Noctilucent Clouds are Back

May 22, 2021: The 2021 season for noctilucent clouds (NLCs) is underway. NASA’s AIM spacecraft detected the first electric-blue NLCs over Ellesmere Island in northern Canada on May 20th:

NLCs are Earth’s highest clouds. Seeded by meteoroids, they float at the edge of space about 83 km above the ground. The clouds form around Earth’s poles when summertime wisps of water vapor rise up to the mesosphere, allowing water to crystallize around specks of meteor smoke. In recent years they have spread as far south as Los Angeles and Las Vegas, setting records for low-latitude sightings.

This year the mesosphere is unusually wet. “2021 is one of the wettest years in the AIM record,” says Lynn Harvey of the University of Colorado’s Laboratory for Atmospheric and Space Physics, who processed data from NASA’s Microwave Limb Sounder (MLS) to check conditions in the noctilucent zone. Click here to see her results. Only once or twice in the past 14 years have NLCs had more water to work with.

The extra water bodes well for a strong season. In fact, there have already been ground sightings. “We saw the first NLC from Germany on May 21st,” reports Gerd Baumgarten of the Leibniz-Institute of Atmospheric Physics. “The clouds appeared in the feed from one of our high resolution cameras located in Collm (51.3N, 13.0E).”

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“The display was quite faint,” he notes. They may not remain faint for long, however. Previous data from AIM show that NLCs are like a great “geophysical light bulb.” They turn on every year in late spring, reaching almost full intensity over a period of no more than 10 days.

Observing tips: Look west 30 to 60 minutes after sunset. If you see luminous blue-white tendrils spreading across the sky, you may have spotted a noctilucent cloud. Early season NLCs are typically confined to high latitudes, spreading south as northern summer unfolds.

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