ALBERT

Description: Modeling atmospheric ammonia and ammonium using a backward-in-time stochastic Lagrangian air quality model (STILT-Chem v0.7) Geoscientific Model Development Discussions, 5, 2745-2788, 2012 Author(s): D. Wen, J. C. Lin, L. Zhang, R. Vet, and M. D. Moran A new chemistry module of atmospheric ammonia (NH 3 ) and ammonium (NH 4 + ) was incorporated into a backward-in-time stochastic Lagrangian air quality model (STILT-Chem) that was originally developed to simulate the concentrations of a variety of gas-phase species at receptors. STILT-Chem simulates the transport of air parcels backward in time using ensembles of fictitious particles with stochastic motions, while simulating emissions, deposition and chemical transformation forward in time along trajectories identified by the backward-in-time simulations. The incorporation of the new chemistry module allows the model to simulate not only gaseous species, but also multi-phase species involving NH 3 and NH 4 + . The model was applied to simulate concentrations of NH 3 and particulate NH 4 + at six sites in the Canadian province of Ontario for a six-month period in 2006. The model-predicted concentrations of NH 3 and particulate NH 4 + were compared with observations, which show broad agreement between simulated concentrations and observations. Since the model is based on back trajectories, the influence of each major process such as emission, deposition and chemical conversion on the concentration of a modeled species at a receptor can be determined for every upstream location at each time step. This makes it possible to quantitatively investigate the upstream processes affecting receptor concentrations. The modeled results suggest that the concentrations of NH 3 at those sites were significantly and frequently affected by southwestern Ontario, northern Ohio, and nearby areas. NH 3 is mainly contributed by emission sources whereas particulate NH 4 + is mainly contributed by the gas-to-aerosol chemical conversion of NH 3 . Dry deposition is the largest removal process for both NH 3 and particulate NH 4 + . This study revealed the contrast between agricultural versus forest sites. Not only were emissions of NH 3 higher, but removal mechanisms (especially chemical loss for NH 3 and dry deposition for NH 4 + ) were less efficient for agricultural sites. This combination explains the significantly higher concentrations of NH 3 and particulate NH 4 + observed at agricultural sites.

Description: How should sparse in situ measurements be compared to continuous model data? Geoscientific Model Development Discussions, 5, 2311-2345, 2012 Author(s): L. de Mora, M. Butenschön, and J. I. Allen This work demonstrates the importance of an adequate method to sub-sample model results when comparing with in situ measurements. A test of model skill was performed by comparing a multi-decadal hindcast against a sparse, unevenly distributed historic in situ dataset. The comparison was performed using a point-to-point method. The point-to-point method masked out all hindcast cells that did not have a corresponding in situ measurement in order to compare each in situ measurement against its most similar cell from the model. The application of the point-to-point method showed that the model was successful at reproducing many inter-annual trends. Furthermore, this success was not immediately apparent using the previous comparison methods, which compared model and measurements aggregated to regional averages. Time series, data density and target diagrams were employed to illustrate the impact of switching from the previous method to the point-to-point method. The comparison based on regional averages gave significantly different and sometimes contradicting results that could lead to erroneous conclusions on the model performance. We therefore recommend that researchers take into account for the limitations of the in situ datasets, process the model to resemble the data as much as possible, and we advocate greater transparency in the publication of methodology.

Description: The chemical transport model Oslo CTM3 Geoscientific Model Development Discussions, 5, 1561-1626, 2012 Author(s): O. A. Søvde, M. J. Prather, I. S. A. Isaksen, T. K. Berntsen, F. Stordal, X. Zhu, C. D. Holmes, and J. Hsu We present here the global chemical transport model Oslo CTM3, an update of the Oslo CTM2. The update comprises a faster transport scheme, an improved wet scavenging scheme for large scale rain, updated photolysis rates and a new lightning parameterization. Oslo CTM3 is better parallelized and allows for stable, large time steps for advection, enabling more complex or high resolution simulations. Thorough comparisons between the Oslo CTM3, Oslo CTM2 and measurements are performed, and in general the Oslo CTM3 is found to reproduce measurements well. Inclusion of tropospheric sulfur chemistry and nitrate aerosols in CTM3 is shown to be important to reproduce tropospheric O 3 , OH and the CH 4 lifetime well. Using the same meteorology to drive the two models, shows that some features related to transport are better resolved by the CTM3, such as polar cap transport, while features like transport close to the vortex edge are resolved better in the Oslo CTM2 due to its required shorter transport time step. The longer transport time steps in CTM3 result in larger errors e.g. near the jets, and when necessary, this can be remedied by using a shorter time step. An additional, more accurate and time consuming, treatment of polar cap transport is presented, however, both perform acceptably. A new treatment of the horizontal distribution of lightning is presented and found to compare well with measurements. Vertical distributions of lighting are updated, and tested against the old vertical distribution. The new profiles are found to produce more NO x in the tropical middle troposphere, and less at the surface and at high altitudes.

Description: Unified parameterization of the planetary boundary layer and shallow convection with a higher-order turbulence closure in the community atmosphere model: single column experiments Geoscientific Model Development Discussions, 5, 1743-1780, 2012 Author(s): P. A. Bogenschutz, A. Gettelman, H. Morrison, V. E. Larson, D. P. Schanen, N. R. Meyer, and C. Craig This paper describes the coupling of the Community Atmosphere Model (CAM) version 5 with a unified multi-variate probability density function (PDF) parameterization, Cloud Layers Unified by Binormals (CLUBB). CLUBB replaces the planetary boundary layer (PBL), shallow convection, and cloud macrophysics schemes in CAM5 with a higher-order turbulence closure based on an assumed PDF. Comparisons of single-column versions of CAM5 and CAM-CLUBB are provided in this paper for several boundary layer regimes. As compared to Large Eddy Simulations (LES), CAM-CLUBB and CAM5 simulate marine stratocumulus regimes with similar accuracy. For shallow convective regimes, CAM-CLUBB improves the representation of cloud cover and liquid water path (LWP). In addition, for shallow convection CAM-CLUBB offers better fidelity for sub-grid scale vertical velocity, which is an important input for aerosol activation. Finally, CAM-CLUBB results are more robust to changes in vertical and temporal resolution when compared to CAM5.

Description: Implementation of the chemistry module MECCA (v2.5) in the modal aerosol version of the Community Atmosphere Model component (v3.6.33) of the Community Earth System Model Geoscientific Model Development Discussions, 5, 1483-1501, 2012 Author(s): M. S. Long, W. C. Keene, R. Easter, R. Sander, A. Kerkweg, D. Erickson, X. Liu, and S. Ghan A coupled atmospheric chemistry and climate system model was developed using the modal aerosol version of the National Center for Atmospheric Research Community Atmosphere Model (modal-CAM) and the Max Planck Institute for Chemistry's Module Efficiently Calculating the Chemistry of the Atmosphere (MECCA) to provide enhanced resolution of multiphase processes, particularly those involving inorganic halogens, and associated impacts on atmospheric composition and climate. Three Rosenbrock solvers (Ros-2, Ros-3, RODAS-3) were tested in conjunction with the basic load balancing options available to modal CAM (1) to establish an optimal configuration of the implicitly-solved multiphase chemistry module that maximizes both computational speed and repeatability of Ros-2 and RODAS-3 results versus Ros-3, and (2) to identify potential implementation strategies for future versions of this and similar coupled systems. RODAS-3 was faster than Ros-2 and Ros-3 with good reproduction of Ros-3 results, while Ros-2 was both slower and substantially less reproducible relative to Ros-3 results. Modal-CAM with MECCA chemistry was a factor of 15 slower than modal-CAM using standard chemistry. MECCA chemistry integration times demonstrated a systematic frequency distribution for all three solvers, and revealed that the change in run-time performance was due to a change in the frequency distribution chemical integration times; the peak frequency was similar for all solvers. This suggests that efficient chemistry-focused load-balancing schemes can be developed that rely on the parameters of this frequency distribution.

