C. Brühl

Max Planck Institute for Chemistry, Mayence, Rheinland-Pfalz, Germany

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Publications (146)333.51 Total impact

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    ABSTRACT: Multiyear simulations with the atmospheric chemistry general circulation model EMAC with a microphysical modal aerosol module at high vertical resolution demonstrate that the sulfur gases COS and SO2, the latter from low-latitude and midlatitude volcanic eruptions, predominantly control the formation of stratospheric aerosol. Marine dimethyl sulfide (DMS) and other SO2 sources, including strong anthropogenic emissions in China, are found to play a minor role except in the lowermost stratosphere. Estimates of volcanic SO2 emissions are based on satellite observations using TOMS and OMI for total injected mass and MIPAS on ENVISAT or SAGE for the spatial distribution. The 10 year SO2 and COS dataset of MIPAS is also used for model evaluation. The calculated radiative forcing of stratospheric background aerosol including sulfate from COS and small contributions by DMS oxidation, and organic aerosol from biomass burning, is about 0.07 W/m2. For stratospheric sulfate aerosol from medium and small volcanic eruptions between 2005 and 2011 a global radiative forcing up to 0.2 W/m2 is calculated, moderating climate warming, while for the major Pinatubo eruption the simulated forcing reaches 5 W/m2, leading to temporary climate cooling. The Pinatubo simulation demonstrates the importance of radiative feedback on dynamics, e.g., enhanced tropical upwelling, for large volcanic eruptions.
    Full-text · Article · Mar 2015
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    ABSTRACT: The modelling of aerosol radiative forcing is a major cause of uncertainty in the assessment of global and regional atmospheric energy budgets and climate change. One reason is the strong dependence of the aerosol optical properties on the mixing state of aerosol components, such as absorbing black carbon and, predominantly scattering sulfates. Using a new column version of the aerosol optical properties and radiative-transfer code of the ECHAM/MESSy atmospheric-chemistry–climate model (EMAC), we study the radiative transfer applying various mixing states. The aerosol optics code builds on the AEROPT (AERosol OPTical properties) submodel, which assumes homogeneous internal mixing utilising the volume average refractive index mixing rule. We have extended the submodel to additionally account for external mixing, partial external mixing and multilayered particles. Furthermore, we have implemented the volume average dielectric constant and Maxwell Garnett mixing rule. We performed regional case studies considering columns over China, India and Africa, corroborating much stronger absorption by internal than external mixtures. Well-mixed aerosol is a good approximation for particles with a black-carbon core, whereas particles with black carbon at the surface absorb significantly less. Based on a model simulation for the year 2005, we calculate that the global aerosol direct radiative forcing for homogeneous internal mixing differs from that for external mixing by about 0.5 W m−2.
    Full-text · Article · Oct 2014 · Geoscientific Model Development
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    ABSTRACT: The modelling of aerosol radiative forcing is a major cause of uncertainty in the assessment of global and regional atmospheric energy budgets and climate change. One reason is the strong dependence of the aerosol optical properties on the mixing state of aerosol components like black carbon and sulphates. Using a new column version of the aerosol optical properties and radiative transfer code of the atmospheric chemistry-climate model EMAC, we study the radiative transfer applying various mixing states. The aerosol optics code builds on the AEROPT submodel which assumes homogeneous internal mixing utilising the volume average refractive index mixing rule. We have extended the submodel to additionally account for external mixing, partial external mixing and multi-layered particles. Furthermore, we have implemented the volume average dielectric-constant and Maxwell Garnett Mixing rule. We performed regional case studies considering columns over China, India and Africa, corroborating much stronger absorption by internal than external mixtures. Well mixed aerosol is a good approximation for particles with a black carbon core, whereas particles with black carbon at the surface absorb significantly less. Based on a model simulation for the year 2005 we calculate that the global aerosol direct radiative-forcing for homogeneous internal mixing differs from that for external mixing by about 0.5 W m−2.
