the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Atmospheric sounding of the boundary layer over alpine glaciers using fixed-wing UAVs
Abstract. Glaciers are an integral part of the high mountain environment and interact with the overlying atmosphere and surrounding terrain in a complex and dynamic manner. The energy exchange between the glacier surface and the overlying atmosphere controls ice melt rates and promotes the formation of a low-level katabatic jet that interacts with other, often thermally driven winds in alpine terrain. Information on the structure of the atmospheric boundary layer over glaciers is crucial for studying the characteristics of the katabatic jet, its broader cooling effect, and its susceptibility to be broken up by strong valley or synoptic winds that promote heat advection from the ice- and snow-free periphery towards the glacier. While the number of ground-based measurements from weather stations and meteorological towers installed on glaciers for boundary layer research has increased in recent years, a lightweight and mobile measurement technique for atmospheric sounding over alpine glaciers has not yet been available. Here we describe a new measurement technique based on a low-cost and open-source fixed-wing UAV, which allows sounding the atmospheric boundary layer over glaciers up to several hundred metres above the surface. Vertical profiles of air temperature, humidity, pressure, wind speed, wind direction and turbulence can be derived from the meteorological and flight recorder data collected by the UAV. The results of a measurement campaign on the Kanderfirn in the Swiss Alps on 16 June 2021 demonstrate the potential of the technique and highlight typical features of the boundary layer above a melting glacier surface. The soundings reveal a persistent low-level katabatic jet, characterised by a pronounced surface-based inversion, relatively dry air, high wind speeds and enhanced turbulence, and a warmer and more humid valley wind aloft.
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RC1: 'Comment on amt-2024-174', Anonymous Referee #1, 05 Dec 2024
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Review of “Atmospheric sounding of the boundary layer over alpine glaciers using fixed-wind UAVs” by Groos et al.
This manuscript describes the use of a fixed wing UAS to profile the lower atmosphere over a mountain glacier environment. Since data from only a single day is shown the results here are illustrative of the types of features that could be observed with a UAS field campaign but do not allow for any broader conclusions about glacial meteorology. While the results presented will be of interest as an illustration of the potential research applications of using a small UAS to study alpine glacier meteorology the presentation requires major revisions as described in the comments below. Once these major revisions are completed the manuscript will be suitable for publication in Atmospheric Measurement Techniques.
Major comments
A figure or series of figures illustrating the data processing described on pages 9 and 10 should be included to illustrate what the raw, unprocessed data from the UAS looks like and how that is modified prior to further scientific analysis. This figure(s) should show:
- unprocessed T profiles and the final smoothed profiles in 1 m bins.
- temperature bias between ascent / descent legs averaged to 1 m bins
- illustrate how lapse rates and inversion height are calculated by showing profile of T’(z). In particular I am interested in seeing how noisy the T’(z) profile is and what impact this has on identifying the height of the SBI.
- show RH, T and derived q profiles
- show profile or time series of original resolution roll rate and derived turbulence intensity proxyThese figures showing original data and derived data used in the results section will allow the reader to clearly see how the data was modified to allow for subsequent scientific analysis.
I found the color shaded time-height plots to be attractive but ultimately not very useful for understanding the features present in the UAS observations. I strongly suggest that the authors replace these figures with single plots for each each variable (T, q, wind speed) showing all descent profiles from all flights. By showing all of the profiles on a single plot it will make it easier to see details in the change in magnitude and vertical structure over the course of the day than the color shaded cross-sections currently shown. To help interpret the time evolution shown in this plot each descent profile should be shown in a different color (maybe ranging from blue to red with increasing time of day).
Showing profiles of wind direction, in addition to the wind roses shown in Figure 12, would make it easier for the reader to see the relationship between the switch from down glacier to up valley wind direction and differences in speed.
It would be useful to show a synthesis plot at a representative time showing profiles of all of the analyzed variables together to illustrate how the different variables and their profiles relate to each other.
What is the explanation for the nearly linear lapse rate for profile 1 down to the lowest observed height in the 16:05 sounding in Figure 6? This differs from all of the other profiles and is markedly different from the profiles at adjacent times. Is this an observational error or a real feature of the atmosphere?
Uncertainty in the observed quantities and the impact on interpretation of the results needs to be included. In particular, what is the uncertainty in the derived wind speed and direction and does this alter the interpretation of the results. In particular I am wondering about the rapid shift in wind direction and how this is handled if the spiral path used to calculate wind speed and direction spans both down and up valley wind directions. Does this account for the low wind speed at the height of the change in wind direction (i.e. it is an artifact of how the wind is derived rather than a true feature of the wind profile?).
Minor comment
Lines 110, 123: Figure 2 should be figure 3
Citation: https://doi.org/10.5194/amt-2024-174-RC1
Data sets
Atmospheric sounding of the boundary layer over alpine glaciers using fixed-wing UAVs Alexander R. Groos, Nicolas Brand, Murat Bronz, and Andreas Philipp https://doi.org/10.5281/zenodo.13889613
Model code and software
mmp - mobile measurement post-processing Andreas Philipp https://git.rz.uni-augsburg.de/philipan/mmp
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