A comparison of ozone transport and chemistry models using the GEOS ozone assimilation system

In the Goddard Earth Observing System (GEOS) ozone data assimilation system (DAS) ozone observations from Total Ozone Mapping Spectrometer (TOMS) and Solar Backscatter Ultraviolet (SBUV) instruments are assimilated into a transport and chemistry model driven by GEOS core DAS assimilated winds. Besides global 3-dimensional analyzed ozone fields the system produces the transport, chemistry and analysis increments, i.e. changes to the ozone field due to advection, photochemical processes, and analysis of observations, respectively. The amplitude and nature of these increments indicate strengths and weaknesses of a transport and chemistry model. For a realistic model, prediction and observations agree and analysis increments are small. In the regions where a model has systematic errors, the analysis increments are large, and they are consistently counteracting the transport or chemistry increments. We compare models in which transport is driven by different winds and chemistry is specified using different parameterizations by including them into the ozone assimilation system. The comparison of analysis, transport and chemistry increments reveals strengths and weaknesses of each model under study.