The Nature of Noctilucent Clouds

Abstract

In the century that has elapsed since systematic observations of noctilucent clouds began, many observational data have been recorded and discussed at length. From the very start of the period, hypotheses have been formed and, to the extent practical, tested. Quite naturally, because noctilucent clouds came to notice with the increased awareness of twilight sky phenomena following the Krakatoa eruption, the earliest suggestions were that noctilucent clouds were simple layers of volcanic dust appearing (after a delay of a year or two) in the uppermost parts of the atmosphere. These hypotheses later gave place to more complex explanations, to account for the clouds appearing at all in a part of the atmosphere that is very dry and at a very low pressure (cf. Chvostikov 1966b; Hesstvedt 1961, 1962, 1964, 1969b; Iwaskawa 1982; Turco et al. 1982; Vestine and Deirmendijan 1961; Webb 1965; Witt 1969).