Radiative scattering by artificially produced clouds of hexagonal plate ice crystals

We have artificially produced ice and mixed phase clouds in a laboratory cold room using a novel nucleation method applied to a cloud of supercooled water droplets. The number density and size distribution of the ice particles have been monitored using a modified PMS 2D probe and the angular scattering behaviour has been studied. Hexagonal plates with maximum dimensions up to ∼ 100 μm have been produced. We find evidence that the appearance of haloes in the phase function is dependent on there being no, or very few, residual small water droplets in the ice cloud rather than on the size of the crystals. The angular scattering behaviour of the mixed phase cloud is dominated by water droplets in the forward scattering regime. Negative values of the degree of polarisation in the forward scattering direction are associated with the presence of ice crystals. We find poor agreement between experimental and theoretical phase functions and also find the use of an effective size parameter to be of little value.