The authors investigated the origins of supercooled liquid water and secondary ice in a stratiform precipitation event. Vertically pointing C-band and W-band radars at the Hyytiälä station, scanning C-band weather radar at Ikaalinen, and sounding at Jokioinen, provide rich information of the microphysical and dynamical properties of the mixed-phase layer embedded in the stratiform precipitation system. Radar doppler moments (reflectivity, linear depolarization ratio, Doppler velocity and spectral width) are used to explore cloud dynamics (turbulent layer and wind shear) and identify various hydrometer types (including supercooled cloud droplets, newly-formed ice columns, and background ice). Path integrated attenuation from the C/W dual-wavelength observations also provide an estimation of supercooled liquid water path. Valuable data and careful analysis provide physical insights of the formation of supercooled liquid water and secondary ice production due to a turbulent layer caused by Kelvin-Helmholtz instability: (1) Shear leads to the formation of the Kelvin-Helmholtz instability; (2) Drizzle forms in the K-H billows due to isobaric mixing; (3) Secondary ice forms in the K-H billows due to either the Hallett-Mossop process or droplet breakup during freezing, or both. The manuscript is well written, and results are quite convincing. I suggest the publication of this paper in ACP with only some minor comments below:

1. Figure 4: Blank regions in the Figure (e.g., above 2.8 km at 20:55 UTC) are when liquid cloud droplet mode does not exist in Doppler spectrum? Please state it clearly in the text or caption.
2. Page 14, Line 13-14: “To assess the back trajectory of ice crystals, a simulation of free-falling growing ice columns was performed.” Please provide more details (e.g., literature, equations) of the ice particle growth model.
3. Page 14, Line 23: “N=mass/IWC”. Should it be “N=IWC/mass”?

Comments on the “Supercooled liquid water and secondary ice production in Kelvin-Helmholtz instability as revealed by radar Doppler spectra observations” by H. Li et al.

Using observations by vertical pointing C- and W-band radars, scanning weather radar, and radiosondes, the authors analyzed dynamics and microphysics of supercooled liquid water and secondary ice in a stratiform drizzling cloud. It is a unique and interesting case that K-H cloud has developed in the stratiform cloud. The authors point out that the K-H instability is induced mainly by wind shear. They also revealed that the number concentration of ice columns is higher than the INP concentration by several degrees of magnitude, which indicates the secondary ice production in the K-H billows.

The manuscript is well written, the subject is relevant, the observation data is most advanced, and the results are well presented and discussed. I believe the manuscript is suitable for publication after a minor revision.

Minor points:

1. Page 2, line 30: The description of the dual-polarization Doppler radar technique should go to the data and methodology section, and what do you find from this study should go to the discussion or conclusion sections. The content of this paragraph does not fit the "introduction".
2. Page 4, line 20: (Hogan et al., 2002) -> Hogan et al. (2002).
3. Figure 1: The text, for example, “Vertically pointing (HYDRA-W)”, is not visible.
4. Figure 2: a potential temperature profile in Kelvin other than temperature is better to interpret the stability in the boundary layer.
5. Figure 4: use the same y-axis limits for heights in (a), (b), (c), and (e).
6. Page 11, line 9: iss -> is.
7. Page 11, line 18-21: Could you explain why your results are different from previous studies?
8. Page 11, line 25: (Majewski and French, 2020) -> Majewski and French (2020).
9. Page 14, line 23: What is “mass” in the equation “N = mass/IWC”, and double-check if the equation is correct.
10. Page 16, line 6: “W band” -> “W-band”.