Attribution of ozone changes to dynamical and chemical processes in CCMs and CTMs

Abstract

Chemistry-climate models (CCMs) are commonly used to simulate the past andfuture development of Earth's ozone layer. The fully coupled chemistryschemes calculate the chemical production and destruction of ozoneinteractively and ozone is transported by the simulated atmospheric flow. Dueto the complexity of the processes acting on ozone it is not straightforwardto disentangle the influence of individual processes on the temporaldevelopment of ozone concentrations. A method is introduced here thatquantifies the influence of chemistry and transport on ozone concentrationchanges and that is easily implemented in CCMs and chemistry-transport models(CTMs). In this method, ozone tendencies (i.e. the time rate of change ofozone) are partitioned into a contribution from ozone production anddestruction (chemistry) and a contribution from transport of ozone(dynamics). The influence of transport on ozone in a specific region isfurther divided into export of ozone out of that region and import of ozonefrom elsewhere into that region. For this purpose, a diagnostic is used thatdisaggregates the ozone mixing ratio field into 9 separate fields accordingto in which of 9 predefined regions of the atmosphere the ozone originated.With this diagnostic the ozone mass fluxes between these regions areobtained. Furthermore, this method is used here to attribute long-termchanges in ozone to chemistry and transport. The relative change in ozonefrom one period to another that is due to changes in production ordestruction rates, or due to changes in import or export of ozone, arequantified. As such, the diagnostics introduced here can be used to attributechanges in ozone on monthly, interannual and long-term time-scales to theresponsible mechanisms. Results from a CCM simulation are shown here asexamples, with the main focus of the paper being on introducing the method. © Author(s) 2011.