    Full-text · Article · Jan 2014 · Geoscientific Model Development Discussions
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    ABSTRACT: Multiyear studies with the atmospheric chemistry general circulation model EMAC with the aerosol module GMXe demonstrate that stratospheric aerosol formation is controlled by COS oxidation and SO2 injected by low-latitude volcanic eruptions. The model consistently uses the same parameters in the troposphere and stratosphere for 7 aerosol modes applied. Calculated radiative heating by aerosol feeds back to stratospheric dynamics. Radiative forcing by stratospheric aerosol can be diagnosed separately. The simulations include the medium size tropical eruptions in 2003, 2005 and 2006 but also the major eruption of Pinatubo in 1991. We show that calculated radiative forcing by stratospheric aerosol agrees well with the corresponding satellite derived quantity and that the medium size tropical eruptions should not be neglected in climate simulations. Changes in temperature, dynamics and tracer transport due to interactive aerosol will be also presented. We show also that calculated aerosol and SO2 concentrations are consistent with the observations by SAGE and by MIPAS on ENVISAT.
    No preview · Article · Apr 2013
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    C. Brühl · J. Lelieveld · M. Höpfner · H. Tost
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    ABSTRACT: A multiyear study with the atmospheric chemistry general circulation model EMAC with the aerosol module GMXe at high altitude resolution demonstrates that the sulfur gases COS and SO2, the latter from low-latitude volcanic eruptions, predominantly control the formation of stratospheric aerosol. The model consistently uses the same parameters in the troposphere and stratosphere for 7 aerosol modes applied. Lower boundary conditions for COS and other long-lived trace gases are taken from measurement networks, while estimates of volcanic SO2 emissions are based on satellite observations. We show comparisons with satellite data for aerosol extinction (e.g. SAGE) and SO2 in the middle atmosphere (MIPAS on ENVISAT). This corroborates the interannual variability induced by the Quasi-Biennial Oscillation, which is internally generated by the model. The model also realistically simulates the radiative effects of stratospheric and tropospheric aerosol including the effects on the model dynamics. The medium strength volcanic eruptions of 2005 and 2006 exerted a nonnegligible radiative forcing of up to -0.6 W m-2 in the tropics, while the large Pinatubo eruption caused a maximum though short term tropical forcing of about -10 W m-2. The study also shows that observed upper stratospheric SO2 can be simulated accurately only when a sulphur sink on meteoritic dust is included and the photolysis of gaseous H2SO4 in the near infrared is higher than assumed previously.
    Full-text · Article · Apr 2013 · Atmospheric Chemistry and Physics
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    ABSTRACT: Sulphur dioxide (SO2) is one of the key species determining the aerosol content of the stratosphere. Apart from this study, only three measured profiles of SO2 concentrations (by ATMOS) covering the altitude range of the stratosphere have been published, two of which are heavily perturbed by the Pinatubo eruption and one by El Chichon. Here we present a climatology of monthly and 10° zonal mean profiles of SO2 volume mixing ratios in the altitude range 15-45 km as derived from MIPAS/Envisat measurements from July 2002 until April 2012. The vertical resolution varies from 3.5-4 km in the lower stratosphere up to 6-10 km at the upper end of the profiles with estimated total errors of 5-20 pptv for background conditions of SO2. Comparisons are made with few available observations of SO2 up to high altitudes from ATMOS, for volcanically perturbed situations in the lower stratosphere from ACE-FTS and at the lowest altitudes with stratospheric in-situ observations. The dataset proves for the first time several features of the stratospheric SO2 distribution, which up to now, have only been shown by models: (1) the local maximum of SO2 at around 25-30 km altitude from conversion of COS as the pre-curser of the Junge layer and (2) the downwelling of SO2-rich air to altitudes of 25-30 km at high latitudes during winter and its subsequent depletion during spring as cause for the sudden appearance of enhanced concentrations of condensation nuclei. Comparison with model results of SO2 from the SPARC aerosol assessment report indicate several inconsistencies between simulations and our observations. Further, dedicated EMAC model runs reveal that the strong increase of SO2 to values of 80-100 pptv in the upper stratosphere can only be explained by taking into account visible and near-IR photolysis of H2SO4 and, in addition, a meteoritic sink. Lower stratospheric variability of SO2 can mainly be explained by volcanic activity. A modulation of the mid-stratospheric maximum could be observed for several equatorial eruptions during the time period of observations.
