http://www.geosci-model-dev.net/Geoscientific Model Development Latest Articlesenhttp://www.geosci-model-dev.net/5/193/2012/<b>A Lagrangian model of air-mass photochemistry and mixing using a trajectory ensemble: the Cambridge Tropospheric Trajectory model of Chemistry And Transport (CiTTyCAT) version 4.2</b><br /><br />Geoscientific Model Development, 5, 193-221, 2012<br /><br />Author(s): T. A. M. Pugh, M. Cain, J. Methven, O. Wild, S. R. Arnold, E. Real, K. S. Law, K. M. Emmerson, S. M. Owen, J. A. Pyle, C. N. Hewitt, and A. R. MacKenzie<br /><br />A Lagrangian model of photochemistry and mixing is described (CiTTyCAT, stemming from the Cambridge Tropospheric Trajectory model of Chemistry And Transport), which is suitable for transport and chemistry studies throughout the troposphere. Over the last five years, the model has been developed in parallel at several different institutions and here those developments have been incorporated into one "community" model and documented for the first time. The key photochemical developments include a new scheme for biogenic volatile organic compounds and updated emissions schemes. The key physical development is to evolve composition following an ensemble of trajectories within neighbouring air-masses, including a simple scheme for mixing between them via an evolving "background profile", both within the boundary layer and free troposphere. The model runs along trajectories pre-calculated using winds and temperature from meteorological analyses. In addition, boundary layer height and precipitation rates, output from the analysis model, are interpolated to trajectory points and used as inputs to the mixing and wet deposition schemes. The model is most suitable in regimes when the effects of small-scale turbulent mixing are slow relative to advection by the resolved winds so that coherent air-masses form with distinct composition and strong gradients between them. Such air-masses can persist for many days while stretching, folding and thinning. Lagrangian models offer a useful framework for picking apart the processes of air-mass evolution over inter-continental distances, without being hindered by the numerical diffusion inherent to global Eulerian models. The model, including different box and trajectory modes, is described and some output for each of the modes is presented for evaluation. The model is available for download from a Subversion-controlled repository by contacting the corresponding authors.Tue, 31 Jan 2012 00:00:00 +0100http://www.geosci-model-dev.net/5/185/2012/<b>Climate forcing reconstructions for use in PMIP simulations of the Last Millennium (v1.1)</b><br /><br />Geoscientific Model Development, 5, 185-191, 2012<br /><br />Author(s): G. A. Schmidt, J. H. Jungclaus, C. M. Ammann, E. Bard, P. Braconnot, T. J. Crowley, G. Delaygue, F. Joos, N. A. Krivova, R. Muscheler, B. L. Otto-Bliesner, J. Pongratz, D. T. Shindell, S. K. Solanki, F. Steinhilber, and L. E. A. Vieira<br /><br />We update the forcings for the PMIP3 experiments for the Last Millennium to include new assessments of historical land use changes and discuss new suggestions for calibrating solar activity proxies to total solar irradiance.Mon, 30 Jan 2012 00:00:00 +0100http://www.geosci-model-dev.net/5/167/2012/<b>CELLS v1.0: updated and parallelized version of an electrical scheme to simulate multiple electrified clouds and flashes over large domains</b><br /><br />Geoscientific Model Development, 5, 167-184, 2012<br /><br />Author(s): C. Barthe, M. Chong, J.-P. Pinty, C. Bovalo, and J. Escobar<br /><br />The paper describes the fully parallelized electrical scheme CELLS which is suitable to simulate explicitly electrified storm systems on parallel computers. Our motivation here is to show that a cloud electricity scheme can be developed for use on large grids with complex terrain. Large computational domains are needed to perform real case meteorological simulations with many independent convective cells. <br><br> The scheme computes the bulk electric charge attached to each cloud particle and hydrometeor. Positive and negative ions are also taken into account. Several parametrizations of the dominant non-inductive charging process are included and an inductive charging process as well. The electric field is obtained by inverting the Gauss equation with an extension to terrain-following coordinates. The new feature concerns the lightning flash scheme which is a simplified version of an older detailed sequential scheme. Flashes are composed of a bidirectional leader phase (vertical extension from the triggering point) and a phase obeying a fractal law (with horizontal extension on electrically charged zones). The originality of the scheme lies in the way the branching phase is treated to get a parallel code. <br><br> The complete electrification scheme is tested for the 10 July 1996 STERAO case and for the 21 July 1998 EULINOX case. Flash characteristics are analysed