Abstract
Abstract. Mountain research stations are advantageous not only for long-term sampling of cloud properties but also for measurements that are prohibitively difficult to perform on airborne platforms due to the large true air speed or adverse factors such as weight and complexity of the equipment necessary. Some cloud–turbulence measurements, especially Lagrangian in nature, fall into this category. We report results from simultaneous, high-resolution and collocated measurements of cloud microphysical and turbulence properties during several warm cloud events at the Umweltforschungsstation Schneefernerhaus (UFS) on Zugspitze in the German Alps. The data gathered were found to be representative of observations made with similar instrumentation in free clouds. The observed turbulence shared all features known for high-Reynolds-number flows: it exhibited approximately Gaussian fluctuations for all three velocity components, a clearly defined inertial subrange following Kolmogorov scaling (power spectrum, and second- and third-order Eulerian structure functions), and highly intermittent velocity gradients, as well as approximately lognormal kinetic energy dissipation rates. The clouds were observed to have liquid water contents on the order of 1 g m−3 and size distributions typical of continental clouds, sometimes exhibiting long positive tails indicative of large drop production through turbulent mixing or coalescence growth. Dimensionless parameters relevant to cloud–turbulence interactions, the Stokes number and settling parameter are in the range typically observed in atmospheric clouds. Observed fluctuations in droplet number concentration and diameter suggest a preference for inhomogeneous mixing. Finally, enhanced variance in liquid water content fluctuations is observed at high frequencies, and the scale break occurs at a value consistent with the independently estimated phase relaxation time from microphysical measurements.
Highlights
Measurements of detailed interactions between turbulence and cloud processes are challenging
We have investigated the suitability of making simultaneous and collocated cloud and turbulence measurements from a mountaintop research station, with the aim of characterizing the fine-scale turbulence and cloud microphysical properties
High-spatial-resolution measurements of liquid water content, droplet diameter, and turbulent velocity fluctuations were made at the environmental research station Umweltforschungsstation Schneefernerhaus (UFS) in summer and fall 2009
Summary
Measurements of detailed interactions between turbulence and cloud processes are challenging. H. Siebert et al.: Cloud microphysics and turbulence at a mountaintop station at scales well in the inertial subrange down to about 10 times the Kolmogorov scale (typically 1 mm or so) and cloud microphysical properties and compare them to conditions observed in free clouds with similar instrumentation. The measurements are analyzed and interpreted in a manner similar to data recorded in cumulus and stratocumulus clouds by the ACTOS (Airborne Cloud Turbulence Observation System) platform (Siebert et al, 2006a) in order to compare the two approaches. Further details on the turbulence and flow characteristics under cloudy conditions at the UFS are given by Risius et al (2015)
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