Some basic aspects of dynamics and transport in polar regions within one or two scale heights of the summer mesopause are examined, and the implications for local one-dimensional photochemical modeling of those regions discussed. Included is a simple thought experiment on gravity wave breaking that throws further light on the so-called ''turbulent Prandtl number'' question, and related questions. The ''downward control'' of time averaged, zonally averaged upwelling by gravity wave breaking is noted, and a one-dimensional modeling strategy suggested in which the transport of water vapor and other constituents from below is characterized by a single parameter, defining a mean upwelling velocity inversely proportional to the mean mass density. It is suggested that, at and below noctilucent cloud altitudes, vertical mixing should be altogether neglected. ¿ American Geophysical Union 1989