Fly ash released from a coal‐fired power plant was detected as active ice nuclei. Observational evidence is presented that the plume aerosol inadvertently seeded supercooled fog and induced local snowfall. Snow crystals were replicated and examined with an electron microscope. Individual ice nuclei were analyzed with an X‐ray energy spectrometer. Most ice nuclei contained Si, Al, S, Ca, and Fe which are major components of fly ash. It is interesting to note that plume aerosol can seed clouds at temperatures as warm as −5°C and produce needle‐shaped snow crystals.

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Atmospheric electric measurements werc madc during the summer of 1958 from the summit of Mt. Washburn in Ycllowstonc Park, Wyoming. Thesc measurements included thc electric field, t h e positive and negative electrical conductivitics, the chargc on individual raindrops, thc sizc and charge of individual cloud droplcts, and thc corona dischargc current from thc carth's surfacc associatcd with high electric fields beneath thunderstorms. Electric fields excceding 600 v em.-' were recorded. Specific results are presented and interpretations made of their significaacc.

To investigate the possibility of inadvertent weather modification from rocket effluent, aerosol samples were collected from an instrumented aircraft subsequent to the Voyager I and II launches. The aerosol's morphology, concentration, and size distribution were examined with an electron microscope. The elemental compositions of individual particles were analyzed with an X-ray energy spectrometer. Ice nucleus concentration was measured with a thermal diffusion chamber. The particles' physical and chemical properties were related to their ice t nucleation activity. A laboratory experiment on rocket propellant exhaust was conducted under controlled conditions. Both laboratory and field experimental results indicated that rocket propellant exhaust can produce active ice nuclei and modify local weather in suitable meteorological conditions.