3-DIMENSIONAL STUDIES OF THE 1991 1992 NORTHERN-HEMISPHERE WINTER USING DOMAIN-FILLING TRAJECTORIES WITH CHEMISTRY/

We describe a new and computationally efficient technique for global t hree-dimensional modeling of stratospheric chemistry. This technique i nvolves integrating a photochemical package along a large number of in dependent trajectories to produce a Lagrangian view of the atmosphere. Although Lagrangian chemical modeling with trajectories is an establi shed procedure, this extension of integrating chemistry along a large number of domain-filling trajectories is a novel technique. This techn ique is complementary to three-dimensional Eulerian chemical transport modeling and avoids spurious mixing caused by low resolutions or diff usive transport schemes in these models. We illustrate the technique b y studying the chlorine activation in the Arctic winter lower stratosp here. A photochemical model was integrated along large ensembles of ca lculated trajectories between 20 and 100 mbar for the 1991/1992 winter in order to produce a three-dimensional chemical picture. Large amoun ts of chlorine was activated at low altitudes (80 to 100 mbar) as well as altitudes near 50 mbar. This activated air was well contained at a ll levels, with little indication of mixing into lower latitudes. Mode l results for early January 1992 were compared to daily Microwave Limb Sounder (MLS) ClO observations at 465 K. The structure and evolution of the activated chlorine was well reproduced, giving faith in the tec hnique, although absolute modeled ClO amounts were smaller than the ML S data. A larger number of domain-filling isentropic trajectories were also run at 475 K to produce a higher-resolution picture of vortex ev olution in late January 1992. The model successfully reproduced the wa ve breaking events which characterized this period causing transport o f activated air to lower latitudes.