Clear blue sky early hours of the morning. The now expected, formerly unusual, ring aroung the sun also developed, due to microscopic hexagonal crystals of uniform size existing in the atmosphere, the appearance of which also was directly associated with aircraft activity. That case itself is considered unusual, exemplified with the introduction of hygroscopic nuclei, such as salts in the atmosphere along the coast. Persistent contrails stated by numerous sources to have the potential to exist only in conditions of near saturation to saturation.
Comments regarding relative humidity with respect to ice are always welcome.
Santa Fe NM July 21, 2000. Clear sky overhead, no significant observed aircraft activity. No ring around the sun. It is noted that the source stated here is from both NASA and NOAA researchers. The United States Naval Postgraduate School Atmosphere, by Vincent Schaefer, inventor of cloud seeding Meteorology, The Atmosphere and the Science of Weather, by Joseph M. Moran Referenced NASA - NOAA study below.