Miscellaneous

These noctilucent clouds were pictured near Stockholm shortly before midnight. Although the sun has already disappeared, the clouds are still directly illuminated. From time and date when the image was taken the sun zenith angle can be determined at which the clouds were illuminated. According to this the clouds were located at an altitude of 80 km above the ground that means far in the upper range of the mesosphere.

Although the water vapour content is extremely low in these altitudes, temperatures - typically between 180 and 200 K (-93 deg C to -73 deg C) - are low enough to support formation and existence of ice-clouds. Aerosol particles deriving from evaporated meteorites most probably acted as nuclei. The size of the ice-particles ranges between 0.1 µm and 0.3 µm.

Noctilucent1-5.jpg: Kevin Noone, Stockholm, Sweden, 14 July 2004, 11:30 p.m. to 11:40 p.m.