Description: Describing Earth System Simulations with the Metafor CIM Geoscientific Model Development Discussions, 5, 1669-1689, 2012 Author(s): B. N. Lawrence, V. Balaji, P. Bentley, S. Callaghan, C. DeLuca, S. Denvil, G. Devine, M. Elkington, R. W. Ford, E. Guilyardi, M. Lautenschlager, M. Morgan, M.-P. Moine, S. Murphy, C. Pascoe, H. Ramthun, P. Slavin, L. Steenman-Clark, F. Toussaint, A. Treshansky, and S. Valcke The Metafor project has developed a Common Information Model (CIM) using the ISO1900 series formalism to describe the sorts of numerical experiments carried out by the earth system modelling community, the models they use, and the simulations that result. Here we describe the mechanism by which the CIM was developed, and its key properties. We introduce the conceptual and application versions and the controlled vocabularies developed in the context of supporting the fifth Coupled Model Intercomparison Project (CMIP5). We describe how the CIM has been used in experiments to describe model coupling properties and describe the near term expected evolution of the CIM.

Description: Lidar signal simulation for the evaluation of aerosols in chemistry-transport models Geoscientific Model Development Discussions, 5, 1691-1741, 2012 Author(s): S. Stromatas, S. Turquety, L. Menut, H. Chepfer, J. C. Péré, G. Cesana, and B. Bessagnet We present an adaptable tool, the OPTSIM (OPTical properties SIMulation) software, for the simulation of optical properties and lidar attenuated backscattered profiles (β ' ) from aerosol concentrations calculated by chemistry-transport models (CTM). It was developed to support model evaluation using an original approach based on the lidar Level 1 observations (β ' ), avoiding the use of Level 2 aerosol retrievals which include specific assumptions on aerosol types that may not be in agreement with the CTM. In addition to an evaluation of the aerosol loading and optical properties, active remote sensing allows the analysis of aerosols' vertical structures. An academic case study for two different species (black carbon and dust) is presented and shows the consistency of the simulator. Illustrations are then given through the analysis of dust events in the Mediterranean region during the summer 2007. These are based on simulations by the CHIMERE regional CTM and observations from the CALIOP space-based lidar, and highlight the potential of this approach to evaluate the concentration, size and vertical structure of the aerosol plumes.

Description: Better constraints on the sea-ice state using global sea-ice data assimilation Geoscientific Model Development Discussions, 5, 1627-1667, 2012 Author(s): P. Mathiot, C. König Beatty, T. Fichefet, H. Goosse, F. Massonnet, and M. Vancoppenolle Short-term and decadal sea-ice prediction systems need a realistic initial state, generally obtained using ice-ocean model simulations with data assimilation. However, only sea-ice concentration and velocity data are currently assimilated. In this work, an Ensemble Kalman Filter system is used to assimilate observed ice concentration and freeboard (i.e. thickness of emerged sea ice) data into a global coupled ocean–sea-ice model. The impact and effectiveness of our data assimilation system is assessed in two steps: firstly, through the assimilation of synthetic data (i.e., model-generated data) and, secondly, through the assimilation of satellite data. While ice concentrations are available daily, freeboard data used in this study are only available during six one-month periods spread over 2005–2007. Our results show that the simulated Arctic and Antarctic sea-ice extents are improved by the assimilation of synthetic ice concentration data. Assimilation of synthetic ice freeboard data improves the simulated sea-ice thickness field. Using real ice concentration data enhances the model realism in both hemispheres. Assimilation of ice concentration data significantly improves the total hemispheric sea-ice extent all year long, especially in summer. Combining the assimilation of ice freeboard and concentration data leads to better ice thickness, but does not further improve the ice extent. Moreover, the improvements in sea-ice thickness due to the assimilation of ice freeboard remain visible well beyond the assimilation periods.

Description: Modeling wet deposition of inorganics over Northeast Asia with MRI-PM/c and the effects of super large sea salt droplets at near-the-coast stations Geoscientific Model Development Discussions, 5, 1341-1379, 2012 Author(s): M. Kajino, M. Deushi, T. Maki, N. Oshima, Y. Inomata, K. Sato, T. Ohizumi, and H. Ueda We conducted a regional-scale simulation (with grid spacing = 60 km) over Northeast Asia for the entire year of 2006 by using an aerosol chemical transport model, the lateral and upper boundary concentrations of which we predicted with a global stratospheric and tropospheric chemistry-climate model, with a horizontal resolution of T42 (grid spacing ~300 km) and a time resolution of 1 h. The present one-way nested global-through-regional-scale model is called the Meteorological Research Institute – Passive-tracers Model system for atmospheric Chemistry (MRI-PM/c). We evaluated the model performance with respect to the major inorganic components in rain and snow measured by stations of the Acid Deposition Monitoring Network in East Asia (EANET). Through statistical analysis, we show that the model successfully reproduced the regional-scale processes of emission, transport, transformation, and wet deposition of major inorganic species derived from anthropogenic and natural sources, including SO 4 2− , NH 4 + , NO 3 − , Na + and Ca 2+ . Interestingly, the only exception was Na + in precipitation at near-coastal stations (where the distance from the coast was from 150 to 700 m), concentrations of which were significantly underestimated by the model, by up to a factor of 30. This result suggested that the contribution of short-lived, super-large sea salt droplets (SLSD; D 〉 10–100 μm) was substantial in precipitation samples at stations near the coast of Japan; thus samples were horizontally representative only within the traveling distances of SLSD (from 1 to 10 km). Nevertheless, the calculated effect of SLSD on precipitation pH was very low, a change of about +0.014 on average, even if the ratio of SLSD to all sea salt in precipitation was assumed to be 90%.

Description: Mid-Pliocene climate modelled using the UK Hadley Centre Model: PlioMIP Experiments 1 and 2 Geoscientific Model Development Discussions, 5, 837-871, 2012 Author(s): F. J. Bragg, D. J. Lunt, and A. M. Haywood The Pliocene Model Intercomparison Project (PlioMIP) project is a sub-project of the Paleoclimate Modelling Intercomparison Project (PMIP) whose objective is to compare predictions of the mid-Pliocene climate from the widest possible range of general circulation models. The mid-Pliocene (3.3–3.0 Ma) is the most recent sustained period of greater warmth and atmospheric carbon dioxide concentration than the pre-industrial times and as such has potential to inform predictions of our warming climate in the coming century. This paper describes the UK contribution to PlioMIP using the Hadley Centre Model both in atmosphere-only mode (HadAM3, PlioMIP Experiment 1) and atmosphere-ocean coupled mode (HadCM3, PlioMIP Experiment 2). The coupled model predicts a greater overall warming (3.3 °C) relative to the control than the atmosphere-only (2.5 °C). The Northern Hemisphere latitudinal temperature gradient is greater in the coupled model with a warmer equator and colder Arctic than the atmosphere-only model, which is constrained by sea surface temperatures from Pliocene proxy reconstructions. The atmosphere-only model predicts a reduction in equatorial precipitation and south Asian monsoon intensity whereas the coupled models shows and increase in the intensity of these systems. Sensitivity studies using alternative boundary conditions for both the Pliocene and the control simulations are presented, which indicate the sensitivity of the mid-Pliocene warming to uncertainties in both pre-industrial and mid-Pliocene climate.

Description: Performance of McRAS-AC in the GEOS-5 AGCM: aerosol-cloud-microphysics, precipitation, cloud radiative effects, and circulation Geoscientific Model Development Discussions, 5, 1381-1434, 2012 Author(s): Y. C. Sud, D. Lee, L. Oreopoulos, D. Barahona, A. Nenes, and M. J. Suarez A revised version of the Microphysics of clouds with Relaxed Arakawa-Schubert and Aerosol-Cloud interaction scheme (McRAS-AC) including, among others, the Barahona and Nenes ice nucleation parameterization, is implemented in the GEOS-5 AGCM. Various fields from a 10-yr long integration of the AGCM with McRAS-AC were compared with their counterparts from an integration of the baseline GEOS-5 AGCM using satellite data as observations. Generally McRAS-AC simulations have smaller biases in cloud fields and cloud radiative effects over most of the regions of the Earth than the baseline GEOS-5 AGCM. Two systematic biases are identified in the McRAS-AC runs: one under-prediction of cloud particles around 40° S–60° S, and one over-prediction of cloud water path during Northern Hemisphere summer over the Gulf Stream and North Pacific. Sensitivity analyses show that these biases potentially originate from biases in the aerosol input. The first bias is largely eliminated in a sensitivity test using 50% smaller sea-salt aerosol particles, while the second bias is much reduced when interactive aerosol chemistry was turned on. The main drawback of McRAS-AC is dearth of low-level marine stratus clouds, probably due to lack of boundary-layer clouds that is an outcome of explicit dry-convection not yet implemented into the cloud model. Nevertheless, McRAS-AC simulates realistic clouds and their optical properties that can further improve with better aerosol-input. Thereby, McRAS-AC has the potential to be a valuable tool for climate modeling research because of its superior simulation capabilities that physically couple aerosols, cloud microphysics, cloud macrophysics, and cloud-radiation interaction for all clouds.

