Evaluation of linear ozone photochemistry parametrizations in a stratosphere-troposphere data assimilation system
1Data Assimilation Research Centre (DARC), University of Reading, Reading, UK
2Now at European Centre for Medium-Range Weather Forecasts (ECMWF), Reading, UK
3Met Office, Exeter, UK
4Centre Européen de Recherche et Formation Avancée en Calcul Scientifique (CERFACS), Toulouse, France and Météo-France, Toulouse, France
5E. O. Hulburt Center for Space Research, Naval Research Laboratory (NRL), Washington D.C., USA
Abstract. This paper evaluates the performance of various linear ozone photochemistry parametrizations using the stratosphere-troposphere data assimilation system of the Met Office. A set of experiments were run for the period 23 September 2003 to 5 November 2003 using the Cariolle (v1.0 and v2.1), LINOZ and Chem2D-OPP (v0.1 and v2.1) parametrizations. All operational meteorological observations were assimilated, together with ozone retrievals from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). Experiments were validated against independent data from the Halogen Occultation Experiment (HALOE) and ozonesondes.
It is shown that the LINOZ scheme is unsuitable for use above 10 hPa, but below this level it works as well as the other schemes. The Cariolle v1.0 scheme shows excessive sensitivity in the term related to overlying column ozone, and this results in erroneous ozone production in the ozone hole. The other three schemes (Cariolle v2.1 and Chem2D-OPP v0.1 and v2.1) all perform well through most of the atmosphere. Exceptions were the troposphere, where modelling and observing ozone remains a substantial challenge, and the upper stratosphere and mesosphere, where the main problems come from biases in the schemes' climatology coefficients. Cariolle v2.1 analyses showed biases of up to 20% against HALOE at levels above 1 hPa. These biases could be partially corrected by substituting the Fortuin and Kelder (1998) ozone climatology into the scheme. Chem2D-OPP v2.1 analyses showed biases up to 20% and unrealistic ozone patterns in the southern hemisphere upper stratosphere, likely due to discrepancies between analysed temperatures and the temperature climatology supplied with the scheme. Future developments should include a better treatment of the troposphere, and a parametrization of the diurnal cycle of ozone above 0.5 hPa.