    No preview · Article · Apr 2013
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    ABSTRACT: The photolysis of HONO is important for the atmospheric HOx (OH + HO2) radical budget and ozone formation, especially in polluted air. Nevertheless, owing to the incomplete knowledge of HONO sources, realistic HONO mechanisms have not yet been implemented in global models. We investigated measurement data sets from 15 field measurement campaigns conducted in different countries worldwide. It appears that the HONO/NOx ratio is a good proxy predictor for HONO mixing ratios under different atmospheric conditions. From the robust relationship between HONO and NOx, a representative mean HONO/NOx ratio of 0.02 has been derived. Using a global chemistry-climate model and employing this HONO/NOx ratio, realistic HONO levels are simulated, being about one order of magnitude higher than the reference calculations that only consider the reaction OH + NO → HONO. The resulting enhancement of HONO significantly impacts HOx levels and photo-oxidation products (e.g, O3, PAN), mainly in polluted regions. Furthermore, the relative enhancements in OH and secondary products are higher in winter than in summer, thus enhancing the oxidation capacity in polluted regions, especially in winter when other photolytic OH sources are of minor importance. Our results underscore the need to improve the understanding of HONO chemistry and its representation in atmospheric models.
    No preview · Article · Oct 2012 · ATMOSPHERIC CHEMISTRY AND PHYSICS
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    ABSTRACT: The photolysis of HONO is important for the atmospheric HOx (OH+HO2) radical budget and ozone formation, especially in polluted air. Nevertheless, owing to the incomplete knowledge of HONO sources, realistic HONO mechanisms have not yet been implemented in global models. We investigated measurement data sets from 15 field measurement campaigns conducted in different countries worldwide. It appears that the HONO/NOx ratio is a good proxy predictor for HONO mixing ratios under different atmospheric conditions. From the robust relationship between HONO and NOx, a representative mean HONO/NOx ratio of 0.02 has been derived. Using a global chemistry-climate model and employing this HONO/NOx ratio, realistic HONO levels are simulated, being about one order of magnitude higher than the reference calculations, which only consider the reaction OH+NO-> HONO. The resulting enhancement of HONO significantly impacts HOx levels and photo-oxidation products (e.g, O3, PAN), mainly in polluted regions. Furthermore, the relative enhancements in OH and secondary products were higher in winter than in summer, thus enhancing the oxidation capacity in polluted regions, especially in winter, when the other photolytic OH sources are of minor importance. Our results underscore the need to improve the understanding of HONO chemistry and its representation in atmospheric models.
    Full-text · Article · May 2012 · Atmospheric Chemistry and Physics
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    ABSTRACT: Simultaneous limb observations of HCOOH, CO, PAN, C2H6, O3, NOx and other species by MIPAS in the upper troposphere and lower stratosphere are compared with results of the chemical circulation model EMAC. To allow for point by point comparisons with the satellite data, the tropospheric meteorology of the CCM is nudged by observations of ECMWF. The method is used for evaluation and further development of the new isoprene oxidation scheme MIM3 and also for checking and distinguishing biogenic and anthropogenic emissions used in the model. We show that the model is able to reproduce the main features of the observations, including the seasonal cycle, and that proper modelling of isoprene chemistry (and to less extent terpene chemistry) is critical for understanding the observed chemical composition of the upper troposphere.
