Investigating KDP signatures inside and below the dendritic growth layer with W-band Doppler Radar and in situ snowfall camera

Kötsche, Anton; Myagkov, Alexander; von Terzi, Leonie; Maahn, Maximilian; Ettrichrätz, Veronika; Vogl, Teresa; Ryzhkov, Alexander; Bukovcic, Petar; Ori, Davide; Kalesse-Los, Heike

doi:https://doi.org/10.5194/egusphere-2025-734

Preprints

https://doi.org/10.5194/egusphere-2025-734

Preprints

27 Feb 2025

| 27 Feb 2025

Investigating KDP signatures inside and below the dendritic growth layer with W-band Doppler Radar and in situ snowfall camera

Anton Kötsche, Alexander Myagkov, Leonie von Terzi, Maximilian Maahn, Veronika Ettrichrätz, Teresa Vogl, Alexander Ryzhkov, Petar Bukovcic, Davide Ori, and Heike Kalesse-Los

Abstract. Polarimetric radars provide variables like the specific differential phase (K_DP) to detect fingerprints of dendritic growth in the dendritic growth layer (DGL) and secondary ice production, both critical for precipitation formation. A key challenge in interpreting radar observations is the lack of in situ validation of particle properties within the radar measurement volume. While high K_DP in snow is usually associated with high particle number concentrations, only few studies attributed K_DP to certain hydrometeor types and sizes. To address this, we combined surface in situ observations from the Video In Situ Snowfall Sensor (VISSS) with remote sensing data from a polarimetric W-band radar and an X-band radar, along with modeling approaches. Data was collected during the CORSIPP project, part of the ARM SAIL campaign (winter 2022/2023, Colorado Rocky Mountains). We found that at W-band, high K_DP magnitudes can result from a broad range of particle number concentrations, between 1 and 100 l^-1. Blowing snow and increased ice collisional fragmentation in a turbulent layer enhanced observed K_DP values. T-matrix simulations indicated that high K_DP values were primarily produced by particles smaller than 0.8 mm in the DGL and 1.2 mm near the surface. Discrete dipole approximation simulations based on VISSS data suggested that dendritic aggregates larger than 2.5 mm contributed 10–20 % to the measured W-band K_DP near the surface. These findings highlight the complexity of interpreting W-band K_DP in snowfall and emphasize the need for combined in situ observations and radar forward simulations to better understand snowfall microphysical processes.

Received: 17 Feb 2025 – Discussion started: 27 Feb 2025

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Journal article(s) based on this preprint

29 Oct 2025

Investigating KDP signatures inside and below the dendritic growth layer with W-band Doppler radar and in situ snowfall camera

Anton Kötsche, Alexander Myagkov, Leonie von Terzi, Maximilian Maahn, Veronika Ettrichrätz, Teresa Vogl, Alexander Ryzhkov, Petar Bukovcic, Davide Ori, and Heike Kalesse-Los

Atmos. Chem. Phys., 25, 14045–14070, https://doi.org/10.5194/acp-25-14045-2025,https://doi.org/10.5194/acp-25-14045-2025, 2025

Short summary

Anton Kötsche, Alexander Myagkov, Leonie von Terzi, Maximilian Maahn, Veronika Ettrichrätz, Teresa Vogl, Alexander Ryzhkov, Petar Bukovcic, Davide Ori, and Heike Kalesse-Los

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-734', Anonymous Referee #1, 21 Apr 2025
Review of “Investigating KDP signatures inside and below the dendritic growth
layer with W-band Doppler Radar and in situ snowfall camera.”

This paper examines the dual polarimetric signatures recorded by LIMRAD94, a W-band profiling radar, during CORSIPP, a project associated with the winter 2022/2023 season of the SAIL field experiment in the Upper Colorado River Basin. The authors installed a Video In
Situ Snowfall Sensor on the second ARM Mobile Facility that was deployed at Gothic during SAIL and then pointed the LIMRAD94 at a 40-degree azimuth to provide a rare dataset of co-located dual polarization and in situ snowfall measurements. The authors, in detail, describe the microphysical processes that could be occurring in four different fall streaks observed by the profiler during SAIL. Overall, I found the paper to be a very interesting read, going into detail about the microphysical processes that affect precipitation in these fall streaks. I would recommend it for publication, pending a few questions/suggestions that I have.

