At high latitudes in the Northern Hemisphere in late spring and summer, it's possible to catch a curious night-time phenomenon: wispy, pale blue clouds shining in the light of a Sun that has already set. These formations are known as noctilucent clouds, and recent reports have them popping up further and further south.
The NASA Earth Observatory recently looked into these reports and, in the process, captured a gorgeous series of satellite images of the clouds reflecting light into space. The photos were taken on June 12 using observations from NASA’s Aeronomy of Ice in the Mesosphere (AIM) spacecraft. The satellite measures the albedo of clouds – essentially, the amount of light they reflect.
The clouds form when water vapor crystalizes high in the atmosphere. This happens more often in the summer months because the upper atmosphere grows cooler as the lower layer of the atmosphere gets warmer. During this process, ice crystals can grow around particles or meteor dust.
These clouds are usually located between 80 and 85 kilometers (50 and 53 miles) in altitude and between 50° and 65° North. This is why it was so surprising to see them as low as the Southern California desert and Europe, a phenomenon that's occurring more often than in previous years. The most likely explanation, according to researchers, is the increased presence of water vapor in the atmosphere – a consequence of the climate crisis.
There’s also another possible factor: solar activity. Our Sun experiences an 11-year cycle, going from a maximum to a minimum of activity. We are currently either at or nearly at the minimum. During these times, there is a little less ultraviolet light coming from our star to break up molecules in the upper atmosphere, leading to more molecules than average.
Noctilucent clouds can also occur due to artificial events. A stunning cloud was formed over Orlando in 2014 after a SpaceX Falcon rocket launch.