Large-scale stratospheric ozone photochemistry and transport during the POLARIS Campaign

Measurements from the Halogen Occultation Experiment (HALOE) on board the U ARS satellite and assimilated winds, temperatures, and diabatic heating rat es from the NASA Goddard data assimilation office (DAO) are used with the N ASA Langley Research Center (LaRC) Lagrangian photochemical model to comput e 3-D air parcel trajectories with photochemistry for all Northern Hemisphe re HALOE observations during the period March-September 1997. Results from ensemble means of the photochemical trajectory calculations provide a globa l perspective for the interpretation of constituent measurements made from the ER-2 and balloon platforms during the POLARIS aircraft campaign. Lagran gian photochemical predictions are shown to compare favorably with ER-2, ba lloon, Total Ozone Mapping Spectometer (TOMS), and subsequent coincident HA LOE observations. Model predictions show large-scale photochemical ozone lo ss in high latitudes at ER-2 flight altitudes of over 10% per month in June and July, in good agreement with steady state photochemical calculations c onstrained with ER-2 observations of radical and long-lived species. Larges t summertime photochemical ozone losses (over 1.4 ppmv/month) are found to occur poleward of 60 degrees N above 30 mbar, in good agreement with steady state photochemical calculations constrained with observations from the ba lloon-borne Fourier transform infrared solar absorption spectrometer (MkIV) instrument. Summertime polar photochemical ozone losses are driven largely by NOx chemistry and are largest for air parcels with high NOx/NOy ratios that have experienced continuous sunlight for several days. Differences bet ween predicted net changes in ozone and changes due to photochemistry are u sed to estimate residual changes due to transport processes. Photochemical and residual transport tendencies tend to be of similar magnitude but oppos ite sign. Photochemical loss of ozone tends to outweigh positive transport tendencies in high latitudes, while upwelling of low ozone below the tropic al ozone maximum moderates photochemical production there. The estimated tr ansport tendencies are generally consistent with expectations based on tran sformed Eulerian circulation derived from the DAO assimilated data and the mean ozone distribution. A net (photochemical plus transport) ozone decreas e of over 0.2 ppmv/month is predicted throughout the middle and lower strat osphere poleward of 70 degrees N during the summer months.