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arxiv: 2605.21730 · v1 · pith:6MDDQOYOnew · submitted 2026-05-20 · 🌌 astro-ph.EP

High-Latitude Zonal Jets in the Martian Upper Atmosphere Driven by Non-Orographic Gravity Waves

Pith reviewed 2026-05-22 08:00 UTC · model grok-4.3

classification 🌌 astro-ph.EP
keywords non-orographic gravity wavesMartian thermospherezonal jetshigh-latitudemomentum divergenceHadley CellMAVEN observations
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The pith

Non-orographic gravity waves drive high-latitude zonal jets in Mars' upper atmosphere via momentum divergence.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper seeks to establish that non-orographic gravity waves are the main driver of zonal jets at high latitudes in the Martian upper atmosphere. Using observations from the MAVEN mission's Neutral Gas and Ion Mass Spectrometer and simulations with the Mars Planetary Climate Model, it demonstrates that these waves cause jet acceleration and deceleration of 280 m/s through momentum divergence amounting to 1,300 m/s per sol. This occurs due to wave saturation and wind filtering, particularly in the hemisphere tied to the descending branches of the Hadley Cell where critical layers are absent in the middle atmosphere. A sympathetic reader would care because this reveals how small-scale waves can significantly influence large-scale circulation and dynamics in planetary upper atmospheres.

Core claim

Jet acceleration and deceleration of 280 m/s arise from momentum divergence of 1,300 m/s/sol driven by wave saturation and wind filtering. Simulations and observations indicate that GWs modulate these jets in the hemisphere associated with the descending branches of the Hadley Cell, due to the absence of wave critical layers in the middle atmosphere. Interactions between GWs and the mean flow can shape the circulation and dynamics of the upper atmosphere of Mars.

What carries the argument

momentum divergence caused by non-orographic gravity wave saturation and wind filtering in the absence of critical layers

If this is right

  • GWs modulate zonal jets specifically in the hemisphere with descending Hadley Cell branches.
  • The lack of wave critical layers in the middle atmosphere allows propagation to the thermosphere.
  • These wave-mean flow interactions shape the circulation of the Martian upper atmosphere.
  • Observed jet changes match model predictions of 280 m/s acceleration from 1,300 m/s/sol divergence.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Similar wave-driven jet mechanisms may operate in the upper atmospheres of other planets like Earth or Venus where orographic waves are limited.
  • Improved parameterization of non-orographic GWs in climate models could enhance predictions of thermospheric variability on Mars.
  • Correlations between middle atmosphere wave activity and thermospheric jets could be tested with future multi-instrument observations.

Load-bearing premise

The high-latitude jets are modulated primarily by non-orographic gravity waves rather than other dynamical processes, and the model accurately represents the absence of critical layers that would otherwise block wave propagation.

What would settle it

Running the model without the non-orographic gravity wave parameterization and finding that high-latitude jets still appear at observed strengths would falsify the driving role of these waves.

Figures

Figures reproduced from arXiv: 2605.21730 by Ehouarn Millour, Fran\c{c}ois Forget, Francisco Gonz\'alez Galindo, Jean-Yves Chaufray, Jiandong Liu.

