Noctilucent clouds are also known as polar mesospheric clouds or night-shining clouds. The clouds, located 50 miles up in the outer band of Earth’s atmosphere, are illuminated as they reflect the sun’s light peeking around Earth’s edge. However, the illuminated mesospheric clouds can only be seen by Earthlings in deep twilight. They were most commonly observed in the summer months at latitudes between 50 and 70 degrees north and south of the equator, but this is changing.
Recent Increase in Sightings of Night-shining Clouds
Recently, the clouds have been observed between 40 and 50 degrees and sparked alarm in Northern Europe and the United States as observers took photos of the weird night-shine for publication in newspapers and blogs. If you were outdoors this summer looking for frogs or bats or other nocturnal critters and trained your eyes up, you may have gasped at the sight too. Were aliens flashing their lights, like deer spotters, on this planet?
Hampton University Center for Atmospheric Sciences
At the Center for Atmospheric Sciences at Hampton University, Dr. James M. Russell and Dr. M. Patrick McCormick have been watching the outer atmospheric light show for some time. They delivered an opening plenary session lecture at the VEE Conference about the Center they founded at HU following careers at nearby NASA. They knew their work was not done. The night-shining clouds were first reported in the late-nineteenth century after the volcanic eruption on the Indonesian island of Krakatoa. Daytime observations of the clouds were made by a satellite in 1969. Regular space-based observations began in 1982. Greater frequency and observations with the naked eye at lower latitudes have occurred since then. In a photo included with a NASA press release, the first ground sightings of noctilucent clouds in the 2007 season were shown. The photo was credited to Veres Viktor of Budapest, Hungary and taken on June 15, 2007.
Aeronomy of Ice in the Mesosphere (AIM)
In their second career lives, Russell and McCormick are working with students to launch the Aeronomy of Ice in the Mesosphere (AIM) spacecraft, the first satellite able to determine the properties of the distant yet increasingly present ethereal bodies. They are collecting data on the mysterious ice clouds that dot the edge of space to help us understand why the clouds, once viewed exclusively over the Polar Regions, are now lighting up the night at lower latitudes.
Lifecycle and Conditions that Favor Formation of Noctilucent Clouds
The clouds form at the poles, the coldest part of the Earth’s atmosphere, in the summer season. In the northern hemisphere they begin appearing in mid-May and last through mid-August, and in the southern hemisphere they begin in mid-November and last through mid-March. The seasonal lifecycle of noctilucent clouds is controlled by complex interactions between temperature, water vapor, solar activity, atmospheric chemistry and small particles on which the cloud crystals form. Human-induced factors like carbon dioxide, methane, and other so-called greenhouse gases that cause warming in the lower atmosphere also cause cooling and more water vapor in the mesosphere, resulting in the increase in upper atmosphere cloud formation. The satellite will simultaneously measure air pressure and temperature, moisture content and cloud dimensions, providing data needed to determine the role of polar mesospheric clouds as important indicators of the planet’s changing climate.
For now, program scientists quoted in a NASA press release say, “These clouds are indicators of conditions in the upper reaches of the Earth’s atmosphere, and are an important link in the chain of processes that result in the deposition of solar energy into Earth’s atmosphere. AIM will provide an understanding of how and why these clouds form, an important contribution toward the NASA goals of understanding the fundamental physical processes of our space environment and how the habitability of planets is affected by the interaction of planetary magnetic fields and atmospheres with solar variability.”
Not Aurora Borealis
Noctilucent clouds should not be confused with the Aurora Borealis, which occurs even farther up, in the ionosphere. The Northern Lights (and Southern Lights) result from the collision of charged particles from the Sun that swirl in solar winds and take quantum leaps when excited by the Earth’s magnetism.
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