Abstract
Abstract. Ice crystals come in a remarkable variety of shapes and sizes that affect a cloud's radiative properties. To better understand the growth of these crystals, we built an improved capillary cryostat (CC2) designed to reduce potential instrumental artifacts that may have influenced earlier measurements. In CC2, a crystal forms at the end of one, two, or three well-separated, ultrafine capillaries to minimize both potential crystal–crystal and crystal–substrate interaction effects. The crystals can be initiated using several ice-nucleation modes. The cryostat has two vapor-source chambers on either side of the growth chamber, each allowing independent control of the growth chamber supersaturation. Crystals can be grown under a range of air pressures, and the supersaturation conditions in the growth chamber can be rapidly changed by switching between the two vapor-source chambers using a sliding valve. Crystals grow fixed to the capillary in a uniform, stagnant environment, and their orientation can be manipulated to measure the growth rate of each face. The high thermal mass of CC2 increases the stability and uniformity of the thermodynamic conditions surrounding the crystals. Here we describe the new instrument and present several sample observations.
Highlights
Ice crystals are important in the radiation balance of the Earth’s climate system (Liou and Yang, 2016; Heymsfield et al, 2017)
Images of small crystals grown on a thin fiber by Kobayashi (1958, 1961) show the fiber often exiting at a crystal corner or edge, which could be showing substrate-induced control over the crystal aspect ratio, but without the capability of rotating the Published by Copernicus Publications on behalf of the European Geosciences Union
This supersaturation is determined by the vapor-source temperature, which is controlled by setting ITEC
Summary
Ice crystals are important in the radiation balance of the Earth’s climate system (Liou and Yang, 2016; Heymsfield et al, 2017). In growing crystals on a flat substrate (e.g., Shaw and Mason, 1955; Hallett, 1961; Lamb and Scott, 1972; Beckmann and Lacmann, 1982; Sei and Gonda, 1989a), the substrate–crystal edge could be a preferred site for new-layer nucleation that does not exist without the substrate Such substrates can have epitaxial-induced strain effects (Cho and Hallett, 1984a, b), and the temperature gradients in the crystal can greatly reduce the growth rates over those predicted assuming equal temperatures of crystal and substrate (Nelson, 1993). In addition, CC2 allows experimenters to follow the growth of, and possible interactions between, several crystals growing under identical conditions It has two vapor-source chambers for making rapid supersaturation changes and for independent temperature and supersaturation control, and it has an associated vacuum system and gauges for control of the growth chamber air pressure. Studying the formation and behavior of air pockets in ice (Nelson and Swanson, 2019)
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