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Judi Lynn

(160,211 posts)
Fri Jul 19, 2019, 04:09 AM Jul 2019

Night-shining 'noctilucent' clouds have crept south this summer


An uptick in atmospheric moisture may be fueling clouds that catch the sun’s rays after dark

BY CAROLYN WILKE 10:00AM, JULY 16, 2019



SHINE ON Noctilucent clouds that catch sunlight after dark are showing up farther south than usual this year. Scientists are studying the upper atmosphere to figure out why.

MATTHIAS SÜSSEN/WIKIMEDIA COMMONS (CC BY-SA 4.0)

High in the sky, sunlit wisps remain aglow even after sundown. This summer, a surprising number of such noctilucent, or “night-shining,” clouds have been spotted in the Northern Hemisphere — and, unusually, as far south as Oklahoma and New Mexico, scientists report.

These clouds typically float in the mesosphere about 80 kilometers above Earth’s surface, and are visible at high latitudes. They gleam blue or white when they catch the sun’s rays, even after the night has fallen on land. “They’re beautiful,” says James Russell, an atmospheric scientist at Hampton University in Virginia. “It’s hard to take your eyes off of them, because they’re so iridescent.”

The clouds form when cold temperatures, around ?130° Celsius, cause water vapor to condense and freeze around dust particles, making nanometer-sized ice crystals. What stood out in June was how wet the mesosphere was. “It’s record-setting,” says Lynn Harvey, an atmospheric scientist at the University of Colorado Boulder.

Possible explanations for that extra wetness include more moist air ascending in summertime than usual, or an increase in the atmosphere of methane, which can be oxidized to form water vapor.

More:
https://www.sciencenews.org/article/night-shining-noctilucent-clouds-have-crept-south-summer?tgt=nr

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