Major comments:
I think a conceptual diagram showing the microphysical mechanisms occurring in each fall streak observed should be in the paper, perhaps in the conclusions section. This would make it easier for the reader to envision the complex microphysics of these fall streaks.

In Section 3.3, the authors use T-matrix simulations to estimate dual polarimetric radar moments from particle size distribution of aggregates at X-band, but then proceed to use DDA for their W-band simulated moment calculations. This leaves the reader wondering why DDA was not used for both the X-band and W-band scattering simulations, since DDA should be much better able to characterize the scattering of irregular ice crystals than T-Matrix based techniques. Why were T-Matrix calculations used for simulating the X-band KDP/Ze? I think it would be more consistent to use DDA for both wavelengths. Either that, or the authors should elucidate as to why they chose T-Matrix for their X-band simulated KDP/Ze values. Perhaps the authors wanted to easily determine how aspect ratio can determine the simulated KDP/Ze. If so, that should be better stated here. I also do not think Figure 10 is needed, as the KDP/Ze ratio seems to only significantly vary with size, with a few hundred microns uncertainty in the size due to oblateness. These estimated ranges of particle sizes can simply be quoted in the text.

Lines 484-490: There are log10 (KDP/Ze) values down to -4 in FS1. Therefore, statements here about log10 (KDP/Ze) being greater than -2.5 do not look to apply here. In addition, it looks like this ratio increases with time as we see the PSD from the VISSS record higher concentrations of small particles, though this would require plotting timeseries of log10(KDP/Ze) for a few given levels to verify. These lower KDP/Ze, especially in FS1, would be consistent with the larger aggregates/graupel below the -10 C level as suggested from the vertical profiles from LIMRAD94 in Figure 8. Since the VISSS-observed PSD in FS1 is radically different from the other 3, I think these points are worth factoring into your discussion of Figure 11.

Minor Comments:
Line 8: It would be nice to be more quantitative about what magnitudes of Kdp we are talking about here.
Line 492: I know that an absolute target calibration of the CSU X-Band was performed pre-campaign. That showed that the CSU X-band had a low bias of 2.6 dB, so it would be worth stating that here. It’s also not clear here if the stated offset is a low offset or a high offset.
Figure 8: The purple color for spectral width is hard to distinguish from the ZDR and sZDR curves. I would suggest changing the color to Orange. I also would remove the figure legends from sub-panels b, c, and d to increase readability.
Technical Comments:
Line 16: The first sentence in Section 1 is a run-on sentence.
Line 126: Missing parentheses around citation.
Line 167: Extra “,” after “40.”
Citation: https://doi.org/10.5194/egusphere-2025-734-RC1
- AC1: 'Reply on RC1', Anton Kötsche, 11 Jul 2025
  
  Dear Reviewer,
  Thank you for carefully reading the manuscript and pointing out several issues where the description needs to be refined for a
  
  better understanding. The requested clarifications and references to ambiguities contribute to the improvement of the
  
  manuscript.
  Please find the pdf attached with answers to your comments and an overview over all changes made to the manuscript.
  Sincerely, on behalf of all authors,
  Anton Kötsche
  
  Citation: https://doi.org/10.5194/egusphere-2025-734-AC1
RC2:
'Comment on egusphere-2025-734', Anonymous Referee #2, 30 May 2025
The manuscript entitled "Investigating KDP signatures inside and below the dendritic growth layer with W-band Doppler Radar and in situ snowfall camera" by Kötsche et al. studies the linkages between KDP both within and below the dendritic growth layer using polarimetric radars and a ground-based snowfall imager during the DOE-ARM funded CORSIPP project in the Colorado Rocky Mountains. The results are mostly clear and concise, and the datasets presented show a clear need to further study the polarimetric response to microphysics properties within ice- and mixed-phase clouds. Provided that the authors address the Major and Minor comments below, the revised text should yield a manuscript worthy of publication
Major comments
Although the CSU X-band radar is less susceptible to non-Rayleigh scattering, why was the T-matrix method used over DDA to remain consistent with the W-band polarization analysis (Sec. 3.3)? At a minimum, the authors should more clearly defend this decision (e.g., computational cost, etc.).

