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arxiv: 1906.12173 · v1 · pith:M5T5ARHAnew · submitted 2019-06-28 · ⚛️ physics.ao-ph · physics.space-ph

SuperDARN Observations of Semidiurnal Tidal Variability in the MLT and the Response to Sudden Stratospheric Warming Events

R. E. Hibbins , P. J. Espy , Y. J. Orsolini , V. Limpasuvan , R. J. Barnes This is my paper

Pith reviewed 2026-05-25 13:13 UTC · model grok-4.3

classification ⚛️ physics.ao-ph physics.space-ph
keywords superdarnsemidiurnal tidemigrating tidesudden stratospheric warmingmesosphere lower thermospheremeteor windstidal variabilityatmospheric coupling
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The pith

SuperDARN data show the migrating semidiurnal tide reduces immediately after SSW onset and strengthens anomalously 10-17 days later.

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

The paper uses meteor wind observations from the SuperDARN radar network spanning nearly 180 degrees of longitude at around 60 degrees north to separate the Sun-synchronous migrating semidiurnal tide from nonmigrating components in the mesosphere and lower thermosphere. A 20-year climatology reveals that the migrating tide accounts for the main peaks in late summer and winter, while nonmigrating tides are equally strong in autumn and spring. During 13 sudden stratospheric warming events, the migrating tide amplitude drops right after onset but then becomes stronger than usual between 10 and 17 days later. This response is linked to shifts in the underlying wind direction, confirming model predictions of enhanced migrating tides at midlatitudes extending to 60N.

Core claim

Using SuperDARN meteor wind data, the migrating semidiurnal tide is extracted from the meridional winds and shown to decrease in amplitude immediately after sudden stratospheric warming onset, then return anomalously strongly around 10-17 days later. The changes in background wind direction are concluded to modulate the tidal amplitude, with the midlatitude enhancement observed up to 60 degrees north.

What carries the argument

Separation of migrating versus nonmigrating semidiurnal tide components from meridional wind data using the SuperDARN network's longitudinal coverage around 60N.

Load-bearing premise

The assumption that the SuperDARN radars' longitudinal spread allows clean separation of migrating from nonmigrating semidiurnal tides without significant aliasing from other wave modes.

What would settle it

Independent high-latitude wind measurements showing no decrease in migrating SDT amplitude right after SSW onset or no anomalous increase 10-17 days later would falsify the reported response.

Figures

Figures reproduced from arXiv: 1906.12173 by P. J. Espy, R. E. Hibbins, R. J. Barnes, V. Limpasuvan, Y. J. Orsolini.

