The WaterBlog

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By Frank van Steenbergen Noctilucent clouds seen over Amsterdam They are visible very, very rarely: lighting up in some nights, around the solstice. Yet when they light up, they create a specter like no other, lines and hues of glow high up the sky. They are called – true to their appearance – noctilucent clouds: clouds that shine at night. The other name they have describes how they are seen from the sky: polar mesospheric clouds. These are not normal clouds. The noctilucent clouds are placed an incredible 80 kilometers high at the end of the mesosphere. This is high above the stratosphere where life on earth takes place, and our climate plays out. The air is incredibly thin in the mesosphere. There is some dust, a very little ice vapour:  the air is more than 1000 times more arid than the Sahara, yet enough to form thin cuspy clouds. By comparison the clouds we normally see are placed between… Continued