the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 06 Jan 2025
Research on 16-day Planetary Waves in the Mid-latitude Troposphere, Stratosphere, Mesosphere, and Lower Thermosphere with Langfang Dual-frequency ST-M Radar Data
Abstract. Horizontal wind observational data by the dual-frequency Stratosphere-Troposphere-Meteor (ST-M) radar at Langfang Observatory from March 2023 to February 2024, was used to investigate spatiotemporal variations, and propagation characteristics of planetary waves, as well as the relationship between planetary waves in the troposphere and stratosphere (ST) and the mesosphere and lower thermosphere (MLT) over Langfang mid-latitude regions. The quasi-16-day planetary wave’s activities are obtained by applying band-pass filtering on the daily averaged horizontal wind. Simultaneous MERRA-2 reanalysis wind data are used to derive the dominant zonal wavenumbers of 16-day waves in ST and mesosphere, and also the background zonal winds through which the planetary may propagate vertically. Results show that 16-day wave activity occurs all the year, its zonal component is stronger than the meridional component, and it is characterized by being strong in winter and weak in summer. It is newly found that the vertical phase propagation direction of 16-day wave got changed during autumn and winter that in autumn August–September it is upward in ST and downward in MLT, and upward in ST but upward in MLT in November–December, and downward in ST and upward in MLT after later December. The dominant zonal wavenumbers for the 16-day wave are (ST: -1, MLT: 2) in August–September, and (ST: 2, MLT: 4) in November–December, and (ST: -1, MLT: 4) in December–January respectively in MERRA-2 data. It can be derived with the information of vertical phase velocity and zonal wavenumber that the group velocity of the 16-days in radar data is downward in ST and downward in MLT in August–September, and upward in ST and upward in MLT in November–December, and downward in ST and Upward in MLT in December–January, respectively. Together with the zonal background winds from MERRA-2 and radar over the field site which provide the vertical propagation condition for planetary waves, it can infer that the observed 16-day wave in ST may be triggered by the jet at about 14km altitude and hence propagated downward in August–September, and the background wind do not allow upward propagating of the wave. So, the observed wave in MLT in August–September may be trigged by another unknown source above or refracted from low-or-high latitude regions. The observed 16-day wave in ST in November–December is not the same as that before, was generated in the lower atmosphere and propagated through the background winds upward maybe into the MLT regions as observed. In December–January, the observed 16-day wave in ST gets changed zonal wavenumber again, it is also generated in the lower atmosphere and propagate upward. However, its upward propagation will be blocked by the above winds and therefore cannot penetrate into the MLT above. The observed wave in MLT in December–January could be the one already existed there before. The newly observations and interpretations help us to further understanding the vertical coupling among the ST and MLT by planetary waves.
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Status: open (until 29 Mar 2025)
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RC1: 'Comment on angeo-2024-27', Anonymous Referee #1, 17 Feb 2025
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Review of Zhang et al. (2025)
"Research on 16-day Planetary Waves in the Mid-latitude Troposphere, Stratosphere, Mesosphere, and Lower Thermosphere with Langfang Dual-frequency ST-M Radar Data"
The reviewer recommends rejecting the manuscript for the following reasons:
- Fatal Flaws in Study Design
- The authors fail to formulate a clear research question or hypothesis.
- The methodology is inadequately developed, lacking proper measurement error propagation and statistical significance tests.
- Lack of Novelty or Contribution
- Similar observations of planetary waves using ST radar and meteor radar at mid-latitudes already exist.
- The study does not present new knowledge about the conditions for vertical PW propagation.
- Poor Writing That Hampers Understanding
- The manuscript is difficult to read due to numerous spelling errors and unusual or misleading word choices.
- Many statements lack clarity.
Methodological Concerns and Suggestions
The authors aim to estimate the period and vertical wavelength (hence vertical phase speed) of observed planetary waves. However, the reviewer finds the approach inefficient. Below are specific concerns and suggestions for improvement:
- Step 1: This step is valid and reasonable. However, the computation of the error of daily mean winds and wind variances should be included. These can be used to establish significance levels in the Lomb-Scargle (LS) analysis.
- Step 2: This step is unnecessary.
- Step 3:
- The choice of Lomb-Scargle spectral analysis is appropriate given the unevenly sampled data. This method provides spectral amplitudes and phases as functions of both frequency and time/altitude thanks to the usage of a sliding window.
- However, a proper significance analysis, based on measurement uncertainties and daily wind variances, is essential to identifying significant peaks in the LS periodogram.
- Band-pass Filtering Concern:
- The reviewer questions the use of a band-pass filter, which requires a Fast Fourier Transform (FFT) and thus necessitates regular gridding of the data.
- Why is interpolation applied at this stage when it was carefully avoided earlier?
- Final Step (Harmonic Fitting & Wave Reconstruction):
- Harmonic fitting could be done without prior filtering since it is already a part of the LS algorithm.
- To determine the uncertainty of vertical wavelengths a Monte Carlo approach should be used in the linear fit of phase lines.
- This is crucial because small errors in phase line slopes can lead to incorrect conclusions about vertical propagation direction.