Figure 1
Figure 1. Figure 1: shows the data coverage from the radar chain during this period. Simultaneous data from at least six individual radars are typically available on any given day after the mid‐1990s. We adopt an approach similar to Kleinknecht et al. (2014) to extract various zonal wavenumber components of the MLT SDT from SuperDARN meteor wind data recorded between 1995 and 2016. The horizontal com￾ponents of the hourly mea… view at source ↗
Figure 2
Figure 2. Figure 2: Example four‐component fit to trial data of varying signal‐to‐ noise ratios. In this case the four components used in the paper are fitted to a pure 10 m/s amplitude SW2 tide over a range of white (Gaussian) noise levels. Error bars represent twice the standard deviation of the fitted amplitudes. DW1 = migrating diurnal, zonal wavenumber 1 tide; SW1 = semidiurnal, westward propagating, zonal wavenumber 1 t… view at source ↗
Figure 3
Figure 3. Figure 3: Example of a surface fit (gray plane) to 1 day of hourly mean mer￾idional wind from the eight SuperDARN radars (orange circles). Data are plotted as a function of radar longitude and UT of day [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: (a) Daily mean amplitude of the three components of the semidiurnal tide (blue) over the period 1995 to 2005 around 60°N (top = SW1; middle = SW2; bottom = SW3). The red vertical lines represent the onset dates of sudden stratospheric warming (with an elevated stratopause) taken from Limpasuvan et al. (2016). (b) As in (a), but covering the period 2006 to 2017. SW1 = semidiurnal, westward propagating, zona… view at source ↗
Figure 5
Figure 5. Figure 5: shows that the two maxima in autumn and winter are predominantly due to the migrating (SW2) component of the SDT with smaller contributions from SW1 and SW3 especially around the equinoxes. The SW1 and SW3 components appear to vary similarly, with the amplitude of the SW1 component slightly lar￾ger throughout most of the year. A striking feature of these resolved components is the rapid reduction in the st… view at source ↗
Figure 6
Figure 6. Figure 6: (top panel) Four‐day running mean amplitude of the 12‐hr varia￾bility in the meridional wind observed with the SKiYMET meteor radar at Trondheim, Norway (63°N) between 82‐ and 97‐km altitude (data from Orsolini et al., 2017). (bottom panel) The three components of the semi￾diurnal tide resolved from the longitudinal chain of SuperDARN radars (green = SW1; black = SW2; red = SW3). Data span the 2013 sudden … view at source ↗
Figure 7
Figure 7. Figure 7: Amplitude of the three components of the semidiurnal tide (color error bar plots) over the 13 SSW events associated with an elevated stratopause identi￾fied by their onset dates (right axis, right‐hand panel) plotted over 5 weeks beginning 1 week before the onset. Left panel = SW1; middle panel = SW2; right panel = SW3. The onset dates marked with an asterisk represent vortex split events. The pale gray li… view at source ↗
Figure 8
Figure 8. Figure 8: The composite behavior of the anomalous amplitude of the three semidiurnal tide components around 60°N and 95 km (top panel = SW1; middle panel = SW2; bottom panel = SW3). The composite is based on the 13 sudden stratospheric warmings presented in [PITH_FULL_IMAGE:figures/full_fig_p008_8.png] view at source ↗
read the original abstract

Using meteor wind data from the Super Dual Auroral Radar Network (SuperDARN) in the Northern Hemisphere, we (1) demonstrate that the migrating (Sun-synchronous) tides can be separated from the nonmigrating components in the mesosphere and lower thermosphere (MLT) region and (2) use this to determine the response of the different components of the semidiurnal tide (SDT) to sudden stratospheric warming (SSW) conditions. The radars span a limited range of latitudes around 60$^{\circ}$ N and are located over nearly 180$^{\circ}$ of longitude. The migrating tide is extracted from the nonmigrating components observed in the meridional wind recorded from meteor ablation drift velocities around 95-km altitude, and a 20-year climatology of the different components is presented. The well-documented late summer and wintertime maxima in the semidiurnal winds are shown to be due primarily to the migrating SDT, whereas during late autumn and spring the nonmigrating components are at least as strong as the migrating SDT. The robust behavior of the SDT components during SSWs is then examined by compositing 13 SSW events associated with an elevated stratopause recorded between 1995 and 2013. The migrating SDT is seen to reduce in amplitude immediately after SSW onset and then return anomalously strongly around 10-17 days after the SSW onset. We conclude that changes in the underlying wind direction play a role in modulating the tidal amplitude during the evolution of SSWs and that the enhancement in the midlatitude migrating SDT (previously reported in modeling studies) is observed in the MLT at least up to 60$^{\circ}$ N.

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 / 1 minor

Summary. The manuscript analyzes meteor wind data from the SuperDARN network in the Northern Hemisphere to separate migrating and nonmigrating semidiurnal tides (SDT) in the mesosphere and lower thermosphere (MLT) around 95 km altitude. Using data from radars spanning ~60°N latitude and nearly 180° longitude, it presents a 20-year climatology of the components and examines their response to 13 sudden stratospheric warming (SSW) events with elevated stratopause by compositing. The key findings are that the migrating SDT amplitude decreases immediately after SSW onset and enhances anomalously 10-17 days later, with the conclusion that background wind changes modulate the amplitude and that mid-latitude enhancements extend to 60°N.

