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This paper introduces and evaluates the second version of the global aerosol-climate model ECHAM-HAM. Major changes have been brought into the model, including new parameterizations for aerosol nucleation and water uptake, an explicit treatment of secondary organic aerosols, modified emission calculations for sea salt and mineral dust, the coupling of aerosol microphysics to a two-moment stratiform cloud microphysics scheme, and alternative wet scavenging parameterizations. These revisions extend the model's capability to represent details of the aerosol lifecycle and its interaction with climate. Nudged simulations of the year 2000 are carried out to compare the aerosol properties and global distribution in HAM1 and HAM2, and to evaluate them against various observations. Sensitivity experiments are performed to help identify the impact of each individual update in model formulation. Results indicate that from HAM1 to HAM2 there is a marked weakening of aerosol water uptake in the lower troposphere, reducing the total aerosol water burden from 75 Tg to 51 Tg. The main reason is the newly introduced κ-Köhler-theory-based water uptake scheme uses a lower value for the maximum relative humidity cutoff. Particulate organic matter loading in HAM2 is considerably higher in the upper troposphere, because the explicit treatment of secondary organic aerosols allows highly volatile oxidation products of the precursors to be vertically transported to regions of very low temperature and to form aerosols there. Sulfate, black carbon, particulate organic matter and mineral dust in HAM2 have longer lifetimes than in HAM1 because of weaker in-cloud scavenging, which is in turn related to lower autoconversion efficiency in the newly introduced two-moment cloud microphysics scheme. Modification in the sea salt emission scheme causes a significant increase in the ratio (from 1.6 to 7.7) between accumulation mode and coarse mode emission fluxes of aerosol number concentration. This leads to a general increase in the number concentration of smaller particles over the oceans in HAM2, as reflected by the higher Ångström parameters. Evaluation against observation reveals that in terms of model performance, main improvements in HAM2 include a marked decrease of the systematic negative bias in the absorption aerosol optical depth, as well as smaller biases over the oceans in Ångström parameter and in the accumulation mode number concentration. The simulated geographical distribution of aerosol optical depth (AOD) is better correlated with the MODIS data, while the surface aerosol mass concentrations are very similar to those in the old version. The total aerosol water content in HAM2 is considerably closer to the multi-model average from Phase I of the AeroCom intercomparison project. Model deficiencies that require further efforts in the future include (i) positive biases in AOD over the ocean, (ii) negative biases in AOD and aerosol mass concentration in high-latitude regions, and (iii) negative biases in particle number concentration, especially that of the Aitken mode, in the lower troposphere in heavily polluted regions., Atmospheric Chemistry and Physics, 12 (19), ISSN:1680-7375, ISSN:1680-7367

Two tracers, SF6 with sources at the earth's surface and 14CO2 with a source in the lower stratosphere, are used to investigate the simulation of global scale transport in an atmospheric general circulation model. The simulated mixing ratios of SF6 in the troposphere are generally in close agreement to observations revealing a realistic description of the large scale tropospheric transport. The interhemispheric exchange time for SF6 is calculated to be 0.9 years, indicating a slightly too strong interhemispheric exchange. In the lowermost stratosphere the simulated vertical gradient of SF6 is in good agreement with observations within the 1st 4 to 5 km above the tropopause indicating that the flux from the troposphere to the lowermost stratosphere is captured by the model. On the other hand, downward transport of 14CO2 from the stratosphere into the troposphere is found to be overestimated. From a comparison with observations it is concluded that it is the downward transport in the subtropics that is overestimated, at high latitudes the vertical gradients in the tropopause region are close to observations. Finally, the tracer tests show that the transport into the uppermost two levels, above 20 km, is underestimated as these levels serve as sponge layers and not as layers with a reasonable transport. Consequently, the tracer concentrations in that altitude interval are underestimated, by up to a factor 2.DOI: 10.1034/j.1600-0889.2000.00882.x

This study investigates changes in extreme temperature and precipitation events under different future scenarios of anthropogenic aerosol emissions (i.e., SO2 and black and organic carbon) simulated with an aerosol-climate model (ECHAM5-HAM) with focus on Europe. The simulations include a maximum feasible aerosol reduction (MFR) sce- nario and a current legislation emission (CLEmod) scenario where Europe implements the MFR scenario, but the rest of the world follows the current legislation scenario and a greenhouse gas scenario. The strongest changes rela- tive to the year 2000 are projected for the MFR scenario, in which the global aerosol reduction greatly enforces the general warming effect due to greenhouse gases and results in significant increases of temperature and pre- cipitation extremes in Europe. Regional warming effects can also be identified from aerosol reductions under the CLEmod scenario. This becomes most obvious in the increase of the hottest summer daytime temperatures in Northern Europe., JRC.H.2-Air and Climate

