Mesospheric Noctilucent Clouds

After boarding the plane, you store your bags in the overhead compartment and under your reclining chair. You take your seat next to the window and prepare for a fast ride to your destination, expecting little turbulence as you soar into and above the fluffy, cotton candy like clouds. Or, you imagine lying stretched out in a wide field and gazing up at the sky. Your eyes move slowly across the sky as you are watching the clouds slowly roll by. You see the clouds forming various shapes and you decide to characterize one cloud as a rabbit and another as a dragon. We see clouds as a plain white to dull gray, easily changing and having no solid construction, listing along as winds blow them in large clumps. From our observational standpoint on the surface of the Earth and even up into the clouds at altitudes which airplanes fly, these are valid views of them. These are, in truth, what many people are accustomed to seeing. What may come as a surprise, however, is the appearance of clouds from a higher reference point. Thanks to the National Aeronautics and Space Administration (NASA), we have been able to gain more insight into cloud formations in the Mesosphere. The mission: Aeronomy of Ice in the Mesosphere, or AIM for short, shows that clouds just at the boundary of space shine as natural light bulbs in the heavens. The research conducted through use of AIM is directed towards explaining why this phenomenon occurs. Although more easily observed from such a high vantage point, there have been sightings of these icy blue clouds by observers from earth.

These blue clouds, or noctilucent clouds (NLCs), were usually seen closer to the Northern and Southern poles. They were first spotted in the late 19th century at these positions. Due to changes in the atmosphere, which NASA is currently collecting information on by use of AIM, these clouds have been spotted in lower latitudes as of recently. Before discussing why these clouds appear in different latitudes (other than high latitudes around the poles), there is another question which can be given attention.  The question that would be asked, and reasonably so, is, “why do these clouds normally form at these high latitudes on the Earth in the first place?” A recent study done by NASA shed some light on why this occurs. A study of water vapor released by space shuttles lifting off and leaving the atmosphere showed the path that these vapors took led directly to the poles. The air currents quickly swept the vapors towards the higher latitudes and with the lower temperatures at such a high latitude and altitude, these vapors were frozen. But is this frozen water vapor all that it takes to make these rippling blue clouds appear? Fortunately, NASA has found more information to explain the creation of these clouds.

Unlike in the water cycle which takes water from the earth to create clouds, the other factor which causes the formation of these noctilucent clouds is one found outside of earth. Scientists in NASA have found that an important component in these higher level clouds is meteor dust. It is logical to conclude that meteor dust is found within these clouds because of their height. NLCs exist in the Mesosphere at a height of 83km above the Earth’s surface. The remnants of meteors which burn up in the atmosphere are usually found around 70 to 100km above the surface of the ground. These meteor dust particles then act as nuclei which draw the water vapor towards them and cause them to chain together. If the meteor dust particle were a nucleus, the water vapors would be the many electrons which come together around it. Through further study, it has been determined that for every ice crystal found in a noctilucent cloud, 3% of the composition is the meteor dust particle.  Understanding that the ice crystals are forming around meteor particles also helps to explain why noctilucent clouds give off a blue color.

Clouds form as water vapors cling onto dust particles and tiny organisms in the atmosphere. Lower in our atmosphere there is an abundance of water vapor to be collected and gathered together by these dust particles. Just as in the water cycle, vapors can come from oceans, living things and even mountain tops. With more water vapor at a given altitude, the clouds that form are thicker and appear whiter as they scatter more sunlight. The greater number of water vapor causes more scattering of sunlight. This is not the same, however, higher up in the atmosphere where there is less vapor condensing. With less vapor to draw towards the meteor dust particles, the ice crystals which are formed are very small in comparison to that of clouds lower in the atmosphere. These smaller crystals refract and scatter blue light more easily due to their small size. This is the cause for the noctilucent clouds appearing blue. But what is the cause for their ‘electric’ or luminous blue color? More research into this matter is still being done.

A strong answer for why these clouds have such a shining color is related to the time at which they can be observed. These clouds are usually seen during the summer, whether in the Northern or Southern hemisphere. The best time of day to find these clouds is at twilight once the sun has set and the earth is dark. The remaining light from the setting Sun shines on these clouds and causes them to illuminate. This is a cause for the electric blue of the noctilucent clouds. Understanding when and where these clouds can be spotted is what makes study of them possible. NASA has a handle on the time of season that they appear and the general latitude that they appear at. Through further observation, as researchers have observed, the location of where these clouds are being seen has been ever changing. NASA’s researchers have already determined why these clouds are more commonly found at the poles. The scientists now set out to explain the migration and expansion of the territory of these NLC’s.

The presence of noctilucent clouds in lower latitudes has presented itself as a new mystery to scientists. A possible explanation for their sudden appearance in these areas was developed by James Russell. Russell is the principal investigator of NASA’s AIM mission. He reasons that these cloud phenomena are appearing in areas such as Colorado, Utah and Nebraska due to the release of more chemicals into the atmosphere. The specific chemical that he references is methane. This methane is oxidized and turned into water vapor once in the atmosphere. This water vapor is then frozen into ice crystals which are formed around the meteor dust particles. Thus, the formation of noctilucent clouds in lower latitudes becomes possible. This increase in methane in the atmosphere is indirectly related to the the NLC’s and directly connected to climate change. Along with water vapor, carbon dioxide and ozone, methane is a greenhouse gas which traps heat on the Earth’s surface. The greenhouse gases are essential to life on Earth, keeping it from plummeting in temperature after nightfall. The increase in greenhouse gases are what lead to problems such as global warming. As too much greenhouse gas enters the atmosphere, more and more heat is retained by the Earth than is necessary. Russell explains that the increase in methane was likely brought about by coal mining, creation of landfills, petroleum systems and other agricultural activities. With these facts, Russell has reached the conclusion that the appearance of NLC’s in lower latitudes is actually a warning for humankind. If greater methane production is causing NLC’s to appear, then the greenhouse effect on the Earth is also increasing. These beautiful clouds are quite possibly a warning sign for global warming damages created by humans. With the vital information that these clouds can convey to scientists, it is no wonder why these clouds are under close observation by NASA. By use of the AIM shuttle, another veil of mystery in life has begun to be lifted.

AIM has helped in slowly uncovering yet another marvelous wonder in the world. These night clouds which shine and move like rippling waves of ice up above are truly amazing. It can almost be said that they are comparable to the Aurora Borealis. There is so much beauty in nature, both on the earth and further out into space. Taking a step back to take in the larger picture with so many aspects to be enjoyed leaves humans with so much to enjoy. As mankind progresses, more and more understanding of these natural phenomena becomes available. With the understanding comes a deeper appreciation and a desire to learn more. With everything that exists there is so much more to be learned and discovered. Many thanks belong to NASA in pioneering on the frontier of space and learning about aspects of life which are a bit closer to home, such as these noctilucent clouds. With so many new discoveries and beautiful scenes to find pleasure in on Earth, it becomes harder to believe that this perfect position in the universe, down to the Milky Way Galaxy and right into the Solar System, could ever be traded for another planet. Mankind can have the most delight in what is right here on our tiny planet.




NASA website

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