Nacreous clouds or polar stratospheric clouds. On the last day
of the year those clouds could be seen on the Lofoten islands in
northern Norway. These clouds are characterized by a strong
iridescence. Their height is determined at about 15-25 km,
where the temperature is -80 degrees Celsius. Clouds are
formed with a small amount of water vapor that leaked to the
upper parts of the atmosphere. The droplets are much smaller
than those that typical building clouds.
They scatter the light differently, that is why the color of the
clouds reminds rainbow. Those clouds occur very rarely.