Single particle database of natural ice crystals acquired during TWP-ICE, ISDAC, and SPARTICUS

Description

During the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE), the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) in the Arctic, and the 2010 Small PARTicles In CirrUS (SPARTICUS) campaign in mid-latitudes, high-resolution images of ice crystals were recorded by a Cloud Particle Imager at temperatures between −87 and 0˚C. The projected maximum dimension, length, and width of pristine columns, plates, and component bullets of bullet rosettes were measured using newly developed software, the Ice Crystal Ruler, at the University of Illinois. The number of bullets in each bullet rosette was also measured. Column crystals were further distinguished as either columns with horizontal orientations or with other orientations to eliminate any orientation effect on the measured dimensions. Dimensions and aspect ratios (dimension of major axis divided by that of minor axis) were determined as functions of temperature, geophysical location, and cirrus type (i.e., anvil or non-anvil clouds). Dimensions of crystals generally increased with temperature. Columns and bullets had larger dimensions (i.e., projected width) of the minor axis for a given dimension (i.e., projected maximum dimension or length) of the major axis, and thus smaller aspect ratio, as temperature increased, whereas this trend did not occur for plate crystals. The average number of branches in bullet rosettes was 5.50±1.35 during the three campaigns and 6.32±1.34 (5.46±1.34; 4.95±1.01) during TWP-ICE (SPARTICUS; ISDAC). The aspect ratio of bullets increased with the number of branches in bullet rosettes. Most dimensions of crystals and aspect ratios of columnar crystals measured during SPARTICUS were larger than those measured during TWP-ICE and ISDAC at −67