Night clouds or noctilucent clouds are tenuous cloud-like phenomena that are the "ragged-edge" of a much brighter and pervasive polar cloud layer called polar mesospheric clouds in the upper atmosphere, visible in a deep twilight. They are made of crystals of water ice. Noctilucent roughly means night shining in Latin. They are most commonly observed in the summer months at latitudes between 50° and 70° north and south of the equator. They can only be observed when the Sun is below the horizon.
They are the highest clouds in the Earth's atmosphere, located in the mesosphere at altitudes of around 76 to 85 kilometres (47 to 53 mi). They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in the Earth's shadow. Noctilucent clouds are not fully understood and are a recently-discovered meteorological phenomenon; there is no record of their observation before 1885.
Noctilucent clouds can form only under very restrictive conditions; their occurrence can be used as a sensitive guide to changes in the upper atmosphere. They are a relatively recent classification. The occurrence of noctilucent clouds appears to be increasing in frequency, brightness and extent. It is theorized that this increase is connected to climate change.
Night clouds or noctilucent clouds are composed of tiny crystals of water ice up to 100 nm in diameter and exist at a height of about 76 to 85 km (47 to 53 mi), higher than any other clouds in Earth's atmosphere. Clouds in the Earth's lower atmosphere form when water collects on particles, but mesospheric clouds may form directly from water vapour in addition to forming on dust particles.
The sources of both the dust and the water vapour in the upper atmosphere are not known with certainty. The dust is believed to come from micrometeors, although particulates from volcanoes and dust from the troposphere are also possibilities. The moisture could be lifted through gaps in the tropopause, as well as forming from the reaction of methane with hydroxyl radicals in the stratosphere.
Noctilucent Clouds at Wikipedia
They’re happening right now north of here
farther north even than Wisconsin
microscopic bits of iron and ice
refracting sunlight down to our world
from outside our world from outer space.
Is more water vapor rising up
or are more meteors falling down
creating electric looking clouds
where our world meets a world more distant
or real distance itself the real north?
No one knows what they are how or why
but north of here they’re happening now
though what and how and why no one knows
iron and ice and sunlight between worlds
the real wild as above so below.
farther north even than Wisconsin
microscopic bits of iron and ice
refracting sunlight down to our world
from outside our world from outer space.
Is more water vapor rising up
or are more meteors falling down
creating electric looking clouds
where our world meets a world more distant
or real distance itself the real north?
No one knows what they are how or why
but north of here they’re happening now
though what and how and why no one knows
iron and ice and sunlight between worlds
the real wild as above so below.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
“meteor smoke is a key ingredient
of Earth's mysterious noctilucent clouds”
at SpaceWeather.com
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