the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Snowfall in Northern Finland derives mostly from ice clouds
- 1Department of Environmental Sciences, University of Basel, 4056 Basel, Switzerland
- 2Space and Earth Observation Centre, Finnish Meteorological Institute, 99600 Sodankylä, Finland
- 3Environmental Remote Sensing Laboratory, Swiss Federal Institute of Technology in Lausanne, 1015 Lausanne, Switzerland
- 1Department of Environmental Sciences, University of Basel, 4056 Basel, Switzerland
- 2Space and Earth Observation Centre, Finnish Meteorological Institute, 99600 Sodankylä, Finland
- 3Environmental Remote Sensing Laboratory, Swiss Federal Institute of Technology in Lausanne, 1015 Lausanne, Switzerland
Abstract. Cloud properties play a critical role in the Arctic surface energy budget. We present ground-level observations of snowfall coinciding with radiosonde launches in Sodankylä (67.367° N, 26.629° E) through a period of eight cold months (October–April) in 2019 and 2020. They comprise 7401 depositing snow particles detected by a snowflake camera and 468 radiosonde profiles. Our results show that precipitating clouds were extending from ground to at least 2.7 km in altitude. Approximately one quarter of them were mixed-phase and the rest were likely fully glaciated. Estimations of the cloud top temperatures indicate that in roughly half of the snowfall events ice might have been initiated through heterogeneous freezing. For such cases, the predicted ice-nucleating particle concentrations active at cloud top temperatures could explain the analysed ice crystal particle concentrations observed near ground. In a warmer climate, the relative proportion of solid to liquid cloud particles will probably decrease, with implications on the Arctic radiation balance.
Claudia Mignani et al.
Status: final response (author comments only)
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RC1: 'Comment on acp-2022-98', Anonymous Referee #3, 05 Apr 2022
Overall Quality
This manuscript utilizes a merged-instrument approach to characterize precipitating ice particle habits at a remote site in inland Finlind. Primarily using 12-hourly soundings and the Multi-Angle Snowflake camera (MASC), the study determines via knowledge of ice particle history and growth regimes that approximately three-quarters of ice particles originate from cloud layers with top temperatures outside of the mixed-phase region (i.e., sub-liquid RH saturation [<99%]), suggesting that the majority of cloud layers are fully glaciated. Using an empirical formulation, they finally determine that the number of ice nucleating particles (INP) were likely sufficient to explain heterogenous ice production, suggesting an inactive ice multiplication mechanism (outside of possible collisions). Overall, the manuscript is of excellent quality in terms of science, documentation, figures, and structure. The authors clearly made a significant effort to explain their data processing in a concise manner. After addressing a few specific comments and technical corrections, I recommend this manuscript pursue publication in ACP.
Specific Comments
Fig 6. & ~Line 183: I would point out to the reader that the color-scales on each panel are different.
Line 159 & Fig. 3: What exactly is “visibility”? If it is similar to cloud base height, then these are an order of magnitude off. It would also be good to mention how cloud base height was detected within the instrumentation at the site. If it is a nm-wavelength active remote sensor, then I would expect my interpretation of visibility to closely optically correspond with cloud base height.
Fig 3: I’m confused about the sea level pressure measurements. If the station is only 179 m ASL, these values are way too low.
Fig 2 & Line 134: Why 15 minutes prior to sounding release? Wouldn’t 15 minutes aftertward be more representative of the cloud that is producing the precipitation?
Line 213: Nice conclusion!
Technical Corrections
Line 61: “automatically” should be “automatic”
Line 63: “summery” should be “summer”
Fig A1: “lowlight” should be “highlight”
Line 81: suggest using “length” instead of “height”
Line 94: Should “An ice particle classified” be “An ice is particle classified”?
Line 153: Should “weighed” be “weighted”?
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RC2: 'Comment on acp-2022-98', Anonymous Referee #2, 05 Apr 2022
The authors use several months of radiosonde soundings and coincident, ground-based hydrometeor imagery at a high-latitude station in northern Finland to infer ice formation pathways during snow events. Relative humidity (RH) profiles (both with respect to water and ice) from radiosonde data are used to develop a simplistic snow event predictor. For snow events, the authors show how imagery-based ice particle habits change as a function of RHw. Using cloud-top temperature the authors conclude that primary ice formation was the main pathway to form snow.
The study is well written and contains many useful plots. I recommend publication after resolving a few major issues.
Major points
The “Results” section includes a few elements of a discussion. However, I feel the study would benefit from a broader discussion that is also placed into its own section. Following points should be relevant to the reader:
- The authors start their study by mentioning the Arctic surface budget. Do the authors think the site in Finland is representative of the Artic? Or could the continental character and the influence from boreal forests (e.g., Schneider et al., 2021) mislead?
- Would other (frequently used) INP parameterization lead to the same conclusions?
- Could the high-RHw group (Fig. 8) be useful as a proxy of snow events in a warmer climate?
- Is a 15 min window appropriate? How long would it take for a particle to fall from ~2.7 km?
Please review the order of the figures. Figure 7 is mentioned earlier (l. 89) than Figure 2 (l. 150). The same review should be applied for supplementary figures.
Minor points
l. 1 This sentence sticks out. Either specify “properties” and their “role” or write it more general as “clouds” (instead of “cloud properties”).
ll. 198-199 Perhaps show examples of unclassifiable particles.
l. 208 This sentence is redundant as the information was provided in l. 206.
l. 225 How is cloud-top temperature obtained?
ll. 226-228 This description needs improvement and perhaps an illustration of the concept. What is meant by “gaps” and how do you determine them?
ll. 244-247 This seems highly relevant and should be shown as its own plot.
Claudia Mignani et al.
Claudia Mignani et al.
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