Aside from the fallstreak analysis from one case (Fig. 6), there is little analysis on the observed particle types/habits observed from the VISS. Have the authors considered identifying these habits statistically to confirm the presence of e.g. dendrites versus much more commonly-occurring irregular crystals? If identifying these habits is too time consuming or beyond the scope of this study, perhaps the VISSS complexity parameter can elucidate the connection of more complex shapes, such as dendrites, to the polarimetric observations in the environments conducive to such particle habits. It is important to provide evidence of the particle types that are related to the microphysical processes discussed (e.g., dendrites in the DGZ, needles with SIP).

Deriving other PSD parameters from the VISSS, such as the slope (Λ) or shape (μ) parameter may further strengthen the relationships/comparisons between the microphysics and remotely-sensed regions of cloud. Statements such as “It is likely that aggregation rapidly depletes the number of small particles” (L376) read as speculative when these parameters can be used to strengthen the arguments made.

The summary/conclusions section may benefit from a conceptual diagram that visualizes the complexities associated with the microphysics and their relation to KDP, etc. as alluded to in the abstract and introduction

Minor comments
Fig. 7: Please confirm whether what’s being plotted is a concentration, as the y-axis units suggests, or if it’s normalized by the bin width which would require the units to be corrected.

Because this study uses data collected near mountainous terrain, it should be stated somewhere that these conclusions represent a particular environment/synoptic setup and may not be valid for all environments (e.g., different forcing mechanisms, presence of supercooled liquid, etc.).

Technical corrections
L55: You can remove “among others” as the “e.g.” implies this

L75: Remove “e.g.”

L84: I recommend capitalizing the words comprising of the CORSIPP acronym

L103: “overview over” -> “overview of”

L113: Add a comma after “respectively”

L150: Parentheses are only needed around the units

L150: “radar reflectivity” -> “equivalent radar reflectivity”

L250: Add a space between 500 m

L321: “Chapter” -> “Section”
Citation: https://doi.org/10.5194/egusphere-2025-734-RC2
- AC2: 'Reply on RC2', Anton Kötsche, 11 Jul 2025
  
  Dear Reviewer,
  Thank you for carefully reading the manuscript and pointing out several issues where the description needs to be refined for a
  
  better understanding. The requested clarifications and references to ambiguities contribute to the improvement of the
  
  manuscript.
  Please find the pdf attached with answers to your comments and an overview over all changes made to the manuscript.
  Sincerely, on behalf of all authors,
  Anton Kötsche
  
  Citation: https://doi.org/10.5194/egusphere-2025-734-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-734', Anonymous Referee #1, 21 Apr 2025
Review of “Investigating KDP signatures inside and below the dendritic growth
layer with W-band Doppler Radar and in situ snowfall camera.”

This paper examines the dual polarimetric signatures recorded by LIMRAD94, a W-band profiling radar, during CORSIPP, a project associated with the winter 2022/2023 season of the SAIL field experiment in the Upper Colorado River Basin. The authors installed a Video In
Situ Snowfall Sensor on the second ARM Mobile Facility that was deployed at Gothic during SAIL and then pointed the LIMRAD94 at a 40-degree azimuth to provide a rare dataset of co-located dual polarization and in situ snowfall measurements. The authors, in detail, describe the microphysical processes that could be occurring in four different fall streaks observed by the profiler during SAIL. Overall, I found the paper to be a very interesting read, going into detail about the microphysical processes that affect precipitation in these fall streaks. I would recommend it for publication, pending a few questions/suggestions that I have.

Major comments:
I think a conceptual diagram showing the microphysical mechanisms occurring in each fall streak observed should be in the paper, perhaps in the conclusions section. This would make it easier for the reader to envision the complex microphysics of these fall streaks.