in detail and additional sensitivity experiments are performed for the STERAO case. Although the simulations were run for flat terrain conditions, they show that the model behaves well on multiprocessor computers. This opens a wide area of application for this electrical scheme with the next objective of running real meterological case on large domains.Thu, 26 Jan 2012 00:00:00 +0100http://www.geosci-model-dev.net/5/149/2012/<b>LOSCAR: Long-term Ocean-atmosphere-Sediment CArbon cycle Reservoir Model v2.0.4</b><br /><br />Geoscientific Model Development, 5, 149-166, 2012<br /><br />Author(s): R. E. Zeebe<br /><br />The LOSCAR model is designed to efficiently compute the partitioning of carbon between ocean, atmosphere, and sediments on time scales ranging from centuries to millions of years. While a variety of computationally inexpensive carbon cycle models are already available, many are missing a critical sediment component, which is indispensable for long-term integrations. One of LOSCAR's strengths is the coupling of ocean-atmosphere routines to a computationally efficient sediment module. This allows, for instance, adequate computation of CaCO₃ dissolution, calcite compensation, and long-term carbon cycle fluxes, including weathering of carbonate and silicate rocks. The ocean component includes various biogeochemical tracers such as total carbon, alkalinity, phosphate, oxygen, and stable carbon isotopes. LOSCAR's configuration of ocean geometry is flexible and allows for easy switching between modern and paleo-versions. We have previously published applications of the model tackling future projections of ocean chemistry and weathering, <i>p</i>CO₂ sensitivity to carbon cycle perturbations throughout the Cenozoic, and carbon/calcium cycling during the Paleocene-Eocene Thermal Maximum. The focus of the present contribution is the detailed description of the model including numerical architecture, processes and parameterizations, tuning, and examples of input and output. Typical CPU integration times of LOSCAR are of order seconds for several thousand model years on current standard desktop machines. The LOSCAR source code in C can be obtained from the author by sending a request to loscar.model@gmail.com.Wed, 25 Jan 2012 00:00:00 +0100http://www.geosci-model-dev.net/5/129/2012/<b>The 1-way on-line coupled atmospheric chemistry model system MECO(n) – Part 3: Meteorological evaluation of the on-line coupled system</b><br /><br />Geoscientific Model Development, 5, 129-147, 2012<br /><br />Author(s): C. Hofmann, A. Kerkweg, H. Wernli, and P. Jöckel<br /><br />Three detailed meteorological case studies are conducted with the global and regional atmospheric chemistry model system ECHAM5/MESSy(→COSMO/MESSy)^<i>n</i>, shortly named MECO(n). The aim of this article is to assess the general performance of the on-line coupling of the regional model COSMO to the global model ECHAM5. The cases are characterised by intense weather systems in Central Europe: a cold front passage in March 2010, a convective frontal event in July 2007, and the high impact winter storm "Kyrill" in January 2007. Simulations are performed with the new on-line-coupled model system and compared to classical, off-line COSMO hindcast simulations driven by ECMWF analyses. Precipitation observations from rain gauges and ECMWF analysis fields are used as reference, and both qualitative and quantitative measures are used to characterise the quality of the various simulations. It is shown that, not surprisingly, simulations with a shorter lead time generally produce more accurate simulations. Irrespective of lead time, the accuracy of the on-line and off-line COSMO simulations are comparable for the three cases. This result indicates that the new global and regional model system MECO(n) is able to simulate key mid-latitude weather systems, including cyclones, fronts, and convective precipitation, as accurately as present-day state-of-the-art regional weather prediction models in standard off-line configuration. Therefore, MECO(n) will be applied to simulate atmospheric chemistry exploring the model's full capabilities during meteorologically challenging conditions.Thu, 19 Jan 2012 00:00:00 +0100http://www.geosci-model-dev.net/5/111/2012/<b>The 1-way on-line coupled atmospheric chemistry model system MECO(n) – Part 2: On-line coupling with the Multi-Model-Driver (MMD)</b><br /><br />Geoscientific Model Development, 5, 111-128, 2012<br /><br />Author(s): A. Kerkweg and P. Jöckel<br /><br />A new, highly flexible model system for the seamless dynamical down-scaling of meteorological and chemical processes from the global to the meso-γ scale is presented. A global model and a cascade of an arbitrary number of limited-area model instances run concurrently in the same parallel environment, in which the coarser grained instances provide the boundary data for the finer grained instances. Thus, disk-space intensive and time consuming