NAccurous clouds, also known by mother-of-pearl or polar stratospheric cloud, are a rare type that is well-known for their vibrant and sometimes luminous colours. Most clouds form in the troposphere. This layer typically extends between 10-15km (6-9 mi) in altitude. However, nacreous cloud forms higher up in atmosphere, between 15-25km in lower stratosphere (the layer of atmosphere above troposphere), where we live.
The stratosphere’s atmosphere is extremely dry. This makes it difficult to form ice crystals in order to make nacreous clouds. The cloud formation requires temperatures below -78C. Temperatures as low are only found in the stratosphere in polar winter. Therefore, nacreous clouds cannot form in stratospheric temperatures lower than -78C. Nacreous clouds are usually only visible at high latitudes, and rarely seen in the UK.
If the conditions are favorable, the best time to see nacreous clouds in the sky is just after sunset or just before dawn, which is known as nautical tide. Because light waves from the Earth’s atmosphere can interfere with the sun’s rays, beautiful and colorful clouds can form when the sun is just a little below the horizon.