Results of an interactively coupled atmospheric chemistry – general circulation model: Comparison with observations

Abstract

Abstract.The coupled climate-chemistry model ECHAM4.L39(DLR)/CHEM is presented which enables a simultaneous treatment of meteorology and atmospheric chemistry and their feedbacks. This is the first model which interactively combines a general circulation model with a chemical model, employing most of the important reactions and species necessary to describe the stratospheric and upper tropospheric ozone chemistry, and which is computationally fast enough to allow long-term integrations with currently available computer resources. This is possible as the model time-step used for the chemistry can be chosen as large as the integration time-step for the dynamics. Vertically the atmosphere is discretized by 39 levels from the surface up to the top layer which is centered at 10 hPa, with a relatively high vertical resolution of approximately 700 m near the extra-tropical tropopause. We present the results of a control simulation representing recent conditions (1990) and compare it to available observations. The focus is on investigations of stratospheric dynamics and chemistry relevant to describe the stratospheric ozone layer.ECHAM4.L39(DLR)/CHEM reproduces main features of stratospheric dynamics in the arctic vortex region, including stratospheric warming events. This constitutes a major improvement compared to earlier model versions. However, apparent shortcomings in antarctic circulation and temperatures persist. The seasonal and interannual variability of the ozone layer is simulated in accordance with observations. Activation and deactivation of chlorine in the polar stratospheric vortices and their inter-hemispheric differences are reproduced. Considering methane oxidation as part of the dynamic-chemistry feedback results in an improved representation of the spatial distribution of stratospheric water vapour concentrations.The current model constitutes a powerful tool to investigate, for instance, the combined direct and indirect effects of anthropogenic trace gas emissions. Key words. Atmospheric composition and structure (mid-Correspondence to: M. Dameris (martin.dameris@dlr.de) dle atmosphere -composition and chemistry) -Meteorology and atmospheric dynamics (general circulation; middle atmosphere dynamics)

Tropospheric NO<sub>2</sub> columns: a comparison between model and retrieved data from GOME measurements

“…Gas emissions, Sea Surface Temperature (SST), and boundary conditions were assumed similar to those measured or determined for the year 1990. A detailed model description and model applications can be found in Hein et al (2001) and Schnadt et al (2001). Table 2 summarizes the Nitrogen Oxide emissions as considered for this model simulation.…”

Climatologies of subtropical mixing derived from 3D models

“…A detailed description of the coupled chemistry-climate model E39/C has been given by Hein et al (2001), who also discussed the main features of the model climatology. The model's horizontal resolution is T30 with a corresponding Gaussian transform latitude-longitude grid of 3.75 • × 3.75 • , on which model physics, chemistry, and tracer transport are calculated.…”

“…Water vapour, cloud water, and tracers are advected by the semi-Lagrangian scheme of Williamson and Rasch (1994), while spectral Eulerian advection is applied to the other prognostic variables. The chemistry module CHEM , updated in (Hein et al, 2001) is based on the family concept, containing the most relevant chemical compounds and reactions necessary to simulate upper tropospheric and lower stratospheric ozone chemistry, including heterogeneous chemical reactions on polar stratospheric clouds (PSCs) and sulfate aerosol, as well as tropospheric NO x -HO x -CO-CH 4 -O 3 chemistry. Physical, chemical, and transport processes are calculated simultaneously at each time step, which is fixed to 30 min.…”

Atmospheric Variability in a Coupled Atmosphere-Ocean-Sea Ice Model with Interactive Stratospheric Ozone Chemistry

“…First integrations including interactive chemistry have been carried out by Eckman et al [4] for short time slices. Later, similar simulations were done by Austin et al and Austin [5,6], while Dameris et al [7] and Hein et al [8] focused on the lower stratosphere due to a *Address correspondence to this author at the Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam, Potsdam, Germany; E-mail: sbrand@awi-potsdam.de model top of about 30 km. Although basically this was sufficient to reproduce most of the observed variability and characteristics, a model top in the middle stratosphere implies the problem of 'cutting' important upper stratospheric parts of the Brewer-Dobson meridional mean circulation (BDC), and thus preventing downward mass transport in polar latitudes.…”