Talk by Peter Hjort Lauritzen, NCAR – Niels Bohr Institute - University of Copenhagen

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Talk by Peter Hjort Lauritzen, NCAR

Evaluating advection/transport schemes using interrelated tracers, scatter plots and numerical mixing diagnostics

Atmospheric tracers are often observed to be functionally related, and these relations can be physically or chemically significant. It is therefore highly desirable that the transport schemes used in chemistry and chemistry-climate models should not disrupt such functional relations in unphysical ways through numerical mixing or, indeed, unmixing. Here, diagnostics are proposed that quantify numerical mixing by a transport scheme for two tracers that are nonlinearly related. The question of how physically reasonable the numerical mixing is can be addressed by using scatter/correlation plots.

The mixing diagnostics do not require the knowledge of the analytical solution to the transport problem for the individual tracers. However, using an idealized flow field and spatial distributions facilitates the use of the mixing diagnostics in transport scheme development. Hence we propose to exercise the new mixing diagnostics using an idealized but highly deformational analytical flow field. Example results using the CSLAM (Conservative Semi-LAgrangian Multi- tracer) scheme are presented. The mixing diagnostics and their relevance to nonlinear chemical parameterizations is discussed as well.