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Title: Studies of stratospheric chemistry using global models and global observations
Author: Goodchild, S. J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1998
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The aim of this thesis is to improve our understanding of the distribution of stratospheric ozone which is determined by both dynamical and photochemical processes. This is of particular importance since ozone adsorbs incoming solar UV radiation which would otherwise be harmful to humans. In 1985 the Antarctic Ozone hole was discovered alerting the world to the impact human activity has had upon stratospheric ozone. In recent years a significant decline in ozone has also been detected at high northern latitudes during spring. This thesis uses numerical models of varying complexity in order to study the stratospheric circulation, and the chemistry occurring therein. The results from the model integrations described are compared to observations made by instruments on board the UARS satellite. A new stratospheric chemistry scheme is described. Simple box model studies show that this model is capable of simulating the almost complete removal of ozone seen to occur at certain altitudes during Antarctic spring. This experiment highlights interesting differences in the behaviour of chlorine compounds in the two hemispheres. Sensitivity studies are performed in order to determine the precise conditions required for severe ozone destruction. It is found that the average ozone destruction rate over the period of the integration is inversely proportional to the maximum C1ONO2 mixing ratio produced by the model. The model shows some sensitivity to the ozone column used in the photolysis calculation, however it is not considered that sufficient improvement would be obtained by using a fully interactive photolysis scheme to justify the computational expense of this calculation. The new chemistry scheme is coupled to the SLIMCAT off-line model in order to study the 1991-92 northern hemisphere winter. It is found that if instead of using 2-dimensional model data to initialise the model a more realistic simulation is produced by using observations of long lived gases made by the UARS satellite. It is found that whilst the model is capable of reproducing ozone depletion, the denoxification within the model is too severe. This results in the deactivation of chlorine being unrealistically slow. In order to investigate the longer term variation of ozone a one year integration of the SLIMCAT model coupled to a parameterised chemistry scheme is performed. When the model results are compared to observations there is evidence that the model's simulation of lower stratosphere tropical dynamics is poor. Budget studies of N2O reveal that the main cause of this problem is the lack of means continuity in this region of the model. When the experiment is repeated, imposing mass continuity on each isentropic surface, the resulting N2O distribution is much more realistic.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available