[P-EM15] [EE] Study of coupling processes in solar-terrestrial system

[PEM15-P09] Anomalous ambipolar diffusion observed using meteor radars in northern high latitudes

*Masaki Tsutsumi¹, Yasunobu Ogawa¹, Satonori Nozawa², Chris Hall³ (1.National Institute of Polar Research, 2.Institute for Space-Earth Environmental Research, Nagoya University, 3.The Arctic University of Norway)

Keywords:ambipolar diffusion coefficient, meteor radars, polar mesosphere and lower thermosphere

Ambipolar diffusion coefficients are estimated through radar echo decay rates of ionized meteor trails. Information of neutral atmosphere temperature in the lower thermosphere can be further deduced from the ambipolar diffusion coefficient when electron and ion temperatures can be regarded the same with the neutral atmosphere temperature [e.g., Tsutsumi et al., 1994,1996; Hocking et al., 1999, 2004].
We found that the ambipolar diffusion in the polar mesopshere was sometimes anomalously enhanced in Arctic meteor radar observations. Comparison with collocated Na lidar and EISCAT radars in Tromsoe showed that such enhancements were not observed in neutral temperature field, and that enhanced electric field in the lower thermosphere seemed responsible for the anomalous ambipolar diffusion. This further indicates that meteor radar observations in polar regions have a potential to give a certain measure of electric field in the lower thermosphere and even the upper mesosphere, which is very difficult to observe without an incoherent scatter radar.