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The Long‐Term Trend of Thermospheric Compositions From Whole Atmospheric Simulation and Satellite Observation.

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Title: The Long‐Term Trend of Thermospheric Compositions From Whole Atmospheric Simulation and Satellite Observation.
Authors: Hsu, Chih‐Ting1 (AUTHOR) chihting@ucar.edu, Wang, Wenbin1 (AUTHOR), Qian, Liying1 (AUTHOR), Aa, Ercha2 (AUTHOR), Mclnerney, Joseph M.1 (AUTHOR), Zhang, Shun‐Rong2 (AUTHOR), Zhang, Yongliang3 (AUTHOR), Newheart, Anastasia4 (AUTHOR), Lin, Dong1,5 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. Oct2025, Vol. 130 Issue 10, p1-13. 13p.
Subject Terms: *Oxygen, *Greenhouse gases, *Nitrogen compounds, Remote sensing, Atmospheric composition, Atmospheric models
Company/Entity: National Center for Atmospheric Research (U.S.)
Abstract: This study examines the long‐term trend of column‐integrated atomic oxygen to molecular nitrogen ratio, ΣO/N2 ${\Sigma }O/{N}_{2}$, in the upper atmosphere and investigates the cause of this long‐term trend in ΣO/N2 ${\Sigma }O/{N}_{2}$. We first validate the feasibility of using a physics‐based model for a long‐term climate reanalysis by applying a model‐data comparison between 2002 and 2018. ΣO/N2 ${\Sigma }O/{N}_{2}$ simulated by NSF NCAR's Whole Atmosphere Community Climate Model (WACCM) with thermosphere and ionosphere extension (WACCM‐X) and measured by Global Ultraviolet Imager (GUVI) aboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission is used to determine the long‐term trend of ΣO/N2 ${\Sigma }O/{N}_{2}$ from 2002 to 2018 and validate the model result. The model and data show good agreement after removing the impact of solar irradiance and geomagnetic activity using a least‐squares fitting method, revealing a decreasing trend of ΣO/N2 ${\Sigma }O/{N}_{2}$ of about −0.54% ${-}0.54\%$ per decade relative to the ΣO/N2 ${\Sigma }O/{N}_{2}$ in 2018 in the model and about −0.45% ${-}0.45\%$ per decade in data along the satellite orbit during the period between 2002 and 2018. A decreasing trend of global ΣO/N2 ${\Sigma }O/{N}_{2}$ of about −0.70% ${-}0.70\%$ per decade is found in the model between 1960 and 2018. After that, four WACCM‐X long‐term simulations are performed from 1960 to 2018 to identify the cause of the decreasing trend of ΣO/N2 ${\Sigma }O/{N}_{2}$. The results show that this decreasing trend is mainly caused by the increase in greenhouse gas concentrations. Plain Language Summary: One of the challenges in studying climate change and long‐term trends in the thermosphere and ionosphere is the limited availability of long‐term data. A long‐term simulation of the whole atmosphere can help mitigate this problem. This paper focuses on the long‐term trend of the column‐integrated atomic oxygen to molecular nitrogen ratio, ΣO/N2 ${\Sigma }O/{N}_{2}$. NSF NCAR's Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X) is applied to simulate the long‐term trend of ΣO/N2 ${\Sigma }O/{N}_{2}$ between 1960 and 2018. We first compare the ΣO/N2 ${\Sigma }O/{N}_{2}$ trend from WACCM‐X with that from Global Ultraviolet Imager (GUVI) aboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics mission after 2002 to validate the simulation results in representing climate change in the upper atmosphere. We find good agreement between the long‐term trend of ΣO/N2 ${\Sigma }O/{N}_{2}$ from WACCM‐X and GUVI data. After that, four WACCM‐X simulations with different forcing conditions are performed to investigate the possible cause of the long‐term trend of ΣO/N2 ${\Sigma }O/{N}_{2}$. A decreasing trend of global ΣO/N2 ${\Sigma }O/{N}_{2}$ with ∼−0.7% ${\sim} -0.7\%$ per decade relative to ΣO/N2 ${\Sigma }O/{N}_{2}$ in 2018 is found in all simulation results. By comparing the simulation results, we identify that the major cause of the decreasing trend of thermospheric ΣO/N2 ${\Sigma }O/{N}_{2}$ is the increase in greenhouse gases over the past decades. Key Points: ΣO/N2 ${\Sigma }O/{N}_{2}$ from long‐term WACCM‐X simulation (1960–2018) is compared with Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)/Global Ultraviolet Imager (GUVI) ΣO/N2 ${\Sigma }O/{N}_{2}$ collected between 2002 and 2018A decreasing trend of ΣO/N2 ${\Sigma }O/{N}_{2}$ is found in both TIMED/GUVI (−0.45% ${-}0.45\%$ per decade) and WACCM‐X ΣO/N2 ${\Sigma }O/{N}_{2}$ (−0.54% ${-}0.54\%$ per decade)Numerical simulations demonstrate that the decreasing trend of ΣO/N2 ${\Sigma }O/{N}_{2}$ is mainly contributed to by the increase in greenhouse gas [ABSTRACT FROM AUTHOR]
