Weather Watch

Contrails from missile tests most visible at dawn or dusk

Condensation trails of the unarmed Minuteman intercontinental ballistic missile launched from Vandenberg Air Force Base on Oct. 21, 2015 taken from Diablo Canyon Power Plant.
Condensation trails of the unarmed Minuteman intercontinental ballistic missile launched from Vandenberg Air Force Base on Oct. 21, 2015 taken from Diablo Canyon Power Plant.

On Oct. 21 an unarmed Minuteman intercontinental ballistic missile (ICBM) from Vandenberg Air Force Base was launched before sunrise and produced a remarkable display of zigzag contrails of ice crystals due to differences in wind velocity with altitude.

Last Saturday, Nov. 7, an unarmed Trident II ICBM missile was launched after sunset from the USS Kentucky, an Ohio-class ballistic missile submarine off the Southern California coast that gave an even more dramatic display that was seen as far away as Arizona, Nevada and even reports of sightings from Utah. It caused a heck of a stir throughout Southern and Central California.

I was in the front yard of our house in Los Osos when my daughter, Chloe, said, “Look at that!” As we looked at the southern sky, a large V-shaped bluish trail of light moved rapidly westward across the sky. Mistakenly, I thought it was a meteor.

Ironically, if these missile tests were conducted during the day or late at night, most of the population probably wouldn’t have even noticed them and here’s why.

These colorful clouds from these missiles are called condensation trails or contrails. They can evaporate swiftly if the relative humidity of the surrounding air is low. However, if the relative humidity is high and the upper-level winds not too strong, contrails can last for much longer.

Contrails typically form when the air temperature is at or below minus-40 degrees Fahrenheit or Celsius. At these temperatures, small water droplets from the missiles or jet airliners exhaust will instantly freeze, forming ice crystals, similar to the wispy strands of cirrus clouds.

Most commercial jet airliners fly at an altitude between 28,000 and 41,000 feet, or roughly about 6 miles up in the sky, where temperatures are frigid. In contrast, the intercontinental ballistic missiles that were launched can reach altitudes of 700 miles and literally fly above the atmosphere.

Even though it was nautical twilight (when the sun is between 6 degrees and 12 degrees below the horizon before sunrise or after sunset) along the Central Coast for both the Minuteman and Trident launches, the sun was shining brightly in the higher altitudes of the sky where these missiles flew. Consequently, even though it was dark at the earth’s surface, the sun’s rays lit up the ice crystals of the condensation trails from these missiles as they streaked into the higher levels of the atmosphere where the sun was still above the earth’s horizon.

Testing of the Minutemen missiles out of Vandenberg Air Force Base are often announced before launch time. However, U.S. Navy submarine locations are highly classified and missile tests from those platforms are not publicized. Both of these missiles flew to a target area near the Kwajalein Atoll in the Marshall Islands in the South Pacific Ocean, some 4,200 miles away and were was fitted with test re-entry vehicles.

John Lindsey’s column is special to The Tribune. He is the PG&E Diablo Canyon meteorologist and media relations representative. Email him at pgeweather@pge.com

Did you know that PG&E delivers to its customers some of the nation’s cleanest electricity? More than 55 percent of the power comes from sources that emit no greenhouse gases, including Diablo Canyon Power Plant. To learn more, please visit http://www.pge.com

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