intermediate and pre-processing steps are entirely avoided and the time interpolation errors of common off-line nesting approaches are minimised. More specifically, the regional model COSMO of the German Weather Service (DWD) is nested on-line into the atmospheric general circulation model ECHAM5 within the Modular Earth Submodel System (MESSy) framework. ECHAM5 and COSMO have previously been equipped with the MESSy infrastructure, implying that the same process formulations (MESSy submodels) are available for both models. This guarantees the highest degree of achievable consistency, between both, the meteorological and chemical conditions at the domain boundaries of the nested limited-area model, and between the process formulations on all scales. <br><br> The on-line nesting of the different models is established by a client-server approach with the newly developed Multi-Model-Driver (MMD), an additional component of the MESSy infrastructure. With MMD an arbitrary number of model instances can be run concurrently within the same message passing interface (MPI) environment, the respective coarser model (either global or regional) is the server for the nested finer (regional) client model, i.e. it provides the data required to calculate the initial and boundary fields to the client model. On-line nesting means that the coupled (client-server) models exchange their data via the computer memory, in contrast to the data exchange via files on disk in common off-line nesting approaches. MMD consists of a library (Fortran95 and some parts in C) which is based on the MPI standard and two new MESSy submodels, MMDSERV and MMDCLNT (both Fortran95) for the server and client models, respectively. <br><br> MMDCLNT contains a further sub-submodel, INT2COSMO, for the interpolation of the coarse grid data provided by the server models (either ECHAM5/MESSy or COSMO/MESSy) to the grid of the respective client model (COSMO/MESSy). INT2COSMO is based on the off-line pre-processing tool INT2LM provided by the DWD. <br><br> The new achievements allow the setup of model cascades for zooming (down-scaling) from the global scale to the lower edge of the meso-γ scale (&approx;1 km) with a very high degree of consistency between the different models and between the chemical and meteorological boundary conditions.Thu, 19 Jan 2012 00:00:00 +0100http://www.geosci-model-dev.net/5/87/2012/<b>The 1-way on-line coupled atmospheric chemistry model system MECO(n) – Part 1: Description of the limited-area atmospheric chemistry model COSMO/MESSy</b><br /><br />Geoscientific Model Development, 5, 87-110, 2012<br /><br />Author(s): A. Kerkweg and P. Jöckel<br /><br />The numerical weather prediction model of the Consortium for Small Scale Modelling (COSMO), maintained by the German weather service (DWD), is connected with the Modular Earth Submodel System (MESSy). This effort is undertaken in preparation of a new, limited-area atmospheric chemistry model. Limited-area models require lateral boundary conditions for all prognostic variables. Therefore the quality of a regional chemistry model is expected to improve, if boundary conditions for the chemical constituents are provided by the driving model in consistence with the meteorological boundary conditions. The new developed model is as consistent as possible, with respect to atmospheric chemistry and related processes, with a previously developed global atmospheric chemistry general circulation model: the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. The combined system constitutes a new research tool, bridging the global to the meso-γ scale for atmospheric chemistry research. MESSy provides the infrastructure and includes, among others, the process and diagnostic submodels for atmospheric chemistry simulations. Furthermore, MESSy is highly flexible allowing model setups with tailor made complexity, depending on the scientific question. Here, the connection of the MESSy infrastructure to the COSMO model is documented and also the code changes required for the generalisation of regular MESSy submodels. Moreover, previously published prototype submodels for simplified tracer studies are generalised to be plugged-in and used in the global and the limited-area model. They are used to evaluate the TRACER interface implementation in the new COSMO/MESSy model system and the tracer transport characteristics, an important prerequisite for future atmospheric chemistry applications. A supplementary document with further details on the technical implementation of the MESSy interface into COSMO with a complete list of modifications to the COSMO code is provided.Thu, 19 Jan 2012 00:00:00 +0100http://www.geosci-model-dev.net/5/73/2012/<b>Pliocene Model Intercomparison Project Experiment 1: implementation strategy and mid-Pliocene global climatology using GENESIS v3.0 GCM</b><br /><br />Geoscientific Model Development, 5, 73-85, 2012<br /><br />Author(s): S. J. Koenig, R. M. DeConto, and