What are these blue clouds that form in the highest layer of the atmosphere?

    Noctilucent clouds are of genuine interest to the scientific community, which hopes to better understand this phenomenon that occurs in the highest and still largely mysterious layer of Earth's atmosphere.

    Clouds unlike the ones we see every day.
    Clouds unlike the ones we see every day.

    An electric blue cloud. It looks unlike any other. Not because of its size, its colour or its location. It is a noctilucent cloud – a formation that provides valuable information to researchers seeking to learn more about one of the least understood layers of the atmosphere. As a result, scientists are eager to unravel all the mysteries surrounding these remarkable clouds.

    Blue clouds, extremely high in the atmosphere and made of ice


    According to meteorologist Jen Carfagno, "Noctilucent clouds are the atmosphere putting on a show from the edge of space. Ghostly ripples of electric blue that shine long after sunset and before sunrise." First of all, they differ from other types of cloud because of where they form. They develop around 80 km above the Earth's surface, in the layer known as the mesosphere.

    The mesosphere is the highest layer of the atmosphere

    For comparison, the white clouds we regularly observe form at around 20 km above the Earth's surface, in a completely different layer known as the troposphere. This, by contrast, is the lowest layer of the atmosphere. Their composition is naturally very different given the vast difference in altitude. Temperatures in the mesosphere can fall as low as -130°C.

    Atmospheric scientist Matt Makens explains the composition of these striking blue clouds: "Unlike ordinary weather clouds, which are made up of water droplets or ice crystals in the lower atmosphere, noctilucent clouds consist of tiny ice crystals that form around particles of meteoric dust in the mesosphere."

    These clouds can be observed one or two hours after sunset.
    These clouds can be observed one or two hours after sunset.

    Researchers are constantly on the lookout for these unusual clouds. So when are you most likely to see them? "Summer provides the ideal combination of extremely low temperatures in the upper mesosphere, sufficient atmospheric moisture and enough dust to form these clouds at the edge of space," says scientist Jen Carfagno.

    To maximise your chances of seeing them, head to Canada, the northern United States or northern Europe. But isn't summer a little contradictory, given that these clouds require intense cooling? In fact, no. The mesosphere actually becomes colder during summer because of atmospheric circulation. It is this atmospheric process that creates the conditions necessary for noctilucent clouds to form.

    Cold, dry air is needed for these clouds to form.
    Cold, dry air is needed for these clouds to form.

    One question remains. Will climate change affect the formation of these clouds? Jen Carfagno explains that "there is more water vapour in our atmosphere because of climate change, and the growing number of rocket launches is probably transporting dust and water vapour to higher latitudes."

    Reference of the news

    Comment repérer ces nuages bleu électrique qui se forment aux confins de l’espace ?, Stefanie Waldek, 12 juin 2026, National Geographic