An Investigation of the Distribution of Ozone-depleting Substances in the Upper Troposphere and Lower Stratosphere

Stratospheric transport in global circulation models and chemistry-climate models is an important component in simulating the recovery of the ozone layer as well as changes in the climate system. The Brewer-Dobson Circulation is not well constrained by observations and further investigation is required to resolve uncertainties related to the mechanisms driving the circulation. This work has assessed the specified dynamics mode of the Canadian Middle Atmosphere Model (CMAM30) by comparing its output to the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) profile measurements of CFC-11, CFC-12, HCFC-22, and N2O. In the CMAM30 simulation, the meteorological fields were nudged using the ERA-Interim Reanalysis and a specified tracer was employed for each halocarbon species, with hemispherically-defined surface measurements used as the boundary condition. This modified halocarbon experiment is known as CMAM30HR. A comprehensive sampling technique along the line-of-sight of the ACE-FTS measurements has been utilized to allow for direct comparisons between the simulated and measured tracer concentrations. Stratospheric transport has been investigated using CFC-11, CFC-12, and N2O. The model consistently overpredicts the concentrations of these tracers in the lower stratosphere, particularly in the Northern Hemisphere winter and spring seasons. The three mixing barriers investigated, namely the polar vortex, the extratropical tropopause, and the tropical pipe, show that there are inconsistencies between the measurements and the simulations. It was found that the simulation under- predicts mixing efficiency in the tropical lower stratosphere during the June-July-August season. The CMAM30HR simulations and the ACE-FTS measurements of HCFC-22 have also been evaluated. ACE-FTS HCFC-22 observations exhibit a small low bias compared to instruments that use a similar measurement technique. However, when compared to in situ measurements, ACE-FTS exhibits a high bias. In general, CMAM30HR exhibits a low concentration bias below approximately 70−30 hPa and a high bias above 30 hPa compared to ACE-FTS. However, the HCFC-22 comparison reveals a peak in differences between approximately 100 hPa and 50 hPa that is not consistent with the previous comparisons of halocarbon concentrations; potential explanations of the discrepancy are discussed. The most recently available ACE-FTS data are also presented and discussed.

Department dc:contributor.department

Physics

Year dc:date.issued

2019

Author dc:creator

• Kolonjari, Felicia

Advisor dc:contributor.advisor

• Walker, Kaley A

• chlorofluorocarbons
• hydrochlorofluorocarbons
• stratospheric transport

Handle dc:identifier.uri

http://hdl.handle.net/1807/97019

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/97019