We would like to sincerely thank the reviewer for their thorough and thoughtful assessment of our manuscript. We appreciate the critical insights and constructive suggestions, which helped us identify several areas for improvement. We have carefully considered each comment and revised the manuscript accordingly. Below, we provide a detailed response to all points raised.

Reviewer Comment: The scientific value and methodological rigor of the manuscript are questionable in its current form. The study relies on only two days of observational data to evaluate several methods for estimating vertical plasma drift, comparing them to a Doppler-based method that appears relatively more reliable. For any objective reader their results, shown, for example, in Figs. 5 and 6, is proof that indirect methods cannot be used for any serious science...

Author Response: We acknowledge the reviewer’s concern regarding the limited data set. We agree that a comprehensive validation of different methods for estimating vertical plasma drift would ideally require a much larger set of observations, covering various seasons, levels of geomagnetic activity, and different geographic locations.

However, the objective of our study was not to provide a complete characterization of each method under all possible conditions. Instead, we deliberately chose a controlled, quiet period at a mid-latitude station and performed specially configured high-cadence measurements—including both ionograms and drift observations. This setting allowed us to explore the intrinsic behavior of the methods under idealized conditions. Our reasoning is that if significant inconsistencies arise even under quiet conditions, the discrepancies will likely be amplified during geomagnetically disturbed periods.

Furthermore, this study required manual post-processing of ionograms to extract height parameters for the different indirect methods, which is labor-intensive due to the high temporal resolution. While our data set is limited in scope, the added value lies in its temporal granularity and the ability to perform direct side-by-side comparisons on a minute-by-minute basis.

We do not claim to generalize the results to all geophysical conditions but aim to highlight potential methodological issues and limitations. We believe this is a necessary step toward a more extensive evaluation of vertical drift estimation methods.

We also agree with the reviewer that Doppler-based DDM is, when properly processed, the most reliable and consistent method available. However, many studies continue to use indirect methods—particularly when drift measurements are unavailable (e.g., for historical ionogram data). We therefore consider it meaningful to analyze differences among methods and identify conditions under which they produce comparable or diverging results.

Finally, in response to the reviewer’s valid point about the lack of stronger critical commentary in the original manuscript, we have revised the discussion section to include a more explicit evaluation of the limitations of each method. We now provide specific recommendations on their applicability depending on time of day, expected variability, and data availability.

Reviewer Comment: Second, the DDM method is based on least-squares fits and therefore not just offers more physically grounded and statistically supported results but also provides per-measurement error estimates... etc.

Author Response: We thank the reviewer for this helpful suggestion. In the revised version of the manuscript, we now include error estimates for each DDM measurement. These uncertainties are based on the least-squares fit used to determine the drift velocity vector and are visualized in Figures 5 and 6.

We also added a brief discussion explaining that the high-cadence mode used during our campaigns resulted in abnormally short measurement durations and, consequently, a lower number of reflected points in each SKYmap. This limitation naturally increases the uncertainty of the DDM results in our data set compared to standard measurements. However, even under these constrained conditions, the DDM-derived vertical drift estimates remain stable and coherent—highlighting the robustness of this technique. This point has also been clarified in the revised discussion.

Reviewer Comment: L. 69–70: Digisondes can detect specific reflection points and measure Doppler shifts...

It’s worth mentioning here that Digisonde requires dedicated, non-ionogram, fixed-frequency mode...

Author Response: We appreciate this observation. The text has been revised to explicitly state that Digisonde drift measurements are performed in a dedicated mode using fixed-frequency sounding, which does not provide full ionogram data during those intervals.

Reviewer Comment: L. 101: Such a data set allows accurate estimation of the drift velocity vector...

Scientific objectivity requires to mention that this technique was first developed by Wright and Pitteway (1994)...

Author Response: We thank the reviewer for pointing this out. The revised manuscript now includes a citation of the earlier work by Wright and Pitteway (1994), acknowledging their contribution to the development of Doppler-based drift estimation techniques.

Reviewer Comment: L. 203: Standard ionogram measurement takes typically several minutes.

The authors probably mean typical ionogram cadence.

Author Response: Correct. This sentence has been rephrased in the revised version to clarify that we refer to the typical cadence of ionogram measurements, not the duration of an individual sweep.

Reviewer Comment: Section 4.2: When the authors speak of smoothing, is it the time series of a parameter itself smoothed before calculating the time derivative...?

Author Response: Thank you for this clarifying question. In our analysis, the vertical drift values were calculated first using the difference in characteristic height parameters (e.g., ΔhmF2/Δt) between two adjacent ionograms. The resulting time series of drift values was then smoothed using a moving average. We have clarified this sequence in the revised manuscript to avoid any confusion. We also briefly mention that we tested both approaches (smoothing height parameters first vs. smoothing the derived drift values) and found no significant differences for the purposes of our analysis.

We thank the reviewer for the constructive feedback and for recognizing the practical value of our study. In response to the specific suggestions:

1.Extended datasets:

We fully agree that applying the comparative methodology over longer periods and under standard observational regimes (e.g., 5-minute schedules) would significantly enhance the robustness of our conclusions. To address this, we have added a new paragraph in the Discussion section (Section 5) explicitly outlining how the methodology could be scaled to longer-term datasets. We also emphasize that many Digisondes now operate at a 5-minute cadence, making our proposed comparison techniques broadly applicable.

2.Uncertainty in vertical drifts (DDA error bars):

Based on the reviewer’s recommendation (and in agreement with Reviewer #1), we have now included a dedicated subsection discussing the standard deviation values reported in the DDA-derived vertical drift velocities. In the revised Figure 2, we visualize the evolution of these uncertainties across different smoothing levels. The discussion addresses:

- How the magnitude of error bars is often inversely related to the number of detected echoes during a given sounding.

- The practical implications of this uncertainty when interpreting short-term fluctuations versus long-term trends.

Furthermore, we explicitly comment on the differences in uncertainty levels between this short-campaign setup (with reduced sounding duration) and standard, longer Digisonde soundings. This comparison helps contextualize the magnitude of the reported standard deviations and suggests that uncertainty values in routine operations are likely lower and more stable.

We believe this addition improves the interpretability and applicability of our results and brings attention to an underexplored but important aspect of vertical drift analyses.