D. Pollard<br /><br />The mid-Pliocene Warm Period (3.29 to 2.97 Ma BP) has been identified as an analogue for the future, with the potential to help understand climate processes in a warmer than modern world. Sets of climate proxies, combined to provide boundary conditions for Global Climate Model (GCM) simulations of the mid-Pliocene, form the basis for the international, data-driven Pliocene Model Intercomparison Project (PlioMIP). Here, we outline the strategy for implementing pre-industrial (modern) and mid-Pliocene forcings and boundary conditions into the GENESIS version 3 GCM, as part of PlioMIP. We describe the prescription of greenhouse gas concentrations and orbital parameters and the implementation of geographic boundary conditions such as land-ice-sea distribution, topography, sea surface temperatures, sea ice extent, vegetation, soils, and ice sheets. We further describe model-specific details including spin-up and integration times. In addition, the global climatology of the mid-Pliocene as simulated by the GENESIS v3 GCM is analyzed and compared to the pre-industrial control simulation. The simulated climate of the mid-Pliocene warm interval is found to differ considerably from pre-industrial. We identify model sensitivity to imposed forcings, and internal feedbacks that collectively affect both local and far-field responses. Our analysis points out the need to assess both the direct impacts of external forcings and the combined effects of indirect, internal feedbacks. This paper provides the basis for assessing model biases within the PlioMIP framework, and will be useful for comparisons with other studies of mid-Pliocene climates.Wed, 18 Jan 2012 00:00:00 +0100http://www.geosci-model-dev.net/5/55/2012/<b>A web service based tool to plan atmospheric research flights</b><br /><br />Geoscientific Model Development, 5, 55-71, 2012<br /><br />Author(s): M. Rautenhaus, G. Bauer, and A. Dörnbrack<br /><br />We present a web service based tool for the planning of atmospheric research flights. The tool provides online access to horizontal maps and vertical cross-sections of numerical weather prediction data and in particular allows the interactive design of a flight route in direct relation to the predictions. It thereby fills a crucial gap in the set of currently available tools for using data from numerical atmospheric models for research flight planning. A distinct feature of the tool is its lightweight, web service based architecture, requiring only commodity hardware and a basic Internet connection for deployment. Access to visualisations of prediction data is achieved by using an extended version of the Open Geospatial Consortium Web Map Service (WMS) standard, a technology that has gained increased attention in meteorology in recent years. With the WMS approach, we avoid the transfer of large forecast model output datasets while enabling on-demand generated visualisations of the predictions at campaign sites with limited Internet bandwidth. Usage of the Web Map Service standard also enables access to third-party sources of georeferenced data. We have implemented the software using the open-source programming language Python. In the present article, we describe the architecture of the tool. As an example application, we discuss a case study research flight planned for the scenario of the 2010 Eyjafjalla volcano eruption. Usage and implementation details are provided as Supplement.Tue, 17 Jan 2012 00:00:00 +0100http://www.geosci-model-dev.net/5/37/2012/<b>Use of agricultural statistics to verify the interannual variability in land surface models: a case study over France with ISBA-A-gs</b><br /><br />Geoscientific Model Development, 5, 37-54, 2012<br /><br />Author(s): J.-C. Calvet, S. Lafont, E. Cloppet, F. Souverain, V. Badeau, and C. Le Bas<br /><br />In order to verify the interannual variability of the above-ground biomass of herbaceous vegetation simulated by the ISBA-A-gs land surface model, within the SURFEX modelling platform, French agricultural statistics for C3 crops and grasslands were compared with the simulations for the 1994–2008 period. While excellent correlations are obtained for grasslands, representing the interannual variability of crops is more difficult. It is shown that, the Maximum Available soil Water Capacity (MaxAWC) has a large influence on the correlation between the model and the agricultural statistics. In particular, high values of MaxAWC tend to reduce the impact of the climate interannual variability on the simulated biomass. Also, high values of MaxAWC allow the simulation of a negative trend in biomass production, in relation to a marked warming trend, of about 0.12 Kyr⁻¹ on average, affecting the daily maximum air temperature during the growing period (April–June). This trend is particularly acute in Northern France. The estimates of MaxAWC for C3 crops and grasslands, currently used in SURFEX, are about 129 mm and do not vary