| The Canadian Middle Atmosphere Model (CMAM) is a general circulation model with a global domain extending from the Earth's surface to about 95 km. This thesis focuses on the mesosphere of the CMAM and consists of three related components, namely, the deposition of solar energy and the related chemical heating, the chemical species distribution, and the impact of the migrating diurnal tide.; First, the CMAM solar heating parameterization above 1 hPa (∼50 km) was modified to allow chemical heating to be explicitly accounted for. The O2 heating in the Schumann-Runge bands and the continuum was also added. The heating efficiencies for the O2 Schumann-Runge continuum and the O3 Hartley band were taken into consideration. The exothermic reactions included were those of the odd-oxygen and odd-hydrogen families. With these modifications, the calculated zonal mean temperature is generally increased by 10 K above 0.01 hPa (∼80 km), mostly due to the contribution of chemical heating at nighttime. The global mean chemical heating, the directly deposited solar heating, and the heating lost by emission, account for about 55%, 30%, and 15%, respectively of the main solar ultraviolet energy.; Secondly, a comprehensive comparison of the modelled chemical species and temperatures with observations was conducted, again with a focus on the mesosphere. It was found that the model temperatures were lower than the COSPAR International Reference Atmosphere (CIRA) by 10 K throughout most of mesosphere, with an extreme value of 30° at equinox. However, they are in better agreement (within 10 K) with the Halogen Occultation Experiment (HALOE) observations. The atomic oxygen and nitric oxide densities are in good agreement with observations of CIRA and HALOE near the model top respectively, and this confirms that the chemistry upper boundary conditions are quite reasonable. The model ozone densities/mixing ratios are lower than measurements for daytime conditions.; The third component pursued was the source of the large mesospheric ozone maximum in the CMAM with its large variation. This was investigated using dynamical experiments. Both an artificial weak-tide experiment and an analysis of the continuity equation indicate that the migrating diurnal tide is responsible for the formation of the mesospheric ozone peak in the model. (Abstract shortened by UMI.)... |