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Abstract:This study examines the long‐term trend of column‐integrated atomic oxygen to molecular nitrogen ratio, ΣO/N2 ${\Sigma }O/{N}_{2}$, in the upper atmosphere and investigates the cause of this long‐term trend in ΣO/N2 ${\Sigma }O/{N}_{2}$. We first validate the feasibility of using a physics‐based model for a long‐term climate reanalysis by applying a model‐data comparison between 2002 and 2018. ΣO/N2 ${\Sigma }O/{N}_{2}$ simulated by NSF NCAR's Whole Atmosphere Community Climate Model (WACCM) with thermosphere and ionosphere extension (WACCM‐X) and measured by Global Ultraviolet Imager (GUVI) aboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission is used to determine the long‐term trend of ΣO/N2 ${\Sigma }O/{N}_{2}$ from 2002 to 2018 and validate the model result. The model and data show good agreement after removing the impact of solar irradiance and geomagnetic activity using a least‐squares fitting method, revealing a decreasing trend of ΣO/N2 ${\Sigma }O/{N}_{2}$ of about −0.54% ${-}0.54\%$ per decade relative to the ΣO/N2 ${\Sigma }O/{N}_{2}$ in 2018 in the model and about −0.45% ${-}0.45\%$ per decade in data along the satellite orbit during the period between 2002 and 2018. A decreasing trend of global ΣO/N2 ${\Sigma }O/{N}_{2}$ of about −0.70% ${-}0.70\%$ per decade is found in the model between 1960 and 2018. After that, four WACCM‐X long‐term simulations are performed from 1960 to 2018 to identify the cause of the decreasing trend of ΣO/N2 ${\Sigma }O/{N}_{2}$. The results show that this decreasing trend is mainly caused by the increase in greenhouse gas concentrations. Plain Language Summary: One of the challenges in studying climate change and long‐term trends in the thermosphere and ionosphere is the limited availability of long‐term data. A long‐term simulation of the whole atmosphere can help mitigate this problem. This paper focuses on the long‐term trend of the column‐integrated atomic oxygen to molecular nitrogen ratio, ΣO/N2 ${\Sigma }O/{N}_{2}$. NSF NCAR's Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X) is applied to simulate the long‐term trend of ΣO/N2 ${\Sigma }O/{N}_{2}$ between 1960 and 2018. We first compare the ΣO/N2 ${\Sigma }O/{N}_{2}$ trend from WACCM‐X with that from Global Ultraviolet Imager (GUVI) aboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics mission after 2002 to validate the simulation results in representing climate change in the upper atmosphere. We find good agreement between the long‐term trend of ΣO/N2 ${\Sigma }O/{N}_{2}$ from WACCM‐X and GUVI data. After that, four WACCM‐X simulations with different forcing conditions are performed to investigate the possible cause of the long‐term trend of ΣO/N2 ${\Sigma }O/{N}_{2}$. A decreasing trend of global ΣO/N2 ${\Sigma }O/{N}_{2}$ with ∼−0.7% ${\sim} -0.7\%$ per decade relative to ΣO/N2 ${\Sigma }O/{N}_{2}$ in 2018 is found in all simulation results. By comparing the simulation results, we identify that the major cause of the decreasing trend of thermospheric ΣO/N2 ${\Sigma }O/{N}_{2}$ is the increase in greenhouse gases over the past decades. Key Points: ΣO/N2 ${\Sigma }O/{N}_{2}$ from long‐term WACCM‐X simulation (1960–2018) is compared with Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)/Global Ultraviolet Imager (GUVI) ΣO/N2 ${\Sigma }O/{N}_{2}$ collected between 2002 and 2018A decreasing trend of ΣO/N2 ${\Sigma }O/{N}_{2}$ is found in both TIMED/GUVI (−0.45% ${-}0.45\%$ per decade) and WACCM‐X ΣO/N2 ${\Sigma }O/{N}_{2}$ (−0.54% ${-}0.54\%$ per decade)Numerical simulations demonstrate that the decreasing trend of ΣO/N2 ${\Sigma }O/{N}_{2}$ is mainly contributed to by the increase in greenhouse gas [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2025JA034285