Seasonal cycle of averages of nitrous oxide and ozone in the Northern and Southern Hemisphere polar, midlatitude, and tropical regions derived from ILAS/ILAS‐II and Odin/SMR observations

Abstract

Northern and Southern Hemispheric monthly averages of ozone (O3) and nitrous oxide (N2O) have been suggested as a tool for evaluating atmospheric photochemical models. An adequate data set for such an evaluation can be derived from measurements made by satellites which, in general, have a high spatial and temporal coverage. Here, we use measurements made by the Improved Limb Atmospheric Spectrometers (ILAS and ILAS‐II) which use the solar occultation technique and by the Odin‐Sub‐Millimetre Radiometer (Odin/SMR) which passively observes thermal emissions from the Earth's limb. From ILAS/ILAS‐II and Odin/SMR observations, 1‐year data sets of monthly averaged O3 and N2O, covering a full seasonal cycle, were derived for the latitude range between 60–90°N and 60–90°S, respectively, by partitioning the data into equal bins of altitude or potential temperature. A comparison between both data sets in this latitude region shows a good agreement and verifies that limited sampling from satellite occultation experiments does not constitute a problem for deriving such a full seasonal cycle of monthly averaged N2O and O3. Since Odin/SMR provides measurements globally, a 1‐year data set of monthly averaged N2O and O3 is reported here for both the entire Northern and Southern Hemispheres from these measurements. Further, these hemispheric data sets from Odin/SMR are separated into data sets of monthly averaged N2O and O3 for the low latitudes, midlatitudes, and high latitudes. The resulting families of curves help to differentiate between O3 changes due to photochemistry from those due to transport. These 1‐year hemispheric data sets of monthly averaged N2O and O3 from Odin/SMR and ILAS/ILAS‐II as well as the data sets of monthly averaged N2O and O3 for the specific latitude regions from Odin/SMR provide a potentially important tool for the evaluation of atmospheric photochemical models. An example of how such an evaluation can be performed is given using data from two chemical transport models (CTMs), the Chemical Lagrangian Model of the Stratosphere (CLaMS) and the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA). We find a good agreement between Odin/SMR and the CTMs CLaMS and KASIMA with differences generally less than ±20%.