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Description of the RIVM 2-dimensional stratosphere model

Beschrijving van het RIVM 2-dimensionaal stratosfeermodel

Synopsis

For performing assessment studies on the stratosphere and studying the influence of changes in the stratosphere on the troposphere and climate, the Air Research Laboratory of the RIVM has recently implemented a model of the stratosphere. In this report, a description of the model will be given and a number of simulations describing the behaviour of the model will be discussed. In the near future the model will be used for analyzing the effects of different scenarios of CFCs, HCFCs and HFCs on stratospheric ozone, UV radiation in the troposphere, radiative forcing of climate and for studying the effects of changes in the stratosphere on the troposphere and climate. The model, obtained from the University of Cambridge in the United Kingdom, is a 2-dimensional model of the atmosphere extending from the North to the South poles and from 0 to 60 km altitude. The model's three major components simulate the dynamics, chemistry and radiation in the atmosphere. Since these three processes are strongly linked in the model, interactions between the different processes can be studied. The version of the model described here uses precalculated transport fields. The ozone, methane, nitrogen, chlorine and bromine chemical cycles are simulated in the model as well as the distribution of anthropogenic compounds such as CFCs. We conclude from the first simulations with the model that the large-scale transport (the Hadley cells, the troposphere-stratosphere exchange and the Brewer-Dobson circulation) in the troposphere and stratosphere is well represented, as well as the chemical reactions. A combination of factors is probably responsible for the slight underestimation of the interhemispheric transport in the model. The box chemistry calculations clearly show the importance of transport in the stratosphere. Stratospheric ozone is produced mainly in the tropics and transported to higher latitudes by the large-scale Brewer-Dobson circulation in the stratosphere. This results in maxima in the ozone column at mid-latitudes in spring and minima in the tropics. The agreement between the modelled ozone columns and satellite measurements with the TOMS instrument is good. The small differences are characteristic for almost all stratosphere models. The tropospheric hydroxyl concentration is very important for the destruction of a number of compounds, e.g. methane, carbon monoxide, HCFCs, HFCs. Scenario calculations of methyl chloroform have been performed and compared with observed atmospheric concentrations to obtain information on the destruction of methyl chloroform and of the hydroxyl concentration in the troposphere. The total loss of methyl chloroform in the troposphere agrees very well with measurements. This indicates that the model can simulate the methyl chloroform concentration, but also the concentration of HCFCs and HFCs, in the atmosphere fairly well. This is very important for studying the effects of different scenarios of HCFCs and HFCs on the destruction or recovery of the ozone layer and on the greenhouse effect.
 

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