Figure 1
Figure 1. Figure 1: Observational geometry of NGIMS/MAVEN during wind sampling from MY33 to MY36. Local Solar Time (LST) is color-coded along with latitude and solar longitude (Ls). High-latitude regions (≥ 60◦ ) are shaded in light gray. Samples C#01 to C#06 correspond to the descending branch of the Hadley Circulation (HC), whereas C#7 to C#9 correspond to the as￾cending branch. The dusty season occurs between Ls 135◦ and 2… view at source ↗
Figure 2
Figure 2. Figure 2: Monthly-mean (30◦ bins in Ls) zonal-mean zonal winds (U) and wave-induced wind changes (dU) during MY29. Wave effects are defined as dU = UGWon − UGWoff (m s−1 ) and are color-coded. Green contours show UGWon (m s−1 ), and bold black contours denote UGWon = 0. Blue arrows indicate the zonal jets, coincident with the descending branch of the Hadley circula￾tion; − damping; + accelerating; −− closing; ++ ope… view at source ↗
Figure 3
Figure 3. Figure 3: Upper winds at 165 ± 10 km, Ls =180◦ , MY35. Simulations without (gray) and with (black) GWs are hown to illustrate the non-orographic GW’s effect. NGIMS-derived winds (blue vectors) are aligned with Local Solar Time (LST). Wave-induced drags are color-coded in the background at an altitude of 125 km. et al., 2025), due to favorable conditions for wave propagation created by dust-induced atmospheric inflat… view at source ↗
Figure 4
Figure 4. Figure 4: Comparisons between PCM simulations and NGIMS winds for C#01 to C#09. Gray and red vectors are simulations without and with GWs, respectively. NGIMS observations are in blue. The simulations and observations are sampled at the same longitudes, latitudes, Ls, LST, and altitudes. The data in panel B are shifted upward by 20 km in altitude for better visibility. The winds during LST 0-3 h maintain the pattern… view at source ↗
Figure 5
Figure 5. Figure 5: Zonal wind magnitudes from NGIMS observations (blue) and PCM simulations (red and gray) for case#01 to case#09. Solid lines for model predicted climatology and dash lines for 2-σ threshold. For example, C#01-7934+4 refers to case 01, starting orbit number 7934 and 4 orbital maneuvers. Note that not all orbit numbers have continuous samples; for instance, C#05-11192+13 comprises a total of 5 samples. –16– … view at source ↗
Figure 6
Figure 6. Figure 6: Five-sols averaged zonal-averaged PCM simulated fields for cases C#01, C#02, C#04, and C#06. The first row displays the U-dU (m s−1 ) map; dU is color-coded and U is in contour lines (black lines denote U=0 m s−1 ). The second row depicts the wave’s drags (m s−1 sol−1 ); Overlapped contour lines to distinct the small values. Note that the contour spacing in the sec￾ond row is nonlinear. C#06, where the Mar… view at source ↗
read the original abstract

We investigate thermosphere responses to non-orographic gravity waves (GWs) using wind measurements from the Neutral Gas and Ion Mass Spectrometer onboard the Mars Atmosphere and Volatile EvolutioN mission, alongside simulations from the Mars Planetary Climate Model. We focus on zonal jets in high-latitude regions of the upper atmosphere. Jet acceleration and deceleration (280 m/s ) arise from momentum divergence (1,300 m/s/sol ) driven by wave saturation and wind filtering. Simulations and observations indicate that GWs modulate these jets in the hemisphere associated with the descending branches of the Hadley Cell, due to the absence of wave critical layers in the middle atmosphere. Interactions between GWs and the mean flow can shape the circulation and dynamics of the upper atmosphere of Mars.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper investigates thermosphere responses to non-orographic gravity waves using MAVEN NGIMS wind measurements and Mars Planetary Climate Model simulations. It focuses on high-latitude zonal jets, claiming that acceleration and deceleration of 280 m/s arise from momentum divergence of 1,300 m/s/sol due to wave saturation and wind filtering. The modulation occurs preferentially in the hemisphere with descending Hadley Cell branches because of the absence of critical layers in the middle atmosphere, allowing GW propagation to the upper atmosphere.

