We know that there are different types of clouds depending on their shape and formation. One of these is noctilucent clouds . Common clouds are made of crystals mixed with dust in the air. Noctilucent clouds form at the edge of the atmospheric layer called the mesosphere. If you're interested in learning more about this atmospheric layer, you can visit this article about the mesosphere.
In this article we are going to tell you everything you need to know about noctilucent clouds and their characteristics.
What are noctilucent clouds
When a meteor strikes the atmosphere, it leaves a trail of dust 100 kilometers above Earth , where air pressure is virtually zero. Water vapor clings to the dust left behind by the meteor. The intense bluish-white color of noctilucent clouds is caused by tiny crystals that form when frozen water vapor adheres to the meteor dust.
These are the highest clouds we know of, forming in the mesosphere at an altitude of about 80 kilometers (70 kilometers above the well-known cirrus clouds). The only atmospheric phenomenon that occurs above noctilucent clouds is the aurora borealis.
It has an impressive appearance, with waves across the night sky gathering into pale strands or glowing electric blue filaments that appear to come from another planet, aliens. That's not too much, as they are made of tiny ice crystals or water ice.
How noctilucent clouds form
Some studies have concluded that part of this cloud may have formed from the freezing of water ejected into the atmosphere by the space shuttle. But it has also been observed that at least 3 percent of the ice crystals that make it up are remnants of meteorites (the so-called "meteorite smoke").
These clouds are also "very shy" and are really only visible at sunset and at high latitudes (between 50 and 70º) and in summer. This is assuming they are "geometrically" very elusive. At the right (high) latitude, one can look west 30 to 60 minutes after sunset, when the sun is hidden between 6 and 16º above the horizon. This sky is located in the regions where noctilucent clouds and their colorful characteristics can be observed .
Although as far as observation is concerned, there is no doubt that the International Space Station has considerable advantages and usually gives us spectacular photographs. It is also worth noting in their characteristics that they are independent, since they do not seem to be related to any particular weather state.
While there is a growing suspicion that they may be good indicators (warning lights) for some aspects of climate change, they are appearing more frequently at lower latitudes.
It is believed that after methane, a major greenhouse gas , rises into the atmosphere and undergoes a complex series of oxidation reactions, it turns into water vapor, leading to an increase in the number of these clouds and their potential spread to higher latitudes. So our noctilucent cloud is more or less the canary that old-time miners used to carry to detect gas leaks.
In fact, NASA's AIM (Aerology of Middle Ice) mission is in charge of studying this type of cloud. On this site, we even have access to "guided imagery" that predicts the visibility and location of these clouds.
clouds on mars
Another curiosity about these clouds is that they have "cousins" on Mars, where noctilucent clouds made of carbon dioxide crystals were discovered in 2006 and may be more "exotic" than the Earthlings with whom they share a structure.
I don't want to end this article without mentioning the strange discoveries of these clouds, as everything related to them is peculiar, to say the least. Krakatoa erupted on August 27, 1883.
It was deadly (36.000 people lost their lives), but very interesting from a meteorological point of view, since the large amount of ash injected into the atmosphere changed weather patterns for several years. A drop in the planet's average temperature of 1,2°C was even recorded, which also gave sunsets around the world a deep reddish hue. If you want to know more, visit the corresponding article.
So one of the most common pastimes at the time was to contemplate these spectacular sunsets. Thus, in 1885, TW Backhouse was a more curious and persistent observer than others, continuing until after dark, when on some nights he could see faint electric blue filaments.
Necessary elements for your training
Polar mesospheric clouds require two elements: dry particles and moisture. Although water vapor is almost nonexistent in the mesosphere, its presence is not uncommon, as its colorful appearance suggests. At this altitude, the air is estimated to be about 100.000 times drier than that of the Sahara, with temperatures of -140 degrees Celsius.
What happens is that very rare water vapor adheres to hygroscopic particles, forming small ice crystals that clump together to form these clouds. This phenomenon only occurs around the summer solstice in both hemispheres, coinciding with the increased visibility of noctilucent clouds.
In the north, it will be at the end of May, June and July, and in the south, at the end of November, December to January. And you can only see them after sunset, because it is so high that they will still receive sunlight. Although the Earth is completely dark, at 80-85 km the sun still touches them.
Countries where it can be seen
Latitude, the distance between parallels and the equator, plays a significant role here. The closer you get to the poles, the more visible these clouds become. This is primarily due to wind circulation and the accumulation of cold air in this layer of the atmosphere. These clouds are typically visible from 50 degrees north latitude. That is, from Paris or London northward and across the Atlantic, much higher than New York.
In the southern hemisphere, it can only be seen in southern Argentina, southern Chile, and New Zealand. But meteorologists have found that the presence of these clouds has increased at lower latitudes in recent years.