SUMMARYA data-assimilation scheme to assimilate the Global Ozone Monitoring Experiment (GOME) total-ozone data is described. The corresponding software (called TM3DAM) has been operational since early 2000 and is used to produce daily ozone analyses and ve-day ozone forecasts. The model is a tracer-transport model with a parametrized description of stratospheric gas-phase and heterogeneous ozone chemistry. It is driven by operational meteorological elds from the ECMWF numerical weather-prediction model. TM3DAM analyses near-real-time level-2 ozone data from the GOME instrument on the ESA ERS-2 satellite. The focus of this paper is on the dataassimilation aspects and the analysis results. The assimilation approach is based on the Kalman-lter equations and provides detailed and realistic maps of the forecast error. The analysis scheme is nevertheless computationally ef cient. The forecast-minus-observation statistics, accumulated over a two-year period, are described in detail. A comparison with TOMS and Brewer observations shows good agreement.

The separate climate effects of middle-atmospheric and tropospheric CO 2 doubling have been simulated and analyzed with the ECHAM middle-atmosphere climate model. To this end, the CO 2 concentration has been separately doubled in the middle-atmosphere, the troposphere, and the entire atmosphere, and the results have been compared to a control run. During NH winter, the simulated uniformly doubled CO 2 climate shows an increase of the stratospheric residual circulation, a small warming in the Arctic lower stratosphere, a weakening of the zonal winds in the Arctic middle-atmosphere, an increase of the NH midlatitude tropospheric westerlies, and a poleward shift of the SH tropospheric westerlies. The uniformly doubled CO 2 response in most regions is approximately equal to the sum of the separate responses to tropospheric and middle-atmospheric CO 2 doubling. The increase of the stratospheric residual circulation can be attributed for about two-thirds to the tropospheric CO 2 doubling and one-third to the middle-atmospheric CO 2 doubling. This increase contributes to the Arctic lower-stratospheric warming and, through the thermal wind relationship, to the weakening of the Arctic middleatmospheric zonal wind. The increase of the tropospheric NH midlatitude westerlies can be attributed mainly to the middle-atmospheric CO 2 doubling, indicating the crucial importance of the middle-atmospheric CO 2 doubling for the tropospheric climate change. Results from an additional experiment show that the CO 2 doubling above 10 hPa, which is above the top of many current GCMs, also causes significant changes in the tropospheric climate.

Abstract. This paper presents a first statistical validation of tropospheric ozone products derived from measurements of the IASI satellite instrument. Since the end of 2006, IASI (Infrared Atmospheric Sounding Interferometer) aboard the polar orbiter Metop-A measures infrared spectra of the Earth's atmosphere in nadir geometry. This validation covers the northern mid-latitudes and the period from July 2007 to August 2008. Retrieval results from four different sources are presented: three are from scientific products (LATMOS, LISA, LPMAA) and the fourth one is the pre-operational product distributed by EUMETSAT (version Correspondence to: M. Eremenko (maxim.eremenko@lisa.univ-paris12.fr) 4.2). The different products are derived from different algorithms with different approaches. The difference and their implications for the retrieved products are discussed. In order to evaluate the quality and the performance of each product, comparisons with the vertical ozone concentration profiles measured by balloon sondes are performed and lead to estimates of the systematic and random errors in the IASI ozone products (profiles and partial columns). A first comparison is performed on the given profiles; a second comparison takes into account the altitude dependent sensitivity of the retrievals. Tropospheric columnar amounts are compared to the sonde for a lower tropospheric column (surface to about 6 km) and a "total" tropospheric column (surface to about 11 km). On average both tropospheric columns have small biases for the scientific products, less than 2 DobsonPublished by Copernicus Publications on behalf of the European Geosciences Union. C. Keim et al.: IASI tropospheric ozone validationUnits (DU) for the lower troposphere and less than 1 DU for the total troposphere. The comparison of the still preoperational EUMETSAT columns shows higher mean differences of about 5 DU.

[1] This paper presents one of the first extensive intercomparisons of models and methods used for estimating stratosphere-troposphere exchange (STE). The study is part of the European Union project Influence of Stratosphere Troposphere Exchange in a Changing Climate on Atmospheric Transport and Oxidation Capacity (STACCATO). Nine different models and methods, including three trajectory methods, one Eulerian method, two Lagrangian and one Eulerian transport model, and two general circulation models applied the same initialization. Stratospheric and tropospheric tracers have been simulated, and the tracer mass fluxes have been calculated through the tropopause and the 700 hPa surface. For a 12-day case study over Europe and the northeast Atlantic the simulated tracer mass fluxes have been intercompared. For this case the STE simulations show the same temporal evolution and the same geographical pattern of STE for most models and methods, but with generally different amplitudes (up to a factor of 4). On the other hand, for some simulations also the amplitudes are very similar.

Tropical tropospheric ozone columns (TTOCs) have been determined with a convective‐cloud‐differential (CCD) method, using ozone column and cloud measurements from the Global Ozone Monitoring Experiment (GOME) instrument. GOME cloud top pressures, derived with the Fast Retrieval Scheme for Clouds from the Oxygen A‐band (FRESCO) method, indicate that most convective cloud top levels are between 300 and 500 hPa and do not extend to the tropical tropopause. The new GOME‐CCD method takes this tropical transition layer below the tropopause into account and uses above‐cloud and clear‐sky ozone column measurements to derive a monthly mean TTOC below 200 hPa. Validation of the GOME‐TTOCs with seven Southern Hemisphere Additional Ozonesondes (SHADOZ) sites shows good agreement, with an RMS difference of about 5 Dobson units. In the northern tropics the GOME‐TTOC compares most of the time well with in situ measurements at Paramaribo (6°N, 55°W) and Abidjan (5°N, 4°W). Analysis of the GOME‐TTOCs for 2000 and 2001, with the aid of the chemistry‐transport model TM3, illustrates that the variability in the TTOC depends on a complex interaction of several processes, including biomass burning, lightning, and large‐scale transport. The much larger extent of the South Atlantic TTOC maximum in September–October 2001, compared to September–October 2000, can be attributed to differences in large‐scale transport. An exceptional situation in the northern tropics occurred during the biomass burning season December 2001 to January 2002, when there were almost no fires over northern Africa. This resulted in strongly reduced TTOCs over the Atlantic between the equator and 10°N.