Distinct secondary ice production processes observed in radar Doppler spectra: insights from a case study

By Billault-Roux et al.

The article presents a case study of a precipitation event that took place during ICE GENESIS campaign. The main focus of the study is to investigate whether SIP took place during this event and what potential SIP processes were responsible for observed signatures. The authors have analyzed W-band Cloud radar doppler spectra for this purpose.

General comments: In the recent years there have a number of studies where polarimetric Doppler radar spectra were used to identify formation of ice particles and linking it to SIP.  In our community it is, unfortunately, common that any spectral bimodality is immediately denoted as SIP. I would like to thank the authors for not following this path and using two distinct methods that can be used to identify potential SIP production. Because the polarimetric signature of columnar-ice production is easy to identify, many studies have mainly focused on that region that coincides with the temperature region where H-M rime splintering processes is expected to take place. That is why I was especially was interested to read the section 5.2.2 where the case of formation of “disk-like” crystals was discussed. Overall, the findings presented in the article are consistent with the previous studies.

I find it a missed opportunity that the WRF modeling was only used to provide temperature and wind information. It would be interested to see whether H-M parametrization in WRF was able to identify and accurately represent the observations (see Sinclair et al. (2016) as an example). As there are concerns of the validity of H-M, this study would have been interesting. Hopefully, the authors would have an opportunity to perform such an analysis in the future.

Sinclair, V. A., Moisseev, D., and von Lerber, A. (2016), How dual-polarization radar observations can be used to verify model representation of secondary ice, J. Geophys. Res. Atmos., 121, 10,954– 10,970,  doi:10.1002/2016JD025381.

1. 6 line 170. Your notation for the primary ice mode as rimer, implies that riming is occurring in all the cases. Is that correct and applicable for the whole event? If not, than another name would be better, for example Verlinde et al. (2013) refer to such particles as background ice. Not sure if this is the best name, but at least it does not imply any processes.

Verlinde, J., M. Rambukkange, E. Clothiaux, G. McFarquhar, and E. Eloranta (2013), Arctic multilayered, mixed-phase cloud processes revealed in millimeter-wave cloud radar Doppler spectra, J. Geophys. Res. Atmos., 118, 13,199– 13,213, doi:10.1002/2013JD020183.

P 12. Figure 4. The bright-band that can be observed starting from 1530 UTC just above 500 m, is it the melting layer? If it is, the panel a). needs to be adjusted. Could you please clarify this.

p.20. line 453 and below, So WRF was also used to understand the origin of SLW. You may want to point it out when you describe the WRF simulations.

p.21 line 491-493 Changes in MDV of the rimer mode is a combination of changes in air motion and particle properties, as manifested by observed fall-streaks in the reflectivity field (Fig. 3). Because of this MDV of the rimer mode may not be the best suited for estimating EDR.  Did you consider using velocity of the liquid peak? That is why in Li et al. (2021) the liquid peak velocity was used to study air motion.

In the conclusions you are stating that more involved multi-sensor approaches should be used to confirm occurrence of SIP, could you explain what you mean. Your study mainly relies on Doppler radar observations. The aircraft data was just used to confirm that your inference is not wrong. So what sensors do you miss and need to make your analysis more conclusive?