Alternative Approach
To avoid interpolation, band-pass filtering, and wave reconstruction, the reviewer suggests the following alternative method:
- Utilizing Phase Shifts in the LS Periodogram
- Phase shifts between altitudes in the LS periodogram provide direct information on instantaneous vertical wavelength.
- To improve accuracy, these phase shifts should be averaged over the altitude range where the signal is significant.
- This approach allows the authors to report both a mean vertical wavelength and its associated uncertainty.
Given the large vertical wavelengths involved, uncertainty estimation is critical. Even a small phase shift can incorrectly indicate a reversal in the vertical propagation direction.
Citation: https://doi.org/10.5194/angeo-2024-27-RC1 -
AC1: 'Reply on RC1', Zengmao Zhang, 28 Mar 2025
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Thank you very much for your valuable feedback and constructive comments.
Please find the detailed replies to Reviewer #1 in the attached PDF file.
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RC2: 'Comment on angeo-2024-27', Anonymous Referee #2, 04 Mar 2025
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Comments on the paper “Research on 16-day Planetary Waves in the Mid-latitude
Troposphere, Stratosphere, Mesosphere, and Lower Thermosphere with Langfang Dual-frequency ST-M Radar Data” by
Zengmao Zhang, Xiong Hu, Qingchen Xu, Bing Cai, Junfeng Yang
The paper presents new data about the wind variability in the MLT and in the troposphere/lower stratosphere, as well as some results on the coupling between these atmospheric layers. The methods used in the analysis are not well justified and are sometimes incorrect. Therefore the paper needs a major revision. The detail comments are given below.
The title does not clearly describe the article. The radar data cover the lower stratosphere and the MERRA data are not mentioned.
Data Sources and Analysis Methods
- Extracting Daily Mean Wind:
Why do the authors use the criterion of 10 hours? What are the errors of the daily wind speeds obtained with the method proposed by the authors?
- Detrending
The MLT winds are characterized by the strong seasonal course and strong changes in spring, sometime in autumn and during SSW (for example, in January 2024). The wind behavior model with a simple linear trend is not correct for these cases. Therefore, the 16-day wave parameters may be obtained with large errors or may be completely incorrect. I recommend removing the seasonal course first.
- Spectral analysis
The time series of the zonal and meridional wind speeds have large gaps from month 3 to month 5 (figure 1). On the one hand, such gaps may easily distort the spectrum obtained with the Lomb-Scargle method. On the other hand, the authors fill in the gaps for their further analysis.
I recommend removing the data with these large gaps.
Figure 3. Please, indicate units of the color levels. What level is significant?
3.3 Spatiotemporal variations of the 16-day period planetary wave
L.325-330 “No significant planetary wave activity is observed in the MLT during summer…”
How do the authors separate significant and non-significant wave activity?
Ln. 350-365 Please, indicate errors of the vertical wavelength you found.
Ln.367-376 It is very important for the analysis provided in this part and below that the errors of the phase speeds are small enough to draw any conclusion.
Ln.380 Qy < 0 is not sufficient for the instability.
Ln.380-383 The authors use the result of the quasi-geostrophic theory. The conclusion from eq.3 is not correct. The vertical phase speed is opposite to the vertical group speed in the coordinate system that moves with the zonal flow (Qy > 0). If one takes into account the background zonal flow U0, then the result will be complex and will depend on U0.
By the way, the authors should explain the notation in the equation and provide a reference.
L.385 “Fig.5. Assuming that the frequency-wavenumber spectrum in the MLT is consistent with that at the 79 km altitude, the dominant wavenumber for each time was selected as the wavenumber for that period. “
Why are the spectra consistent? The MERRA-2 data are given at the model level, but the MR winds are given at altitudes. The difference between the true heights may be significant.
There is no confidence that oscillations presented in Fig.5 are statistically significant.
3.4 Propagation characteristics of the 16-day period planetary wave
The aim of this part is “To investigate the location of the wave source in the ST” and “the relationship between the planetary waves in the two regions”.
The analysis is confined in latitude and longitude to the region where the radar is located. Therefore, the authors (and the readers) do not know how 16-day waves propagate in the neighboring region. Hence, the authors can’t really reach their aim.
Additional note, the real atmospheric 16-day waves are transient, their amplitudes are changing with time as observed. The theory used in this part does not work for such waves.
I propose to find and plot the E-P flux for the waves.
Conclusion
Ln.465 “The quasi-16-day and quasi-10-day waves dominate in both the ST and MLT regions” – this conclusion may be a result of the 32-day segment used for the analysis and a linear trend model. The waves with shorter periods are just averaged over the segment and their transient behavior is not taken into account.
Conclusions (2) and (3) repeat the first one. The errors of phase speeds are not clear. Therefore, the statements about their changes are not supported in the text.
Ln.475-479 Please, see above. The authors’ statements are incorrect.
Ln. 480 Conclusion (4). This conclusion does not have a solid support from the analysis as it is noted above. The sign of speeds, the wavenumber estimations are in question.
Please, directly indicate height intervals and/or time intervals on each plot.
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AC2: 'Reply on RC2', Zengmao Zhang, 28 Mar 2025
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Thank you very much for your valuable feedback and constructive comments.
Please find the detailed replies to Reviewer #2 in the attached PDF file.
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