Animations by
Susan Twardy
Released on November 4, 2003
Because of their high altitude, near the edge of space, noctilucent clouds shine at night when the Sun's rays hit them from below while the lower atmosphere is bathed in darkness. Also known as Polar Mesospheric Clouds or PMCs, they typically form in the cold, summer polar mesosphere and are made of water ice crystals. In April 2007 the Aeronomy of Ice in the Mesosphere (AIM) Mission was launched with the express purpose of studying noctilucent clouds.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 8.0.0.0.0