General comment

This study attempts to validate the high resolution re-analysis dataset by using clear air Radar echoes in Germany. The results show some consistencies in the diurnal-cycle between the two datasets and the usefulness of the clear air echoes. The methodologies are reasonable. However, as described in specific comments, the motivation to examine the divergence of horizontal winds is unclear. This manuscript may be acceptable after a considerable revision.

Specific comments



The atmosphere at the height of 10 m is generally in the surface layer. It sounds strange that divergence in the horizontal winds in the surface layer are used to characterize the larger scale structures that span the entire boundary layer.

Authors should reconsider a variable that physically relates to the organized structures in the boundary layer, while variables archived in the reanalysis dataset may be limited.

If authors wish to use the present variable, it may be better to examine surface observations regarding the variations in the divergence in the real atmosphere. Otherwise, investigating the divergence would illuminate an unrealistic aspect of the surface layer in the simulation.

 

As mentioned above, the structures extracted from the reanalysis are more or less artificial. According to Table 2, validations by the clear Radar echos are possible only for the summer. The results shown in Section 5.1 should limit those that can be validated in Section 5.2. 

The image of fig. 4 does not appear in the manuscript (only its caption appears). I could not evaluate the discussion associated with the figure.

In the visual appearances as Figs. 2 and 7, the horizontal scales of organized structures are different between the reanalysis and radar images. Figure 8 shows that the scale in the radar images is even larger.

It would be better to add a clear explanation for this very counter institutive result.

-Line 133

Is the lack of insects at the top of the boundary layer only due to the temperature?

Technical corrections

Many acronyms are used without definitions. Please check throughout.

-Line 90: 

It should be described as λ~2d

-Figure 2

Units and explanations of shading in panel a are missing. 

-Line 159:

"+10dB" may be a mistake for "-10dB".

-Figure 6:

Box plots and definitions of "rx" and "reference" are not clearly explained.  

-Line 268:

I'm not sure the use of "see" is grammatically correct.

In this study, the authors investigate the use of the composite clear-sky radar reflectivity data from German radar network to verify the low-level divergence structures derived from a regional NWP model reanalysis product. Using a two-dimensional wavelet transform, this study shows that divergences derived from the NWP model reanalysis product and radar composite reflectivities can be quantitatively compared in terms of their spatial scale, horizontal pattern, and direction. A long-term validation shows close agreement. The manuscript is well written and should be interesting to the meteorological community. I suggest that the manuscript is accepted after major revisions.  

I have only one major comment about this study. Given that multi-Doppler wind retrieval techniques exist (Bousquet et al. 2008, and Beck et al. 2014 cited in this manuscript by the authors), why the authors did not retrieve two-dimensional or three- dimensional wind fields first, then compare the retrieved winds, or divergence product from multiple radars and compare with the regional analysis COSMO-REA2? Please explain why.

Abstract: It’s not good to use acronyms COSMO-REA2 and RADOLAN without explanation first. You may put these acronyms into a list and put it as an appendix?  

Page 3, line 66-67: Why not use the same large data-base of radial velocities to retrieve winds, then derive divergence structures and do comparison with the model reanalysis COSMO-REA2?

Page 4, line 106-107: What are TerrSysMP and COMSO? Please explain.

Page 5, line 118: Please explain what is the “modified Tiedtke mass-flux scheme? You may need to add a reference here?

Page 6, Figure 2: Please explain units used in the color bars? What do these numbers for the color bars represent?

Page 11, Figure 4: is missed out from the manuscript.

Page 12, Figure 5: If DJF, MAM, JJA, SON represent seasons, please use English.

Page 15, figure 8: Please add units for both x- and y- ordinates.

Page 15, line 288-289: Rewording “The remaining three cases are all relatively small in scale with both data-sets agreeing that 2009-07-29…”.

Page 18, Figure 10: Please add “hours” for the x- ordinate.

Page 20, line 374: Should “20.000 individual…” be “20,000 individual…”?

Page 23, Figure B1: What are the units for these x- or y- ordinates? Please explain the correlation numbers in the up-left corner of each image in the caption. Why (b) misses those correlation numbers?

Comments on “Verification of Near Surface Wind Patterns in Germany using Clear Air Radar Echoes”

The manuscript “Verification of Near Surface Wind Patterns in Germany using Clear Air Radar Echoes” by Buschow and Friederichs, submitted to the Geoscientific Model Development describes the use of Radar observed surface divergence field during clear sky conditions to evaluate the simulated surface winds in COSMO-REA2 regional reanalysis. The evaluation is conducted in terms of the dominant size, anisotropy and orientation of the spatial wind patterns. I believe such direct verification of the wind field of reanalysis data is very important, but seldom conducted, and I applaud the authors for carrying out this study. The manuscript is well-written, and I have only a few minor suggestions as listed below.

Not so major comments:

Fig. 7, Honestly, I found it difficult to compare the radar reflectivity patterns with the COSMO-REA2 10 m divergence. While the model data show coherent small-scale structures that are typical of the surface layer under convective conditions, the radar reflectivity field seems to be filled with much smaller “cellular” structures, and is somewhat noisy. Perhaps I am not well-trained in reading clear-sky radar echo, but I hope the authors could expand the discussion of Fig. 7, pick a case and help the readers compare these images qualitatively?

Minor comments:

Line 140, did you mean “SW/NW” instead?

Line 265, not sure what you mean by “at these time-steps”.

Line 302-303, “It is however worth noting that, despite the offset, both data sets agree that the smallest-scaled patterns occur later in the day than at other stations”, so what does such delay tell us?

Line 374, did you mean you mean “20,000” rather than “20.000”?

Line 396, fix the reference “(Banghoff et al., 01 Aug. 2018)”.