Laboratory Observations of Cloud–Clear Air Mixing at Small Scales

Abstract

Cloud?clear air mixing at scales from 1 mm to 1 m is observed in a laboratory chamber. Cross sections through the volume in which the mixing takes place are obtained by illuminating a planar sheet of cloud with laser light (? = 0.488 ?m, 1.2-mm thickness); the light is scattered by cloud droplets and photographed. Images indicate that complicated filament-like structures are created during mixing. Due to the properties of Mie scattering, this technique is in principle more sensitive to the larger cloud drops, and volumes with the small droplets may be underrepresented in the images. After digitization of the images, an interface between cloudy and clear-air filaments is investigated. Preliminary results indicate that at the scale of 2 cm the nature of the interface changes: at larger scales it exhibits self-similar properties, whereas at smaller scales it has a simple geometrical structure.