much. Therefore, more accurate grid-cell values of this parameter are needed.Wed, 11 Jan 2012 00:00:00 +0100http://www.geosci-model-dev.net/5/15/2012/<b>The application of the Modified Band Approach for the calculation of on-line photodissociation rate constants in TM5: implications for oxidative capacity</b><br /><br />Geoscientific Model Development, 5, 15-35, 2012<br /><br />Author(s): J. E. Williams, A. Strunk, V. Huijnen, and M. van Weele<br /><br />A flexible and explicit on-line parameterization for the calculation of tropospheric photodissociation rate constants (<i>J</i>-values) has been integrated into the global Chemistry Transport Model TM5. Here we provide a comprehensive description of this Modified Band Approach (MBA) including details of the optimization procedure employed, the methodology applied for calculating actinic fluxes, the photochemical reaction data used for each chemical species, the aerosol climatology which is adopted and the parameterizations adopted for improving the description of scattering and absorption by clouds. The resulting <i>J</i>-values change markedly throughout the troposphere when compared to the offline approach used to date, with significant increases in the boundary layer and upper troposphere. Conversely, for the middle troposphere a reduction in the actinic flux results in a decrease in <i>J</i>-values. Integrating effects shows that application of the MBA introduces seasonal dependent differences in important trace gas oxidants. Tropospheric ozone (O₃) changes by &plusmn;10% in the seasonal mean mixing ratios throughout the troposphere, especially over land. These changes and the perturbations in the photolysis rate of O₃ induce changes of &plusmn;15% in tropospheric OH. In part this is due to an increase in the re-cycling efficiency of nitrogen oxides. The overall increase in northern hemispheric tropospheric ozone strengthens the oxidizing capacity of the troposphere significantly and reduces the lifetime of CO and CH₄ by ~5 % and ~4%, respectively. Changes in the tropospheric CO burden, however, are limited to a few percent due to competing effects. Comparing the distribution of tropospheric ozone in the boundary layer and middle troposphere against observations in Europe shows there are improvements in the model performance during boreal winter in the Northern Hemisphere near regions affected by high nitrogen oxide emissions. Monthly mean total columns of nitrogen dioxide and formaldehyde also compare more favorably against OMI and SCIAMACHY total column observations.Fri, 06 Jan 2012 00:00:00 +0100http://www.geosci-model-dev.net/5/1/2012/<b>Partial Derivative Fitted Taylor Expansion: an efficient method for calculating gas/liquid equilibria in atmospheric aerosol particles – Part 2: Organic compounds</b><br /><br />Geoscientific Model Development, 5, 1-13, 2012<br /><br />Author(s): D. Topping, D. Lowe, and G. McFiggans<br /><br />A flexible mixing rule is presented which allows the calculation of activity coefficients of organic compounds in a multi-component aqueous solution. Based on the same fitting methodology as a previously published inorganic model (Partial Differential Fitted Taylor series Expansion; PD-FiTE), organic PD-FiTE treats interactions between binary pairs of solutes with polynomials of varying order. The numerical framework of organic PD-FiTE is not based on empirical observations of activity coefficient variation, rather a simple application of a Taylor Series expansion. Using 13 example compounds extracted from a recent sensitivity study, the framework is benchmarked against the UNIFAC model. For 1000 randomly derived concentration ranges and 10 relative humidities between 10 and 99%, the average deviation in predicted activity coefficients was calculated to be 3.8%. Whilst compound specific deviations are present, the median and inter-quartile values across all relative humidity range always fell within ±20% of the UNIFAC value. Comparisons were made with the UNIFAC model by assuming interactions between solutes can be set to zero within PD-FiTE. In this case, deviations in activity coefficients as low as −40% and as high as +70% were found. Both the fully coupled and uncoupled organic PD-FiTE are up to a factor of &approx;12 and &approx;66 times more efficient than calling the UNIFAC model using the same water content, and &approx;310 and ≈1800 times more efficient than an iterative model using UNIFAC. The use of PD-FiTE within a dynamical framework is presented, demonstrating the potential inaccuracy of prescribing fixed negative or positive deviations from ideality when modelling the evolving chemical composition of aerosol particles.Wed, 04 Jan 2012 00:00:00 +0100http://www.geosci-model-dev.net/4/1133/2011/<b>Improved convergence and stability properties in a three-dimensional higher-order ice sheet model</b><br /><br />Geoscientific Model Development, 4, 1133-1149, 2011<br /><br />Author(s): J. J. Fürst, O. Rybak, H. Goelzer, B. De