CANADIAN MIDDLE ATMOSPHERE MODEL - PRELIMINARY-RESULTS FROM THE CHEMICAL-TRANSPORT MODULE

All important objective of middle atmosphere global climate modelling is the development of the capability of predicting the response of the middle atmosphere to natural or anthropogenic perturbations. To achie ve this, a comprehensive chemistry package interactively coupled with radiative and dynamical modules is required This paper presents prelim inary results obtained with a photochemistry module which has been inc orporated in the Canadian Middle Atmosphere Model (CMAM). The module c ontains 42 species including necessary oxygen, hydrogen, nitrogen, chl orine, bromine and methane oxidation cycle species. Photochemical bala nce equations are solved on-line throughout the middle atmosphere at e very dynamical time step. A full diurnal cycle is simulated with photo lysis rates provided by a look-up table. The chemistry solver is a mas s conserving, fully implicit, backward difference scheme which current ly uses less than 10% of the CCM run time. We present the results obta ined from short integrations and compare them with UARS measurements. The model ozone distribution appears in quantitative agreement with ob servations showing peak values near 10 ppmv and confined to the 35-km region. The abundance of nitrogen, chlorine, bromine oxides and their respective contributions to the overall ozone budget is realistic. The study illustrates the capability of the model to simulate middle atmo sphere photochemistry for the disparate conditions occurring throughou t the region.