The extensive nuclear bomb testing of the fifties and sixties and the final tests in the seventies caused a strong 36Cl peak that has been observed in ice cores world-wide. The measured 36Cl deposition fluxes in eight ice cores (Dye3, Fiescherhorn, Grenzgletscher, Guliya, Huascarán, North GRIP, Inylchek (Tien Shan) and Berkner Island) were compared with an ECHAM5-HAM general circulation model simulation (1952–1972). We find a good agreement between the measured and the modeled 36Cl fluxes assuming that the bomb test produced global 36Cl input was ~80 kg. The model simulation indicates that the fallout of the bomb test produced 36Cl is largest in the subtropics and mid-latitudes due to the strong stratosphere-troposphere exchange. In Greenland the 36Cl bomb signal is quite large due to the relatively high precipitation rate. In Antarctica the 36Cl bomb peak is small but is visible even in the driest areas. The model suggests that the large bomb tests in the Northern Hemisphere are visible around the globe but the later (end of sixties and early seventies) smaller tests in the Southern Hemisphere are much less visible in the Northern Hemisphere. The question of how rapidly and to what extent the bomb produced 36Cl is mixed between the hemispheres depends on the season of the bomb test. The model results give an estimate of the amplitude of the bomb peak around the globe., Atmospheric Chemistry and Physics, 9 (12), ISSN:1680-7375, ISSN:1680-7367

Aerosol indirect effects continue to constitute one of the most important uncertaintiesfor anthropogenic climate perturbations. Within the international AEROCOM initiative,the representation of aerosol-cloud-radiation interactions in ten different general cir-culation models (GCMs) is evaluated using three satellite datasets. The focus is on stratiform liquid water clouds since most GCMs do not include ice nucleation effects,and none of the models explicitly parameterizes aerosol effects on convective clouds.We compute statistical relationships between aerosol optical depth (τa) and variouscloud and radiation quantities in a manner that is consistent between the models andthe satellite data. It is found that the model-simulated influence of aerosols on cloud droplet number concentration (Nd) compares relatively well to the satellite data at leastover the ocean. The relationship betweenτaand liquid water path is simulated muchtoo strongly by the models. It is shown that this is partly related to the representationof the second aerosol indirect effect in terms of autoconversion. A positive relationshipbetween total cloud fraction (fcld) andτaas found in the satellite data is simulated by the majority of the models, albeit less strongly than that in the satellite data in most of them.In a discussion of the hypotheses proposed in the literature to explain the satellite-derived strongfcld–τarelationship, our results indicate that none can be identified asunique explanation. Relationships similar to the ones found in satellite data betweenτaand cloud top temperature or outgoing long-wave radiation (OLR) are simulated by only a few GCMs. The GCMs that simulate a negative OLR –τarelationship show a strongpositive correlation betweenτaandfcld. The short-wave total aerosol radiative forc-ing as simulated by the GCMs is strongly influenced by the simulated anthropogenicfraction ofτa, and parameterisation assumptions such as a lower bound onNd. Never-theless, the strengths of the statistical relationships are good predictors for the aerosol forcings in the models. An estimate of the total short-wave aerosol forcing inferred fromthe combination of these predictors for the modelled forcings with the satellite-derivedstatistical relationships yields a global annual mean value of−1.5±0.5 Wm−2. An alternative estimate obtained by scaling the simulated clear- and cloudy-sky forcingswith estimates of anthropogenicτaand satellite-retrievedNd–τaregression slopes,respectively, yields a global annual mean clear-sky (aerosol direct effect) estimate of−0.4±0.2 Wm−2and a cloudy-sky (aerosol indirect effect) estimate of−0.7±0.5 Wm−2, with a total estimate of−1.2±0.4 Wm−2., Atmospheric Chemistry and Physics Discussions, 9 (3), ISSN:1680-7375, ISSN:1680-7367