Smedt, P. de Groen, and P. Huybrechts<br /><br />We present a finite difference implementation of a three-dimensional higher-order ice sheet model. In comparison to a conventional centred difference discretisation it enhances both numerical stability and convergence. In order to achieve these benefits the discretisation of the governing force balance equation makes extensive use of information on staggered grid points. Using the same iterative solver, a centred difference discretisation that operates exclusively on the regular grid serves as a reference. The reprise of the ISMIP-HOM experiments indicates that both discretisations are capable of reproducing the higher-order model inter-comparison results. This setup allows a direct comparison of the two numerical implementations also with respect to their convergence behaviour. First and foremost, the new finite difference scheme facilitates convergence by a factor of up to 7 and 2.6 in average. In addition to this decrease in computational costs, the accuracy for the resultant velocity field can be chosen higher in the novel finite difference implementation. Changing the discretisation also prevents build-up of local field irregularites that occasionally cause divergence of the solution for the reference discretisation. <br><br> The improved behaviour makes the new discretisation more reliable for extensive application to real ice geometries. Higher accuracy and robust numerics are crucial in time dependent applications since numerical oscillations in the velocity field of subsequent time steps are attenuated and divergence of the solution is prevented.Mon, 19 Dec 2011 00:00:00 +0100http://www.geosci-model-dev.net/4/1115/2011/<b>The CSIRO Mk3L climate system model v1.0 coupled to the CABLE land surface scheme v1.4b: evaluation of the control climatology</b><br /><br />Geoscientific Model Development, 4, 1115-1131, 2011<br /><br />Author(s): J. Mao, S. J. Phipps, A. J. Pitman, Y. P. Wang, G. Abramowitz, and B. Pak<br /><br />The CSIRO Mk3L climate system model, a reduced-resolution coupled general circulation model, has previously been described in this journal. The model is configured for millennium scale or multiple century scale simulations. This paper reports the impact of replacing the relatively simple land surface scheme that is the default parameterisation in Mk3L with a sophisticated land surface model that simulates the terrestrial energy, water and carbon balance in a physically and biologically consistent way. An evaluation of the new model's near-surface climatology highlights strengths and weaknesses, but overall the atmospheric variables, including the near-surface air temperature and precipitation, are simulated well. The impact of the more sophisticated land surface model on existing variables is relatively small, but generally positive. More significantly, the new land surface scheme allows an examination of surface carbon-related quantities including net primary productivity which adds significantly to the capacity of Mk3L. Overall, results demonstrate that this reduced-resolution climate model is a good foundation for exploring long time scale phenomena. The addition of the more sophisticated land surface model enables an exploration of important Earth System questions including land cover change and abrupt changes in terrestrial carbon storage.Thu, 08 Dec 2011 00:00:00 +0100http://www.geosci-model-dev.net/4/1103/2011/<b>Evaluation of a Global Vegetation Model using time series of satellite vegetation indices</b><br /><br />Geoscientific Model Development, 4, 1103-1114, 2011<br /><br />Author(s): F. Maignan, F.-M. Bréon, F. Chevallier, N. Viovy, P. Ciais, C. Garrec, J. Trules, and M. Mancip<br /><br />Atmospheric CO₂ drives most of the greenhouse effect increase. One major uncertainty on the future rate of increase of CO₂ in the atmosphere is the impact of the anticipated climate change on the vegetation. Dynamic Global Vegetation Models (DGVM) are used to address this question. ORCHIDEE is such a DGVM that has proven useful for climate change studies. However, there is no objective and methodological way to accurately assess each new available version on the global scale. In this paper, we submit a methodological evaluation of ORCHIDEE by correlating satellite-derived Vegetation Index time series against those of the modeled Fraction of absorbed Photosynthetically Active Radiation (FPAR). A perfect correlation between the two is not expected, however an improvement of the model should lead to an increase of the overall performance. <br><br> We detail two case studies in which model improvements are demonstrated, using our methodology. In the first one, a new phenology version in ORCHIDEE is shown to bring a significant impact on the simulated annual cycles, in particular for C3 Grasses and C3 Crops. In the second case study, we compare the simulations when using two different weather fields to