University of Oulu

Oyama, S., Hosokawa, K., Vanhamäki, H., Aikio, A., Sakanoi, T., Cai, L., et al. (2023). IMF dependence of midnight bifurcation in the thermospheric wind at an auroral latitude based on nine winter measurements in Tromsø, Norway. Geophysical Research Letters, 50, e2023GL104334.

IMF dependence of midnight bifurcation in the thermospheric wind at an auroral latitude based on nine winter measurements in Tromsø, Norway

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Author: Oyama, S.1,2; Hosokawa, K.3; Vanhamäki, H.4;
Organizations: 1Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Japan
2National Institute of Polar Research, Tokyo, Japan
3The University of Electro-Communications, Chofu, Japan
4Space Physics and Astronomy, University of Oulu, Oulu, Finland
5Graduate School of Science Planetary Plasma and Atmospheric Research Center, Tohoku University, Sendai, Japan
Format: article
Version: published version
Access: open
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Language: English
Published: American Geophysical Union, 2023
Publish Date: 2023-09-28


A thermospheric wind data set from a Fabry-Perot interferometer (630 nm) and the ion velocity from a Dynasonde in Tromsø, Norway, was analyzed for nine winter seasons to study the dynamics of the thermosphere and F-region ionosphere at an auroral latitude. This study focused on bifurcation in the zonal component of the neutral wind and ion velocity at midnight and its dependence on the Y component of the interplanetary magnetic field (IMF). Ionospheric plasma convection patterns are evidently imprinted on the thermospheric wind variations as aspects of the westward and eastward accelerations at dusk and late morning, respectively. The zonal wind bifurcates immediately before midnight for IMF By < 0, but for By > 0, it inverts gradually into the postmidnight sector. Neutral wind streams, originating from higher latitudes, may result in the dependence because of anti-sunward plasma flow distorted in the polar cap.

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Series: Geophysical research letters
ISSN: 0094-8276
ISSN-E: 1944-8007
ISSN-L: 0094-8276
Volume: 50
Issue: 14
Article number: e2023GL104334
DOI: 10.1029/2023GL104334
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This work was supported by JSPS KAKENHI JP 16H06286, 21H04518, 21K18651, 21KK0059, 22H01283, 22H00173, and 22K21345. H. V. was partially supported by Academy of Finland AF314664. This work was conducted by the joint research program of Planetary Plasma and Atmospheric Research Center, Tohoku University.
Academy of Finland Grant Number: 314664
Detailed Information: 314664 (Academy of Finland Funding decision)
Copyright information: © 2023. The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.