Extratropical Lower Stratosphere Research Articles

Diagnosing ozone loss in the extratropical lower stratosphere

Chemical ozone loss in the Southern Hemisphere lower stratosphere during winter and spring 1996 is investigated using a three‐dimensional chemical transport model. Model diagnostic quantities are developed to determine the underlying chemical mechanisms controlling the distribution of ozone. These diagnostic tracers quantify the ozone change due to individual catalytic cycles or reaction mechanisms that form or destroy ozone. Results from these tracers confirm the importance of halogens not only in the development of the ozone hole but also in midlatitude ozone depletion of which almost 50% is due to cycles involving halogens. The dominant chemical ozone loss mechanism in the middle latitudes is due to the cycle whose rate determining step involves the bimolecular collision between HO2 and O3. Observational evidence from ozonesonde measurements shows substantial ozone depletion in the polar subvortex region (altitudes below ∼14 km). These measurements also indicate that this ozone depletion must be due, at least in part, to in situ chemical ozone loss. Model results show that over a quarter of the ozone depletion associated with the ozone hole resides at subvortex altitudes. Diagnostic tracers designed to quantify ozone loss occurring above and below the subvortex transition altitude show that the majority of this ozone depletion is in situ ozone loss. Furthermore, at altitudes below the subvortex transition, polar ozone loss is efficiently transported to middle latitudes, where it contributes to midlatitude ozone decline.

Ozone and atmospheric transport processes

A systematic program to measure vertical ozone distribution was established by the Air Force Cambridge Research Laboratories in January 1963. High resolution measurements with the Regener chemiluminescent ozonesonde have been obtained from a network of twelve stations in North America, which extends from the Canal Zone to the Arctic region. Processed data from the first two years of network operation were used to analyze the broad-scale characteristics of the ozone distribution. Detailed meridional cross sections of ozone mixing ratio were constructed and compared with simultaneous distributions of other atmospheric tracers including potential vorticity and radioactive debris. The striking consistency in the behavior of these tracers, each having quite different sources and sinks, suggests that the extratropical lower stratosphere is strongly stratified but on the average remains well mixed along surfaces which have a significant slope downward toward higher latitudes. To a good first approximation in all seasons, trace substances in this region of the atmosphere tend toward a uniform distribution along surfaces of constant potential vorticity. Direct computations of the temporal eddy ozone flux indicate that the northward transport across middle latitudes over North America occurs predominately at the base of the stratosphere near the tropopause. The average flux strength observed in the summer and fall seasons is less than one-third of the average winter and spring transport. DOI: 10.1111/j.2153-3490.1966.tb00244.x

Ozone and atmospheric transport processes

A systematic program to measure vertical ozone distribution was established by the Air Force Cambridge Research Laboratories in January 1963. High resolution measurements with the Regener chemiluminescent ozonesonde have been obtained from a network of twelve stations in North America, which extends from the Canal Zone to the Arctic region. Processed data from the first two years of network operation were used to analyze the broad-scale characteristics of the ozone distribution. Detailed meridional cross sections of ozone mixing ratio were constructed and compared with simultaneous distributions of other atmospheric tracers including potential vorticity and radioactive debris. The striking consistency in the behavior of these tracers, each having quite different sources and sinks, suggests that the extratropical lower stratosphere is strongly stratified but on the average remains well mixed along surfaces which have a significant slope downward toward higher latitudes. To a good first approximation in all seasons, trace substances in this region of the atmosphere tend toward a uniform distribution along surfaces of constant potential vorticity. Direct computations of the temporal eddy ozone flux indicate that the northward transport across middle latitudes over North America occurs predominately at the base of the stratosphere near the tropopause. The average flux strength observed in the summer and fall seasons is less than one-third of the average winter and spring transport. DOI: 10.1111/j.2153-3490.1966.tb00244.x