Radiative and transport characteristics of 3D greenhouse gases

This work examines the thermal and dynamical response of the Canadian Centre for Climate Modelling and Analysis (CCCma) third-generation AGCM to the replacement of uniform greenhouse gas tracer concentrations with prognostic three-dimensional (3D) fields. A simplified chemical parameterization is used to represent the destruction of N₂O, CH₄, CFCl₃ (CFC-11), and CF₂Cl₂ (CFC-12) in the stratosphere, and also the in situ oxidation of CH₄ into water vapour. As chemically and radiatively active tracers, these species provide additional insight into the model transport and thermal properties, particularly in the stratosphere. Differences in the local and global radiative energy balance between models having uniform and 3D greenhouse gases will be highlighted using several diagnostics. Due to the dominant radiative influence of water vapor, the net effect is a cooling of order 1 degree K throughout the stratosphere. While this represents only a small change to the overall radiation budget, the spatial distributions of the temperature, heating rate, and velocity field differences give some insight into the circulation changes wrought by these model improvements.