Small-scale mixing at cloud top observed in a laboratory cloud chamber – preliminary results

Mixing between cloud and unsaturated clear air is investigated a laboratory cloud chamber by means of PIV – Particle Imaging Velocimetry technique. In order to compare with recent field and numerical studies, the experiment is set-up to mimic some features of small-scale mixing at the Stratocumulus top. This is achieved by slow (almost laminar) filling of the chamber from below with cloudy moist and dense air containing droplets. Evaporative cooling in the laminar upper border of negatively buoyant cloudy volume strengthens inversion at the top of the cloudy layer. Locally induced turbulent eddies mix air across the inversion, resulting in evaporative cooling within the volumes of the mixing events. Structures of mixing events are visualized with the laser sheet technique. PIV, adopted to subsequently collected pairs images allows to retrieve flow velocities in the laser sheet plane.