    No preview · Article · Apr 2012
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    ABSTRACT: In the Project on Solar Effects on Chemistry and Climate Including Ocean Interactions (ProSECCO) fundamental questions of the impact of solar variability on Earth's Climate have been investigated with improved climate system models and observations. On the decadal time scale, the atmospheric signatures of the 11-year Schwabe cycle and the underlying mechanisms have been studied using a comprehensive troposphere-stratosphere-chemistry model. This study included the impact of variations in UV radiation (with 27d rotational cycle) and particle precipitation on stratospheric chemistry and ozone, as well as on the solar signal in the troposphere and on climate. A clear solar signal can be detected not only in the stratosphere, but also in the troposphere. On the centennial to millenium time scale, effects of solar variability on climate of different pre-industrial periods, focusing on the Maunder Minimum and the mid-Holocene, have been addressed using a coupled troposphere-stratosphere-ocean model. A link between the stratospheric polar vortex strength and the solar variability can be detected on the decadal and centennial timescales. A tropospheric signal as response to the solar forcing, for example in the North Atlantic Oscillation, becomes visible once the stratosphere is treated in a realistic way.
    No preview · Article · Apr 2012
  • C. Bruehl · J. Lelieveld · P. J. Crutzen · H. Tost
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    ABSTRACT: A multiyear study with the modular atmospheric chemistry circulation model EMAC with the aerosol module GMXe and high vertical resolution demonstrates that the most abundant sulfur gas in the atmosphere COS is to a large degree responsible for the formation of the stratospheric background aerosol. The model consistently uses the same parameters in the troposphere and stratosphere for the 7 aerosol modes applied. Lower boundary conditions for COS and other longlived gases are taken from observations. We show comparisons with satellite data for aerosol extinction (e.g. SAGE) as well as for SO2 in the middle atmosphere (e.g. ATMOS) and COS. This includes the variation induced by the Quasi-Biennial Oscillation which is internally generated by the model. We also show that organic aerosol contributes significantly to aerosol in the lowermost tropical stratosphere. The radiative impacts of COS and of the COS-induced aerosol will be discussed. Globally, the effects of the anthropogenic contribution of COS on radiative forcing almost cancel. We show that the model is also able to simulate aerosol from SO2 injected by big volcanic eruptions including its radiative effects and implications for geoengineering applications.
    No preview · Article · Dec 2011
  • A. Kubin · U. Langematz · C. Brühl
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    ABSTRACT: The results from two simulations with the coupled chemistry climate model (CCM) ECHAM5/MESSy (EMAC-FUB) are analyzed for the effect of solar variability at the 27 day rotational time scale on ozone. One simulation is forced with constant spectral irradiances at the top of the atmosphere and the other one with daily varying irradiances using data of 1 year for solar maximum conditions. Consistent changes are applied to the photolysis scheme of the model. The model results show the main features of observed correlations between ozone and solar irradiance variability with a maximum positive correlation in the upper stratosphere and an anticorrelation in the mesosphere. The relative sensitivity of upper stratospheric ozone to changes in the solar ultraviolet flux is estimated to be 0.3 to 0.4% per 1% change in 205 nm flux. During periods of strong 27 day variability, a similar upper stratospheric ozone sensitivity is derived. However, when the daily solar irradiance variability is weak and dominated by the 13.5 day period, the ozone sensitivity is reduced in the subtropics. The modeled temperature response is consistent with the ozone signal. When averaged over one rotational cycle, the ozone and temperature response to a neglect of the 27 day cycle is weak and statistically insignificant in the stratosphere but of nonnegligible magnitude and statistically significant in the equatorial mesosphere. Our results suggest that ignoring daily solar flux variations on the 27 day time scale in transient CCM simulations does not lead to a significant degradation of the time mean ozone response in the stratosphere, while in the tropical mesosphere, significant errors of up to 3% may occur. This result does not exclude potential additional effects of 27 day solar cycle variability on stratospheric dynamics in winter which were, however, not the subject of this study.
