Preprints
https://doi.org/10.5194/egusphere-2025-3303
https://doi.org/10.5194/egusphere-2025-3303
15 Jul 2025
 | 15 Jul 2025

Impacts of Increasing CO2 on Diurnal Migrating Tide in the Equatorial Lower Thermosphere

Masaru Kogure, In-Sun Song, Huixin Liu, and Han-Li Liu

Abstract. We investigate impacts of increased CO2 concentration on migrate diurnal tide (DW1). A future climate simulation is conducted using a WACCM-X model, with surface CO2 levels increasing according to the RCP 8.5 scenario. The DW1 (1,1) mode, a propagating tide peaking near the equator, exhibits a positive trend of ~+1 % per decade in a range of 20–70 km, and a negative trend of ~-2 % per decade in a range of 90–110 km. The positive trend is likely driven by depression in atmospheric density in the mesosphere and enhanced equatorial convective activity, while the negative trend appears to result from increased eddy diffusion in the mesosphere, which overwhelms the positive trend. Two potential mechanisms may explain the negative trend. First, increasing CO2 enhances mesospheric stability, reducing tidal vertical wavelengths. In our simulation, equatorial temperatures around ~50–70 km become cooler than those in ~70–90 km. This strong cooling could be linked to CO2 mixing and transport, as well as the contraction of the mesospheric ozone layer due to CO2-induced cooling. Second, stronger convective activity intensifies gravity wave generation, increasing gravity wave diffusion in the mesosphere. This strong convective activity also likely intensifies the tide below ~70 km. While our positive DW1 trend is consistent with McLandress and Fomichev (2006), the negative trend in the lower thermosphere contrasts with their results. This discrepancy might arise because their model used a time-independent diffusion coefficient, whereas WACCM-X accounts for CO2-driven changes in gravity wave diffusion.

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Journal article(s) based on this preprint

15 Jan 2026
Impacts of increasing CO2 on diurnal migrating tide in the equatorial lower thermosphere
Masaru Kogure, In-Sun Song, Huixin Liu, and Han-Li Liu
Atmos. Chem. Phys., 26, 665–680, https://doi.org/10.5194/acp-26-665-2026,https://doi.org/10.5194/acp-26-665-2026, 2026
Short summary
Masaru Kogure, In-Sun Song, Huixin Liu, and Han-Li Liu

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-3303', Yosuke Yamazaki, 08 Aug 2025
    • AC3: 'Reply on RC1', Masaru Kogure, 27 Nov 2025
  • RC2: 'Comment on egusphere-2025-3303', Anonymous Referee #2, 02 Oct 2025
    • AC2: 'Reply on RC2', Masaru Kogure, 27 Nov 2025
  • AC1: 'Comment on egusphere-2025-3303', Masaru Kogure, 27 Nov 2025

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-3303', Yosuke Yamazaki, 08 Aug 2025
    • AC3: 'Reply on RC1', Masaru Kogure, 27 Nov 2025
  • RC2: 'Comment on egusphere-2025-3303', Anonymous Referee #2, 02 Oct 2025
    • AC2: 'Reply on RC2', Masaru Kogure, 27 Nov 2025
  • AC1: 'Comment on egusphere-2025-3303', Masaru Kogure, 27 Nov 2025

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload
AR by Masaru Kogure on behalf of the Authors (28 Nov 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (28 Nov 2025) by John Plane
RR by Anonymous Referee #2 (14 Dec 2025)
RR by Yosuke Yamazaki (24 Dec 2025)
ED: Publish subject to technical corrections (05 Jan 2026) by John Plane
AR by Masaru Kogure on behalf of the Authors (05 Jan 2026)  Author's response   Manuscript 

Journal article(s) based on this preprint

15 Jan 2026
Impacts of increasing CO2 on diurnal migrating tide in the equatorial lower thermosphere
Masaru Kogure, In-Sun Song, Huixin Liu, and Han-Li Liu
Atmos. Chem. Phys., 26, 665–680, https://doi.org/10.5194/acp-26-665-2026,https://doi.org/10.5194/acp-26-665-2026, 2026
Short summary
Masaru Kogure, In-Sun Song, Huixin Liu, and Han-Li Liu

Data sets

CESM2/WACCM-X future simulation data from 2000 to 2090 Han Ma https://doi.org/10.5281/zenodo.15189573

Masaru Kogure, In-Sun Song, Huixin Liu, and Han-Li Liu

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Short summary
This study examines the impact of increased CO2 on the migrating diurnal tide (DW1), which is generated by solar absorption and latent heating. Using WACCM-X under the RCP 8.5 scenario, we find a +1 %/decade trend in DW1 amplitude at 20–70 km and a −2 %/decade trend at 90–110 km. The increase is likely due to reduced density and stronger convection near the equator, while the decrease may result from enhanced eddy diffusion in the mesosphere that suppresses tidal growth.
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