Significance. If the central result holds, the work would demonstrate a concrete mechanism by which non-orographic gravity waves shape zonal jets and circulation in the Martian thermosphere, linking middle-atmosphere filtering to thermospheric momentum deposition. This could improve dynamical understanding of upper-atmosphere variability on Mars and provide a testable link between observed wind changes and parameterized wave processes.

major comments (2)
  1. The headline attribution of 280 m/s jet changes and 1,300 m/s/sol momentum divergence to GW saturation and filtering rests on the Mars PCM producing middle-atmosphere zonal winds that lack critical layers (|u - c| away from zero) for the relevant GW phase speeds. No direct comparison of simulated middle-atmosphere zonal winds or vertical shear against independent observations is shown to confirm this condition; without it the diagnosed thermospheric forcing risks being an artifact of the model winds rather than a robust physical mechanism.
  2. Abstract and model-observation comparison sections: quantitative values for jet speed change (280 m/s) and momentum divergence (1,300 m/s/sol) are stated without error bars, data-selection criteria, or altitude-specific model-observation residuals, limiting assessment of whether the reported forcing magnitudes are statistically distinguishable from other dynamical contributions.
minor comments (2)
  1. Clarify the vertical range and exact altitudes at which NGIMS winds are compared to the model thermospheric jets.
  2. Add a brief statement on the GW source spectrum and phase-speed range used in the Mars PCM parameterization to allow readers to assess the critical-layer filtering argument.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive and detailed comments, which help improve the clarity and robustness of our work. We respond to each major comment below and have revised the manuscript to address the concerns raised.

read point-by-point responses
  1. Referee: The headline attribution of 280 m/s jet changes and 1,300 m/s/sol momentum divergence to GW saturation and filtering rests on the Mars PCM producing middle-atmosphere zonal winds that lack critical layers (|u - c| away from zero) for the relevant GW phase speeds. No direct comparison of simulated middle-atmosphere zonal winds or vertical shear against independent observations is shown to confirm this condition; without it the diagnosed thermospheric forcing risks being an artifact of the model winds rather than a robust physical mechanism.

    Authors: We agree this is an important point for establishing that the diagnosed thermospheric forcing is not an artifact of the model. The Mars PCM middle-atmosphere winds have been validated against observations in earlier publications, but a direct comparison was not included here. In the revised manuscript we will add a dedicated panel or subsection comparing the simulated zonal winds and vertical shear profiles in the middle atmosphere (roughly 20–80 km) to independent datasets such as Mars Climate Sounder temperature-derived winds and radio-occultation profiles, explicitly showing that |u − c| remains sufficiently far from zero for the relevant GW phase speeds. revision: yes

  2. Referee: Abstract and model-observation comparison sections: quantitative values for jet speed change (280 m/s) and momentum divergence (1,300 m/s/sol) are stated without error bars, data-selection criteria, or altitude-specific model-observation residuals, limiting assessment of whether the reported forcing magnitudes are statistically distinguishable from other dynamical contributions.

    Authors: We accept that the quantitative results should be presented with greater statistical context. The revised manuscript will (i) specify the exact MAVEN NGIMS data-selection criteria (local time, latitude, season, and quality flags) in the methods section, (ii) attach error bars to the 280 m/s and 1,300 m/s/sol values based on the observed standard deviation across the selected orbits and across an ensemble of model realizations, and (iii) include a supplementary table or figure of altitude-resolved model–observation residuals in the thermosphere to allow readers to judge the contribution of GW forcing relative to other terms. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation relies on independent model-observation comparison

full rationale

The paper attributes high-latitude zonal jet changes to non-orographic GW momentum divergence based on direct comparison of MAVEN NGIMS wind data with Mars PCM simulations that include a GW parameterization. The reported 280 m/s accelerations and 1300 m/s/sol divergences are diagnosed outputs from the model runs and observations, not parameters fitted to the target jets or self-defined quantities. The absence of critical layers is presented as a model result in the descending Hadley branch rather than an imposed condition that forces the outcome by construction. No equations, self-citations, or ansatzes are shown in the abstract or context that reduce the central claim to its inputs; the analysis remains self-contained against external wind measurements.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The abstract does not introduce new free parameters, axioms, or invented entities; it relies on standard gravity-wave saturation and filtering concepts already present in the cited Mars climate model.

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Reference graph

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