A new calculation of chemical eddy transport for several middle atmospheric tracers

We describe a new approach to calculating transport of chemically active tracers by nonbreaking planetary waves (chemical eddy transport). This approach uses the horizontal displacements calculated from a planetary wave model to estimate the time variation of the photolysis rates experienced at each grid point. We contrast our method with a previously documented approach that assumes linear photochemical relaxation and calculates separate diffusion coefficients for each species. Our results are presented for five middle atmospheric tracers, O₃, NO₂, NO, CO, and H₂. For 63, greater transport into the polar region is seen around 30 km. For mesospheric NO, the increased exposure of polar air to UV sunlight leads to more photodissociation and thus less net downward transport into the stratosphere. Mesospheric CO and H₂ are less sensitive to chemical eddy transport because their chemical lifetimes are longer.