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Title: An investigation of the circulation in a numerical model using tracer distributions
Author: Douglas, Peter Murray
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1997
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Recent observations of trace constituents were used as a basis for comparing the circulation of the UGAMP General Circulation Models with that of the real atmosphere. Measurements of two different constituents were used; upper-tropospheric water vapour and the volcanic aerosol injected into the stratosphere by Mt. Pinatubo. The study of upper-tropospheric water vapour in the UGCM was motivated by reports of an interhemispheric asymmetry in aircraft measurements; the northern winter hemisphere contained 2 to 4 times more H2O than the southern winter hemisphere [Kelly et al., 1991]. The UGCM did exhibit an interhemispheric asymmetry in water vapour fields between 200 and 300mb, but to a lesser degree than claimed by Kelly et al. A further analysis of water vapour in the UGCM revealed that, due to the longitudinal variability of the distribution, a different choice of measurement sites could significantly alter claims made about interhemispheric asymmetry. Confidence in the severity of the asymmetry was further decreased after examining MLS retrievals of H2O AT 215MB. The MLS measurements, with a near global coverage, showed very little difference in water vapour mixing ratios between the two winter hemispheres. The UGCM and EUGCM were used to simulate the dispersal of the Mt. Pinatubo aerosol cloud. With a lifetime of years in the stratosphere a well documented evolution, the Pinatubo cloud serves as a good test for model dynamics. Both models showed evidence of the two different mixing regimes seen in the real atmosphere; material mixing into the northern mid-latitudes below 20km and material mixing into the southern mid-latitudes above 20km. The two Pinatubo simulations developed a tropical stratospheric reservoir, similar to that in the real atmosphere. The tropical confinement of material was maintained in the EUGCM by steep PV gradients, acting as a barrier to isentropic transport, situated in the low latitudes. Material only escaped from the tropics into the mid-latitudes via a channel of low PV gradient.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available