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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

Clouds play an important role in the formation of precipitation, in the radiative balance, in the hydrological cycle, and chemistry of the atmosphere. 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.

Instrument development

Our field instrument HOLIMO II (HOLographic Imager for Microscopic Objects II) 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 II is capable of discriminating between water and ice particles, and of measuring number size distributions and water content with a high spatial resolution. HOLIMO II 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). Data of more than 100 h on 14 different days was analyzed, representing the longest time series from a holographic instrument in atmospheric science. Two topologically influenced wind regimes were identified, each with distinct cloud properties. For southerly winds, associated with a smoother ascent, the properties of the MPCs were similar to findings of stratiform Arctic MPCs. During north wind cases, associated with a sharper ascent, more intermediate ice-water-content to total-water-content ratios (IWC/TWC), and higher ice crystal concentrations, were observed. At the measured ice crystal concentrations the cloud would efficiently glaciate in relatively short time, which leads to the hypothesis that the high updraft velocities stabilize the MPCs at Jungfraujoch to more intermediate IWC/TWC fractions.

 

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© 2014 ETH Zurich | Imprint | Disclaimer | 29 November 2013
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