Electrodynamic trapping and manipulation of ice crystals

We have developed a double-ring double-disk electrodynamic balance with hum idity control provided by an internal thermal diffusion chamber to study se veral atmospherically important processes involving 10-200 mu m ice particl es. The balance constants needed to quantify the particle size and mass wer e determined by a three-dimensional relaxation-method calculation of the no n-axisymmetric electric fields, and by experimental measurement of the onse t of particle stability using polystyrene latex microspheres of known size and mass. We have levitated frost particles of various shapes and sizes und er a range of atmospherically relevant temperature and humidity conditions. The measured mass changes during growth and sublimation are consistent wit h predictions based on vapour and thermal diffusion to equivalent spheres. The electrodynamic balance is shown to be a useful tool for exploring singl e particle growth and sublimation rates, and for measuring their Light-scat tering characteristics.