Chemical–Dynamical Coupling in the Mesosphere and Lower Thermosphere
A chemistry climate model is used to illustrate several ways in which dynamics and chemistry are coupled in the mesosphere and lower thermosphere (50–120 km in altitude). First the mean chemical state of the modeled atmosphere is presented, including the distribution of key radiatively-active species that determine heating and cooling rates. This is followed by a description of the major dynamical modes of variability resolved by the model, which span timescales from hours to seasons, and includes the mean meridional circulation, the upper atmospheric response to a sudden stratospheric warming, and upward propagating tidal modes. It is demonstrated that all these have significant effects on composition, either through advection, or by the temperature and pressure dependence of chemical reaction rates. For those constituents modified by dynamics that play a role in the energy budget, the potential for a feedback on the dynamics exists.
KeywordsZonal Wind Vertical Wind Meridional Circulation Lower Thermosphere Stratospheric Warming
The National Center for Atmospheric Research is sponsored by the National Science Foundation. Any opinions, findings and conclusions or recommendations expressed in the publication are those of the author and do not necessarily reflect the views of the National Science Foundation. Support for this research was also provided by the National Aeronautics and Space Administration, grants NNX08AL61G and NNX08AX28G. The author would like to thank Anne Smith for providing insightful comments on this manuscript.
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