Abstract
Abstract. A modified form of tracer–tracer correlations of N2O and O3 has been used as a tool for the evaluation of atmospheric photochemical models. Applying this method, monthly averages of N2O and O3 are derived for both hemispheres by partitioning the data into altitude (or potential temperature) bins and then averaging over a fixed interval of N2O. In a previous study, the method has been successfully applied to the evaluation of two chemical transport models (CTMs) and one chemistry–climate model (CCM) using a 1 yr climatology derived from the Odin Sub-Millimetre Radiometer (Odin/SMR). However, the applicability of a 1 yr climatology of monthly averages of N2O and O3 has been questioned due to the inability of some CCMs to simulate a specific year for the evaluation of CCMs. In this study, satellite measurements from Odin/SMR, the Aura Microwave Limb Sounder (Aura/MLS), the Michelson Interferometer for Passive Atmospheric Sounding on ENVISAT (ENVISAT/MIPAS), and the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA-1 and CRISTA-2) as well as model simulations from the Whole Atmosphere Community Climate Model (WACCM) are considered. By using seven to eight years of satellite measurements derived between 2003 and 2010 from Odin/SMR, Aura/MLS, ENVISAT/MIPAS and six years of model simulations from WACCM, the interannual variability of lower stratospheric monthly averages of N2O and O3 is assessed. It is shown that the interannual variability of the monthly averages of N2O and O3 is low, and thus can be easily distinguished from model deficiencies. Furthermore, it is investigated why large differences are found between Odin/SMR observations and model simulations from the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) and the atmospheric general circulation model ECHAM5/Messy1 for the Northern and Southern Hemisphere tropics (0° to 30° N and 0° to −30° S, respectively). The differences between model simulations and observations are most likely caused by an underestimation of the quasi-biennial oscillation and tropical upwelling by the models as well as due to biases and/or instrument noise from the satellite instruments. A realistic consideration of the QBO in the model reduces the differences between model simulation and observations significantly. Finally, an intercomparison between Odin/SMR, Aura/MLS, ENVISAT/MIPAS and WACCM was performed. The comparison shows that these data sets are generally in good agreement, although some known biases of the data sets are clearly visible in the monthly averages. Nevertheless, the differences caused by the uncertainties of the satellite data sets are sufficiently small and can be clearly distinguished from model deficiencies. Thus, the method applied in this study is not only a valuable tool for model evaluation, but also for satellite data intercomparisons.
Highlights
Nitrous oxide (N2O) is a long-lived species in the troposphere and lower stratosphere and can be used as a tracer for atmospheric transport
(3) Odin/SubMillimetre Radiometer (SMR), Aura/Microwave Limb Sounder (MLS), ENVISAT/Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) and Whole Atmosphere Community Climate Model (WACCM) are compared for the years 2003, 2006 and 2009 in order to test the applicability of the monthly averages of N2O and O3 for satellite data intercomparisons
Another interesting feature in this comparison is that the curves at 500 ± 25 K from ENVISAT/MIPAS, Aura/MLS and specified dynamical (SD)-WACCM are not as flat as the ones derived from Odin/SMR
Summary
Nitrous oxide (N2O) is a long-lived species in the troposphere and lower stratosphere and can be used as a tracer for atmospheric transport. The method applied in Khosrawi et al (2009) was introduced by Proffitt et al (2003) for the Northern Hemisphere lower stratosphere and based on aircraft and balloonborne measurements This type of analysis helps to separate O3 variability due to latitudinal transport from photochemical changes. The main purposes of this study are the following: (1) to apply eight years of Odin/SMR (2003–2010), seven years of Aura/MLS (2004–2010), seven years of ENVISAT/MIPAS (2003–2009) measurements, and six years of WACCM simulations (2005–2010) so that the interannual variability of monthly averages of N2O and O3 can be assessed This assessment allows the criticism on e.g. Khosrawi et al (2009) to be addressed that the application of solely one year of monthly averages of N2O and O3 for the evaluation of CCMs is not sufficient. This assessment allows the criticism on e.g. Khosrawi et al (2009) to be addressed that the application of solely one year of monthly averages of N2O and O3 for the evaluation of CCMs is not sufficient. (2) To utilize CRISTA-1 and CRISTA-2 data to examine the cause of the large differences in N2O at 650 ± 25 K that were found between Odin/SMR and model simulations in our recent model evaluation study (Khosrawi et al, 2009). (3) Odin/SMR, Aura/MLS, ENVISAT/MIPAS and WACCM are compared for the years 2003, 2006 and 2009 in order to test the applicability of the monthly averages of N2O and O3 for satellite data intercomparisons
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