Description: Modelling mid-Pliocene climate with COSMOS Geoscientific Model Development Discussions, 5, 917-966, 2012 Author(s): C. Stepanek and G. Lohmann In this manuscript we describe the experimental procedure employed at the Alfred Wegener Institute in Germany in the preparation of the simulations for the Pliocene Model Intercomparison Project (PlioMIP). We present a description of the utilized community earth system models (COSMOS) and document the procedures which we applied to transfer the Pliocene Research, Interpretation and Synoptic Mapping Project (PRISM) mid-Pliocene reconstruction into model forcing fields. The model setup and spin-up procedure are described for both the paleo and preindustrial (PI) time-slices of PlioMIP experiments 1 and 2, and general results that depict the performance of our model setup for mid-Pliocene conditions are presented. The mid-Pliocene as simulated with our COSMOS-setup and PRISM boundary conditions is both warmer and wetter than the PI. The globally averaged annual mean surface air temperature in the mid-Pliocene standalone atmosphere (fully coupled atmosphere-ocean) simulation is 17.35 °C (17.82 °C), which implies a warming of 2.23 °C (3.40 °C) relative to the respective PI control simulation.

Description: TopoSUB: a tool for efficient large area numerical modelling in complex topography at sub-grid scales Geoscientific Model Development Discussions, 5, 1041-1076, 2012 Author(s): J. Fiddes and S. Gruber Mountain regions are highly sensitive to global climate change. However, large scale assessments of mountain environments remain problematic due to the high resolution required of model grids to capture strong lateral variability. To alleviate this, tools are required to bridge the scale gap between gridded climate datasets (climate models and re-analyses) and unresolved (by coarse grids) sub-grid mountain topography. We address this problem with a sub-grid method. It relies on sampling the most important aspects of land surface heterogeneity through a lumped scheme, allowing for the application of numerical land surface models (LSM) over large areas in mountain regions. This is achieved by including the effect of mountain topography on these processes at the sub-grid scale using a multidimensional informed sampling procedure together with a 1-D lumped model that can be driven by gridded climate datasets. This paper provides a description of this sub-grid scheme, TopoSUB, as well as assessing its performance against a distributed model. We demonstrate the ability of TopoSUB to approximate results simulated by a distributed numerical LSM at around 10 4 less computations. These significant gains in computing resources allow for: (1) numerical modelling of processes at fine grid resolutions over large areas; (2) extremely efficient statistical descriptions of sub-grid behaviour; (3) a "sub-grid aware" aggregation of simulated variables to course grids; and (4) freeing of resources for treatment of uncertainty in the modelling process.

Description: Impact of a time-dependent background error covariance matrix on air quality analysis Geoscientific Model Development Discussions, 5, 873-916, 2012 Author(s): E. Jaumouillé, S. Massart, A. Piacentini, D. Cariolle, and V.-H. Peuch In this article we study the influence of different characteristics of our assimilation system on the surface ozone analyses over Europe. Emphasis is placed on the evaluation of the background error covariance matrix (BECM). Data assimilation systems require a BECM in order to obtain an optimal representation of the physical state. A posteriori diagnostics are an efficient way to check the consistency of the used BECM. In this study we derived a diagnostic to estimate the BECM. On the other hand an increasingly used approach to obtain such a covariance matrix is to estimate it from an ensemble of perturbed assimilation experiments. We applied this method, combined with variational assimilation, while analysing the surface ozone distribution over Europe. We first show that the resulting covariance matrix is strongly time (hourly and seasonally) and space dependent. We then built several configurations of the background error covariance matrix with none, one or two of its components derived from the ensemble estimation. We used each of these configurations to produce surface ozone analyses. All the analyses are compared between themselves and compared to assimilated data or data from independent validation stations. The configurations are very well correlated with the validation stations, but with varying regional and seasonal characteristics. The largest correlation is obtained with the experiments using time and space dependent correlation of the background errors. Results show that our assimilation process is efficient in bringing the model assimilations closer to the observations than the direct simulation, but we cannot conclude which BECM configuration is the best. The impact of the background error covariances configuration on four-days forecasts is also studied. Although mostly positive, the impact depends on the season and lasts longer during the winter season.

Description: Numerical uncertainty at mesoscale in a Lagrangian model in complex terrain Geoscientific Model Development Discussions, 5, 967-991, 2012 Author(s): J. Brioude, W. M. Angevine, S. A. McKeen, and E.-Y. Hsie Recently, it has been shown that mass conservation in Lagrangian models is improved by using time-average winds out of Eulerian models. In this study, we evaluate the mass conservation and trajectory uncertainties in complex terrain at mesoscale using the FLEXPART Lagrangian particle dispersion model coupled with the WRF mesoscale model. The specific form of vertical wind used is found to have a large effect. Time average wind with time average sigma dot (σ · ), instantaneous wind with geometric cartesian vertical wind ( w ) and instantaneous wind with σ · are used to simulate mixing ratios of a passive tracer in forward and backward runs using different time interval outputs and horizontal resolutions in California. Mass conservation in the FLEXPART model was not an issue when using time-average wind or instantaneous wind with σ · . However, mass was poorly conserved using instantaneous wind with w , with a typical variation of 25% within 24 h. Uncertainties in surface residence time (a backtrajectory product commonly used in source receptor studies or inverse modeling) calculated for each backtrajectory run were also analyzed. The smallest uncertainties were systematically found when using time-average wind. Uncertainties using instantaneous wind with σ · were slightly larger, as long as the time interval of output was sufficiently small. The largest uncertainties were found when using instantaneous wind with w . Those uncertainties were found to be linearly correlated with the local average gradient of orography. Differences in uncertainty were much smaller when trajectories were calculated over flat terrain. For a typical run at mesoscale in complex terrain, 4 km horizontal resolution and 1 h time interval output, the average uncertainty and bias in surface residence time is, respectively 8.4% and −2.5% using time-average wind, and 13% and −3.7% using instantaneous wind with σ · in complex terrain. The corresponding values for instantaneous wind with cartesian w were 24% and −11%. While the use of time-average wind systematically improves uncertainty in FLEXPART, the improvements are small, and therfore a systematic use of time-average wind in Lagrangian models is not necessarily required. Use of cartesian vertical wind in complex terrain, however, should be avoided.

Description: Models of soil organic matter decomposition: the SOILR package, version 1.0 Geoscientific Model Development Discussions, 5, 993-1039, 2012 Author(s): C. A. Sierra, M. Müller, and S. E. Trumbore Organic matter decomposition is a very important process within the Earth System because it controls the rates of mineralization of carbon and other biogeochemical elements, determining their flux to the atmosphere and the hydrosphere. SOILR is a modeling framework that contains a library of functions and tools for modeling soil organic matter decomposition under the R environment for computing. It implements a variety of model structures and tools to represent carbon storage and release from soil organic matter. In SOILR organic matter decomposition is represented as a linear system of ordinary differential equations that generalizes the structure of most compartment-based decomposition models. A variety of functions is also available to represent environmental effects on decomposition rates. This document presents the conceptual basis for the functions implemented in the package. It is complementary to the help pages released with the software.

Description: A semi-analytical solution to accelerate spin-up of a coupled carbon and nitrogen land model to steady state Geoscientific Model Development Discussions, 5, 803-836, 2012 Author(s): J. Xia, Y. Luo, Y.-P. Wang, E. Weng, and O. Hararuk The spin-up of land models to steady state of coupled carbon-nitrogen processes is computationally so costly that it becomes a~bottleneck issue for global analysis. In this study, we introduced a semi-analytical solution (SAS) for the spin-up issue. SAS is fundamentally based on the analytic solution to a set of equations that describe carbon transfers within ecosystems over time. SAS is implemented by three steps: (1) having an initial spin-up with prior pool-size values until net primary productivity (NPP) reaches steady state, (2) calculating quasi steady-state pool sizes by letting fluxes of the equations equal zero, and (3) having a final spin-up to meet the criterion of steady state. Step 2 is enabled by averaged time-varying variables over one period of repeated driving forcings. SAS was applied to both site-level and global scale spin-up of the Australian Community Atmosphere Biosphere Land Exchange (CABLE) model. For the carbon-cycle-only simulations, SAS saved 95.7% and 92.4% of computational time for site-level and global spin-up, respectively, in comparison with the traditional method. For the carbon-nitrogen-coupled simulations, SAS reduced computational cost by 84.5% and 86.6% for site-level and global spin-up, respectively. The estimated steady-state pool sizes represent the ecosystem carbon storage capacity, which was 12.1 kg C m −2 with the coupled carbon-nitrogen global model, 14.6% lower than that with the carbon-only model. The nitrogen down-regulation in modeled carbon storage is partly due to the 4.6% decrease in carbon influx (i.e., net primary productivity) and partly due to the 10.5% reduction in residence times. This steady-state analysis accelerated by the SAS method can facilitate comparative studies of structural differences in determining the ecosystem carbon storage capacity among biogeochemical models. Overall, the computational efficiency of SAS potentially permits many global analyses that are impossible with the traditional spin-up methods, such as ensemble analysis of land models against parameter variations.

