Institute of Meteorology and Climate Research

MIPAS provides measurements of the total ice volume of noctilucent clouds, for the first time at all relevant latitudes

 

 Ice volume density at 84 km altitude in the Northern Hemisphere. The red line surrounds the region where the temperature is below the frost point.

Polar mesospheric clouds aka noctilucent clouds form a continuous layer of ice clouds extending between 81 to 88-89 km altitude. The ice concentration is largest at the poles. The ice content is larger in the Northern Hemisphere than in the Southern Hemisphere.
For more information see http://www.atmos-chem-phys-discuss.net/acp-2016-116/