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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 5 | Copyright
Ann. Geophys., 36, 1471-1481, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 26 Oct 2018

Regular paper | 26 Oct 2018

Variations of the 630.0 nm airglow emission with meridional neutral wind and neutral temperature around midnight

Chih-Yu Chiang1, Sunny Wing-Yee Tam1, and Tzu-Fang Chang1,2 Chih-Yu Chiang et al.
  • 1Institute of Space and Plasma Sciences, National Cheng Kung University, Tainan 70101, Taiwan
  • 2Institute for Space-Earth Environmental Research, Nagoya University, Nagoya 464-8601, Japan

Abstract. The ISUAL payload onboard the FORMOSAT-2 satellite has often observed airglow bright spots around midnight at equatorial latitudes. Such features had been suggested as the signature of the thermospheric midnight temperature maximum (MTM) effect, which was associated with temperature and meridional neutral winds. This study investigates the influence of neutral temperature and meridional neutral wind on the volume emission rates of the 630.0nm nightglow. We utilize the SAMI2 model to simulate the charged and neutral species at the 630.0nm nightglow emission layer under different temperatures with and without the effect of neutral wind. The results show that the neutral wind is more efficient than temperature variation in affecting the nightglow emission rates. For example, based on our estimation, it would require a temperature change of 145K to produce a change in the integrated emission rate by 9.8km-photonscm−3s−1, while it only needs the neutral wind velocity to change by 1.85m−1s−1 to cause the same change in the integrated emission rate. However, the emission rate features a local maximum in its variation with the temperature. Two kinds of tendencies can be seen regarding the temperature that corresponds to the turning point, which is named the turning temperature (Tt) in this study: firstly, Tt decreases with the emission rate for the same altitude; secondly, for approximately the same emission rate, Tt increases with the altitude.

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Short summary
Based on our simulation results, both temperature change and meridional neutral wind could cause the 630.0 nm nightglow intensity to vary, while the latter is more effective. An unexpected aspect of the results is the non-monotonic dependence of the emission rate on temperature, featuring a turning point as the temperature changes. Our findings of these turning temperature tendencies can guide future modeling attempts to match the observed nightglow brightness intensities.
Based on our simulation results, both temperature change and meridional neutral wind could cause...