| Summary: | Ozone and water vapour are important trace gases in the atmosphere, where both play an important role in radiative and chemical processes. Ozone protects the Earth's biosphere, humans and materials from the harmful ultraviolet (UV) radiation. The distributions and changes of ozone and water vapour are thus important to understand. Restrictions on the production and use of ozone depleting substances (ODS) within the Montreal Protocol have stopped the growth of the ozone loss, even signs of recovery of the ozone layer have been seen. However, many ODSs are long lived in the atmosphere and it will take decades before they are removed. Stratospheric water vapour influences the polar ozone loss by controlling the formation of polar stratospheric clouds (PSC). The climate change will cool the stratosphere, which could favour the formation of PSCs. This could cause significant ozone depletion despite the lower chlorine loadings in the future stratosphere. Atmospheric models are needed for studying these phenomena, because the number of observations is limited. Also the prediction of future ozone loss requires models. In this study simulations of the middle atmosphere have been made using the FinROSE chemistry transport model (FinROSE-CTM). It is an off-line 3-dimensional model, covering the altitude range of ca. 10–80 km, including the stratosphere. The model can be used for short term case studies, as well as for decadal simulations. The FinROSE-CTM needs pre-calculated winds, temperature and surface pressure, and then calculates the chemistry and transport using the meteorology. In this study ECMWF reanalysis data and climate model data have been used. Model results have been compared to ground based and satellite observations, and the model has been shown to be suitable for polar stratospheric ozone and water vapour studies. When running the model with climate model data also future conditions can be predicted. Both observations and simulations show an increase in the water vapour concentration in the Arctic ...
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