RADIATIVE SCATTERING BY ARTIFICIALLY PRODUCED CLOUDS OF HEXAGONAL PLATE ICE CRYSTALS

We have artificially produced ice and mixed phase clouds in a laborato ry cold room using a novel nucleation method applied to a cloud of sup ercooled water droplets. The number density and size distribution of t he ice particles have been monitored using a modified PMS 2D probe and the angular scattering behaviour has been studied. Hexagonal plates w ith maximum dimensions up to similar to 100 mu m have been produced. W e find evidence that the appearance of haloes in the phase function is dependent on there being no, or very few, residual small water drople ts in the ice cloud rather than on the size of the crystals. The angul ar scattering behaviour of the mixed phase cloud is dominated by water droplets in the forward scattering regime. Negative values of the deg ree of polarisation in the forward scattering direction are associated with the presence of ice crystals. We find poor agreement between exp erimental and theoretical phase functions and also find the use of an effective size parameter to be of little value. (C) 1997 Elsevier Scie nce B.V.