Refining of atmospheric transport model entries by the globally observed passive tracer distributions of (85)krypton and sulfur hexafluoride (SF6)

Our high precision database of the global distribution of SF6 in the troposphere [Maiss et al., 1996] is used in a two-dimensional atmospheric transport model (2D-HD model) to study the behavior of this new tracer in comparison to the classical global atmospheric transport tracer krypton 85. The 2D-HD model grid has been derived from the three-dimensional Hamburg TM2 model with the same resolution in the vertical and meridional direction and was designed to run on any standard personal computer. The same vertical convection scheme and wind fields as in the TM2 model, reduced to two dimensions, were used in the calculations. In addition, the horizontal diffusion parameter of the model was adjusted by matching the model-estimated mean meridional Kr-85 distribution with observations over the Atlantic Ocean. To simulate global tropospheric SF6 concentrations, an almost linearly increasing SF6 source strength has been applied since 1970. The latitudinal distribution of the SF6 source was assumed to be similar to the global electrical power production. Excellent agreement between SF6 model results and observations is achieved with the Kr-85-tuned 2D-HD transport model with respect to the global meridional concentration distribution, and particularly in middle to high northern latitudes. In the southern hemisphere at the German Antarctic station Neumayer, a significant seasonal cycle of SF6 has been observed which is reproduced by the model, however, with a smaller amplitude. This finding may point to possible shortcomings of the model's transport scheme when simulating the seasonality of stratosphere-troposphere exchange in high southern latitudes.