Green Comet

We’ve worked our way from the ground up to the wispy extremes of the high etage (over 20,000 feet.) From the puffy delights of fair weather cumulus all the way up to the enchanting veils of cirrostratus. So where do we go from here? Why, up, of course. Why stop at a mere 20,000 feet when we can carry on up to 50,000, or even 80,000 feet? That’s where today’s cloud, nacreous, lives.

Nacreous clouds are among the most beautiful, being iridescent and highly colorful. Unfortunately, the beauty comes with a barb. Nacreous clouds, also known as polar stratospheric clouds, are composed of nitric acid and sulfuric acid, along with water, and are implicated in depleting the ozone layer.

Given their composition, nacreous clouds form in the high atmosphere at very cold temperatures – below minus 78 Celsius. The requirement of very low temperature accounts for their prevalence in polar regions. The origin of the name – nacreous – comes from nacre, or mother of pearl, because they share a colorful iridescence.

There is never any precipitation from nacreous clouds.

Some of today’s pictures come from the website of Deven Stross, where he has posted some photographs he took in Antarctica. I highly recommend visiting his site.

rjb