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1. The Sensitivity of Polar Mesospheric Clouds to Mesospheric Temperature and Water Vapor

   https://doi.org/10.3390/rs16091563  

   Lee, Jae N; Wu, Dong L; Thurairajah, Brentha; Hozumi, Yuta; Tsuda, Takuo (May 2024, Remote Sensing)

   Polar mesospheric cloud (PMC) data obtained from the Aeronomy of Ice in the Mesosphere (AIM)/Cloud Imaging and Particle Size (CIPS) experiment and Himawari-8/Advanced Himawari Imager (AHI) observations are analyzed for multi-year climatology and interannual variations. Linkages between PMCs, mesospheric temperature, and water vapor (H2O) are further investigated with data from the Microwave Limb Sounder (MLS). Our analysis shows that PMC onset date and occurrence rate are strongly dependent on the atmospheric environment, i.e., the underlying seasonal behavior of temperature and water vapor. Upper-mesospheric dehydration by PMCs is evident in the MLS water vapor observations. The spatial patterns of the depleted water vapor correspond to the PMC occurrence region over the Arctic and Antarctic during the days after the summer solstice. The year-to-year variabilities in PMC occurrence rates and onset dates are highly correlated with mesospheric temperature and H2O. They show quasi-quadrennial oscillation (QQO) with 4–5-year periods, particularly in the southern hemisphere (SH). The combined influence of mesospheric cooling and the mesospheric H2O increase provides favorable conditions for PMC formation. The global increase in mesospheric H2O during the last decade may explain the increased PMC occurrence in the northern hemisphere (NH). Although mesospheric temperature and H2O exhibit a strong 11-year variation, little solar cycle signatures are found in the PMC occurrence during 2007–2021. 

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2. Mesospheric Bores: Global and Seasonal Occurrence

   Smith, S.M. (June 2020, NSF CEDAR Virtual Workshop, 22–26 June 2020.)

   None (Ed.)

   Initial results into investigations of the global occurrence of mesospheric bores. 

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3. Mesospheric Bores: Global and Seasonal Occurrence

   Smith, Steven M. (June 2020, NSF CEDAR 2020 Workshop)

   None (Ed.)

   First results of seasonal and global mesospheric bore climatology. 

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4. Mesospheric anomalous diffusion during noctilucent cloud scenarios

   https://doi.org/10.5194/acp-19-5259-2019  

   Laskar, Fazlul I.; Stober, Gunter; Fiedler, Jens; Oppenheim, Meers M.; Chau, Jorge L.; Pallamraju, Duggirala; Pedatella, Nicholas M.; Tsutsumi, Masaki; Renkwitz, Toralf (January 2019, Atmospheric Chemistry and Physics)

   Abstract. The Andenes specular meteor radar shows meteor trail diffusion rates increasing on average byabout 10 % at times and locations where a lidar observes noctilucentclouds (NLCs). This high-latitude effect has been attributed to the presenceof charged NLC after exploring possible contributions from thermal tides. Tomake this claim, the current study evaluates data from three stations athigh, middle, and low latitudes for the years 2012 to 2016 to show that NLCinfluence on the meteor trail diffusion is independent of thermal tides. Theobservations also show that the meteor trail diffusion enhancement during NLCcover exists only at high latitudes and near the peaks of NLC layers. Thispaper discusses a number of possible explanations for changes in the regionswith NLCs and leans towards the hypothesis that the relative abundance ofbackground electron density plays the leading role. A more accurate model ofthe meteor trail diffusion around NLC particles would help researchersdetermine mesospheric temperature and neutral density profiles from meteorradars at high latitudes. 

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5. Photochemistry on the bottom side of the mesospheric Na layer

   https://doi.org/10.5194/acp-19-3769-2019  

   Yuan, Tao; Feng, Wuhu; Plane, John M.; Marsh, Daniel R. (January 2019, Atmospheric Chemistry and Physics)

   Abstract. Lidar observations of the mesospheric Na layer have revealed considerablediurnal variations, particularly on the bottom side of the layer, where morethan an order-of-magnitude increase in Na density has been observed below 80 kmafter sunrise. In this paper, multi-year Na lidar observations areutilized over a full diurnal cycle at Utah State University (USU) (41.8^∘ N,111.8^∘ W) and a global atmospheric model of Na with 0.5 kmvertical resolution in the mesosphere and lower thermosphere (WACCM-Na) to explorethe dramatic changes of Na density on the bottom side of the layer. Photolysis of the principal reservoir NaHCO₃ is shown to beprimarily responsible for the increase in Na after sunrise, amplified by theincreased rate of reaction of NaHCO₃ with atomic H, which is mainlyproduced from the photolysis of H₂O and the reaction of OH withO₃. This finding is further supported by Na lidar observation at USUduring the solar eclipse (>96 % totality) event on 21 August 2017, when a decrease and recovery of the Na density on thebottom side of the layer were observed. Lastly, the model simulation showsthat the Fe density below around 80 km increases more strongly and earlierthan observed Na changes during sunrise because of the considerably fasterphotolysis rate of its major reservoir of FeOH. 

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