drive ORCHIDEE. The ERA-Interim forcing leads to a better description of the FPAR interannual anomalies than the simulation forced by a mixed CRU-NCEP dataset. This work shows that long time series of satellite observations, despite their uncertainties, can identify weaknesses in global vegetation models, a necessary first step to improving them.Mon, 05 Dec 2011 00:00:00 +0100http://www.geosci-model-dev.net/4/1077/2011/<b>Towards an online-coupled chemistry-climate model: evaluation of trace gases and aerosols in COSMO-ART</b><br /><br />Geoscientific Model Development, 4, 1077-1102, 2011<br /><br />Author(s): C. Knote, D. Brunner, H. Vogel, J. Allan, A. Asmi, M. Äijälä, S. Carbone, H. D. van der Gon, J. L. Jimenez, A. Kiendler-Scharr, C. Mohr, L. Poulain, A. S. H. Prévôt, E. Swietlicki, and B. Vogel<br /><br />The online-coupled, regional chemistry transport model COSMO-ART is evaluated for periods in all seasons against several measurement datasets to assess its ability to represent gaseous pollutants and ambient aerosol characteristics over the European domain. Measurements used in the comparison include long-term station observations, satellite and ground-based remote sensing products, and complex datasets of aerosol chemical composition and number size distribution from recent field campaigns. This is the first time these comprehensive measurements of aerosol characteristics in Europe are used to evaluate a regional chemistry transport model. We show a detailed analysis of the simulated size-resolved chemical composition under different meteorological conditions. Mean, variability and spatial distribution of the concentrations of O₃ and NO_x are well reproduced. SO₂ is found to be overestimated, simulated PM_2.5 and PM₁₀ levels are on average underestimated, as is AOD. We find indications of an overestimation of shipping emissions. Time evolution of aerosol chemical composition is captured, although some biases are found in relative composition. Nitrate aerosol components are on average overestimated, and sulfates underestimated. The accuracy of simulated organics depends strongly on season and location. While strongly underestimated during summer, organic mass is comparable in spring and autumn. We see indications for an overestimated fractional contribution of primary organic matter in urban areas and an underestimation of SOA at many locations. Aerosol number concentrations compare well with measurements for larger size ranges, but overestimations of particle number concentration with factors of 2–5 are found for particles smaller than 50 nm. Size distribution characteristics are often close to measurements, but show discrepancies at polluted sites. Suggestions for further improvement of the modeling system consist of the inclusion of a revised secondary organic aerosols scheme, aqueous-phase chemistry and improved aerosol boundary conditions. Our work sets the basis for subsequent studies of aerosol characteristics and climate impacts with COSMO-ART, and highlights areas where improvements are necessary for current regional modeling systems in general.Fri, 02 Dec 2011 00:00:00 +0100http://www.geosci-model-dev.net/4/1051/2011/<b>Development and evaluation of an Earth-System model – HadGEM2</b><br /><br />Geoscientific Model Development, 4, 1051-1075, 2011<br /><br />Author(s): W. J. Collins, N. Bellouin, M. Doutriaux-Boucher, N. Gedney, P. Halloran, T. Hinton, J. Hughes, C. D. Jones, M. Joshi, S. Liddicoat, G. Martin, F. O'Connor, J. Rae, C. Senior, S. Sitch, I. Totterdell, A. Wiltshire, and S. Woodward<br /><br />We describe here the development and evaluation of an Earth system model suitable for centennial-scale climate prediction. The principal new components added to the physical climate model are the terrestrial and ocean ecosystems and gas-phase tropospheric chemistry, along with their coupled interactions. <br><br> The individual Earth system components are described briefly and the relevant interactions between the components are explained. Because the multiple interactions could lead to unstable feedbacks, we go through a careful process of model spin up to ensure that all components are stable and the interactions balanced. This spun-up configuration is evaluated against observed data for the Earth system components and is generally found to perform very satisfactorily. The reason for the evaluation phase is that the model is to be used for the core climate simulations carried out by the Met Office Hadley Centre for the Coupled Model Intercomparison Project (CMIP5), so it is essential that addition of the extra complexity does not detract substantially from its climate performance. Localised changes in some specific meteorological variables can be identified, but the impacts on the overall simulation of present day climate are slight. <br><br> This model is proving valuable both for climate predictions, and for investigating the strengths of biogeochemical feedbacks.Tue, 29 Nov 2011 00:00:00 +0100http://www.geosci-model-dev.net/4/1035/2011/<b>Simulating the mid-Pliocene climate with the MIROC general circulation model: experimental design and initial results</b><br /><br />Geoscientific Model Development, 4, 1035-1049, 2011<br /><br />Author(s): W.