Laboratory study of the deformation of micrometer-size frozen droplets

LOPEZ M.L.; AVILA E. E.

Leipzig

Conferencia; 16th International Conference on Clouds and Precipitation; 2012

Cirrus clouds influence the radiative energy budget of the Earth. They mainly consist of nonspherical ice crystals with complicated scattering and absorption features. The characterization of the shape and morphology of ice particles is important toward the understanding of the optical properties of cirrus clouds. In this work, laboratory experiments were conducted to study the ice crystal shape formed from the freezing of water droplets at -40ºC. Liquid and ice clouds were separately formed and sampled in a cloud chamber at -30 and -40ºC, respectively. The effective water droplet diameter ranged from 8 to 20 μm, while the effective ice particle diameter ranged from 8 to 30 μm. The average effective diameters were 11 μm for water drops and 14 μm for frozen droplets. The deformation of the frozen droplets was evident during inspection under microscope; bulges and spikes protuberances were found in many of the observed ice particles. The results show that the average aspect ratio of the frozen droplets is 1.2. These results are relevant to the estimation of the optical properties of cirrus clouds and the collection of supercooled droplets by the non-uniform frozen ice particles, with the consequent production of graupel. Effective size and aspect ratio of the particles are the key parameters required to determine the optical parameters that are included in modeling and prediction of climate; their parameterizations need to be as accurate as possible.