New images of noctilucent clouds taken by a NASA spacecraft may help solve the mystery about why they form – and why they are changing.
Noctilucent (night shining) clouds are the highest on Earth and can be seen as thin bands in twilight skies about 50 miles up. But these latest pictures give a global view of them rotating round the Arctic, allowing scientists to measure them.
Data returned by the Aeronomy of Ice in the Mesosphere (AIM) satellite may explain why the clouds are getting brighter, are being seen more often and are appearing at lower latitudes.
One theory is that a build-up of greenhouse gases in the upper atmosphere may be responsible. The clouds, also known as Polar Mesospheric Clouds, appear to be extremely sensitive to temperature variation and may be acting as thermometers for climate change.