Variability of the Lagrangian turbulent diffusion in the lower stratosphere in the lower stratosphere

Ozone and nitrous oxide are measured at high spatial and temporal resolution by instruments flying on the ER-2 NASA research aircraft.

Comparing the airborne transects to reconstructions by ensemble of diffusive backward trajectories allows to estimate the average vertical Lagrangian turbulent diffusion experienced by the air parcels. The resulting estimates show large Lagrangian diffusion of the order of 0.1 m2/s outside the polar vortex in the surf zone and smaller values of the order of 0.01 m2/s inside. Locally, large variation of Lagrangian diffusion occur over mesoscale distances and are not necessarily predicted by variations in strain.

It is found that high temporal resolution (3 hours or less) is required for off-line transport calculations and that the reconstructions are also sensitive to spurious motion induced by assimilation in standard analysed winds.