Intercomparison and evaluation of atmospheric transport in a Lagrangian model (STOCHEM), and an Eulerian model (UM), using 222Rn as a short-lived tracer.

Transport of the short-lived (half-life 3.83 days) isotope Rn-222, which is emitted from unfrozen soils, is used to compare transport in several versions of the UK Meteorological Office Lagrangian chemistry-transport model and in the Unified Model, the UK Meteorological Office general circulation model. The same Rn-222 experiment is repeated for all the model versions, illustrating the impact on global transport of various model improvements: adding boundary-layer schemes, including sub-grid scale convection, increasing model spatial resolution, and increasing the temporal resolution of the meteorological fields used for driving the off-line model. Results from all model versions are compared with a limited observational data set, and also with results from the same Rn-222 simulations carried out with several global atmospheric transport models as part of the World Climate Research Program in December 1993 (Jacob et al. 1997). Versions of the Lagrangian chemistry-transport model that include sub-grid scale convection, transport Rn-222 in a manner that is similar to the Unified Model and most general circulation models, supporting the simple and computationally inexpensive Lagrangian approach taken.