    No preview · Article · Aug 2011 · Journal of Geophysical Research Atmospheres
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    C. Brühl · J. Lelieveld · P. J. Crutzen · H. Tost
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    ABSTRACT: Globally, carbonyl sulphide (COS) is the most abundant sulphur gas in the atmosphere. Our chemistry-climate model of the lower and middle atmosphere with aerosol module realistically simulates the background stratospheric sulphur cycle, as observed by satellites in volcanically quiescent periods. The model results indicate that upward transport of COS from the troposphere largely controls the sulphur budget and the aerosol loading of the background stratosphere. This differs from most previous studies which indicated that short-lived sulphur gases are also important. The model realistically simulates the modulation of the particulate and gaseous sulphur abundance in the stratosphere by the quasi-biennial oscillation (QBO). In the lowermost stratosphere organic carbon aerosol contributes significantly to extinction. Further, we compute that the radiative forcing efficiency by 1 kg of COS is 724 times that of 1 kg CO2, which translates into an overall radiative forcing by anthropogenic COS of 0.003 W m-2. The global warming potentials of COS over time horizons of 20 and 100 yr are GWP(20 yr) = 97 and GWP(100 yr) = 27, respectively (by mass). Furthermore, stratospheric aerosol particles produced by the photolysis of COS contribute to a negative radiative forcing, which amounts to -0.007 W m-2 at the top of the atmosphere for the anthropogenic fraction, more than two times the warming forcing of COS. Considering that the lifetime of COS is twice that of stratospheric aerosols the warming and cooling tendencies approximately cancel. If the forcing of the troposphere near the tropopause is considered, the cooling dominates.
    Full-text · Article · Jun 2011 · Atmospheric Chemistry and Physics
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    ABSTRACT: We describe the setup and first results of an inverse modelling system for atmospheric N2O, based on a four-dimensional variational (4DVAR) technique and the atmospheric transport zoom model TM5. We focus in this study on the European domain, utilizing a comprehensive set of quasi-continuous measurements over Europe, complemented by N2O measurements from the Earth System Research Laboratory of the National Oceanic and Atmospheric Administration (NOAA/ESRL) cooperative global air sampling network. Despite ongoing measurement comparisons among networks parallel measurements at a limited number of stations show that significant offsets exist among the different laboratories. Since the spatial gradients of N2O mixing ratios are of the same order of magnitude as these biases, the direct use of these biased datasets would lead to significant errors in the derived emissions. Therefore, in order to also use measurements with unknown offsets, a new bias correction scheme has been implemented within the TM5-4DVAR inverse modelling system, thus allowing the simultaneous assimilation of observations from different networks. The N2O bias corrections determined in the TM5-4DVAR system agree within ~0.1 ppb (dry-air mole fraction) with the bias derived from the measurements at monitoring stations where parallel NOAA discrete air samples are available. The N2O emissions derived for the northwest European and east European countries for 2006 show good agreement with the bottom-up emission inventories reported to the United Nations Framework Convention on Climate Change (UNFCCC). Moreover, the inverse model can significantly narrow the uncertainty range reported in N2O emission inventories for these countries, while the lack of measurements does not allow to reduce the uncertainties of emission estimates in southern Europe. Several sensitivity experiments were performed to test the robustness of the results. It is shown that also inversions without detailed a priori spatio-temporal emission distributions are capable to reproduce major regional emission patterns within the footprint of the existing atmospheric network, demonstrating the strong constraints of the atmospheric observations on the derived emissions.
    Full-text · Article · Mar 2011 · Atmospheric Chemistry and Physics
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    ABSTRACT: Abstract. The submodel PSC of the ECHAM5/MESSy Atmospheric Chemistry model (EMAC) has been developed to simulate the main types of polar stratospheric clouds (PSC). The parameterisation of the supercooled ternary solutions (STS, type 1b PSC) in the submodel is based on Carslaw et al. (1995b), the thermodynamic approach to simulate ice particles (type 2 PSC) on Marti and Mauersberger (1993). For the formation of nitric acid trihydrate (NAT) particles (type 1a PSC) two different parameterisations exist. The first is based on an instantaneous thermodynamic approach from Hanson and Mauersberger (1988), the second is new implemented and considers the growth of the NAT particles with the aid of a surface growth factor based on Carslaw et al. (2002). It is possible to choose one of this NAT parameterisation in the submodel. This publication explains the background of the submodel PSC and the use of the submodel with the goal of simulating realistic PSC in EMAC.
