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  1. Abstract

    It is well‐known that solar eclipses can significantly impact the ionosphere and thermosphere, but how an eclipse influences the magnetosphere‐ionosphere system is still unknown. Using a coupled magnetosphere‐ionosphere‐thermosphere model, we examined the impact on geospace of the northern polar‐region eclipse that occurred on June 10, 2021. The simulations reveal that the eclipse‐induced reduction in polar ionospheric conductivity causes large changes in field‐aligned current, cross‐polar cap potential and auroral activity. While such effects are expected in the northern hemisphere where solar obscuration occurred, they also occurred in the southern hemisphere through electrodynamic coupling. Eclipse‐induced changes in monoenergetic auroral precipitation differ significantly between the northern hemisphere and southern hemisphere while diffuse auroral precipitation is interhemispherically symmetric. This study demonstrates that the geospace response to a polar‐region solar eclipse is not limited just to the eclipse region but has global implications.

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  2. Abstract

    Previous work suggested that the peak response time of the mass densities of atomic oxygen (O) and molecular nitrogen (N2) in the thermosphere had more than a 1‐day difference relative to the peak of the 27‐day periodic variation of solar extreme ultraviolet (EUV) flux. In this study, we used the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) to explore the physical mechanisms responsible for the different peak response times of the daytime thermospheric neutral species. It was found that the peak response time of O or N2mass density corresponds to the time of equilibrium between the contributions from the barometric effect and the change in its abundance. The peak response time of O is shorter than that of thermospheric temperature Tn, due to a dynamic change in the circulation that acts to cancel out the contribution from the barometric process prior to the peak of Tn. On the contrary, the change of N2abundance contributes further to a decrease of N2mass density on a constant pressure surface when the thermosphere is expanding. The change of chemical loss leads to a longer peak response time of N2abundance than that due to barometric motion. Therefore, an equilibrium is reached after the barometric effect turns from expansion (contraction) to contraction (expansion), so that the peak response time of N2is longer than that of Tn. Moreover, the meridional circulation in the thermosphere modulates the latitudinal dependence of the peak response time of thermospheric neutral species.

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