-L. Chan, A. Abe-Ouchi, and R. Ohgaito<br /><br />Recently, PlioMIP (Pliocene Model Intercomparison Project) was established to assess the ability of various climate models to simulate the mid-Pliocene warm period (mPWP), 3.3–3.0 million years ago. We use MIROC4m, a fully coupled atmosphere-ocean general circulation model (AOGCM), and its atmospheric component alone to simulate the mPWP, utilizing up-to-date data sets designated in PlioMIP as boundary conditions and adhering to the protocols outlined. In this paper, a brief description of the model is given, followed by an explanation of the experimental design and implementation of the boundary conditions, such as topography and sea surface temperature. Initial results show increases of approximately 10&deg;C in the zonal mean surface air temperature at high latitudes accompanied by a decrease in the equator-to-pole temperature gradient. Temperatures in the tropical regions increase more in the AOGCM. However, warming of the AOGCM sea surface in parts of the northern North Atlantic Ocean and Nordic Seas is less than that suggested by proxy data. An investigation of the model-data discrepancies and further model intercomparison studies can lead to a better understanding of the mid-Pliocene climate and of its role in assessing future climate change.Tue, 29 Nov 2011 00:00:00 +0100http://www.geosci-model-dev.net/4/1019/2011/<b>Validation of modelled forest biomass in Germany using BETHY/DLR</b><br /><br />Geoscientific Model Development, 4, 1019-1034, 2011<br /><br />Author(s): M. Tum, M. Buchhorn, K. P. Günther, and B. C. Haller<br /><br />We present a new approach to the validation of modelled forest Net Primary Productivity (NPP), using empirical data on the mean annual increment, or MAI, in above-ground forest stock. The soil-vegetation-atmosphere-transfer model BETHY/DLR is used, with a particular focus on a detailed parameterization of photosynthesis, to estimate the NPP of forest areas in Germany, driven by remote sensing data from VEGETATION, meteorological data from the European Centre for Medium-Range Weather Forecasts (ECMWF), and additional tree coverage information from the MODIS Vegetation Continuous Field (VCF). The output of BETHY/DLR, Gross Primary Productivity (GPP), is converted to NPP by subtracting the cumulative plant maintenance and growth respiration, and then validated against MAI data that was calculated from German forestry inventories. Validation is conducted for 2000 and 2001 by converting modelled NPP to stem volume at a regional level. Our analysis shows that the presented method fills an important gap in methods for validating modelled NPP against empirically derived data. In addition, we examine theoretical energy potentials calculated from the modelled and validated NPP, assuming sustainable forest management and using species-specific tree heating values. Such estimated forest biomass energy potentials play an important role in the sustainable energy debate.Fri, 18 Nov 2011 00:00:00 +0100http://www.geosci-model-dev.net/4/1011/2011/<b>Development of an ensemble-adjoint optimization approach to derive uncertainties in net carbon fluxes</b><br /><br />Geoscientific Model Development, 4, 1011-1018, 2011<br /><br />Author(s): T. Ziehn, M. Scholze, and W. Knorr<br /><br />Accurate modelling of the carbon cycle strongly depends on the parametrization of its underlying processes. The Carbon Cycle Data Assimilation System (CCDAS) can be used as an estimator algorithm to derive posterior parameter values and uncertainties for the Biosphere Energy Transfer and Hydrology scheme (BETHY). However, the simultaneous optimization of all process parameters can be challenging, due to the complexity and non-linearity of the BETHY model. Therefore, we propose a new concept that uses ensemble runs and the adjoint optimization approach of CCDAS to derive the full probability density function (PDF) for posterior soil carbon parameters and the net carbon flux at the global scale. This method allows us to optimize only those parameters that can be constrained best by atmospheric carbon dioxide (CO₂) data. The prior uncertainties of the remaining parameters are included in a consistent way through ensemble runs, but are not constrained by data. The final PDF for the optimized parameters and the net carbon flux are then derived by superimposing the individual PDFs for each ensemble member. We find that the optimization with CCDAS converges much faster, due to the smaller number of processes involved. Faster convergence also gives us much increased confidence that we find the global minimum in the reduced parameter space.Fri, 18 Nov 2011 00:00:00 +0100