On Dynamics and Transport Near the Polar Mesopause in Summer

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.