Laserfiche WebLink
<br />2. The physical hypothesis <br /> <br />The static seeding concept is rooted in the classical work of Bergeron <br />(1933) on the role of ice in the initiation of precipitation in supercooled <br />clouds. Invoking the description of physical processes in mixed phase <br />clouds that was put forth earlier by Wegener (1911), Bergeron postulated <br />that the inherent colloidal stability of supercooled liquid clouds could be <br />upset by the presence of a few ice particles which would rapidly grow by <br />deposition at the expense of the water droplets to sizes that were large <br />enough to fall. He believed that the ice particles most likely formed by <br />the freezing of a few cloud droplets. Findeisen (1938) expanded on <br />Bergeron1s precipitation initiation concept and suggested that the ice <br />crystals formed by the IIsublimationll of vapor on special nuclei rather than <br />by the freezing of droplets. This concept of precipitation initiation in <br />mixed phase clouds is commonly referred to in the scientific literature as <br />the Wegener-Bergeron mechanism, the Bergeron-Findeisen theory or simply the <br />Bergeron process. <br /> <br />Findeisen recognized the potential for weather modification in these fin- <br />dings and wrote lilt can be boldly stated that, at comparatively moderate <br />expense, it will, in time, be possible to bring about rain by scientific <br />means, to obviate the danger of icing, and to prevent the formation of <br />hailstorms.1I However, it was not until the next decade when Schaefer <br />(1946) conducted his historic dry ice experiment and Vonnegut (1947) disco- <br />vered the ice nucleating ability of silver iodide, that a practical method <br />became available for artifically introducing the required concentrations of <br /> <br />2 <br />