Lightning sprites, or red sprites, often occurring in tandem with lightning. They are short-lived electrical discharges that flash high above thunderstorms in the mesosphere layer of the atmosphere. (Photo by Stephen Hummel, McDonald Observatory, Texas, United States)
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).
While we still don’t yet know exactly how NLC form, we know it happens in the mesosphere - the region of the atmosphere from 50km (31 miles) to 85km (53 miles). The mesosphere is the coldest layer of the atmosphere with temperatures in the highest part, the part where NLC are found, dropping to -100C. That’s cold enough to turn water vapor into tiny ice crystals. If there are enough ice crystals, they can become NLC if the conditions are right.
NLC need dust, water vapor, and extremely cold temperatures to form. According to AIM scientists, the clouds are seeded by meteor smoke - a haze of tiny particles leftover from meteors that burn up in our atmosphere. Other scientists suggest particulates from volcanoes may also supply dust. Rocket launches have been known to artificially create NLC even at latitudes below 50°.
NLC are very faint so they are only visible just after sunset and just before sunrise when sunlight hits the clouds from below the horizon. The clouds are able to reflect enough light that they appear electric-blue against the relatively dark sky. Once the sun rises, there is too much light to see the NLC anymore. Since the sun never goes below the horizon near the poles during summer, humans can rarely observe NLC at the highest latitudes.
While considered rare, NLC are forming more frequently, and this year started appearing earlier than expected. Scientists do not yet know why. It’s worth noting that there were no reports of NLC prior to 1885, meaning the clouds may be a relatively new phenomenon.
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Photo Credit: https://flic.kr/p/2isTtFpt
References:
http://slate.me/1lTW63a
http://bit.ly/1tFzcjz
http://bit.ly/1JnDyYL
https://projectpossum.org/research/noctilucent-cloud/about-noctilucent-clouds/
Clouds typical of polar skies have been showing up over the lower United States. Scientists want to know why.
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.
The scientists plan to use computers to model the conditions under which clouds form. They’re hoping to explain what seems to be a trend of these clouds to increasingly form outside of polar skies.
Working together with space researchers, Finnish amateur photographers have discovered a new auroral form. Named "dunes" by the hobbyists, the phenomenon is believed to be caused by waves of oxygen atoms glowing due to a stream of particles released from the Sun.
Noctilucent -- literally night-shining -- clouds are a phenomenon unique to high latitudes during the summer months. Too dim and sparse to see in daylight, these clouds shine at night because their altitude of around 80 km allows them to catch sunlight long after dusk has fallen at the surface. They form when temperatures in the summer mesosphere drop to nearly -150 degrees Celsius, driven by perturbations that can originate in lower layers of the atmosphere on the opposite side of the Earth. Complex interactions and feedback between atmospheric waves, buoyancy, and Coriolis effect circulate those disturbances in such a way that the summer mesosphere can reach temperatures colder than any other place on Earth. Those frigid temperatures allow clouds to form even in this dry region near the edge of space. (Image credit: S. Stephens; see also: B. Karlsson and T. Shepard)
Noctilucent Clouds by l4ts
Via Flickr:
Noctilucent Clouds seen last night. These very bright ice clouds form in the Mesosphere part of the Earth's atmosphere at a height of between 80 to 100km.
