Association between the mid-winter stratospheric circulation and the first observation in the following summer of noctilucent clouds

Abstract

NOCTILUCENT clouds (NLCs) are seen mainly in the summer months at high latitudes over both hemispheres. They appear in a thin layer at a height of about 82 km in the mesopause region where temperatures are the coldest in the Earth's atmosphere. A temperature of 150 K or less at the mesopause has been shown, by rocket soundings in the presence of NLCs, to be a necessary condition for the existence of these clouds¹. Rocket sampling experiments and ground-based observations indicate that NLC particles probably consist of a volatile substance, believed to be ice, coated on volatile nuclei that may be hydrated ions^2,3.