Description: A community diagnostic tool for Chemistry Climate Model Validation Geoscientific Model Development Discussions, 5, 1229-1261, 2012 Author(s): A. Gettelman, V. Eyring, C. Fischer, H. Shiona, I. Cionni, M. Neish, O. Morgenstern, S. W. Wood, and Z. Li This technical note presents an overview of the Chemistry-Climate Model Validation Diagnostic (CCMVal-Diag) tool for model evaluation. The CCMVal-Diag tool is a flexible and extensible open source package that facilitates the complex evaluation of global models. Models can be compared to other models, ensemble members (simulations with the same model), and/or many types of observations. The tool can also compute quantitative performance metrics. The initial construction and application is to coupled Chemistry-Climate Models (CCMs) participating in CCMVal, but the evaluation of climate models that submitted output to the Coupled Model Intercomparison Project (CMIP) is also possible. The package has been used to assist with analysis of simulations for the 2010 WMO/UNEP Scientific Ozone Assessment and the SPARC Report on the Evaluation of CCMs. The CCMVal-Diag tool is described and examples of how it functions are presented, along with links to detailed descriptions, instructions and source code. The CCMVal-Diag tool is supporting model development as well as quantifying model improvements, both for different versions of individual models and for different generations of community-wide collections of models used in international assessments. The code allows further extensions by different users for different applications and types, e.g. to other components of the Earth System. User modifications are encouraged and easy to perform with a minimum of coding.

Description: Description of a hybrid ice sheet-shelf model, and application to Antarctica Geoscientific Model Development Discussions, 5, 1077-1134, 2012 Author(s): D. Pollard and R. M. DeConto The formulation of a 3-D ice sheet-shelf model is described. The model is designed for long-term continental-scale applications, and has been used mostly in paleoclimatic studies. It uses a hybrid combination of the scaled Shallow Ice and Shallow Shelf Approximations for ice flow. Floating ice shelves and grounding-line migration are included, with parameterized ice fluxes at grounding lines that allows relatively coarse resolutions to be used. All significant components and parameterizations of the model are described in some detail. Basic results for modern Antarctica are compared with observations, and simulations over the last 5 million yr are shown to be similar to previously published results using an earlier model version. The sensitivity of ice retreat during the last deglaciation to basal sliding coefficients is discussed.

Description: A new marine ecosystem model for the University of Victoria Earth system climate model Geoscientific Model Development Discussions, 5, 1135-1201, 2012 Author(s): D. P. Keller, A. Oschlies, and M. Eby Earth system climate models (ESCMs) are valuable tools that can be used to gain a better understanding of the climate system, global biogeochemical cycles, and how anthropogenically-driven changes may affect them. Here we describe improvements made to the marine biogeochemical ecosystem component of the University of Victoria's ESCM (version 2.9). Major changes include corrections to the code and equations describing phytoplankton light limitation and zooplankton grazing, the implementation of a more realistic zooplankton growth and grazing model, and the implementation of an iron limitation scheme to constrain phytoplankton growth. The new model is evaluated after a 10 000-yr spin-up and compared to both the previous version and observations. For the majority of biogeochemical tracers and ecosystem processes the new model shows significant improvements when compared to the previous version and evaluated against observations. Many of the improvements are due to better simulation of seasonal changes in higher latitude ecosystems and the effect that this has on ocean biogeochemistry. This improved model is intended to provide a basic new ESCM model component, which can be used as is or expanded upon (i.e., the addition of new tracers), for climate change and biogeochemical cycling research.

Description: Development of a parameterization of black carbon aging for use in general circulation models Geoscientific Model Development Discussions, 5, 1263-1293, 2012 Author(s): N. Oshima and M. Koike A parameterization of black carbon (BC) aging in the atmosphere is developed for use in general circulation models (GCMs) that separately treats size distributions of hydrophobic BC and hydrophilic BC using lognormal modes. The rate of BC aging is expressed as the conversion rate from hydrophobic BC to hydrophilic BC modes (i.e., inverse of the e-folding time of the conversion, 1/ τ BC ). In this study, the conversion rates are estimated using results of detailed calculations by a size and mixing state resolved aerosol box model with numerous initial conditions. We introduce a new concept, the hydrophobic-BC-mass-normalized coating rate ( V BC ), defined as the rate of increase of the mass concentration of condensed materials on hydrophobic BC normalized by the hydrophobic BC mass concentration. Although the conversion rate largely varies depending on the atmospheric conditions and the concentrations of chemical species, we find that the variations of the conversion rate are generally expressed well by a unique function of V BC for given lognormal size distributions of hydrophobic BC. The parameterized conversion rate is expressed as a function of V BC , which enables the representation of diurnal and seasonal variations of the BC aging rate and its spatial differences in polluted and clean air, while other widely used constant conversion rates cannot. Application of our newly developed parameterization to GCMs will provide more reliable estimates of the spatial distribution of BC and its radiative effects at regional and global scales.

Description: Pre-industrial and mid-Pliocene simulations with NorESM-L – AGCM simulations Geoscientific Model Development Discussions, 5, 1203-1227, 2012 Author(s): Z. Zhang and Q. Yan In the Pliocene Model Intercomparison Project (PlioMIP), two sets of experiments are suggested. One includes a reference and a mid-Pliocene experiment run with atmosphere general circulation models (AGCM experiments, referred to as Experiments I), the other includes a pre-industrial and a mid-Pliocene experiment run with coupled ocean-atmosphere general circulation models (AOGCM experiments, referred to as Experiment II). In this paper, we describe the AGCM experiments with the atmosphere model in the low resolution version of the Norwegian Earth System Model (NorESM-L), and also assess the potential uncertainties in analyzing mid-Pliocene climate anomalies, due to choosing SST fields for the reference experiment. We carry out a mid-Pliocene experiment, a control experiment forced by the modern SST fields, and a pre-industrial experiment forced by the monthly SST fields from HadISST averaged between 1879 and 1900. Our experiments illustrate that the simulated mid-Pliocene global annual mean SAT is 17.1 °C. It is 2.5 °C warmer than the control experiment, but 2.7 °C warmer than the pre-industrial experiment. We find that the uncertainties in analyses of mid-Pliocene climate anomalies are small on a global scale, but still large on a regional scale. On the regional scale, these uncertainties should be noticed and assessed in future PlioMIP studies.

Description: Implementation of splitting methods for air pollution modeling Geoscientific Model Development Discussions, 4, 2937-2972, 2011 Author(s): M. Schlegel, O. Knoth, M. Arnold, and R. Wolke Explicit time integration methods are characterized by a small numerical effort per time step. In the application to multiscale problems in atmospheric modeling, this benefit is often more than compensated by stability problems and step size restrictions resulting from stiff chemical reaction terms and from a locally varying Courant-Friedrichs-Lewy (CFL) condition for the advection terms. Splitting methods may be applied to efficiently combine implicit and explicit methods (IMEX splitting). Complementarily multirate time integration schemes allow for a local adaptation of the time step size to the grid size. In combination these approaches lead to schemes which are efficient in terms of evaluations of the right hand side. Special challenges arise when these methods are to be implemented. For an efficient implementation it is crucial to locate and exploit redundancies. Furthermore the more complex program flow may lead to computational overhead which in the worst case more than compensates the theoretical gain in efficiency. We present a general splitting approach which allows both for IMEX splittings and for local time step adaptation. The main focus is on an efficient implementation of this approach for parallel computation on computer clusters.

