[P-EM16] Physics and Chemistry in the Atmosphere and Ionosphere

[PEM16-03] Spatial distribution of the polar thermospheric wind acceleration and importance of the 2D measurement

*Shin-ichiro Oyama^1,2,3, Anita Aikio², Mark G Conde⁴, Heikki Vanhamaki², Ilkka Virtanen², Thomas Ulich⁵, Urban Brandstrom⁶, Pekka Verronen⁷, Monika Andersson⁷, Niilo Kalakoski⁷, Lassi Roininen⁸, Sari Lasanen⁸, Abiyot Workayehu², Kazuo Shiokawa¹, Heqiucen XU¹, Mamoru Ishii⁹, Masafumi Hirahara¹, Takeshi Sakanoi¹⁰, Masato Kagitani¹⁰, Juha Sorri⁵, Tomi Teppo⁵, Yoshimasa Tanaka³, Christopher Fallen⁴, Brenton J Watkins⁴, Mikko Orispaa⁵, Yasunobu Ogawa³, Lei Cai¹¹, Esa Turunen⁵, Kirsti Kauristie⁷, Takuo T. Tsuda¹², Junichi Kurihara¹³ (1.Institute for Space-Earth Environmental Research, Nagoya University, Japan, 2.University of Oulu, Finland, 3.National Institute of Polar Research, Japan, 4.Geophysical Institute, University of Alaska Fairbanks, US, 5.Sodankyla Geophysical Observatory, University of Oulu, Finland, 6.The Swedish Institute of Space Physics (IRF), Sweden, 7.Finnish Meteorological Institute, Finland, 8.Lappeenranta-Lahti University of Technology, Finland, 9.National Institute of Information and Communications Technology, Japan, 10.Tohoku University, Japan, 11.KTH Royal Institute of Technology, Sweden, 12.The University of Electro-Communications, 13.Hokkaido University)

Keywords:aurora, substorm, Thermosphere, Ionosphere

Understanding the flow of energy and mass throughout the magnetosphere-ionosphere-thermosphere coupled system is a fundamental goal of solar-terrestrial physics. Since substantial energy accumulated in the substorm growth phase in the magnetospheric tail flows into the polar ionosphere immediately after the substorm onset, investigating the energy dissipation process at high latitudes around the time of substorm onset can contribute significantly to achieving that objective. The energy dissipation generates acceleration and heating of the ionosphere and thermosphere, but this might occur not only near aurora but also far from it by hundreds kilometers equatorward. We analyzed ionospheric and thermospheric measurements in the northern Scandinavian area (65-80 N) during periods of considerably low geomagnetic activity but with some aurorae above Svalbard (75-80 N). Thermospheric winds measured with a Fabry-Perot interferometer (FPI; 630.0 nm) at Tromsø, Norway (69.6 N) showed westward accelerations coinciding with auroral brightening at the Svalbard area at the dusk sector though the relative distance from Tromsø to the aurora was 200-500 km in some cases. Moving into the dawn sector with the earth’s rotation, the acceleration direction turned to southeastward through stagnation area or period seen at magnetic local midnight. The acceleration pattern well represents thermospheric responses to the ionospheric convection, but of particular interest is its location, in which the thermospheric wind have been obtained at the sub-auroral region far from the main auroral oval. In this analysis, we cannot infer to horizontal patterns of the wind acceleration because we have only a point measurement from the Tromsø FPI. While this result suggests the importance of two-dimensional measurements of ionosphere and the thermosphere, we need a new configuration of the observation network to infer horizontal winds and accelerations. In this presentation, we will introduce “SDI-3D” project, which aims at developing 3 Scanning Doppler Imagers (SDIs) and deploying them at the same area as for the EISCAT_3D, which may start in operation in 2022.