Unexpected outbreak of noctilucent clouds (NLCs) illuminates Europe’s night sky

On June 23, 2024, Europe experienced an unexpected outbreak of noctilucent clouds (NLCs) despite high solar activity, which typically inhibits NLC formation. Earth-orbiting satellites also detected the display, noting NLCs down to a latitude of 55° N over the British Isles.

On the night of June 23, Europe witnessed the most significant outbreak of noctilucent clouds (NLCs) of the year. These clouds, also known as ‘electric blue clouds,’ were captured by photographers and skywatchers across Europe, including Denmark, Austria, Germany, the Netherlands, England, Poland, Slovakia, Russia and Belgium.

“I took these pictures from my window in the south of Paris. Some very bright noctilucent clouds were visible,” said Bertrand Kulik, a French photographer about the iconic image he took on June 23:

This display was unexpected in 2024, a year predicted to be unfavorable for noctilucent clouds due to high solar activity. Typically, NLCs tend to retreat during years around Solar Max because the increased solar activity warms Earth’s upper atmosphere, breaking apart water molecules necessary for NLC ice formation. However, recent events suggest additional factors might be at play in 2024.

One contributing factor is the extra moisture in the atmosphere from the undersea eruption of the Tonga volcano. This eruption has pumped significant amounts of water vapor into the upper atmosphere, providing additional material for NLC formation. Furthermore, interhemispheric teleconnections are influencing the temperature and moisture levels available for these clouds.

Earth-orbiting satellites also detected the June 23 display. NOAA’s Suomi NPP weather satellite mapped the clouds, with each dot on the map below representing a cloud of “noctilucent ice.”

“These data show a nice line of NLCs down to a latitude of ~55° N over the British Isles,” said Matthew Deland, Chief Research Scientist at NASA contractor SSAI. Ground-based observers, such as those in Paris at +48.9° N, saw the clouds at even lower latitudes than the satellites.

This event followed another brilliant display of noctilucent clouds in Lithuania on June 18. These clouds form approximately 80 km (50 miles) above the Earth’s surface, near the edge of space, a stark contrast to most clouds which form within the lowest 16 km (10 miles) of the atmosphere.

As the Northern Hemisphere entered summer solstice on June 20, 2024, the season’s longest day marked the beginning of a period when noctilucent clouds are more visible. The summer solstice ushers in over 93 days of summer, and during this season, the unique phenomenon of noctilucent clouds can be observed in the Northern Hemisphere. Conversely, in the Southern Hemisphere, these clouds are visible during December and January.

Typically, noctilucent clouds are most visible in regions between 45 and 60 degrees latitude, including North American cities like Seattle, Montreal, and Calgary. However, recent years have seen sightings at lower latitudes, with records in places such as Las Vegas (36 degrees) and Los Angeles (34 degrees).

Observing noctilucent clouds requires precise timing, as they are typically visible during a two-hour window after sunset in the western sky or before sunrise in the eastern sky. During these periods, the sun is below the horizon from the viewer’s perspective but lights up the high altitudes where these clouds form, causing them to glow. A telltale sign of NLCs is their bright blue and white tendrils appearing about 30 minutes after sunset.

These clouds form from ice crystals on dust particles left by meteors. They require both water to form ice crystals and extremely low temperatures, which are found in the mesosphere. Despite the warmth on the ground during summer, the mesosphere can drop below 200 degrees F, conditions conducive to NLC formation by mid-May.

Noctilucent clouds can also result from human activities, such as rocket launches. For instance, a SpaceX Falcon 9 rocket launch in early May 2022 created a phenomenon dubbed a “space jellyfish,” sharing characteristics with noctilucent clouds, including their distinctive glow.

References:

¹ What’s up in space – SpaceWeather – June 24, 2024

² Unique electric blue clouds help mark return of summer in Northern Hemisphere – AccuWeather – June 19, 2024

Rishav Kothari

I am an Assistant Editor and Severe Weather & Science Journalist at The Watchers, specializing in real-time severe weather coverage, geophysical event reporting, and research-driven scientific analysis. You can reach me at rishav(at)watchers(.)news.

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