What are Noctilucent Clouds?
Noctilucent clouds are clouds that are not visible during daylight, but in the twilight, as they are quite tenuous. Noctilucent is a Latin word, which can be roughly translated as night shine. These clouds shine when the sunlight is not bright.
These clouds, unlike other clouds, are farthest from the earth’s surface, in the earth’s atmosphere, or in mesosphere to be precise. These cannot be spotted during the night as it needs some light to shine. Hence, it is ideally visible when weak sun rays fill the sky before the dawn, or after the sunset. These are very rare sightings, and hence, details of these clouds are not found on many sites.
Some researchers claim that these clouds appear where there are some changes in the mesosphere, or in the environment of the earth. There were several instances of sightings of noctilucent clouds in the past few months, which suggest that drastic climate changes are happening these days, more than ever.
Now that we know what are noctilucent clouds, let us understand how these clouds are formed. These clouds essentially contain tiny water ice, diameter of each being about 90 to 100 nanometers. Clouds that are commonly seen in the sky are formed when vapor accumulates on dust particles. However, Noctilucent Clouds are formed purely with water vapor.
These clouds were first potted in the year 1885, and there is no evidence of existence of such clouds before 1885. It is also believed that these clouds are made up of volcano dust and water vapor. Although not much of the earth’s dust could reach an altitude of about 80 kms above, where these clouds are formed, volcanic eruptions can throw dust at such an altitude.
Colors of these clouds vary, depending on the intensity of the light in which they are visible. However, they are generally seen in shades of blue, and occasionally in green and red color. The forms of these clouds vary from a simple colorless band to thick bubbles. These clouds appear to be blue when the sunlight is absorbed by the ozone, before reaching noctilucent clouds.
There are several other kinds of unusual kinds of strange clouds that can be found at various places and during different seasons. These include cirrus clouds, lenticular clouds, mammatus clouds, etc.