Variations in the Polar Mesospheric Summer Echoes during the Appearance of Irregularities of Noctilucent Clouds

Variations in the amplitude of the ordinary wave from a received signal on a partial reflection radar at a short-wave range on the Kola Peninsula during the appearance of noctilucent clouds on August 12, 2016, are examined. Noctilucent clouds are registered by the all-sky camera located 100 km southward of the partial reflection radar. They extended over the entire celestial hemisphere observed by the all-sky camera; all of them moved in the southern direction, and the clouds had a tenuous structure and showed gravity waves with spatial periods of 15-100 km. During the presence of noctilucent clouds over the partial reflection radar, polar mesospheric summer echoes (PMSEs) were recorded at heights of 83-86 km. It was found that the presence of only noctilucent clouds in diagram of the antenna pattern of partial frequency radar is not sufficient for the appearance of PMSEs; noctilucent clouds must also have irregularities of several kilometers. The PMSE heights decreased with a velocity of 0.5 and 1.3 m/s. The issue of aerosols that cause the appearance of PMSEs and noctilucent clouds is discussed.