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Originally posted by Novatrino
If I can get factual evidence of why a 2 engine TUTOR aircraft creates 4 contrails I would be very interested. Seriously I would. As well these white jets do not have any markings on them for some reason.
Cloud seeding has been conducted in California for over 55 years, one of the longest records of
operational weather modification anywhere in the world. The earliest program was at the
Bishop Creek watershed in the eastern Sierra in 1948, sponsored by the California Electric
Power Company, now Southern California Edison (SCE) (Henderson 2004). The Lake Almanor
and Mokelumne projects of Pacific Gas and Electric (PG&E) (Marler 1992) and Upper San
Joaquin project of SCE have both operated for over fifty years. The Santa Barbara operational
precipitation enhancement project (Griffith et al. 2005) began in 1950, with some research
phases between 1957–1960 and 1967–1974. Other programs have been operated in Los Angeles and Monterey counties.
Success in cloud seeding requires substantial knowledge of the physical processes in natural
clouds and how seeding materials change those processes to augment precipitation. There have
been two major research projects related to cloud seeding in California. The larger effort was
the Sierra Cooperative Pilot Project (SCPP), which was conducted by Reclamation and the states
of California and Nevada between 1977 and 1987. The SCPP (Reynolds and Arnett 1986)
focused on physical mechanisms affecting Sierra Nevada clouds, so that sound cloud seeding technologies could be developed. Ground‐based and airborne silver iodide seeding was done, along with the release of tracer materials to assess the transport and diffusion (T&D) of seeded plumes (Section 2.3.1 below). Major findings were: Sierra Nevada storms often have rapidly changing phases that affect seedability; a low‐level barrier jet stream frequently complicates T&D and targeting of seeding materials; clouds are frequently efficient natural snowfall producers because of a process known as ice multiplication; and most of the SLW that is needed
for seeding to be effective is within 3000 feet of the ground, at temperatures warmer than ‐10°C
(Marwitz 1987; Reynolds 1989; Rangno 1986).
2.2.2. Are There Any Adverse Impacts?
Regarding the second concern, Reclamation has studied environmental and health impacts
extensively (Bureau of Reclamation 1977; Harris 1981; Howell 1977). The toxicity of silver and
silver compounds (from silver iodide) was shown to be of low order. According to Reclamation,
the small amounts of silver used in cloud seeding are 100 times less than industry emissions
into the atmosphere in many parts of the country or individual exposure from tooth fillings.
Accumulations in the soil, vegetation, and surface runoff have not been large enough to
measure above natural background (Klein 1978). A 2004 study for Snowy Hydro Limited in
Australia confirmed these earlier findings. The expansion of LP as a gas is another possible
seeding method. Regarding the flammability of propane released from dispensers (Vardiman
et al. 1971), it was shown that it was necessary to bring the ignition source to within four feet of
the dispenser nozzle to cause the propane plume to burn under very light winds. A modest
increase in wind speed would blow out the flame. It was further noted that, ”Propane is a
colorless, odorless, hydrocarbon that is harmless to plant and animal life. The quantities used in
seeding are so small, 0.75 lb per minute from each dispenser, that there is no accumulation
leading to a pollution problem.” Another study (Super and Heimbach 2005a) noted that ”There
is a great deal of propane (C3H8) and butane (C4H10), another hydrocarbon, being released by
human activities at a scale far larger than for propane seeding. Propane does not present an
environmental hazard because of its rapid oxidative degradation. Although technically a
greenhouse gas, its approximate one month lifetime in the atmosphere is too short to function in
this manner. In contrast, chlorofluorocarbons (CFCs) have atmospheric lifetimes in the range of