Description: Simulations over South Asia using the Weather Research and Forecasting model with Chemistry (WRF-Chem): set-up and meteorological evaluation Geoscientific Model Development Discussions, 4, 3067-3125, 2011 Author(s): R. Kumar, M. Naja, G. G. Pfister, M. C. Barth, and G. P. Brasseur The configuration and evaluation of the meteorology is presented for simulations over the South Asian region using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). Temperature, water vapor, dew point temperature, zonal and meridional wind components, precipitation and tropopause pressure are evaluated against radiosonde and satellite-borne (AIRS and TRMM) observations along with NCEP/NCAR reanalysis fields for the year 2008. Chemical fields, with focus on tropospheric ozone, are evaluated in a separate paper. The spatial and temporal variability in meteorological variables is well simulated by the model with temperature, dew point temperature and precipitation showing higher values during summer/monsoon and lower during winter. The index of agreement for all the parameters is estimated to be greater than 0.6 indicating that WRF-Chem is capable of simulating the variations around the observed mean. The mean bias (MB) and root mean square error (RMSE) in modeled temperature, water vapor and wind components show an increasing tendency with altitude. MB and RMSE values are within ±2 K and 1–4 K for temperature, 30% and 20–65% for water vapor and 1.6 m s −1 and 5.1 m s −1 for wind components. The spatio-temporal variability of precipitation is also reproduced reasonably well by the model but the model overestimates precipitation in summer and underestimates precipitation during other seasons. Such a behavior of modeled precipitation is in agreement with previous studies on South Asian monsoon. The comparison with radiosonde observations indicates a relatively better model performance for inland sites as compared to coastal and island sites. The MB and RMSE in tropopause pressure are estimated to be less than 25 hPa. Sensitivity simulations show that biases in meteorological simulations can introduce errors of ±(10–25%) in simulations of tropospheric ozone, CO and NO x . Nevertheless, a comparison of statistical metrics with benchmarks indicates that the model simulated meteorology is of sufficient quality for use in chemistry simulations.

Description: Wavelet-based spatial comparison technique for analysing and evaluating two-dimensional geophysical model fields Geoscientific Model Development Discussions, 4, 3161-3183, 2011 Author(s): S. Saux Picart, M. Butenschön, and J. D. Shutler Complex numerical models of the Earth's environment, based around 3-D or 4-D time and space domains are routinely used for applications including climate predictions, weather forecasts, fishery management and environmental impact assessments. Quantitatively assessing the ability of these models to accurately reproduce geographical patterns at a range of spatial and temporal scales has always been a difficult problem to address. However, this is crucial if we are to rely on these models for decision making. Satellite data are potentially the only observational dataset able to cover the large spatial domains analysed by many types of geophysical models. Consequently optical wavelength satellite data is beginning to be used to evaluate model hindcast fields of terrestrial and marine environments. However, these satellite data invariably contain regions of occluded or missing data due to clouds, further complicating or impacting on any comparisons with the model. A methodology has recently been developed to evaluate precipitation forecasts using radar observations. It allows model skill to be evaluated at a range of spatial scales and rain intensities. Here we extend the original method to allow its generic application to a range of continuous and discontinuous geophysical data fields, and therefore allowing its use with optical satellite data. This is achieved through two major improvements to the original method: (i) all thresholds are determined based on the statistical distribution of the input data, so no a priori knowledge about the model fields being analysed is required and (ii) occluded data can be analysed without impacting on the metric results. The method can be used to assess a model's ability to simulate geographical patterns over a range of spatial scales. We illustrate how the method provides a compact and concise way of visualising the degree of agreement between spatial features in two datasets. The application of the new method, its handling of bias and occlusion and the advantages of the novel method are demonstrated through analyzing model fields from a marine ecosystem model.

Description: Mass-flux subgrid-scale parameterization in analogy with multi-component flows: a formulation towards scale independence Geoscientific Model Development Discussions, 4, 3127-3160, 2011 Author(s): J.-I. Yano The mass-flux parameterization formulation is generalized by taking an analogy of the large-scale atmospheric flow with multi-component flows. This generalization permits to include any subgrid-scale variability into the mass-flux parameterization. Those include stratiform clouds as well as cold pools in the boundary layer. An important finding under the present formulation is that the subgrid-scale quantities are advected by the velocities characteristic of given subgrid-scale components (subcomponent flows), rather than by the large-scale flows as simply defined by grid-box average. This formulation, as a result, ensures the lateral interaction of subgrid-scale variability crossing the grid boxes, which are missing in the current parameterizations, and leading to a reduction of the grid-size dependence in its performance. It is shown that the subcomponent flows are driven by subcomponent pressure gradients. The formulation, as a result, furthermore includes a self-contained description of subgrid-scale momentum transport. The formulation is applicable to a situation in which the scale separation is still satisfied, but fractional areas occupied by individual subgrid-scale components are no longer small. A complete formulation is presented and various implementation issues are discussed. The present formulation is also expected to alleviate problems arising from increasing resolutions of operational forecast models without invoking more extensive overhaul of parameterizations. The main purpose of the present paper is to appeal the importance of this new possibility suggested herein to the numerical weather forecast community with implications for the other parameteizations (cloud fraction, mesoscale organization) as well as resolution-dependence of parameterizations.

Description: Influence of parallel computational uncertainty on simulations of the Coupled General Climate Model Geoscientific Model Development Discussions, 4, 3295-3312, 2011 Author(s): Z. Song, F. Qiao, X. Lei, and C. Wang This paper investigates the impact of the parallel computational uncertainty on climate simulations using the Community Climate System Model Version 3 (CCSM3). A series of sensitivity experiments have been conducted and the analyses are focused on the Global and Nino3.4 sea surface temperatures. It is shown that the amplitude of the deviation induced by the parallel computational uncertainty is the same order as that of the climate system change. However, the ensemble mean method can reduce the influence and the ensemble member number of 15 is enough to ignore simulated errors. For climatology, the influence can be ignored when the climatological mean is calculated by using more than 30-yr simulations. It is also found that the parallel computational uncertainty has no effect on the simulated periods of climate variability such as ENSO. Finally, it is suggested that the influence of the parallel computational uncertainty on Coupled General Climate Models (CGCMs) can be a quality standard or a metric for developing CGCMs.

Description: Importance of the surface size distribution of erodible material: an improvement of the Dust Entrainment And Deposition DEAD Geoscientific Model Development Discussions, 4, 2893-2936, 2011 Author(s): M. Mokhtari, L. Gomes, P. Tulet, and T. Rezoug This paper is based on dust aerosol cycle modelling in the atmospheric model ALADIN (Aire Limitée Adaptation dynamique Développement InterNational) coupled with the EXternalised SURFace scheme SURFEX. Its main goal is to create a global mineral dust emission parameterization compatible with the global database of land surface parameters ECOCLIMAP and the Food and Agriculture Organization (FAO) soil type database in SURFEX, based on both Shao (1993) and Marticorena and Bergametti (1995) parameterizations. An arrangement on the Dust Entrainment And Deposition scheme (DEAD) is proposed in this paper by introducing the geographic variation of surface size distribution, the Marticorena and Bergametti (1995) formulation of horizontal saltation flux and the Shao (2001) formulation of sandblasting efficiency α. To show the importance of the modifications introduced in the code DEAD, both sensitivity and comparative studies are realized in 0 dimensions (0-D) and then in 3 dimensions (3-D) between the old DEAD and that developed in this paper. The results in the 0-D simulations indicate that the developed DEAD scheme represents the dust source emission better, particularly in the Bodélé depression and provides a reasonable friction threshold velocity. In 3-D simulations, small differences are found between the DEAD and developed DEAD schemes for the simulated Aerosol Optical Depth (AOD) compared with the photometer AErosol RObotic NETwork (AERONET) measurements available in the African Monsoon Multidisciplinary Analyses (AMMA) databases. But, for the surface concentration a remarkable improvement is noted for the developed DEAD scheme.