    Full-text · Article · Mar 2011 · Geoscientific Model Development
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    ABSTRACT: 1] The stratospheric climate and variability from simulations of sixteen chemistry‐ climate models is evaluated. On average the polar night jet is well reproduced though its variability is less well reproduced with a large spread between models. Polar temperature biases are less than 5 K except in the Southern Hemisphere (SH) lower stratosphere in spring. The accumulated area of low temperatures responsible for polar stratospheric cloud formation is accurately reproduced for the Antarctic but underestimated for the Arctic. The shape and position of the polar vortex is well simulated, as is the tropical upwelling in the lower stratosphere. There is a wide model spread in the frequency of major sudden stratospheric warnings (SSWs), late biases in the breakup of the SH vortex, and a weak annual cycle in the zonal wind in the tropical upper stratosphere. Quantitatively, "metrics" indicate a wide spread in model performance for most diagnostics with systematic biases in many, and poorer performance in the SH than in the Northern Hemisphere (NH). Correlations were found in the SH between errors in the final warming, polar temperatures, the leading mode of variability, and jet strength, and in the NH between errors in polar temperatures, frequency of major SSWs, and jet strength. Models with a stronger QBO have stronger tropical upwelling and a colder NH vortex. Both the qualitative and quantitative analysis indicate a number of common and long‐standing model problems, particularly related to the simulation of the SH and stratospheric variability.
    Full-text · Article · Mar 2011 · Journal of Geophysical Research Atmospheres
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    ABSTRACT: Coupled chemistry-climate model simulations covering the recent past and continuing throughout the 21st century have been completed with a range of different models. Common forcings are used for the halogen amounts and greenhouse gas concentrations, as expected under the Montreal Protocol (with amendments) and Intergovernmental Panel on Climate Change A1b Scenario. The simulations of the Antarctic ozone hole are compared using commonly used diagnostics: the minimum ozone, the maximum area of ozone below 220 DU, and the ozone mass deficit below 220 DU. Despite the fact that the processes responsible for ozone depletion are reasonably well understood, a wide range of results is obtained. Comparisons with observations indicate that one of the reasons for the model underprediction in ozone hole area is the tendency for models to underpredict, by up to 35%, the area of low temperatures responsible for polar stratospheric cloud formation. Models also typically have species gradients that are too weak at the edge of the polar vortex, suggesting that there is too much mixing of air across the vortex edge. Other models show a high bias in total column ozone which restricts the size of the ozone hole (defined by a 220 DU threshold). The results of those models which agree best with observations are examined in more detail. For several models the ozone hole does not disappear this century but a small ozone hole of up to three million square kilometers continues to occur in most springs even after 2070.
    No preview · Article · Nov 2010 · Journal of Geophysical Research Atmospheres
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    ABSTRACT: The submodel PSC of the ECHAM5/MESSy Atmospheric Chemistry model (EMAC) has been developed to simulate the main types of polar stratospheric clouds (PSC). The parameterisation of the supercooled ternary solutions (STS, type 1b PSC) in the submodel is based on Carslaw et al. (1995b), the thermodynamical approach to simulate ice particles (type 2 PSC) on Marti and Mauersberger (1993). For the formation of nitric acid trihydrate (NAT) particles (type 1a PSC) two different parameterisations exist. The first one is based on an instantaneous thermodynamical approach from Hanson and Mauersberger (1988), the second one (new implemented by Kirner, 2008) considers the growth of the NAT particles with aid of a surface growth factor based on Carslaw et al. (2002). Via namelist switches the NAT parameterisation, as well as some parameters for the NAT and ice formation can be chosen. This publication explains the background of the submodel PSC and the use of the submodel with the goal to simulate realistic PSC in EMAC.
