TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 64 (No. 6), pp. 459-465, 2012

Polar cap ionosphere and thermosphere during the solar minimum period: EISCAT Svalbard radar observations and GCM simulations

Hitoshi Fujiwara1,2, Satonori Nozawa3, Sawako Maeda4, Yasunobu Ogawa5, Yasunobu Miyoshi6, Hidekatsu Jin7, Hiroyuki Shinagawa7, and Kaori Terada1

1Department of Geophysics, Tohoku University, Sendai, Japan
2Faculty of Science and Technology, Seikei University, Japan
3Solar Terrestrial Environment Laboratory, Nagoya University, Nagoya, Japan
4Kyoto Women's University, Kyoto, Japan
5National Institute of Polar Research, Tokyo, Japan
6Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan
7National Institute of Communication Technology, Tokyo, Japan

(Received June 2, 2010; Revised February 14, 2011; Accepted May 6, 2011; Online published July 27, 2012)

Abstract: The IPY long-run data were obtained from the European Incoherent Scatter Svalbard radar (ESR) observations during March 2007 and February 2008. Since the solar and geomagnetic activities were quite low during the period, this data set is extremely helpful for describing the basic states (ground states) of the thermosphere and ionosphere in the polar cap region. The monthly-averaged ion temperatures for 12 months show similar local time (or UT) variations to each other. The ion temperatures also show significant seasonal variations. The amplitudes of the local time and seasonal variations observed are much larger than the ones predicted by the IRI-2007 model. In addition, we performed numerical simulations with a general circulation model (GCM), which covers all the atmospheric regions, to investigate variations of the neutrals in the polar thermosphere. The GCM simulations show significant variations of the neutral temperature in the polar region in comparison with the NRLMSISE-00 empirical model. These results indicate that both the ions and neutrals would show larger variations than those described by the empirical models, suggesting significant heat sources in the polar cap region even under solar minimum and geomagnetically quiet conditions.
Key words: Polar cap, ionosphere, thermosphere, EISCAT radar, GCM, simulation, IPY, solar minimum.

Corresponding author E-mail: h_fujiwara@st.seikei.ac.jp

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