Description: Detection, tracking and event localization of interesting features in 4-D atmospheric data Geoscientific Model Development Discussions, 4, 3013-3045, 2011 Author(s): S. Limbach, E. Schömer, and H. Wernli We introduce a novel algorithm for the efficient detection and tracking of interesting features in spatial-temporal atmospheric data, as well as for the precise localization of the occurring genesis, lysis, merging and splitting events. The algorithm is based on the well-known region growing segmentation method. We extended the basic idea towards the analysis of the complete 4-D dataset, identifying segments representing the spatial features and their development over time. Each segment consists of one set of distinct 3-D features per time step. The algorithm keeps track of the successors of each 3-D feature, constructing the so-called event graph of each segment. The precise localization of the splitting events is based on a search for all grid points inside the initial 3-D feature which have a similar distance to all successive 3-D features of the next time step. The merging event is localized analogously considering inverted direction of time. We tested the implementation on a four-dimensional field of wind speed data from European Centre for Medium-Range Weather Forecasts (ECMWF) analyses and computed a climatology of upper-tropospheric jet streams and their events. We compare our results with a previous climatology, investigate the statistical distribution of the merging and splitting events, and illustrate the meteorological significance of the jet splitting events with a case study. A brief outlook is given on additional potential applications of the 4-D data segmentation technique.

Description: The FAMOUS climate model (versions XFXWB and XFHCC): description update to version XDBUA Geoscientific Model Development Discussions, 4, 3047-3065, 2011 Author(s): R. S. Smith FAMOUS is an ocean-atmosphere general circulation model of low resolution, based on version 4.5 of the UK MetOffice Unified Model. Here we update the model description to account for changes in the model as it is used in the CMIP5 EMIC model intercomparison project (EMICmip) and a number of other studies. Most of these changes correct errors found in the code. The EMICmip version of the model (XFXWB) has a better-conserved water budget and additional cooling in some high latitude areas, but otherwise has a similar climatology to previous versions of FAMOUS. A variant of XFXWB is also described, with changes to the dynamics at the top of the model which improve the model climatology (XFHCC).

Description: Identifying the causes of differences in ozone production from the CB05 and CBMIV chemical mechanisms Geoscientific Model Development Discussions, 4, 2687-2721, 2011 Author(s): R. D. Saylor and A. F. Stein An investigation was conducted to identify the mechanistic differences between two versions of the carbon bond gas-phase chemical mechanism (CB05 and CBMIV) which consistently lead to larger ground-level ozone concentrations being produced in the CB05 version of the National Air Quality Forecasting Capability (NAQFC) modeling system even though the two parallel forecast systems utilize the same meteorology and base emissions and similar initial and boundary conditions. Box models of each of the mechanisms as they are implemented in the NAQFC were created and a set of 12 sensitivity simulations was designed. The sensitivity simulations independently probed the conceptual mechanistic differences between CB05 and CBMIV and were exercised over a 45-scenario simulation suite designed to emulate the wide range of chemical regimes encountered in a continental-scale atmospheric chemistry model. Results of the sensitivity simulations indicate that two sets of reactions that were included in the CB05 mechanism, but which were absent from the CBMIV mechanism, are the primary causes of the greater ozone production in the CB05 version of the NAQFC. One set of reactions recycles the higher organic peroxide species of CB05 (ROOH), resulting in additional photochemically reactive products that act to produce additional ozone in some chemical regimes. The other set of reactions recycles reactive nitrogen from less reactive forms back to NO 2 , increasing the effective NO x concentration of the system. In particular, the organic nitrate species (NTR), which was a terminal product for reactive nitrogen in the CBMIV mechanism, acts as a reservoir species in CB05 to redistribute NO x from major source areas to potentially NO x -sensitive areas where additional ozone may be produced in areas remote from direct NO x sources.

Description: Development and evaluation of a building energy model integrated in the TEB scheme Geoscientific Model Development Discussions, 4, 2973-3011, 2011 Author(s): B. Bueno, G. Pigeon, L. K. Norford, and K. Zibouche The use of air-conditioning systems is expected to increase as a consequence of global-scale and urban-scale climate warming. In order to represent future scenarios of urban climate and building energy consumption, the Town Energy Budget (TEB) scheme must be improved. This paper presents a new building energy model (BEM) that has been integrated in the TEB scheme. BEM-TEB makes it possible to represent the energy effects of buildings and building systems on the urban climate and to estimate the building energy consumption at city scale (~10 km) with a resolution of a neighbourhood (~100 m). The physical and geometric definition of buildings in BEM has been intentionally kept as simple as possible, while maintaining the required features of a comprehensive building energy model. The model considers a single thermal zone, where the thermal inertia of building materials associated with multiple levels is represented by a generic thermal mass. The model accounts for heat gains due to transmitted solar radiation, heat conduction through the enclosure, infiltration, ventilation, and internal heat gains. As a difference with respect to other building parameterizations used in urban climate, BEM includes specific models for real air-conditioning systems. It accounts for the dependence of the system capacity and efficiency on indoor and outdoor air temperatures and solves the dehumidification of the air passing through the system. Furthermore, BEM includes specific models for passive systems, such as window shadowing devices and natural ventilation. BEM has satisfactorily passed different evaluation processes, including testing its modelling assumptions, verifying that the chosen equations are solved correctly, and validating the model with field data.

Description: A contrail cirrus prediction model Geoscientific Model Development Discussions, 4, 3185-3293, 2011 Author(s): U. Schumann A new model to simulate and predict the properties of a large ensemble of contrails as a function of given air traffic and meteorology is described. The model is designed for approximate prediction of contrail cirrus cover and analysis of contrail climate impact, e.g. within aviation system optimization processes. The model simulates the full contrail life-cycle. Contrail segments form between waypoints of individual aircraft tracks in sufficiently cold and humid air masses. The initial contrail properties depend on the aircraft. The advection and evolution of the contrails is followed with a Lagrangian Gaussian plume model. Mixing and bulk cloud processes are treated quasi analytically or with an effective numerical scheme. Contrails disappear when the bulk ice content is sublimating or precipitating. The model has been implemented in a "Contrail Cirrus Prediction Tool" (CoCiP). This paper describes the model assumptions, the equations for individual contrails, and the analysis-method for contrail-cirrus cover derived from the optical depth of the ensemble of contrails and background cirrus. The model has been applied for a case study and compared to the results of other models and in-situ contrail measurements. The simple model reproduces a considerable part of observed contrail properties. Mid-aged contrails provide the largest contributions to the product of optical depth and contrail width, important for climate impact.

Description: Seasonal leaf dynamics for tropical evergreen forests in a process based global ecosystem model Geoscientific Model Development Discussions, 5, 639-681, 2012 Author(s): M. De Weirdt, H. Verbeeck, F. Maignan, P. Peylin, B. Poulter, D. Bonal, P. Ciais, and K. Steppe The influence of seasonal phenology in tropical humid forests on canopy photosynthesis remains poorly understood and its representation in global vegetation models highly simplified, typically with no seasonal variability of canopy leaf area properties taken into account. However, recent flux tower and remote sensing studies suggest that seasonal phenology in tropical rainforests exerts a large influence over carbon and water fluxes, with feedbacks that can significantly influence climate dynamics. A more realistic description of the underlying mechanisms that drive seasonal tropical forest photosynthesis and phenology could improve the correspondence of global vegetation model outputs with the wet-dry season biogeochemical patterns measured at flux tower sites. Here, we introduce a leaf Net Primary Production (NPP) based canopy dynamics scheme for evergreen tropical forests in the global terrestrial ecosystem model ORCHIDEE and validated the new scheme against in-situ carbon flux measurements. Modelled Gross Primary Productivity (GPP) patterns are analyzed in details for a flux tower site in French Guiana, in a forest where the dry season is short and where the vegetation is considered to have developed adaptive mechanisms against drought stress. By including leaf litterfall seasonality and a coincident light driven leaf flush and seasonal change in photosynthetic capacity in ORCHIDEE, modelled carbon and water fluxes more accurately represent the observations. The fit to GPP flux data was substantially improved and the results confirmed that by modifying canopy dynamics to benefit from increased light conditions, a better representation of the seasonal carbon flux patterns was made.

Description: A dynamic continental runoff routing model applied to the last Northern Hemisphere deglaciation Geoscientific Model Development Discussions, 4, 2723-2750, 2011 Author(s): H. Goelzer, I. Janssens, J. Nemec, and P. Huybrechts We describe and evaluate a dynamical continental runoff routing model for the Northern Hemisphere that calculates the runoff pathways in response to topographic modifications due to changes in ice thickness and isostatic adjustment. The algorithm is based on the steepest gradient method and takes as simplifying assumption that depressions are filled at all times and water drains through the lowest outlet points. It also considers changes in water storage and lake drainage that become important in the presence of large ice dammed proglacial lakes. Although applicable to other scenarios as well, the model was conceived to study the routing of freshwater fluxes during the last Northern Hemisphere deglaciation. For that specific application we simulated the Northern Hemisphere ice sheets with an existing 3-D thermomechanical ice sheet model, which calculates changes in topography due to changes in ice cover and isostatic adjustment, as well as the evolution of freshwater fluxes resulting from surface ablation, iceberg calving and basal melt. The continental runoff model takes this input, calculates the drainage pathways and routes the freshwater fluxes to the surface grid points of an existing ocean model. This results in a chronology of temporally and spatially varying freshwater fluxes from the Last Glacial Maximum to the present day. We analyse the dependence of the runoff routing to grid resolution and parameters of the isostatic adjustment module of the ice sheet model.

