the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 01 Jul 2026
The Max Planck CloudKite (MPCK): High-Resolution Airborne Measurements of Turbulence and Cloud Microphysics
Abstract. We present the airborne Max Planck CloudKite (MPCK) platform, an instrumented tethered aerostat for atmospheric and cloud research, together with its first dedicated measurement system, the Advanced Max Planck CloudKite (MPCK+) instrument, designed for high-resolution observations of cloud microphysics and turbulence up to 2 km above ground level. The platform and instrument design are described, and their performance is evaluated through laboratory characterisation, wind-tunnel experiments, and multiple field campaigns over land and aboard research vessels. These evaluations also include assessments of mounting strategies and flight stability. The MPCK+ instrument combines advanced airborne imaging techniques: inline holography, which characterises particle size, concentration, and shape in three dimensions, and particle image velocimetry (PIV), implemented here for the first time in an in-situ airborne setting. Together, they enable co-located, high-cadence observations of cloud microphysics and turbulence. Intercomparisons with conventional probes (e.g. cloud droplet probes and pitot tubes) show consistent measurements of bulk quantities, while MPCK+ uniquely provides spatially resolved, co-located particle and flow fields, enabling direct observation of localised cloud microphysics–turbulence interactions inaccessible to conventional non-imaging instrumentation. Field performance evaluations demonstrate robust measurements of droplet size, concentration, and turbulence properties across a wide range of cloud conditions. These results demonstrate that the MPCK platform and MPCK+ instrument provide an advanced observational capability for studying cloud microphysics–turbulence interactions, bridging micrometre-scale resolution with continuous sampling over tens of kilometres.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-3456', Anonymous Referee #1, 14 Aug 2026
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RC2: 'Comment on egusphere-2026-3456', Anonymous Referee #2, 20 Aug 2026
The Max Planck CloudKite (MPCK) platform and its MPCK+ instrument package enable high-resolution, low-airspeed airborne observations of cloud microphysics and atmospheric turbulence using a tethered aerostat. This paper is thorough and even painstaking in its rigorous attention to detailed characterization of the system and all component instruments. The authors have achieved what they claim in the closing sentence: “These results establish MPCK platform and MPCK+ as a capable and versatile platform and instrument for probing small-scale processes in clouds and the atmospheric boundary layer, and they provide a solid foundation for future developments.”
Key novel advances include:
- Airborne PIV system: Demonstrates a highly novel airborne two-frame 2D Particle Image Velocimetry (PIV) system, enabling direct calculation of instantaneous velocity gradients and turbulence kinetic energy dissipation rates without relying on long spatial averaging via Taylor's frozen-turbulence hypothesis.
- Synchronized co-located Imaging: Combines 2D PIV with a fast 3D digital in-line holography system. The consecutive hologram spacing is less than 1 m. Every fifth hologram coincides with a PIV frame, creating a co-located volume to observe 3D droplet positions/sizes alongside 2D flow fields.
- Tethered aerostat operation: Deploys a 250 m^3 HeliKite operating at low true airspeeds (~10 m/s) to achieve continuous sampling across tens of kilometers, up to 2 km altitude AGL.
- Aerodynamic characterization: Provides systematic wind-tunnel testing and aerodynamic flow corrections while evaluating flight stability across a wide range of conditions.
I recommend the paper be accepted, and suggest the authors take into consideration the following points:
- Lines 8, 181, and various other places: I shy away from claims of “first”. It’s sufficient to point out that the system is novel.
- Line 29: New single-photon lidar systems can resolve ~1-cm scales, so the statement is not precisely correct. The statement is true for typical atmospheric remote sensing systems.
- Line 89: Possibly a grammatical error… delete “developed”?
- Line 169: The meaning of “key parameters” is vague… be specific.
- Table 1 column labels: MSM82/2 and MSM89 need to be defined in the caption.
- Table 1 acronyms: There are many of them, and they should be defined in the caption, or in the text close to where Table 1 is first cited. Also, it would be very helpful to indicate the subsection numbers where each instrument is discussed in the paper, since the paper is quite long.
- Table 1 caption: Should it be “GPS weak rollover”?… In any case, I have no idea what it means.
- Figure 3 caption: What is meant by “the removed holography and PIV structure”? Do you mean the holography and PIV instrument with the cover removed?
- Line 261: Does the inclusion of a pinhole spatial filer make the system alignment susceptible to vibration? How robust is this approach for spatial filtering?
- Line 284: Grammatical error in “In separate study”.
- Line 319: Sonic anemometers do not require long spatial averaging… they provide local velocity information. I guess you are referring to the use of a sonic anemometer or similar for calculation of energy dissipation rate. Please clarify.
- Lines 344-345: Unclear what this sentence about pulse separation adjustment means.
- Lines 457 and 460: Parentheses for Schroeder reference are incorrect.
- Line 533: I guess “softer” should be software?
- Page 32: Could the poor performance of the CDP be a result of rain water collecting on the instrument optics? Its windows are designed for higher true air speeds, and you mention that drizzle was present. Please discuss.
- Figure 14: In the figure axis label and earlier in the paper, \varepsilon is used for dissipation rate, but in the figure caption and in the surrounding text, \epsilon is used. Please be consistent.
Citation: https://doi.org/10.5194/egusphere-2026-3456-RC2
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Referee Comment is attached as a pdf file