Abstract
Distributions of noctilucent cloud are studied in relation to the circulation of the lower atmosphere. The information available on water vapor abundance and on factors influencing it in the upper mesosphere is reviewed and a plausible model of noctilucent cloud genesis, consistent with it, proposed. It is shown that a local increase in the vertical turbulent transfer, generated by internal gravity waves originating in the tropospheric jet stream, could produce a supersaturated layer when the mesopause temperature is below −140K.