In Section 3.3, the authors use T-matrix simulations to estimate dual polarimetric radar moments from particle size distribution of aggregates at X-band, but then proceed to use DDA for their W-band simulated moment calculations. This leaves the reader wondering why DDA was not used for both the X-band and W-band scattering simulations, since DDA should be much better able to characterize the scattering of irregular ice crystals than T-Matrix based techniques. Why were T-Matrix calculations used for simulating the X-band KDP/Ze? I think it would be more consistent to use DDA for both wavelengths. Either that, or the authors should elucidate as to why they chose T-Matrix for their X-band simulated KDP/Ze values. Perhaps the authors wanted to easily determine how aspect ratio can determine the simulated KDP/Ze. If so, that should be better stated here. I also do not think Figure 10 is needed, as the KDP/Ze ratio seems to only significantly vary with size, with a few hundred microns uncertainty in the size due to oblateness. These estimated ranges of particle sizes can simply be quoted in the text.

Lines 484-490: There are log10 (KDP/Ze) values down to -4 in FS1. Therefore, statements here about log10 (KDP/Ze) being greater than -2.5 do not look to apply here. In addition, it looks like this ratio increases with time as we see the PSD from the VISSS record higher concentrations of small particles, though this would require plotting timeseries of log10(KDP/Ze) for a few given levels to verify. These lower KDP/Ze, especially in FS1, would be consistent with the larger aggregates/graupel below the -10 C level as suggested from the vertical profiles from LIMRAD94 in Figure 8. Since the VISSS-observed PSD in FS1 is radically different from the other 3, I think these points are worth factoring into your discussion of Figure 11.

Minor Comments:
Line 8: It would be nice to be more quantitative about what magnitudes of Kdp we are talking about here.
Line 492: I know that an absolute target calibration of the CSU X-Band was performed pre-campaign. That showed that the CSU X-band had a low bias of 2.6 dB, so it would be worth stating that here. It’s also not clear here if the stated offset is a low offset or a high offset.
Figure 8: The purple color for spectral width is hard to distinguish from the ZDR and sZDR curves. I would suggest changing the color to Orange. I also would remove the figure legends from sub-panels b, c, and d to increase readability.
Technical Comments:
Line 16: The first sentence in Section 1 is a run-on sentence.
Line 126: Missing parentheses around citation.
Line 167: Extra “,” after “40.”
Citation: https://doi.org/10.5194/egusphere-2025-734-RC1
- AC1: 'Reply on RC1', Anton Kötsche, 11 Jul 2025
  
  Dear Reviewer,
  Thank you for carefully reading the manuscript and pointing out several issues where the description needs to be refined for a
  
  better understanding. The requested clarifications and references to ambiguities contribute to the improvement of the
  
  manuscript.
  Please find the pdf attached with answers to your comments and an overview over all changes made to the manuscript.
  Sincerely, on behalf of all authors,
  Anton Kötsche
  
  Citation: https://doi.org/10.5194/egusphere-2025-734-AC1
RC2:
'Comment on egusphere-2025-734', Anonymous Referee #2, 30 May 2025
The manuscript entitled "Investigating KDP signatures inside and below the dendritic growth layer with W-band Doppler Radar and in situ snowfall camera" by Kötsche et al. studies the linkages between KDP both within and below the dendritic growth layer using polarimetric radars and a ground-based snowfall imager during the DOE-ARM funded CORSIPP project in the Colorado Rocky Mountains. The results are mostly clear and concise, and the datasets presented show a clear need to further study the polarimetric response to microphysics properties within ice- and mixed-phase clouds. Provided that the authors address the Major and Minor comments below, the revised text should yield a manuscript worthy of publication
Major comments
Although the CSU X-band radar is less susceptible to non-Rayleigh scattering, why was the T-matrix method used over DDA to remain consistent with the W-band polarization analysis (Sec. 3.3)? At a minimum, the authors should more clearly defend this decision (e.g., computational cost, etc.).

