#mesosphere

"Los sprites"

Red sprites are large-scale electrical discharges that are produced in the mesosphere, much more than storm clouds or cumulonimbus, giving place to a variety of visual forms that flicker in the night sky.

Generally, they are triggered by discharges of positive rays between a storm cloud and the ground.

Noctilucent Cloud Season Begins for Northern Hemisphere Noctilucent clouds (NLC) are the highest cloud formations on our planet. In this photo from the International Space Station, they are the blue wispy layers seen at the top of the atmosphere. They mostly form at latitudes of 50° or higher, with the majority found in polar regions during the summer. We've previously covered them (http://on.fb.me/1HHqVDj, http://on.fb.me/1RG4UvU), but we may know a little more about them now thanks to NASA’s Aeronomy of Ice in the Mesosphere (AIM) mission (http://on.fb.me/1FpEruW).

This summer, scientists have reported seeing a surprising number of night-shining clouds in the Northern Hemisphere. High in the sky, such noctilucent clouds remain aglow even after sundown. Typically, these sunlit wisps develop up high in polar skies. Making it as far south as Oklahoma and New Mexico — as some did this summer — is a rarity.

Explainer: Why some clouds glow in the dark

These clouds gleam blue or white as they catch the sun’s rays, even after sundown. “They’re beautiful,” observes James Russell. He’s an atmospheric scientist at Hampton University in Virginia. “It’s hard to take your eyes off of them,” he says, “because they’re so iridescent.” They float in the mesosphere, some 80 kilometers (50 miles) up, and normally at high latitudes.

The clouds form at −130° Celsius (-200° Fahrenheit), when water vapor condenses onto and then freezes around dust particles. This makes 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.

One possible explanation is that more moist air than usual rose this summertime. There may also have been a rise in methane within the upper atmosphere. It can enter chemical reactions that form water vapor.

This satellite image measures sunlight reflected off of noctilucent clouds that covered the Arctic on June 12. White areas denote areas reflecting sunlight the most. Dark blue areas reflected light least. CREDIT:  JOSHUA STEVENS/NASA EARTH OBSERVATORY

NASA’s Earth Observatory released a satellite image that shows these noctilucent clouds covering the Arctic on June 12, 2019. It showed in easy-to-see white areas where sunlight was reflecting off of the clouds most effectively.

Russell and Harvey have been part of a team that’s been monitoring these clouds for 13 years. They’re trying to learn more about how these clouds form and whether they might reveal atmospheric changes due to global warming.