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6214204 
Book/Book Chapter 
MESOSPHERE | Polar Summer Mesopause 
Kelley, MC; Varney, RH 
2015 
Academic Press 
Oxford 
Encyclopedia of Atmospheric Sciences (Second Edition) 
436-443 
Synopsis The summer polar mesosphere is one of the most fascinating regions of the atmosphere. In full sunlight, the temperature reaches as low as 100 K, far colder than all but a few regions in the solar system. Even though the upper atmosphere is freeze dried, enough water still remains to allow ice crystals to form around meteoric dust particles, leading to the formation of the highest clouds on earth (near 85 km), which form beautiful structures seen in the polar twilight. Interestingly, these clouds were never reported until the end of the nineteenth century and have increased throughout the twentieth century. Many researchers relate this phenomenon to atmospheric change since, as the lower atmosphere heats up, the upper atmosphere cools. In addition, since methane is the main cause of hydrogen in mesospheric water vapor, its increase is a factor in the formation of these clouds. Increased interest in this region was due in part to the huge radar target this region exhibits, 10000000 times as large as elsewhere outside of the polar summer. Explanation of these signals has led to a new understanding of the role of dust in a plasma. 
Dynamics; Mesosphere; Noctilucent clouds 
Zhang, Fuqing