Aside from the fallstreak analysis from one case (Fig. 6), there is little analysis on the observed particle types/habits observed from the VISS. Have the authors considered identifying these habits statistically to confirm the presence of e.g. dendrites versus much more commonly-occurring irregular crystals? If identifying these habits is too time consuming or beyond the scope of this study, perhaps the VISSS complexity parameter can elucidate the connection of more complex shapes, such as dendrites, to the polarimetric observations in the environments conducive to such particle habits. It is important to provide evidence of the particle types that are related to the microphysical processes discussed (e.g., dendrites in the DGZ, needles with SIP).

Deriving other PSD parameters from the VISSS, such as the slope (Λ) or shape (μ) parameter may further strengthen the relationships/comparisons between the microphysics and remotely-sensed regions of cloud. Statements such as “It is likely that aggregation rapidly depletes the number of small particles” (L376) read as speculative when these parameters can be used to strengthen the arguments made.

The summary/conclusions section may benefit from a conceptual diagram that visualizes the complexities associated with the microphysics and their relation to KDP, etc. as alluded to in the abstract and introduction

Minor comments
Fig. 7: Please confirm whether what’s being plotted is a concentration, as the y-axis units suggests, or if it’s normalized by the bin width which would require the units to be corrected.

Because this study uses data collected near mountainous terrain, it should be stated somewhere that these conclusions represent a particular environment/synoptic setup and may not be valid for all environments (e.g., different forcing mechanisms, presence of supercooled liquid, etc.).

Technical corrections
L55: You can remove “among others” as the “e.g.” implies this

L75: Remove “e.g.”

L84: I recommend capitalizing the words comprising of the CORSIPP acronym

L103: “overview over” -> “overview of”

L113: Add a comma after “respectively”

L150: Parentheses are only needed around the units

L150: “radar reflectivity” -> “equivalent radar reflectivity”

L250: Add a space between 500 m

L321: “Chapter” -> “Section”
Citation: https://doi.org/10.5194/egusphere-2025-734-RC2
- AC2: 'Reply on RC2', Anton Kötsche, 11 Jul 2025
  
  Dear Reviewer,
  Thank you for carefully reading the manuscript and pointing out several issues where the description needs to be refined for a
  
  better understanding. The requested clarifications and references to ambiguities contribute to the improvement of the
  
  manuscript.
  Please find the pdf attached with answers to your comments and an overview over all changes made to the manuscript.
  Sincerely, on behalf of all authors,
  Anton Kötsche
  
  Citation: https://doi.org/10.5194/egusphere-2025-734-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Anton Kötsche on behalf of the Authors (11 Jul 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (19 Jul 2025) by Matthew Lebsock

RR by Anonymous Referee #1 (01 Aug 2025)

RR by Anonymous Referee #2 (10 Aug 2025)

ED: Publish as is (11 Aug 2025) by Matthew Lebsock

AR by Anton Kötsche on behalf of the Authors (12 Aug 2025)

Journal article(s) based on this preprint

29 Oct 2025

Investigating KDP signatures inside and below the dendritic growth layer with W-band Doppler radar and in situ snowfall camera

Anton Kötsche, Alexander Myagkov, Leonie von Terzi, Maximilian Maahn, Veronika Ettrichrätz, Teresa Vogl, Alexander Ryzhkov, Petar Bukovcic, Davide Ori, and Heike Kalesse-Los

Atmos. Chem. Phys., 25, 14045–14070, https://doi.org/10.5194/acp-25-14045-2025,https://doi.org/10.5194/acp-25-14045-2025, 2025

Short summary

Anton Kötsche, Alexander Myagkov, Leonie von Terzi, Maximilian Maahn, Veronika Ettrichrätz, Teresa Vogl, Alexander Ryzhkov, Petar Bukovcic, Davide Ori, and Heike Kalesse-Los

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Short summary

Our study combines radar observations of snowf with snowfall camera observations on the ground to enhance our understanding of radar variables and snowfall properties. We found that values of an important radar variable (K_DP) can be related to many different snow particle properties and number concentrations. We were able to constrain which particle sizes contribute to K_DP by using computer models of snowflakes and showed which microphysical processes during snow formation can influence K_DP.

Investigating KDP signatures inside and below the dendritic growth layer with W-band Doppler Radar and in situ snowfall camera

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