Ice crystal habits from cloud chamber studies obtained by in-line holographic microscopy related to depolarization measurements

We investigate hydrometeor habits at the AIDA chamber with a newly developed in-line holographic microscope HOLographic Imager for Microscopic Objects (HOLIMO). Sizes and habits of ice crystals and droplets in a mixed-phase cloud experiment are related to relative humidity with respect to ice (RHice), temperature (T), and experiment time. This experiment is initiated with supercooled water drops. As a result, ice crystals within a maximum particle diameter size range of 2 to 118 mu m (average size of 19 mu m) are detected and 63% of them reveal regular habits. The observed particle habits match those predicted for a given RHice and T. Two different growth modes emerge from this cloud. The first one appears during water injection and reveals mainly optical particle sizes in the range of 5 to 250 mu m. The second mode grows to sizes of 5 to 63 mu m, just after the particles of the first one fall out. It is found that an increasing aspect ratio chi of maximum length over thickness from 2 to 20 as obtained by HOLIMO corresponds to a decreasing linear depolarization ratio from 0.1 to 0.04, as independently obtained by depolarization measurements. (C) 2009 Optical Society of America