Description: Description of EQSAM4: gas-liquid-solid partitioning model for global simulations Geoscientific Model Development Discussions, 4, 2791-2847, 2011 Author(s): S. Metzger, B. Steil, L. Xu, J. E. Penner, and J. Lelieveld We introduce version 4 of the EQuilibrium Simplified Aerosol Model (EQSAM4), which is part of our aerosol chemistry-microphysics module (GMXe) and chemistry-climate model (EMAC). We focus on the relative humidity of deliquescence (RHD) based water uptake of atmospheric aerosols, as this is important for atmospheric chemistry and climate modeling, e.g. to calculate the aerosol optical depth (AOD). Since the main EQSAM4 applications will involve large-scale, long-term and high-resolution atmospheric chemistry-climate modeling with EMAC, computational efficiency is an important requirement. EQSAM4 parameterizes the composition and water uptake of multicomponent atmospheric aerosols by considering the gas-liquid-solid partitioning of single and mixed solutes. EQSAM4 builds on analytical, and hence CPU efficient, aerosol hygroscopic growth parameterizations to compute the aerosol liquid water content (AWC). The parameterizations are described in the companion paper (Metzger et al., 2011) and only require a compound specific coefficient ν i to derive the single solute molality and the AWC for the whole range of water activity ( a w ). ν i is pre-calculated and applied during runtime by using internal look-up tables. Here, the EQSAM4 equilibrium model is described and compared to the more explicit thermodynamic model ISORROPIA II. Both models are imbedded in EMAC/GMXe. Box model inter-comparisons, including the reference model E-AIM, and global simulations with EMAC show that gas-particle partitioning, including semi-volatiles and water, is in good agreement. A more comprehensive box model inter-comparison of EQSAM4 with EQUISOLV II is subject of the revised publication of Xu et al. (2009), i.e. Xu et al. (2011).

Description: GEWEX Cloud System Study (GCSS) cirrus cloud working group: modelling case development based on 9 March 2000 ARM SGP observations Geoscientific Model Development Discussions, 4, 2751-2790, 2011 Author(s): H. Yang, S. Dobbie, G. G. Mace, A. Ross, and M. Quante The GCSS working group on cirrus focuses on inter-comparison of model simulations for models ranging from very detailed microphysical and dynamical models through to general circulation models (GCMs). In the previous GCSS inter-comparison, it was a surprise to the modeling community how much of a range there was in ice water path predictions by different cirrus models for such idealized cases. There was some grouping according to the complexity of models; however, there were no observations with which to distinguish between model performance. The aim of the current GCSS cirrus inter-comparison is to base the study on a rigorously observed case study. In this way, the case may be used to identify which models in the inter-comparison are performing well and highlight areas for model development as well as provide a base case for future models to compare against when being developed or when testing new developments within existing models. In this paper, we present the case development for the current GCSS working group study on cirrus cloud. This paper summarizes how the case was developed and based on the 9 March 2000 Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) intensive observation period (IOP). To our knowledge, this case offers the most detailed case study for cirrus comparison available, with extensive effort to derive the most appropriate large scale forcing as possible which is such a significant determinant of clouds. We anticipate this will offer significant improvement over past comparisons which have mostly been loosely based on observations. Notably this study makes use of retrievals of observations of ice water content, ice number concentration, and fall velocity, thus offering several constraints to evaluate model performance. The case study is developed utilizing various observations including ARM SGP remote sensing including the Millimeter cloud radar (MMCR), radiometers, radiosondes, aircraft observations, satellite observations, objective analysis and complemented with results from the Rapid Update Cycle (RUC) model output and bespoke gravity wave simulations using the 3-dimensional velocities over mountains (3DVOM) model. An initial modelling assessment of the case has been shown using the UK Met Office Large Eddy Simulation Model (LEM) which supports the use of this case for the full inter-comparison study.

Description: 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 Geoscientific Model Development Discussions, 4, 2469-2544, 2011 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 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.

Description: CELLS v1.0: updated and parallelized version of an electrical scheme to simulate multiple electrified clouds and flashes over large domains Geoscientific Model Development Discussions, 4, 2849-2892, 2011 Author(s): C. Barthe, M. Chong, J.-P. Pinty, C. Bovalo, and J. Escobar 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. The scheme computes the bulk electric charge attached to each cloud particle. 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. 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 meteorological case on large domains.

Description: The Joint UK Land Environment Simulator (JULES), Model description – Part 2: Carbon fluxes and vegetation Geoscientific Model Development Discussions, 4, 641-688, 2011 Author(s): D. B. Clark, L. M. Mercado, S. Sitch, C. D. Jones, N. Gedney, M. J. Best, M. Pryor, G. G. Rooney, R. L. H. Essery, E. Blyth, O. Boucher, R. J. Harding, and P. M. Cox The Joint UK Land Environment Simulator (JULES) is a process-based model that simulates the fluxes of carbon, water, energy and momentum between the land surface and the atmosphere. Past studies with JULES have demonstrated the important role of the land surface in the Earth System. Different versions of JULES have been employed to quantify the effects on the land carbon sink of separately changing atmospheric aerosols and tropospheric ozone, and the response of methane emissions from wetlands to climate change. There was a need to consolidate these and other advances into a single model code so as to be able to study interactions in a consistent manner. This paper describes the consolidation of these advances into the modelling of carbon fluxes and stores, in the vegetation and soil, in version 2.2 of JULES. Features include a multi-layer canopy scheme for light interception, including a sunfleck penetration scheme, a coupled scheme of leaf photosynthesis and stomatal conductance, representation of the effects of ozone on leaf physiology, and a description of methane emissions from wetlands. JULES represents the carbon allocation, growth and population dynamics of five plant functional types. The turnover of carbon from living plant tissues is fed into a 4-pool soil carbon model. The process-based descriptions of key ecological processes and trace gas fluxes in JULES mean that this community model is well-suited for use in carbon cycle, climate change and impacts studies, either in standalone mode or as the land component of a coupled Earth system model.

Description: Pliocene Model Intercomparison Project (PlioMIP): experimental design and boundary conditions (Experiment 2) Geoscientific Model Development Discussions, 4, 445-456, 2011 Author(s): A. M. Haywood, H. J. Dowsett, M. M. Robinson, D. K. Stoll, A. M. Dolan, D. J. Lunt, B. Otto-Bliesner, and M. A. Chandler The Palaeoclimate Modelling Intercomparison Project has expanded to include a model intercomparison for the mid-Pliocene warm period (~3.3 to 3.0 million yr ago). This project is referred to as PlioMIP (Pliocene Model Intercomparison Project). Two experiments have been agreed and together compose phase 1 of PlioMIP. The first (Experiment 1) is being performed with atmosphere-only climate models. The second (Experiment 2) is utilising fully coupled ocean-atmosphere climate models. Following on from the publication of the experimental design and boundary conditions for Experiment 1 in Geoscientific Model Development, this short paper provides the necessary description of differences and/or additions to the experimental design for Experiment 2.

Description: The atmosphere-ocean general circulation model EMAC-MPIOM Geoscientific Model Development Discussions, 4, 457-495, 2011 Author(s): A. Pozzer, P. Jöckel, B. Kern, and H. Haak The ECHAM/MESSy Atmospheric Chemistry (EMAC) model is coupled to the ocean general circulation model MPIOM using the Modular Earth Submodel Sytem (MESSy) interface. MPIOM is operated as a MESSy submodel, thus the need of an external coupler is avoided. The coupling method is tested for different model configurations, proving to be very flexible in terms of parallel decomposition and very well load balanced. The run time performance analysis and the simulation results are compared to those of the COSMOS (Community earth System MOdelS) climate model, using the same configurations for the atmosphere and the ocean in both model systems. It is shown that our coupling method is, for the tested conditions, approximately 10% more efficient compared to the coupling based on the OASIS (Ocean Atmosphere Sea Ice Soil, version 3) coupler. The standard (CMIP3) climate model simulations performed with EMAC-MPIOM show that the results are comparable to those of other Atmosphere-Ocean General Circulation models.

