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This week, sky watchers in the upper United States, Canada and Europe have detected a burst of glare and ghosts in the night sky. The blue-silver stripes shine brightly only after the sun has disappeared beyond the horizon, captivating viewers with its beautiful but somewhat strange appearance.
These are not your everyday clouds.
Researchers say these noctilucent or bright nocturnal clouds are the rarest, driest, and tallest clouds on Earth. According to satellite data, the recent increase in activity has been different from anything seen in at least the last 15 years. There could be more activity this weekend.
“People in the northern United States and Canada should be absolutely aware of the noctilucent clouds over the long weekend,” Cora Randall, a professor at the University of Colorado Boulder, said in an email. “We are nearing the peak of the season of noctilucent clouds, and even in the absence of extraordinary events, they may appear in the northern continental United States.”
Clouds usually appear near the poles, but sometimes also appear at lower latitudes. Rare and vibrant sightings have been reported in recent days from Oregon, Washington, Canada, Britain and Denmark. The best opportunity to see the clouds is to find a clear view near the horizon and look north.
“There’s really nothing else like them,” the Seattle National Meteorological Service office wrote on social media. Before sunrise on Friday, they tweeted photos of the “most vivid displays of noctilucent clouds” that had been seen in decades in the area.
Noctilucent clouds, also known as polar mesosphere clouds, appear during the summer in each hemisphere at an altitude of about 50 miles in the layer of the atmosphere called the mesosphere. They form when water vapor congregates around dust spots of meteors floating in the mesosphere and freezes, forming ice crystals.
These thin, wavy ice clouds glow bright blue and white and usually appear at dusk or dawn. Unlike other clouds, they form so high in the atmosphere that they can continue to reflect sunlight after the sun falls below the horizon, illuminating the clouds from below.
“This season has been pretty extraordinary in the last few days,” said Randall, who is also the lead researcher on the cloud imaging and particle size instrument for the Aeronomy of Ice in the Mesosphere (AIM) mission. NASA that was designed to study night glow. clouds. “The season started as a fairly average season, but over the last week the frequencies of the clouds have increased dramatically.”
He said the frequency of noctilucent clouds in recent days has been higher than ever observed in at least 15 years of observations by the AIM mission. However, the reason is a bit of a mystery.
Noctilucent clouds are based on two main ingredients in the mesosphere: high water vapor and cold temperatures to aid in the formation of ice crystals. Randall and colleague Lynn Harvey said data from NASA’s Aura satellite Microwave Limb Sounder showed that temperatures near mesopause rose in recent days and are roughly average for this time of year. the year. But water vapor concentrations are at a record level for this time of year in 15 years of observations.
“Rising temperatures would be unfavorable for clouds, but rising water vapor would be favorable,” Randall said.
Randall said an explanation for the rise in water vapor could be linked to rocket launches. Earlier, researchers found water vapor released from these missions it can cause the formation of noctilucent clouds.
At least 16 rockets were launched in June, “any of which could have been responsible for the formation of some clouds,” Michael Stevens told the Naval Research Laboratory. He said two launches from the U.S. on June 18 and 19 are probably the best candidates to contribute to the most recent increase in cloud sightings, as the rocket’s water vapor plume can take up to 10 days to reach the latitudes where clouds form. However, this explanation is preliminary and would require a quantitative analysis to confirm it.
Atmospheric scientist Matthew Deland said the eruption of the Hunga Tonga submarine volcano on January 15 also pumped large amounts of water vapor into the stratosphere. The volcano even vomited material at 36 miles high and reached the mesosphere, setting a world record for the highest volcanic plume of the satellite record. However, he said it might take a while to see the effect on the behavior of the clouds.
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“This season may be too early to have some impacts,” said Deland, a scientist at Science, Systems, and Applications, Inc. at NASA. “[The] The question is how long it takes to transport water vapor up into the atmosphere to the region where the clouds form. “
Deland said vibrant cloud activity at lower latitudes like Seattle is uncommon and not sure if it will persist for the rest of the season. He said it depends on the circulation patterns and whether there are embedded waves that allow cold temperatures or additional water vapor to be poured at lower latitudes. On rare occasions in recent years, clouds have appeared in latitudes as low as London, central California and Oklahoma.
“They’re really remarkable to see,” Deland said. “The clouds really shine against the dark sky.”