitude variations and the solar cycle under the quiet geomagnetic conditions. For the period of 1984-2004 it is found that time series of the peak electron density in the F2 region (NmF2) and its height (hmF2) around local noon (1000-1400 LT) is strongly influenced by solar activity (Ex., the hmF2 falls (rises) to about 230 km (350 km) at solar minima (maxima)). The diurnal variation of electron density in the altitude range of 275-325 km is primarily controlled by photoionization, and then reaching its maximum value near local noon and decaying away from there. Under the high solar activity level the electron temperature in the same altitude range is characterized by double peaks around 9 and 15 LT and by a lower temperature around noon in its diurnal variation. The electron temperature depression near noon results from the electron cooling. The ion temperature in the same altitude range tends to be lower compared with the electron temperature. In the diurnal variation the ion temperature is slightly higher in midnight at both low and high solar activity levels, which would be due to Joule heating in the midnight auroral zone. For seasonal variation, the well-known semiannual electron density variation, which is characterized by peaks at equinox and depression in summer, can be seen. The semiannual electron temperature changes in the F2 region are nearly opposite to the semiannual electron density changes. The ion temperature indicates a weak semiannual variation with equinoctial peaks. In addition to the ionospheric variations mentioned above, we will also discuss possible long-term trend of the F2-layer peak height over the last two decades.
DE: 2407 Auroral ionosphere (2704)
DE: 2427 Ionosphere/atmosphere interactions (0335)
DE: 2467 Plasma temperature and density
SC: SPA-Aeronomy [SA]
MN: Fall Meeting 2005