Earth’s rarest clouds are looking pretty good right now.
The most uncommon sort of cloud, known as noctilucent or “night-shining” clouds, only appear after the Sun has set or just before it rises. They show in the Northern Hemisphere sky for only a few months each summer, but this year they are the most colorful in 15 years, so go outdoors and look up.
Long, thin wisps that appear to shimmer and glow blue are noctilucent clouds. Tens of kilometers above weather clouds in the mesosphere, in the top reaches of the Earth’s atmosphere, they develop. The high-altitude clouds, which are too thin to be seen in daytime, continue to reflect the Sun’s light as it sinks below the horizon, lighting them against the sky’s growing darkness.
They are seen between June and August in the Northern Hemisphere, usually above the poles, but a recent flurry of lovely images shared online shows they are visible across North America, Canada, and Europe right now. In fact, according to the Washington Post, they are the best seen in 15 years, with views ranging from Oregon to Denmark and the UK in the last week.
The clouds, which are regarded by scientists as the rarest, driest, and tallest clouds, are created when water vapor collects on meteorite dust particles in the mesosphere and freezes, creating ice crystals. They may still reflect the Sun’s light long after it has set because they are so high in the atmosphere.
It was believed that significant events like this were required for the clouds to develop until it was first observed in 1885, just two years after the Krakatoa eruption sent enormous volumes of water vapor into the atmosphere. However, they have been substantially increasing for a number of years, and a variety of factors are to blame for this.
A 2018 study found that the human influence on the climate was to blame for the increased visibility of noctilucent clouds. Methane, which creates water vapor at high altitudes, is one of the greenhouse gases that have been released into the atmosphere as a result of the exploitation and combustion of fossil fuels. The survey indicated that the amount of water vapor 80 kilometers (50 miles) high at mid-northern latitude has increased by 40% since 1871, which means that there is now a decent probability of viewing the clouds many times per summer.
According to Professor Cora Randall, lead scientist for the NASA Aeronomy of Ice in the Mesosphere (AIM) mission’s Cloud Imaging and Particle Size instrument, which examines noctilucent clouds, “this season has been rather unusual in recent days.” The season started off as being quite typical, but over the past week or two, the frequency of clouds has substantially risen.
Regarding the potential cause of their current abundance, Randall notes that while temperatures in the mesopause are now average, water vapor is at a record high in 15 years of observations with AIM.
So once the Sun has set, go outdoors and gaze up!
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