Preprints
https://doi.org/10.5194/egusphere-2025-5427
https://doi.org/10.5194/egusphere-2025-5427
18 Dec 2025
 | 18 Dec 2025

Revisiting barotropic instability from the perspective of wave evolution theory

Yaokun Li

Abstract. The instability of Rossby waves has been a long-standing topic in dynamical meteorology. The classic theoretical analysis had provided in–depth physical understanding of the problem. However, developing a systematic and quantitative comprehension of wave energy and amplitude evolution remains challenging. With an eye to such issues, this investigation provides a novel and practicable algorithm to solve the wave action conservation equation. Theoretical analysis establishes that wave packet energy evolves through two competing factors: direct proportionality to intrinsic frequency and inverse proportionality to group velocity magnitude. Energy density attains extremal values at turning points where group velocity magnitudes become extremized. To ensure a ray can be reflected by a turning point, zonal phase speed must be smaller than an upper limit determined by dispersion relation at the turning point. Crucially, a specific zonal phase speed range emerges below this maximum threshold where concurrent transient growth of both wave energy and amplitude occurs when a ray is moving toward the turning point, with the upper limit corresponding to optimal wave development conditions. Numerical experiments on a prototype westerly jet reveal distinct instability mechanisms: substantial transient growth–capable of triggering nonmodal instability–arises when rays moves toward turning points, while exponential amplification characteristic of modal instability develops at inflection points with positive energy growth rate. The derived zonal phase speed thresholds and transient growth metrics form a diagnostic framework applicable to observed atmospheric flows, enabling quantitative evaluation of both modal and nonmodal instability potentials. By unifying wave evolution dynamics with classical instability criteria, this work provides an operational bridge between theoretical predictions and real–world flow diagnostics.

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Journal article(s) based on this preprint

01 Jul 2026
Revisiting barotropic instability from the perspective of wave evolution theory
Yaokun Li
Weather Clim. Dynam., 7, 1073–1088, https://doi.org/10.5194/wcd-7-1073-2026,https://doi.org/10.5194/wcd-7-1073-2026, 2026
Short summary
Yaokun Li

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-5427', Anonymous Referee #1, 12 Feb 2026
    • AC1: 'Reply on RC1', Yaokun Li, 25 Feb 2026
  • RC2: 'Comment on egusphere-2025-5427', Anonymous Referee #2, 19 Mar 2026
    • AC2: 'Reply on RC2', Yaokun Li, 28 Mar 2026
  • EC1: 'Comment on egusphere-2025-5427', Gwendal Rivière, 23 Mar 2026
    • AC3: 'Reply on EC1', Yaokun Li, 05 Apr 2026

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload
AR by Yaokun Li on behalf of the Authors (05 Apr 2026)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (13 Apr 2026) by Gwendal Rivière
RR by Anonymous Referee #2 (16 May 2026)
ED: Publish subject to revisions (further review by editor and referees) (26 May 2026) by Gwendal Rivière
AR by Yaokun Li on behalf of the Authors (29 May 2026)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (15 Jun 2026) by Gwendal Rivière
RR by Anonymous Referee #2 (16 Jun 2026)
ED: Publish subject to technical corrections (17 Jun 2026) by Gwendal Rivière
AR by Yaokun Li on behalf of the Authors (20 Jun 2026)  Author's response   Manuscript 

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-5427', Anonymous Referee #1, 12 Feb 2026
    • AC1: 'Reply on RC1', Yaokun Li, 25 Feb 2026
  • RC2: 'Comment on egusphere-2025-5427', Anonymous Referee #2, 19 Mar 2026
    • AC2: 'Reply on RC2', Yaokun Li, 28 Mar 2026
  • EC1: 'Comment on egusphere-2025-5427', Gwendal Rivière, 23 Mar 2026
    • AC3: 'Reply on EC1', Yaokun Li, 05 Apr 2026

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload
AR by Yaokun Li on behalf of the Authors (05 Apr 2026)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (13 Apr 2026) by Gwendal Rivière
RR by Anonymous Referee #2 (16 May 2026)
ED: Publish subject to revisions (further review by editor and referees) (26 May 2026) by Gwendal Rivière
AR by Yaokun Li on behalf of the Authors (29 May 2026)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (15 Jun 2026) by Gwendal Rivière
RR by Anonymous Referee #2 (16 Jun 2026)
ED: Publish subject to technical corrections (17 Jun 2026) by Gwendal Rivière
AR by Yaokun Li on behalf of the Authors (20 Jun 2026)  Author's response   Manuscript 

Journal article(s) based on this preprint

01 Jul 2026
Revisiting barotropic instability from the perspective of wave evolution theory
Yaokun Li
Weather Clim. Dynam., 7, 1073–1088, https://doi.org/10.5194/wcd-7-1073-2026,https://doi.org/10.5194/wcd-7-1073-2026, 2026
Short summary
Yaokun Li
Yaokun Li

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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
This work offers a novel theoretical perspective on classical barotropic instability by integrating modal and nonmodal instabilities within a unified diagnostic framework that emphasizes energy and amplitude variations along propagating wave packets.
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