It is actually two radars, an ST radar and a meteor radar.

Review comments:

A New Dual-Frequency Stratospheric Tropospheric / Meteor Radar: System Description and First Results

by

Qingchen Xu, Iain Murray Reid, Bing Cai, Christian Adami, Zengmao Zhang, Mingliang Zhao, Wen Li

General comment:

The manuscript presents the initial results of a recently installed ST/meteor radar at Langfang, China. The radar uses a dual-frequency transmitter and receiver system layout for interleaved operation in meteor and stratosphere-troposphere measurement mode. The system performance is demonstrated by wind observations. The stratospheric-tropospheric measurements are cross-compared to radiosondes. There are also results shown deriving gravity wave momentum fluxes. However, there are some concerns related to the analysis and conclusions of how this analysis. The manuscript fits well into the scope of the journal and will become publishable after addressing some concerns.

Comment:

Figures 16 and 17:

These Figures are a duplication of content and should be merged by including a second x-axis on top and a different line color.

Line 306-308:

The sentence seems to refer to Figure 15. However, this Figure shows the momentum fluxes as <u’w’> in m2/s2. Please change the sentence that is matches the units shown in Figure 15?

Section 4.2.2.

This section contains three lines and one equation. Figure 18, which the reviewer assumes, belongs to this section is not mentioned. The reviewer suggests removing this section entirely or expanding this part. This section appears to be disconnected from the main narrative of the paper. In its present form it cannot be published. However, the topic is scientifically important and might can be investigated in the future.

Lines 339-345:

This paragraph is very confusing. At first, different wavelet filters are described, but later Figure 19 and 20 show monthly mean and hourly mean winds? It is recommended to add information when the measurements were taken. The use of Figure 20 is unclear in the context of this paragraph. How do the mean winds compare to the other observations nearby e.g, Mohe, Wuhan?

The reviewer assumes that this section is supposed to path the way for the momentum flux analysis, it is recommended to show the original hourly time series with all waves included and the two filtered data products.

Sections 4.3.1 to 4.3.4:

GW momentum fluxes inferred from meteor radar observations are not straightforward. The most critical aspect is the vertical wind, which is severely biased. A simple least square fit might be not sufficient and more sophisticated mathematical approaches seem to be necessary (https://amt.copernicus.org/articles/15/5769/2022/amt-15-5769-2022.html). As described in the paper, some least square fits result in negative values of the Reynolds-stress tensor on the main diagonal. The momentum fluxes shown in Figure 21 reach values of up to 150 m/s. When applying equation (4), this would lead to mean flow accelerations in the order of 1000 m/s/day for the instantaneous observation. The reviewer suggests discussing these results with other measurements in the literature (e.g., https://doi.org/10.5194/angeo-33-1091-2015,https://doi.org/10.1002/2014GL060501, https://doi.org/10.1002/2016GL068599, https://doi.org/10.1002/2016GL072311). It would be also good to calculate the cooling rate that is associated with such a mean flow acceleration. The reviewer also suggests merging all four sections into one. Figure 22 is not needed.

Line 399-400:

Why not fill the gap region with radiometric temperature and wind observations, which are less sensitive to tropospheric clouds?

Conclusions/summary/outlook:

The conclusions should be revised. The new system is valuable, and the paper demonstrates very good science opportunities. These achievements should be emphasized in this section.

Minor comment:

Line 12: ‘novel’ – new is the better term as it is used in the title. Dual frequency operation with shared hardware is not entirely ‘novel’.

Line 37:  ‘the’ is too much …regions with one radar.

Line 45: remove ‘directly by’

Line 46: cite Hocking, 2005 here

Figure 2: The figure Quality is low

Line 107: The ST-radar antenna array consists of linear polarized antennas?

Line 119: PRF of 200 kHz (700m monostatic range)???

Line 135: accumulated – may be collected.

Line 148-150: The spatial averaging of about 400 km in diameter removes many of the small-scale waves and thus limits the benefit of a 10- or 15-minute temporal resolution.  

Figure 8 and 9 should be reduced. It is maybe sufficient to show one Figure with a few days (or a month) comparing both wind components.

Line 178-180: maybe reference: https://angeo.copernicus.org/articles/35/893/2017/

Line 223: Radar profiles from 30 minutes before …..

Line 264:265: Please add whether these velocities are the line-of-sight measurements of the vertical beam or fitted data from all five beams. Please also include in this section how the spectra are analyzed (moments method vs. fit?) and whether additional coherent or incoherent integrations are added. Also information of the dwell time can be summarized here.

Line 358-361:  Maybe reference: https://angeo.copernicus.org/articles/39/1/2021/angeo-39-1-2021.html

Line 365: one 'window' too much