The Scandinavians call them mother of pearls because of their spectacular iridescent colors.
For comparison, some of the highest clouds in the troposphere have a ceiling height of about 40,000 feet.
Clouds generally do not form in the stratosphere because there is not enough moisture.
But nacreous clouds are different.
Decades ago, we started using substances such as chlorofluorocarbons (CFCs) in aerosols and refrigeration.
These chemicals have been phased out, but they are so stable they persist to this date.
Photo credit:Stefan Tariczky/Flickr
Thankfully, ozone is not the only molecule the chlorine atom reacts with.
The process can only stop once the nacreous clouds are destroyed by air flows from lower latitudes.
Such chemical reactions could not take place anywhere else in the atmosphere.
This is why the ozone hole is more prominent in the polar regions than elsewhere.
Also, nacreous clouds are more commonly observed in the southern hemisphere.
Consequently, the ozone layer is more depleted over the south pole, compared with the north pole.
