I met Dr. Vincent J. Schaefer during the Summer of 1961, after my junior year of high school. He was teaching the weather course at a special Natural Sciences Institute (since discontinued) for 40 boys from around the country. He liked the way I did my assigned research project and invited me to join a group of NSI students visiting a real cloud seeding project in Flagstaff, Arizona, in June 1962, right after graduating from high school. I got to work under the top weather scientists in the country. That confirmed that I wanted to do weather research in the future. Dr. Schaefer advised me to avoid weather courses during the undergraduate years and concentrate on math and physics. I took that advice, added six astronomy courses, and earned my B.S. in astrophysics (1966, University of Rochester, NY). Then I went to graduate school at the State University of New York at Albany (now University at Albany) and earned my Ph.D. in atmospheric science (1971), specializing in cloud physics and weather modification. During that decade I was in frequent contact with Dr. Schaefer, especially through the Atmospheric Sciences Research Center, and worked with others on the team that made the original cloud seeding discoveries.
In August 1966 I made it snow for hours in an entire room (walk-in freezer normally used for freezing ice cream) for the Department of Atmospheric Science at Colorado State University, Fort Collins. My assignment was to measure the fall speeds of the tiny crystals resulting from cloud seeding. To get a continuous snowstorm I had some water heating on a hot plate on the floor. To seed the cloud I burned a piece of string that had been soaked in silver iodide. Then as long as I kept my hot plate of water steaming I had a continuous snowstorm. At the end of the week I was able to scrape up off the floor enough snow to make six large snowballs. I took them outside where the temperature was about 95 degrees. I had to be dressed for zero in the freezer. It looked strange. I hit only trees with the snowballs.
At other times, in the dark of night, I have filled my back yard with snow when there was a supercooled fog in the neighborhood. I used a CO2 fire extinguisher to trigger the snow and was soon able to see the sparkling crystals in the beam of the yard light. Some airports use similar techniques to clear supercooled fog to increase the visibility for their aircraft operations.
How did I determine that 100 million ice crystals are produced by one bubble of bubble wrap? In the early 1970's in a room-sized freezer in a C.S.I.R.O. Division of Cloud Physics laboratory in Sydney, Australia, we had a smaller cloud chamber, about a two meter cube. With a continuous cloud going, I popped one bubble into the supercooled cloud. I had a glass microscope slide on the floor of the chamber. When all the crystals had settled out to the floor of the chamber, I made a Formvar preservation of the crystals. I then counted the crystals on a representative area of the slide and multiplied by the ratio of the floor area of the chamber to that which I counted on the slide.
While in Australia I participated in some seeding experiments on tropical cumulus clouds and thunderstorms. We dropped silver iodide flares and dry ice pellets (finger-sized) into new cauliflower-like turrets of cloud. We dropped about 2 liters of dry ice pellets in a line across or through the cloud for a distance of 2 to 3 kilometers. When we turned the airplane around we saw that the new turret had totally changed to ice crystals in about 5 minutes. Sometimes we were able to measure precipitation falling from the cloud thereafter. Once we seeded a tall cloud generated by a forest fire; we got it to rain downwind of the fire.
From the mid-1970s until 2005 I worked for the U.S. Bureau of Reclamation, initially on cloud seeding projects. My main role was to evaluate our seeding effects, primarily by examining changes in the snow crystal sizes, concentrations, and shapes. We compare seeded cloud with adjacent natural cloud to see how they differ. In our last experiments using liquid propane as a seeding (chilling) agent, my analyses were able to determine how many (one or two) nozzles were being used 4.3 kilometers away to seed the clouds during half-hour seeding pulses.
Dr. Schaefer took several expeditions to Yellowstone Park in the wintertime. The hot springs provided lots of moisture for supercooled fogs in the valleys. Before sunrise he placed a piece of dry ice in a nylon stocking and tied a rope to the stocking. He then went outside and swung the stocking (and dry ice) in circles for several minutes. As a result the valley soon became filled with new sparkling ice crystals. When the sun rose the crystals acted like tiny prisms. The ice crystals produced many pillars and arcs of rainbow colors throughout the sky, often in directions seldom seen by most people. The photographs of such demonstrations were beautiful.
Though I was not present at those times (my expedition there had temperatures warmer than freezing) the next pages show numerous optical phenomena created by liquid water droplets and ice crystals.
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