Aerosol indirect effects continue to constitute one of the most important uncertainties for anthropogenic climate perturbations. Within the international AEROCOM initiative, the representation of aerosol-cloud-radiation interactions in ten different general circulation models (GCMs) is evaluated using three satellite datasets. The focus is on stratiform liquid water clouds since most GCMs do not include ice nucleation effects, and none of the model explicitly parameterises aerosol effects on convective clouds. We compute statistical relationships between aerosol optical depth (tau a) and various cloud and radiation quantities in a manner that is consistent between the models and the satellite data. cloud droplet number concentration (N d) compares relatively well to the satellite data at least over the ocean. The relationship between (tau a) and liquid water path is simulated much too strongly by the models. This suggests that the implementation of the second aerosol indirect effect mainly in terms of an autoconversion parameterisation has to be revisited in the GCMs. A positive relationship between total cloud fraction (fcld) and tau a as found in the satellite data is simulated by the majority of the models, albeit less strongly than that in the satellite data in most of them. In a discussion of the hypotheses proposed in the literature to explain the satellite-derived strong fcld–tau a relationship, our results indicate that none can be identified as a unique explanation. Relationships similar to the ones found in satellite data between tau a and cloud top temperature or outgoing long-wave radiation (OLR) are simulated by only a few GCMs. The GCMs that simulate a negative OLR - tau a relationship show a strong positive correlation between tau a and fcld. The short-wave total aerosol radiative forcing as simulated by the GCMs is strongly influenced by the simulated anthropogenic fraction of tau a, and parameterisation assumptions such as a lower bound on Nd. Nevertheless, the strengths of the statistical relationships are good predictors for the aerosol forcings in the models. An estimate of the total short-wave aerosol forcing inferred from the combination of these predictors for the modelled forcings with the satellite-derived statistical relationships yields a global annual mean value of −1.5±0.5Wm−2. In an alternative approach, the radiative flux perturbation due to anthropogenic aerosols can be broken down into a component over the cloud-free portion of the globe (approximately the aerosol direct effect) and a component over the cloudy portion of the globe (approximately the aerosol indirect effect). An estimate obtained by scaling these simulated clearand cloudy-sky forcings with estimates of anthropogenic tau a and satellite-retrieved Nd–tau a regression slopes, respectively, yields a global, annual-mean aerosol direct effect estimate of −0.4±0.2Wm−2 and a cloudy-sky (aerosol indirect effect) estimate of −0.7±0.5Wm−2, with a total estimate of −1.2±0.4Wm−2.

In der Atmosphäre, in Oberflächen‐ und Meerwasser, auch in Regionen fernab der Zivilisation finden Umweltforscher immer wieder bisher nicht nachgewiesene Chemikalien, aktuell unter anderem Flammschutzmittel, Textilhilfsmittel und Pestizide. Gegenstand bodenchemischer Forschungsaktivitäten sind vermehrt bioaktive Substanzen, insbesondere Veterinärpharmaka.

Strategies to detect and attribute aerosol global impacts on clouds and climate from synergetic approaches involving modeling and observational evidence at different spatial and temporal scales.

The AeroCom exercise diagnoses multi-component aerosol modules in global modeling. In an initial assessment simulated global distributions for mass and mid-visible aerosol optical thickness (aot) were compared among 20 different modules. Model diversity was also explored in the context of previous comparisons. For the component combined aot general agreement has improved for the annual global mean. At 0.11 to 0.14, simulated aot values are at the lower end of global averages suggested by remote sensing from ground (AERONET ca. 0.135) and space (satellite composite ca. 0.15). More detailed comparisons, however, reveal that larger differences in regional distribution and significant differences in compositional mixture remain. Of particular concern are large model diversities for contributions by dust and carbonaceous aerosol, because they lead to significant uncertainty in aerosol absorption (aab). Since aot and aab, both, influence the aerosol impact on the radiative energy-balance, the aerosol (direct) forcing uncertainty in modeling is larger than differences in aot might suggest. New diagnostic approaches are proposed to trace model differences in terms of aerosol processing and transport: These include the prescription of common input (e.g. amount, size and injection of aerosol component emissions) and the use of observational capabilities from ground (e.g. measurements networks) or space (e.g. correlations between aerosol and clouds)., Atmospheric Chemistry and Physics, 6 (7), ISSN:1680-7375, ISSN:1680-7367

A parameterization for cloud processing is presented that calculates activation of aerosol particles to cloud drops, cloud drop size, and pH-dependent aqueous phase sulfur chemistry. The parameterization is implemented in the global aerosol-climate model ECHAM5-HAM. The cloud processing parameterization uses updraft speed, temperature, and aerosol size and chemical parameters simulated by ECHAM5-HAM to estimate the maximum supersaturation at the cloud base, and subsequently the cloud drop number concentration (CDNC) due to activation. In-cloud sulfate production occurs through oxidation of dissolved SO2 by ozone and hydrogen peroxide. The model simulates realistic distributions for annually averaged CDNC although it is underestimated especially in remote marine regions. On average, CDNC is dominated by cloud droplets growing on particles from the accumulation mode, with smaller contributions from the Aitken and coarse modes. The simulations indicate that in-cloud sulfate production is a potentially important source of accumulation mode sized cloud condensation nuclei, due to chemical growth of activated Aitken particles and to enhanced coalescence of processed particles. The strength of this source depends on the distribution of produced sulfate over the activated modes. This distribution is affected by uncertainties in many parameters that play a direct role in particle activation, such as the updraft velocity, the aerosol chemical composition and the organic solubility, and the simulated CDNC is found to be relatively sensitive to these uncertainties., JRC.H.2-Climate change

