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Finding the Magnetopause Standoff Distance Using Soft X‐Ray Images: Application for the SMILE Mission.

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Title: Finding the Magnetopause Standoff Distance Using Soft X‐Ray Images: Application for the SMILE Mission.
Authors: Samsonov, Andrey1 (AUTHOR) a.samsonov@ucl.ac.uk, Carter, Jennifer Alyson2 (AUTHOR), Sembay, Steven2 (AUTHOR), Read, Andrew2 (AUTHOR), Forsyth, Colin1 (AUTHOR), Wharton, Samuel2 (AUTHOR), Escoubet, Philippe3 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. Feb2026, Vol. 131 Issue 2, p1-17. 17p.
Subject Terms: Magnetopause, Soft X rays, Magnetosphere, Plasma interactions, Space sciences, X-ray imaging, Plasma magnetism
Abstract: Soft X‐rays are emitted in the magnetosheath and cusps because of solar wind charge exchange. The soft X‐ray Imager (SXI) on board Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) will measure these X‐rays. We developed a new method for finding the magnetopause standoff distance from simulations that reproduce the expected X‐ray images using software developed by the SXI instrument team. We consider three points near the SMILE apogee. We apply this method to a three‐hour interval with an interplanetary shock and a southward interplanetary magnetic field turning when the magnetosphere was moderately compressed. The results show that the magnetopause position can be reconstructed with an accuracy better than 0.5 RE ${R}_{E}$ for a five‐minute integration time, which matches the SMILE scientific requirements. Moreover, we can even determine the magnetopause position using one‐minute integration when the magnetosphere is strongly compressed and the spacecraft's position and SXI's orientation are favorable for magnetopause observations. Plain Language Summary: The magnetopause marks the three‐dimensional boundary between the solar wind with the embedded interplanetary magnetic field and the Earth's magnetosphere. The imminent Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) will observe the magnetopause from a distant vantage point, using its Soft X‐ray Imager (SXI) camera, by detecting X‐rays emitted in the vicinity of Earth through interactions between the solar wind and exosphere hydrogen. This will allow for long‐term monitoring of the dynamics and shape of this boundary as it responds to changing upstream solar wind conditions. Preparations for SMILE have a strong focus on reconstructing the three‐dimensional magnetopause from the two‐dimensional SXI images. A critical parameter is the magnetopause standoff distance along the Earth‐Sun line. In this paper, we present a method to find the standoff distance using simulations developed by the SXI instrument team. We have tested this method under various solar wind input conditions, including for times when the magnetopause is pushed considerably Earthward. We can locate the magnetopause with an accuracy better than 3,200 km for SXI exposure times of 5 min or less, in the case of strong solar wind dynamic pressure. Key Points: We describe a new method for finding the magnetopause position from soft X‐ray imagesThe magnetopause position can be reconstructed with an accuracy better than 0.5 RE ${R}_{E}$ for a five‐minute integration timeThe magnetopause position can be found using one‐minute integration for a strong magnetospheric compression [ABSTRACT FROM AUTHOR]
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Abstract:Soft X‐rays are emitted in the magnetosheath and cusps because of solar wind charge exchange. The soft X‐ray Imager (SXI) on board Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) will measure these X‐rays. We developed a new method for finding the magnetopause standoff distance from simulations that reproduce the expected X‐ray images using software developed by the SXI instrument team. We consider three points near the SMILE apogee. We apply this method to a three‐hour interval with an interplanetary shock and a southward interplanetary magnetic field turning when the magnetosphere was moderately compressed. The results show that the magnetopause position can be reconstructed with an accuracy better than 0.5 RE ${R}_{E}$ for a five‐minute integration time, which matches the SMILE scientific requirements. Moreover, we can even determine the magnetopause position using one‐minute integration when the magnetosphere is strongly compressed and the spacecraft's position and SXI's orientation are favorable for magnetopause observations. Plain Language Summary: The magnetopause marks the three‐dimensional boundary between the solar wind with the embedded interplanetary magnetic field and the Earth's magnetosphere. The imminent Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) will observe the magnetopause from a distant vantage point, using its Soft X‐ray Imager (SXI) camera, by detecting X‐rays emitted in the vicinity of Earth through interactions between the solar wind and exosphere hydrogen. This will allow for long‐term monitoring of the dynamics and shape of this boundary as it responds to changing upstream solar wind conditions. Preparations for SMILE have a strong focus on reconstructing the three‐dimensional magnetopause from the two‐dimensional SXI images. A critical parameter is the magnetopause standoff distance along the Earth‐Sun line. In this paper, we present a method to find the standoff distance using simulations developed by the SXI instrument team. We have tested this method under various solar wind input conditions, including for times when the magnetopause is pushed considerably Earthward. We can locate the magnetopause with an accuracy better than 3,200 km for SXI exposure times of 5 min or less, in the case of strong solar wind dynamic pressure. Key Points: We describe a new method for finding the magnetopause position from soft X‐ray imagesThe magnetopause position can be reconstructed with an accuracy better than 0.5 RE ${R}_{E}$ for a five‐minute integration timeThe magnetopause position can be found using one‐minute integration for a strong magnetospheric compression [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2025JA034787