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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/amt-2019-210
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2019-210
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 24 Jul 2019

Submitted as: research article | 24 Jul 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Using a holographic imager on a tethered balloon system for microphysical observations of boundary layer clouds

Fabiola Ramelli, Alexander Beck, Jan Henneberger, and Ulrike Lohmann Fabiola Ramelli et al.
  • Institute for Atmospheric and Climate Science, ETH Zurich, 8092 Zurich, Switzerland

Abstract. Conventional techniques to measure boundary layer clouds such as research aircrafts are unable to sample in orographic or densely-populated areas. In this paper, we present a newly developed measurement platform on a tethered balloon system (HoloBalloon) to measure in situ vertical profiles of microphysical and meteorological cloud properties up to 1 kilometer above ground. The main component of the HoloBalloon platform is a holographic imager, which uses digital in-line holography to image cloud particles in a velocity independent sample volume, making it particularly well suited for measurements on a balloon. The unique combination of holography and balloon-borne measurements allows observations with high spatial resolution, covering cloud structures from the kilometer down to the millimeter scale.

We present observations of a supercooled low stratus cloud (high fog event) during a Bise situation over the Swiss Plateau in February 2018. In situ microphysical profiles up to 700 m altitude above the ground and at temperatures down to −8 °C and wind speeds up to 15 m s−1 were performed. We were able to capture unique microphysical features from the kilometer down to the meter scale. For example, we observed cloud regions with decreased cloud droplet number concentration (CDNC) and cloud droplet size at scales of 30–50 meters. These cloud inhomogeneities could arise from adiabatic compression and heating and subsequent droplet evaporation in descending air parcels. Moreover, we observed conditions favorable for the formation of boundary layer waves and Kelvin-Helmholtz instability at the cloud top. This potentially influenced the cloud structure on a scale of 10–30 kilometers, which is reflected in the variability of the CDNC.

Fabiola Ramelli et al.
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Short summary
Boundary layer clouds are influenced by many physical and dynamical processes, making accurate forecasting difficult. Here we present a new measurement platform on a tethered balloon to measure cloud microphysical and meteorological profiles. The unique combination of holography and balloon-borne observations allows high-resolution measurements in a well-defined volume. Field measurements obtained over the Swiss Plateau revealed inhomogeneities in the cloud structure of stratus clouds.
Boundary layer clouds are influenced by many physical and dynamical processes, making accurate...
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