Significance. This observational study provides direct evidence from radar winds for the behavior of SDT components during SSWs, supporting previous modeling results on mid-latitude enhancements. The climatology distinguishes the contributions of migrating and nonmigrating tides to seasonal maxima. If the separation is valid, it advances understanding of tidal variability and SSW impacts on the MLT region.

major comments (2)
  1. [Methods (tidal separation and extraction)] The tidal separation method (described where the migrating tide is extracted from nonmigrating components in meridional winds): with radars spanning only ~180° of longitude at a narrow latitude band around 60°N, the decomposition risks aliasing nonmigrating components (s=1, s=3, etc.) onto the migrating (s=2) estimate, directly affecting the reported post-SSW amplitude drop and 10-17 day enhancement.
  2. [Results (SSW event compositing)] The SSW composite analysis (13 events): the reported amplitude reduction immediately after onset and anomalous strengthening 10-17 days later lacks error bars, statistical significance tests, or sensitivity checks on the decomposition, undermining assessment of whether the changes are robust or contaminated by aliasing.
minor comments (1)
  1. [Abstract] The abstract states the radars are 'located over nearly 180° of longitude' but does not detail how this coverage is used in the least-squares or Fourier fit to isolate components.

Simulated Author's Rebuttal

2 responses · 0 unresolved

Thank you for the opportunity to respond to the referee's comments. We have carefully considered the points raised regarding the tidal separation method and the SSW composite analysis. Our responses are provided below, and we will make revisions to strengthen the manuscript.

read point-by-point responses

  1. Referee: [Methods (tidal separation and extraction)] The tidal separation method (described where the migrating tide is extracted from nonmigrating components in meridional winds): with radars spanning only ~180° of longitude at a narrow latitude band around 60°N, the decomposition risks aliasing nonmigrating components (s=1, s=3, etc.) onto the migrating (s=2) estimate, directly affecting the reported post-SSW amplitude drop and 10-17 day enhancement.

    Authors: We recognize the potential for aliasing in the tidal decomposition due to the limited longitudinal coverage of the SuperDARN radars. Our approach uses the meridional wind observations across the available longitudes to fit the migrating and nonmigrating components, assuming the dominant semidiurnal signals. However, to address this valid concern, we will expand the methods section to explicitly discuss the limitations of the longitude coverage and include sensitivity tests by excluding certain radars or assuming additional components to evaluate the robustness of the migrating tide estimates. revision: yes

  2. Referee: [Results (SSW event compositing)] The SSW composite analysis (13 events): the reported amplitude reduction immediately after onset and anomalous strengthening 10-17 days later lacks error bars, statistical significance tests, or sensitivity checks on the decomposition, undermining assessment of whether the changes are robust or contaminated by aliasing.

    Authors: The referee is correct that the composite results would be strengthened by the inclusion of uncertainty estimates and statistical analysis. In the revised manuscript, we will add error bars to the composite plots (e.g., standard error of the mean across events) and perform statistical significance testing on the amplitude changes. Additionally, we will conduct sensitivity checks by varying the SSW event selection criteria and the tidal decomposition assumptions to confirm that the reported post-SSW behavior is not an artifact of aliasing. revision: yes

Circularity Check

0 steps flagged

No circularity: direct observational analysis of radar winds

full rationale

The paper performs a direct observational study: it extracts semidiurnal tidal components from measured meteor wind velocities at ~95 km using the longitudinal spacing of SuperDARN radars (~180° at ~60°N), then composites 13 SSW events to examine amplitude changes. No equations, parameters, or derivations are presented that reduce by construction to fitted inputs, self-definitions, or self-citation chains. The migrating/nonmigrating separation is a data-processing step based on the radar geometry and Fourier decomposition of observed meridional winds; it does not invoke any uniqueness theorem, ansatz smuggled via citation, or renaming of known results. The central claims rest on measured velocities and event compositing, which are externally falsifiable against independent instruments. This matches the default expectation of a non-circular observational paper.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claims rest on the assumption that meteor ablation velocities yield unbiased horizontal winds at 95 km and that the 13 selected SSW events can be meaningfully composited; no free parameters or new entities are introduced.

axioms (1)
  • domain assumption Meteor ablation drift velocities provide unbiased measurements of the horizontal wind at approximately 95 km altitude.
    Invoked when the recorded velocities are used to extract tidal components.

pith-pipeline@v0.9.0 · 5882 in / 1369 out tokens · 31175 ms · 2026-05-25T13:13:46.186625+00:00 · methodology

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Reference graph

Works this paper leans on

5 extracted references · 5 canonical work pages

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