the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Observations of cold cloud properties in the Norwegian Arctic using ground-based and spaceborne lidar
- 1Department of Geosciences, University of Oslo, Oslo, Norway
- 2Andøya Space Center, Bleiksveien 46, 8480 Andenes, Norway
- 3Nord University, Bodø, Norway
- 1Department of Geosciences, University of Oslo, Oslo, Norway
- 2Andøya Space Center, Bleiksveien 46, 8480 Andenes, Norway
- 3Nord University, Bodø, Norway
Abstract. The role of clouds for the surface radiation budget is particularly complex in the rapidly changing Arctic. However, despite their importance, long-term observations of Arctic clouds are relatively sparse. Here we present observations of cold clouds based on 7 years (2011–2017) of ground-based lidar observations at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) in Andenes in the Norwegian Arctic. In two case studies, we assess (1) the agreement between a collocated cirrus cloud observation from the ground-based lidar and the spaceborne lidar onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite, and (2) the ground-based lidar’s capability of determining cloud phase in mixed-phase clouds from depolarization measurements. We then compute multi-year statistics of cold clouds from both platforms with respect to their occurence, cloud top and base height, cloud top temperature and thermodynamic phase for the period 2011–2017. We find that satellite and ground-based observations agree well for the coincident cirrus measurement, and that the vertical phase distribution within a liquid-topped mixed-phase cloud could be identified from depolarization measurements. On average, 8 % of all satellite profiles were identified as single-layer cold clouds with no apparent seasonal differences. The average cloud top and base heights combining the ground-based and satellite instrument are 9.1 km and 6.9 km, respectively, resulting in an average thickness of 2.2 km. Seasonal differences between the average top and base heights are on the order of 1–2 km and are largest when comparing autumn (highest) and spring (lowest). However, seasonal variations are small compared to the observed day-to-day variability. Cloud top temperatures agree well between both platforms with warmer cloud top temperatures in summer. The presented study demonstrates the capabilities of long-term cloud observations in the Norwegian Arctic from the ground-based lidar at Andenes.
Britta Schäfer et al.
Status: final response (author comments only)
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RC1: 'Comment on acp-2021-1072', Anonymous Referee #1, 17 Mar 2022
This manuscript compares cloud macrophysical properties from ground-based and spaceborne lidar observations. For two case studies and a 7-year long data set, the cloud base and top heights, and the phase of the clouds observed over Andenes in the Norwegian Arctic were derived. By means of thermodynamic profiles, the temperature at cloud top was estimated. For the ground-based lidar, the closest radiosonde or ERA-5 was applied, while for the spaceborne system the ECMWF-AUX data product was used. Additionally, the phase separation capability of a polarization lidar is highlighted. The manuscript is well structured and it provides a valuable contribution to the study of Arctic clouds. The paper is of interest to the community, especially the comparison between the ground-based and spaceborne lidar systems is of importance and it should be published after some major revisions were made.
The reason to apply different methods for the estimation of the cloud top temperature is not clear to me. If the goal was to assess the ECMWF-AUX data product, this should be made more clear in the manuscript. However, if the objective was to compare the observations of the two lidar systems, the same approach to derive the cloud top temperature should be applied. In this case, I do not see a reason, to not also not apply the radiosonde/ERA-5 approach to derive the cloud top temperature for the spaceborne observations.
In addition, I doubt that indeed the cloud top temperature can be derived as accurately as it is suggested by Figure 7 a+b. Here the histogram bins have been set to 1K, which seems rather accurate when considering, e.g., that only two radiosondes were launched per day and the radiosonde may have drifted up 20-50km (e.g., according to Seidel, JGR, 2011, https://doi.org/10.1029/2010JD014891) until it reaches the upper troposphere / lower stratosphere.
Besides these comments, I have some minor comments:
A general comment: Consider reducing connector words, like “however, nevertheless, …”. Especially however is used rather often (e.g., 3 times between lines 37 and 45).
