Assessment of the interannual variability of lower stratospheric monthly averages of O3 and N2O using observations from Odin/SMR

The Sub-Millimetre Radiometer (SMR) was launched on 20 February 2001 on board of Odin. Observations of thermal emission of trace gases originating from the Earth's limb are performed in a time-sharing mode with astronomical observations. In aeronomy mode, various target bands are dedicated to profile measurements of trace constituents relevant to stratospheric and mesospheric chemistry and dynamics such as e.g. O3, ClO, N2O, HNO3, H2O, CO, and NO, as well as isotopes of H2O and O3. Here, we focus on measurements of ozone (O3) and nitrous oxide (N2O). N2O is photochemically long-lived in the lower stratosphere while O3 is variing due to O3 photchemistry and due to horizontal and vertical transport. Using averages of N2O and O3 helps to separate between photochemical and dynamical processes and thus can be used as a tool for the evaluation of atmospheric photochemical models. The data is organized monthly for both hemispheres by partitioning the data into equal bins of altitude or potential temperature. Within these bins of altitude or potential temperature the O3 and N2O data is averaged over a fixed interval of N2O (20 ppbv). So far we used only one year of data, but by comparison to data sets with different temporal resolution we concluded that interannual variability must be low in the monthly averages. However, this has been a major point of criticism in our analyses. Here, we present 5-years of Odin/SMR observations to assess the interannual variability of lower stratospheric monthly averages of N2O and ozone O3 binned by potential temperature in the polar, midlatitude and tropical regions. Thereby, we can show that interannual differences are quite low as suggested earlier and that these differences can be easily distinguished from model deficiencies.