Laboratory and Field Observations of the Growth of Columnar and Plate Crystals from Frozen Droplets

Abstract

A laboratory experiment was initiated to grow the banded columnar crystals found in cirrus clouds and to determine if they nucleated through a freezing nucleus. Banded columnar crystals were collected in cirrus clouds and also grown in a laboratory cold box over a temperature range of ?20 to ?46C. They were observed to grow from a frozen droplet through several distinct crystalline transitions. The first distinct crystalline form observed following the growth of a frozen droplet was a polyhedral crystal. With further growth, the polyhedral crystal developed end plates, and it appeared to be a ?double plate.? Then the separation between the plates nearly filled in to leave the characteristic band. Certain columns (?6 to ?10C) and plates (?10 to ?20C) were also observed to grow from a frozen droplet and showed similar crystalline transitions.