Strange clouds like the space veil sometimes appear in medium and high latitudes during the summer season, commonly called mesosphere or night clouds. How do these mysterious clouds form? Is it true that they are meeting more and more often? The purpose of this article is to answer some of the many questions about these strange entities.
The polar mesosphere clouds, also called silver or night luminous clouds, are the highest clouds that can be seen in the Earth ' s atmosphere. They are formed between 80 and 85 kilometres above sea level in the summer polar mesosphere, the coldest part of the gas lining surrounding our planet. Very little water vapour present at these altitudes due to extremely low temperatures crystallizes around small meteoric dusts, creating a kind of phantom veil. They can be found in medium and high latitudes in the summer when the sun is below the horizon and its rays shine at the bottom. Finally, they often appear to be a wave of gravitational waves.
Mesosphere Clouds — A Marker of Climate Change?
The first recorded observations of these meteorological objects date back to 1885, following the eruption of the Krakatau volcano, which has caused a large amount of dust and water vapour to enter the upper atmosphere. Since then, reports have appeared more and more frequently, to the extent that scientists have wondered whether there is a link between climate change and the emergence of mesosphere clouds. What if their increasing appearance is a visual indicator of changes that have affected our planet for more than a century? According to recent studies, these clouds are actually becoming more visible.
One explanation that has been offered in recent decades is that climate change increases the formation of these clouds by cooling the medium atmosphere; indeed, the anthropogenic increase in greenhouse gases results in a more efficient containment of heat in the lowest layer of the atmosphere; this leads to cooling of higher layers, such as the stratosphere or the mesosphere; however, it has been found that lower temperatures have led to the formation of ever smaller ice crystals, which ultimately makes them less visible; moreover, cooling is mostly present in the middle and lower mesosphere, but not very visible or even absent at the height where the crystals are formed; perhaps the answer is to increase the amount of water vapour in the mesosphere, which makes the crystals larger and therefore the clouds more visible.
Methane growth causes excess water vapour
From where does this water vapour come from? There are two main sources: natural transport from the surface to the upper atmosphere as a result of atmospheric circulation and photochemical destruction of methane at high altitude due to solar radiation. Since 1880, the concentration of methane in the atmosphere has increased dramatically as a result of anthropogenic emissions. This has led to an increase in the water vapour content in the medium atmosphere by about 40 per cent during the period under study. Mesosphere clouds are very sensitive to these changes, with the amount of ice more than doubling between 1871 and 2008. In short, these atmospheric phenomena are now more visible than a century ago, allowing people in medium and high latitudes to observe them several times every summer. "