Page 2, line 55: Mention the difficulties of satellites to detect lower clouds due to ground clutter
Page 3, line 72: Define “cold cloud”
Page 3, line 86: Add “profiling” before “the middle and upper atmosphere”
Page 4, line 112: Better reword: “The cloud optical depth is another…”
Page 5, line 123: Explain how you get the molecular backscatter.
Page 5, line 132: How many false classifications were manually detected? What could cause such a false classification?
Page5, line 136: How far is Bodø from Andenes?
Page 6, line 165: Remove “This increases the number of satellite overpasses”
Page 9, line 209: Add “cirrus” before “category” and change “found” to “observed”
Page 9, line 223: I suggest rewording this paragraph and stating the information, that the radiosonde did not penetrate the observed layer already at the beginning.
Page 9, line 230: What is meant by "the center of the cloud"? I guess the base of the liquid dominated layer. Later the virga is described as “below cloud”, which sounds like, the base of the liquid-dominated layer is the cloud base. Please be more specific.
Page 11, line 166: “This is less ...”. What does “this” refer to?
Page 13, Figure 6: I suggest combining Figure 6 a+b into one plot. The same holds for Fig. 7 c+d (I am not sure about Fig. 7 a+b).
Page 13, line 290/291: remove “as well”
Page 13, line 302/303: please change Barrow to Utqiaġvik
Page 14, line 308: Remove “In terms of geometrical properties”
Page 16, line 329/330: “ice nucleating particle concentrations are often sufficient to completely glaciate single-layer clouds at the given temperatures”. This statement is too strong, as some of the observed clouds may have formed via homogeneous ice formation.
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RC2: 'Comment on acp-2021-1072', Anonymous Referee #3, 25 Apr 2022
Review of: "Observations of cold cloud properties in the Norwegian Arctic using ground-based and spaceborne lidar"
by Britta Schäfer, Tim Carlsen, Ingrid Hanssen, Michael Gausa, and Trude Storelvmo
Comments:
The authors present ground-based lidar observations of cold clouds in Andenes (Norway), covering a period of seven years. They explored two case studies to assess 1) the agreement between a co-located cirrus observation from ground-based lidar and CALIPSO, and 2) the ground-based lidar’s capability of determining cloud phase in mixed-phase clouds from depolarization measurements. Also, they presented statistics of cold clouds macrophysical properties for the period 2011-2017.
I find the manuscript interesting and well-organized. I have the following comments that require clarifications before publication of the manuscript.
Clarification needed:
- The authors mentioned that they used 137 ERA5 pressure levels. What is known is that ERA5 are available at 137 model levels (not pressure level) and 37 pressure levels (coarse). Please clarify if some conversion procedures have been used or correction is needed?
- Based on Figure 1, in average ERA5 can overestimates (underestimates) cloud top temperature with a difference that can reach ~10 K. Please, elaborate on the effect of this differences on your results and conclusion, especially for the period before 2014 ?
- In addition to the spatial difference, what is the average time lag between the radiosonde and ERA5 (for cloud top temperature) ?
- Also, the vertical resolution of ERA5 at pressure levels is still coarse (not the case for model level, especially at the cirrus cloud levels). Using the interpolation can omit some important details, especially for thin cirrus. Please elaborate?
- Line195: Which method is used to estimate the tropopause? Please clarify?
- Please clarify further about phase discrimination between cirrus, mixed-phase and liquid clouds, during maintenance break from April 2013 to July 2015 ?
- The authors mentioned that “…. Thus, the cirrus cloud is extending well into the tropopause, dehumidifying the upper troposphere and lower stratosphere region through ice crystal growth and sedimentation.”
- Can you provide evidence (quantification) on dehumidifying the lower stratosphere caused by cirrus? Also, on cirrus reaching lower stratosphere causing dehydration.
- I would like to see figures and discussion about the corresponding relative humidity with respect to ice (in-cloud and clear-sky) associated with cirrus cloud. Also, its impact on cirrus cloud, dehydration, and your conclusion.
Minor comments:
Correct “occurence" --> occurrence. (lines 8, 22, 57, 64,66, 291 and y-axis of Fig.5b)
Britta Schäfer et al.
Britta Schäfer et al.
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