    Full-text · Article · Nov 2010 · Geoscientific Model Development Discussions
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    ABSTRACT: A multimodel assessment of the performance of chemistry‐climate models (CCMs) in the extratropical upper troposphere/lower stratosphere (UTLS) is conducted for the first time. Process‐oriented diagnostics are used to validate dynamical and transport characteristics of 18 CCMs using meteorological analyses and aircraft and satellite observations. The main dynamical and chemical climatological characteristics of the extratropical UTLS are generally well represented by the models, despite the limited horizontal and vertical resolution. The seasonal cycle of lowermost stratospheric mass is realistic, however with a wide spread in its mean value. A tropopause inversion layer is present in most models, although the maximum in static stability is located too high above the tropopause and is somewhat too weak, as expected from limited model resolution. Similar comments apply to the extratropical tropopause transition layer. The seasonality in lower stratospheric chemical tracers is consistent with the seasonality in the Brewer‐Dobson circulation. Both vertical and meridional tracer gradients are of similar strength to those found in observations. Models that perform less well tend to use a semi‐Lagrangian transport scheme and/or have a very low resolution. Two models, and the multimodel mean, score consistently well on all diagnostics, while seven other models score well on all diagnostics except the seasonal cycle of water vapor. Only four of the models are consistently below average. The lack of tropospheric chemistry in most models limits their evaluation in the upper troposphere. Finally, the UTLS is relatively sparsely sampled by observations, limiting our ability to quantitatively evaluate many aspects of model performance.
    Full-text · Article · Oct 2010 · Journal of Geophysical Research Atmospheres
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    ABSTRACT: The performance of 18 coupled Chemistry Climate Models (CCMs) in the Tropical Tropopause Layer (TTL) is evaluated using qualitative and quantitative diagnostics. Trends in tropopause quantities in the tropics and the extratropical Upper Troposphere and Lower Stratosphere (UTLS) are analyzed. A quantitative grading methodology for evaluating CCMs is extended to include variability and used to develop four different grades for tropical tropopause temperature and pressure, water vapor and ozone. Four of the 18 models and the multi‐model mean meet quantitative and qualitative standards for reproducing key processes in the TTL. Several diagnostics are performed on a subset of the models analyzing the Tropopause Inversion Layer (TIL), Lagrangian cold point and TTL transit time. Historical decreases in tropical tropopause pressure and decreases in water vapor are simulated, lending confidence to future projections. The models simulate continued decreases in tropopause pressure in the 21st century, along with ∼1K increases per century in cold point tropopause temperature and 0.5–1 ppmv per century increases in water vapor above the tropical tropopause. TTL water vapor increases below the cold point. In two models, these trends are associated with 35% increases in TTL cloud fraction. These changes indicate significant perturbations to TTL processes, specifically to deep convective heating and humidity transport. Ozone in the extratropical lowermost stratosphere has significant and hemispheric asymmetric trends. O3 is projected to increase by nearly 30% due to ozone recovery in the Southern Hemisphere (SH) and due to enhancements in the stratospheric circulation. These UTLS ozone trends may have significant effects in the TTL and the troposphere.
    Full-text · Article · Oct 2010 · Journal of Geophysical Research Atmospheres

Publication Stats

4k Citations
333.51 Total Impact Points

Institutions

  • 1988-2014
    • Max Planck Institute for Chemistry
      • Department of Atmospheric Chemistry
      Mayence, Rheinland-Pfalz, Germany
  • 2006
    • Instituto De Astrofisica De Andalucia
      Granata, Andalusia, Spain
  • 1997
    • Johannes Gutenberg-Universität Mainz
      Mayence, Rheinland-Pfalz, Germany