Night in Shining… Clouds? - Noctilucents (Photo Credits: Sharon Sullivan, Spaceweather Gallery, Jessica Voveris)
On an early June morning, several NWS meteorologists ventured outside to see a cloud shimmering above the horizon, like the inside of a pearl. Noctilucent clouds (NLC’s), or “night shining” clouds, are high- altitude clouds that form about 50 miles above the Earth, in contrast to the 12 miles up that cumulus, stratus, cirrus are typically found. They are believed to be made up of tiny ice crystals. This rare sight is typically seen during the summer months between 50 and 60 degrees latitude, but has been documented as far south as Oklahoma and even parts of Arizona before. These features can only be seen during astronomical twilight when the sun is below the observer’s horizon (around the summer solstice) and reflects off the ice crystals, making them glow.
There is not much documentation on these clouds before 1885 (2 years after the eruption of Krakatoa) and there is still mystery surrounding as to how they form. There is very little moisture in the mesosphere layer of the atmosphere to form these clouds otherwise, almost one hundred millionth that of the Sahara. In addition, temperatures can reach nearly -200 degrees Fahrenheit, the less moisture the atmosphere is able to hold. However, meteor entries, rocket launches, and volcanoes may allow thin layers of dust to be deposited, acting as “nuclei” for ice to form. Veils, bands, billows, and whirls are the shapes that they come in.
Noctilucent clouds have been observed more frequently in recent years, and outside of their normal latitudes. It is thought that a changing climate could enhance the observation of these clouds, having more methane to interact with water vapor processes and acting as a guide for the state of the atmosphere for future generations to come. Currently, there is no way to predict their appearance- but keeping your eyes to the sky an hour after sunset or before sunrise may allow you to see one lucky sight.
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©2019 Meteorologist Sharon Sullivan
Noctilucent clouds over Juneau, Alaska on July 3, 2018. Taken by former NWS Juneau meteorologist Jessica Voveris.
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