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Institute for Atmospheric and Climate Science
 
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Jan Henneberger

Jan Henneberger

ETH Zürich
Jan Henneberger
Institut f. Atmosphäre und Klima
CHN O 15.1
Universitätstrasse 16
8092 Zürich
SWITZERLAND

Phone: ++41 44 632 74 26
E-Mail: 

PostDoc in the lab and field group of Prof. Ulrike Lohmann

Research interests

Puplications

Henneberger, J., Fugal, J. P., Stetzer, O., and Lohmann, U.: HOLIMO II: a digital holographic instrument for ground-based in situ observations of microphysical properties of mixed-phase clouds, Atmos. Meas. Tech., 6, 2975-2987, doi:10.5194/amt-6-2975-2013, 2013.

Motivation

A mixed-phase cloud (MPC), which consist of a mixture of supercooled liquid droplets and ice crystals, is thermodynamically unstable. MPCs without any noticeable vertical velocity and turbulence will thoroughly glaciate on relative short time scales. However, observations have shown that MPCs are a common phenomenon and have been observed in all seasons, under a variety of conditions and at all latitudes worldwide. To understand the processes leading to this longevity measurements of the microphysical properties of the liquid and the ice phase of MPCs with high spatial resolution are important.

Therefore, it is important to study the microphysical properties of mixed-phase clouds because:

Instrument development

We developed the field instrument HOLIMO (HOLographic Imager for Microscopic Objects, Henneberger et. al, 2013), which uses digital in-line holography to in-situ image ensembles of cloud particles within a well defined sample volume. Two-dimensional images of single cloud particles between 6 and 250 m in diameter are algorithmically extracted. Particle shape is analyzed to classify cloud particles larger than 20 m as water droplets (circular) or ice crystals (noncircular). Thus phase-resolved size distributions, concentrations, and cloud water contents are obtained.

HOLIMO is capable of discriminating between water and ice particles, and of measuring number size distributions and water content with a high spatial resolution. HOLIMO provides a method to quantify variations in microphysical properties on a 25m-scale and to reduce uncertainties in ice crystal number concentration measurements.

Field campaigns

Mountain-top field measurements are taken at the High Alpine Research Station Jungfraujoch (elevation 3571 masl) during several field campaigns. The data set of MPCs at JFJ shows that for northerly wind cases partially-glaciated MPCs are more frequently observed than for southerly wind cases. The higher frequency of these intermediate states of MPCs at the JFJ suggests either higher updraft velocities, and therefore higher water-vapor supersaturations, or the absence of sufficiently high ice nuclei concentrations to quickly glaciate the MPC.

In the future, we plan to establish this measurement platform on a cable car. This will yield cost-efficient measurements of vertical profiles of cloud properties. Switzerland with its many mountains is the perfect place to exploit such a new technology. A data set of microphysical properties of orographic MPCs in high spatial resolution with small uncertainties in ice crystal number concentration will be created. This will improve our understanding of the microphysical processes and structure in mixed-phase clouds, in particular the formation of precipitation. The results will be used to improve parameterizations of microphysical processes in regional and global climate models.

 

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© 2014 ETH Zurich | Imprint | Disclaimer | 14 October 2014
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