A diagram showing the three AIM instruments
Carbon Dioxide Concentrations PMC formation
requires cold temperatures; thus global CO2 changes
may be one cause of increasing NLCs. CO2 buildup
in the lower atmosphere causes warming but increases
in the upper atmosphere should cause cooling.
Limited data suggest large mesospheric cooling;
newer data give mixed results. H2O chemistry must
be important since major NLCs consist of water
ice. Poor knowledge exists of how NLCs nucleate,
the environment for nucleation and how the mesosphere
responds to forcings.
NLCs Occur Near the Cold Summer Mesopause Cold
temperatures and H2O (water) appear to be essential
for PMC formation.
What are noctilucent or "night shining" clouds?
* They are the highest altitude clouds in our
atmosphere ( ~ 82 km). * They form at coldest
place on Earth (~130 K) in polar summers. * They
were first reported in 1885. * They have been
increasing over the past 30 years.
PMCs display complicated structure driven by
A diagram illustrating when NLCs are visible
to observers on Earth.