Lamination frequencies as a diagnostic for horizontal mixing in a 3D transport model

Ozone simulations are performed in an attempt to simulate laminar events wi th the frequency observed in balloon ozone sondes. The winds are taken from the Goddard Earth Observing System Data Assimilation System (GEOS DAS); th e importance of horizontal and vertical resolution to production of lamina are investigated, A simulation with a high horizontal reolution (grid spaci ng 1 degrees latitude by 1.25 degrees longitude) and high vertical resoluti on (similar to 300 m grid spacing) isentropic model produces lamination fre quencies close to the balloon sonde climatology near the polar vortex edge but exhibits too much lamination in the subtropics. This indicates that the GEOS DAS winds contain the information to produce laminar events, although such small-scale features are not manifest in the more commonly used 2 deg rees latitude by 2.5 degrees longitude transport model, which uses the hybr id sigma-pressure vertical coordinate. The zonal average ozone tendencies d ue to horizontal mixing in the lamina-producing models are similar to the t endencies in coarser resolution models that show no lamination, suggesting that it is not necessary to resolve laminar events to maintain a realistic ozone budget. The comparison of the modeled lamination frequency with the b alloon sonde climatology indicates that the model horizontal mixing at the vortex edge is accurate but in the subtropics the mixing is excessive.