Clouds Formation

o Pyrocumulus (No official abbreviation): Cumulus clouds associated with volcanic eruptions and large scale fires. Pyrocumulus is not recognised by the WMO as a distinct genus or species.
Above the troposphere
A few relatively uncommon clouds can be found above the troposphere where moisture is very scarce. These include polar mesospheric noctilucent clouds and nacreous polar stratospheric clouds. They are composed mostly of ice crystals and occur at high latitudes, mostly within 40 degrees of the poles in the mesosphere and stratosphere respectively. Most clouds above the troposphere have a wispy or fibrous appearance and can be mistakenly identified as high tropospheric cirrus clouds.