Interesting new images of Earth's highest and most mysterious clouds have been captured by a Nasa spacecraft. The AIM probe (Aeronomy of Ice in the Mesosphere) has now returned the first truly global pictures of these phenomena which appear to be increasing in frequency and extent. These clouds are known as Noctilucent, or "night-shining", clouds and they appear as thin bands in twilight skies, some 80km (50miles) above the surface. Scientists say their observations show how the clouds alter rapidly, hour by hour and day by day. They hope their studies will reveal the key triggers to the clouds' formation and why these triggers appear to be undergoing long-term change.
These Noctilucent clouds, or polar mesospheric clouds are the highest clouds in Earth's atmosphere, located in the mesosphere at altitudes of around 85 km, ands are visible from earth only when illuminated by sunlight from below the horizon while the ground and lower layers of the atmosphere are in the Earth's shadow; otherwise they are too faint to be seen. They are primarily composed of water ice (confirmed by UARS). It has been suggested that they may be related to climate change. At least one researcher, Dr. Michael Stevens of the US Naval Research Laboratory, believes space shuttle exhaust may contribute to the formation of noctilucent clouds. Imaging has also shown that some debris clouds from various space disasters have been mistaken for noctilucent clouds. Nevertheless it has been suggested that a transition to a hydrogen economy could increase the number of noctilucent clouds in the future through mass water vapour emissions. Gee, what does that mean ?
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