The Second Aerosol Characterization Experiment (ACE-2) data set along with ECMWF reanalysis meteorological fields provided the basis for the single column model (SCM) simulations, performed as part of the PACE (Parameterization of the Aerosol Indirect Climatic Effect) project. Six different SCMs were used to simulate ACE-2 case studies of clean and polluted cloudy boundary layers, with the objective being to identify limitations of the aerosol/cloud/radiation interaction schemes within the range of uncertainty in in situ, reanalysis and satellite retrieved data. The exercise proceeds in three steps. First, SCMs are configured with the same fine vertical resolution as the ACE-2 in situ data base to evaluate the numerical schemes for prediction of aerosol activation, radiative transfer and precipitation formation. Second, the same test is performed at the coarser vertical resolution of GCMs to evaluate its impact on the performance of the parameterizations. Finally, SCMs are run for a 24–48 hr period to examine predictions of boundary layer clouds when initialized with large-scale meteorological fields. Several schemes were tested for the prediction of cloud droplet number concentration (N). Physically based activation schemes using vertical velocity show noticeable discrepancies compared to empirical schemes due to biases in the diagnosed cloud base vertical velocity. Prognostic schemes exhibit a larger variability than the diagnostic ones, due to a coupling between aerosol activation and drizzle scavenging in the calculation of N. When SCMs are initialized at a fine vertical resolution with locally observed vertical profiles of liquid water, predicted optical properties are comparable to observations. Predictions however degrade at coarser vertical resolution and are more sensitive to the mean liquid water path than to its spatial heterogeneity. Predicted precipitation fluxes are severely underestimated and improve when accounting for sub-grid liquid water variability. Results from the 24–48 hr runs suggest that most models have problems in simulating boundary layer cloud morphology, since the large-scale initialization fields do not accurately reproduce observed meteorological conditions. As a result, models significantly overestimate optical properties. Improved cloud morphologies were obtained for models with subgrid inversions and subgrid cloud thickness schemes. This may be a result of representing subgrid scale effects though we do not rule out the possibility that better large-forcing data may also improve cloud morphology predictions.

Das hier beschriebene Forschungsprojekt beschäftigte sich mit einer Analyse des Beitrags europäischer und aussereuropäischer Quellen auf die Konzentration klimarelevanter Spurenstoffe in Europa. Als Modellsubstanz wurde troposphärisches Ozon gewählt. Ein wesentlicher Beitrag des Vorhabens war die Entwicklung zeitabhängiger Emissions−Datensätze mit Hilfe einer einfachen Skalierungsmethode sowie die Weiterentwicklung des globalen Chemie−Transport−Modells MOZART 2, das jetzt der deutschen und internationalen Forschergemeinde zur Verfügung steht. Mit diesem Modell wurde die Ozonverteilung des Jahres 1990 simuliert. Um den Einfluss einzelner Quelltypen und −regionen auf die Schadstoffkonzentration in Europa zu bestimmen, wurde ein Tracer−Markierungsmodell für CO in das globale Zirkulationsmodell ECHAM implementiert. Mit diesem Modell wurde die 15 Jahresperiode 1979−1993 simuliert und die Ergebnisse wurden im Hinblick auf das CO Budget an den Messstationen Izaña, Teneriffa, und Schauinsland, Schwarzwald, analysiert. Rückschlüsse auf das Ozonbudget sind mit diesem Verfahren nur qualitativ möglich. The goal of this study is the analysis of the contribution of European and non− European sources on the budgets of trace gases that are relevant for climate in Europe. Tropospheric ozone was selected as a model substance. Significant contributions from this project were the development of annual emission data sets using a simple scale factor approach, and the participation in the development of the MOZART 2 chemistry transport model, which is now available to the international scientific community. The MOZART 2 model was used to simulate tropospheric ozone for the year 1990. In order to assess the impact of individual source types and −regions, a tagged tracer model for CO was implemented in the general circulation model ECHAM. This model was then used to simulate the 15−year period from 1979 to 1993. The results of this simulation were analysed in terms of the CO budget at the observing stations Izaña, Tenerife, and Schauinsland, Schwarzwald. Implications for the ozone budget at these stations can only be made qualitatively.

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