Preprints
https://doi.org/10.5194/egusphere-2025-1466
https://doi.org/10.5194/egusphere-2025-1466
17 Apr 2025
 | 17 Apr 2025

Process-based diagnostics using atmospheric budget analysis and nudging technique to identify sources of model systematic errors

Chihiro Matsukawa, José M. Rodríguez, and Sean F. Milton

Abstract. Identifying sources of model systematic errors is a fundamental step to successfully reduce them in general circulation models by improving the representation of relevant physical processes. In this study, we examine model error sources in the Met Office Unified Model at numerical weather prediction timescale by the combined use of two diagnostics: 1) the relaxation or "nudging" in which wind and/or temperature fields are relaxed back towards analyses throughout the simulations, and 2) atmospheric zonal-mean zonal momentum and thermal budgets. The budget analysis quantifies resolved processes and subsequently estimates unresolved processes as a residual, corresponding to model dynamics and physics, respectively. This correspondence is demonstrated by a direct comparison between the budgets and the model tendencies. A systematic error addressed in this paper is the Northern Hemisphere mid-latitude zonal wind bias in the lower stratosphere in boreal winter, characterized by an initial easterly bias that subsequently develops as a westerly bias. The momentum and thermal budget analysis for control and nudging experiments indicates that a mechanical forcing predominantly from parametrized gravity wave drag causes the easterly error and an overly strong temperature gradient around the tropopause is one of the main sources of the westerly error through the Coriolis forcing. The relevant warm bias over the tropical tropopause is mainly attributed to the budget residual term that corresponds to a thermal forcing dominated by radiative processes. This is consistent with the experimental result that temperature nudging over the tropical tropopause significantly reduces the westerly wind bias.

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Journal article(s) based on this preprint

26 Nov 2025
Process-based diagnostics using atmospheric budget analysis and nudging technique to identify sources of model systematic errors
Chihiro Matsukawa, José M. Rodríguez, and Sean F. Milton
Weather Clim. Dynam., 6, 1539–1564, https://doi.org/10.5194/wcd-6-1539-2025,https://doi.org/10.5194/wcd-6-1539-2025, 2025
Short summary
Chihiro Matsukawa, José M. Rodríguez, and Sean F. Milton

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-1466', Anonymous Referee #1, 23 May 2025
    • AC1: 'Reply on RC1', Chihiro Matsukawa, 04 Jul 2025
  • RC2: 'Comment on egusphere-2025-1466', Anonymous Referee #2, 02 Jun 2025
    • AC2: 'Reply on RC2', Chihiro Matsukawa, 04 Jul 2025

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-1466', Anonymous Referee #1, 23 May 2025
    • AC1: 'Reply on RC1', Chihiro Matsukawa, 04 Jul 2025
  • RC2: 'Comment on egusphere-2025-1466', Anonymous Referee #2, 02 Jun 2025
    • AC2: 'Reply on RC2', Chihiro Matsukawa, 04 Jul 2025

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload
AR by Chihiro Matsukawa on behalf of the Authors (01 Aug 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (05 Aug 2025) by Thomas Birner
RR by Anonymous Referee #2 (22 Aug 2025)
RR by Anonymous Referee #1 (27 Aug 2025)
ED: Publish subject to minor revisions (review by editor) (29 Aug 2025) by Thomas Birner
AR by Chihiro Matsukawa on behalf of the Authors (18 Sep 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Publish subject to technical corrections (14 Oct 2025) by Thomas Birner
AR by Chihiro Matsukawa on behalf of the Authors (22 Oct 2025)  Manuscript 

Journal article(s) based on this preprint

26 Nov 2025
Process-based diagnostics using atmospheric budget analysis and nudging technique to identify sources of model systematic errors
Chihiro Matsukawa, José M. Rodríguez, and Sean F. Milton
Weather Clim. Dynam., 6, 1539–1564, https://doi.org/10.5194/wcd-6-1539-2025,https://doi.org/10.5194/wcd-6-1539-2025, 2025
Short summary
Chihiro Matsukawa, José M. Rodríguez, and Sean F. Milton
Chihiro Matsukawa, José M. Rodríguez, and Sean F. Milton

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Short summary
To identify sources of the model systematic errors, we investigate northern hemisphere mid-latitude wind errors at short- to medium-range timescale using the atmospheric zonal-mean budgets analysis and the relaxation technique. These process-based diagnostics specify to what extent the individual components in the budgets contribute to the total tendency of the corresponding variable. This study shows disentanglements of compensating errors caused by mechanical and thermal forcings.
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