The roles of dynamical and chemical processes in determining the stratospheric concentration of ozone in one‐dimensional and two‐dimensional models

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Abstract
The local concentration of stratospheric ozone in any region of the stratosphere is set by a balance among photochemical production and transport into the region versus local photochemical removal and export out of the region. In a given region of the atmosphere, however, different terms (or processes) may dominate, resulting in various modes of balance. Such modes include balances between chemical production and chemical removal (the photochemical equilibrium state), chemical production and export, import and chemical removal, or strict balance between the transport terms. In this study, we analyze the results from a two‐dimensional model to determine the principal modes of balance for different regions of the stratosphere. The analysis showed that except near the poles, ozone is in photochemical equilibrium above 35 km. In the lower stratosphere, equatorward of 50°, concentration of ozone is neither photochemically controlled nor transport controlled, but is set by a balance between transport and chemical processes. The low abundance of O3 in the tropics is a result of the balance between photochemical production and transport out of the region. The seasonal behavior at high latitudes, as evident from the springtime maxima, results from a balance between photochemical removal and transport into the region. It is this “mixed” mode of balance that distinguishes two‐dimensional models from the one‐dimensional models in which the bulk of the O3 content is chemically controlled. The budget analysis has implications for assessing the response of ozone in two‐dimensional models to changes in the photochemical environment. This response is contrasted with that of one‐dimensional models to highlight the limitation of one‐dimensional model studies.