Evaluation of linear ozone photochemistry parametrizations in a stratosphere-troposphere data assimilation system

[摘要] This paper evaluates the performance of various linear ozone photochemistryparametrizations using the stratosphere-tropospheredata assimilation system of the Met Office. A set of experimentswere 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. Alloperational meteorological observations were assimilated, togetherwith ozoneretrievals from the Michelson Interferometer forPassive Atmospheric Sounding (MIPAS). Experiments were validated againstindependent data from the Halogen Occultation Experiment (HALOE)and ozonesondes. Additionally, a simple offline method for comparing the parametrizations is introduced.

It is shown that in the upper stratosphere and mesosphere, outside the polarnight, ozone analyses are controlled by the photochemistry parametrizationsand not by the assimilated observations. The most important factor in gettinggood results at these levels is to pay attention to the ozone and temperatureclimatologies in the parametrizations. There should be no discrepanciesbetween the climatologies and the assimilated observations or the model, butthere is also a competing demand that the climatologies be objectivelyaccurate in themselves. Conversely, in the lower stratosphere outside regionsof heterogeneous ozone depletion, the ozone analyses are dominated byobservational increments and the photochemistry parametrizations have littleinfluence.

We investigate a number of known problems in LINOZ and Cariolle v1.0 in moredetail than previously, and we find discrepancies in Cariolle v2.1 andChem2D-OPP v2.1, which are demonstrated to have been removed in the latestavailable versions (v2.8 and v2.6 respectively). In general, however, all theparametrizations work well through much of the stratosphere, helped by thepresence of good quality assimilated MIPAS observations.

[学科分类] 大气科学