Institut f. Atmosphäre und Klima
CHN O 15.1
Phone: ++41 44 632 74 26
Mixed-phase clouds are common in the atmosphere. The radiative budget and hydrological cycle are particularly sensitive to the scale of phase partitioning within these clouds. However, observations of the micro structure of mixed-phase clouds, with high temporal and spatial resolution, are lacking.
We have developed a new version of the HOLographic Imager for Microscopic Objects (HOLIMO II), a digital in-line holographic microscope. HOLIMO II is a ground-based field instrument with a pixel resolution of 3 um. Single particle properties like size, shape, and phase are obtained using image analysis algorithms. Cloud properties such as ice crystal concentrations, water droplet concentrations, size distributions and the mixing state can be derived through a statistical approach.
To avoid particle losses, the inlet of the new instrument is directed into the wind by a 2-axis rotating system. Inlet aspiration efficiencies for different particle sizes and ambient wind speeds were simulated using the computational fluid dynamics software ANSYS/FLUENT and were in good agreement with analytical formulas.
Measurements are taken at the High Alpine Research Station Jungfraujoch (elevation 3571 masl) during winter time. In addition to HOLIMO II, a 3D sonic anemometer was used to align the inlet into the wind and also to deliver turbulence data. Data from a fog monitor, which sizes particles through forward scattering, are compared to the HOLIMO II measurements to validate the new instrument.
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