Description: The Joint UK Land Environment Simulator (JULES), Model description – Part 1: Energy and water fluxes Geoscientific Model Development Discussions, 4, 595-640, 2011 Author(s): M. J. Best, M. Pryor, D. B. Clark, G. G. Rooney, R. L. H. Essery, C. B. Ménard, J. M. Edwards, M. A. Hendry, A. Porson, N. Gedney, L. M. Mercado, S. Sitch, E. Blyth, O. Boucher, P. M. Cox, C. S. B. Grimmond, and R. J. Harding This manuscript describes the energy and water components of a new community land surface model called the Joint UK Land Environment Simulator (JULES). This is developed from the Met Office Surface Exchange Scheme (MOSES). It can be used as a stand alone land surface model driven by observed forcing data, or coupled to an atmospheric global circulation model. The JULES model has been coupled to the Met Office Unified Model (UM) and as such provides an opportunity for the research community to contribute their research into world-leading operational weather forecasting and climate change prediction systems. JULES has a modular structure aligned to physical processes, providing the basis for a flexible modelling platform.

Description: Evaluation of ice and snow content in the global numerical weather prediction model GME with CloudSat Geoscientific Model Development Discussions, 4, 419-443, 2011 Author(s): S. Eikenberg, K. Fröhlich, A. Seifert, S. Crewell, and M. Mech The present study evaluates the global numerical weather prediction model GME with respect to frozen particles, both ice and snow, focusing on the performance of a diagnostic versus a prognostic precipitation scheme. As a reference, CloudSat Cloud Profiling Radar observations are utilized – the so far only near-globally available data set which vertically resolves clouds. Both the observation-to-model and the model-to-observation approach are applied and compared to each other. For the latter, the radar simulator QuickBeam is utilized. Criteria are applied to further improve the comparability between model and observations. The two model versions are statistically evaluated for a four-month period. The comparison reveals that the prognostic scheme reproduces the shape of the CloudSat frequency distributions for both ice water content (IWC) and reflectivity factor well, while the diagnostic scheme produces no large IWCs or reflectivity factors because snow falls out instantaneously. However, the prognostic scheme overestimates the occurrence of high ice water paths (IWP), especially in the mid-latitudes. Sensitivity tests show that an increased fall speed of snow successfully reduces IWP. Both approaches capture the general features, but for details, the two together deliver the largest informational content. In case of limited resources, the model-to-observation approach is preferred. Finally, the results indicate that the lack of IWC in most global circulation models might be attributed to the use of diagnostic precipitation schemes, i.e., the lack of snow aloft. Based on its good performance the prognostic scheme went into operational mode in February 2010. The adjusted snow fall speed went operational in December 2010. However, continual improvements of the ice microphysics are necessary, which can be assessed by the proposed evaluation technique.

Description: The role of phytoplankton dynamics in the seasonal variability of carbon in the subpolar North Atlantic – a modeling study Geoscientific Model Development Discussions, 4, 289-342, 2011 Author(s): S. R. Signorini, S. Häkkinen, K. Gudmundsson, A. Olsen, A. M. Omar, J. Olafsson, G. Reverdin, S. A. Henson, and C. R. McClain We use an ecosystem/biogeochemical model, which includes multiple phytoplankton functional groups and carbon cycle dynamics, to investigate physical-biological interactions in Icelandic waters. Satellite and in situ data were used to validate the model. The seasonality of the coccolithophore and "other phytoplankton" (diatoms and dinoflagellates) blooms is in general agreement with satellite ocean color products. Nutrient supply, biomass and calcite concentrations are modulated by light and mixed layer depth seasonal cycles. Diatoms are the most abundant with a large bloom in early spring and a secondary bloom in fall. The diatom bloom is followed by blooms of dinoflagellates and coccolithophores. The effect of biological changes on the seasonal variability of the surface ocean p CO 2 is nearly twice the temperature effect. The inclusion of multiple functional groups in the model played a major role in the accurate representation of CO 2 uptake by biology. For instance, at the peak of the bloom, the exclusion of coccolithophores causes an increase in alkalinity of up to 4 μmol kg −1 with a corresponding increase in DIC of up to 16 μmol kg −1 . The net effect of the absence of the coccolithophores bloom is an increase in p CO 2 of more than 20 μatm and a reduction of atmospheric CO 2 uptake of more than 6 mmol m −2 d −1 .

Description: Ground-level ozone concentration over Spain: an application of Kalman Filter post-processing to reduce model uncertainties Geoscientific Model Development Discussions, 4, 343-384, 2011 Author(s): V. Sicardi, J. Ortiz, A. Rincón, O. Jorba, M. T. Pay, S. Gassó, and J. M. Baldasano The CALIOPE air quality modelling system, namely WRF-ARW/HERMES-EMEP/CMAQ/BSC-DREAM8b, has been used to perform the simulation of ground level O 3 concentration for the year 2004, over the Iberian Peninsula. We use this system to study the daily ground-level O 3 maximum. We investigate the use of a post-processing such as the Kalman Filter bias-adjustment technique to improve the simulated O 3 maximum. The Kalman Filter bias-adjustment technique is a recursive algorithm to optimally estimate bias-adjustment terms from previous measurements and model results. The bias-adjustment technique is found to improve the simulated O 3 maximum for the entire year and the whole domain. The corrected simulation presents improvements in statistical indicators such as correlation, root mean square error, mean bias, standard deviation, and gross error. After the post-processing the exceedances of O 3 concentration limits, as established by the European Directive 2008/50/CE, are better reproduced and the uncertainty of the modelling system is reduced from 20% to 7.5%. Such uncertainty in the model results is under the established EU limit of the 50%. Significant improvements in the O 3 average daily cycle and in its amplitude are also observed after the post-processing. The systematic improvements in the O 3 maximum simulations suggest that the Kalman Filter post-processing method is a suitable technique to reproduce accurate estimate of ground-level O 3 concentration.

Description: An aerosol dynamics model for simulating particle formation and growth in a mixed flow chamber Geoscientific Model Development Discussions, 4, 385-417, 2011 Author(s): M. Vesterinen, H. Korhonen, J. Joutsensaari, P. Yli-Pirilä, A. Laaksonen, and K. E. J. Lehtinen In this work we model the aerosol size distribution dynamics in a mixed flow chamber in which new particles are formed via nucleation and subsequent condensation of oxidation products of VOCs emitted from Norway spruce seedlings. The microphysical processes included in the model are nucleation, condensation, deposition and coagulation. The aerosol dynamics in the chamber is a competition between aerosol growth and scavenging/deposition which results in a cyclic particle formation process. With a simple 1-product model, in which the formed gas is able to both condense to the particles and nucleate, we are able to catch both the oscillatory features of the particle formation process and the evolution of the number concentration in a reasonable way. The gas-phase chemistry was adjusted using pre-estimated reaction rate constant in the simulations and the particle deposition rate as a function of size was determined experimentally. Despite this, some of the essential features of the physical properties of the aerosol population could still be captured and investigated without the detailed knowledge of the physical processes underlying the problem by using the constructed model. The size dependency of the wall loss coefficient was investigated using a slightly modified measurement set-up.

Description: The CSIRO Mk3L climate system model version 1.0 – Part 1: Description and evaluation Geoscientific Model Development Discussions, 4, 219-287, 2011 Author(s): S. J. Phipps, L. D. Rotstayn, H. B. Gordon, J. L. Roberts, A. C. Hirst, and W. F. Budd The CSIRO Mk3L climate system model is a coupled general circulation model, designed primarily for millennial-scale climate simulations and palaeoclimate research. Mk3L includes components which describe the atmosphere, ocean, sea ice and land surface, and combines computational efficiency with a stable and realistic control climatology. This paper describes the model physics and software, and evaluates its ability to simulate the present-day climate. Mk3L incorporates a spectral atmospheric general circulation model, a z -coordinate ocean general circulation model, a dynamic-thermodynamic sea ice model and a land surface scheme with static vegetation. The source code is highly portable, and has no dependence upon proprietary software. The model distribution is freely available to the research community. A 1000-year climate simulation can be completed in around one-and-a-half months on a typical desktop computer, with greater throughput being possible on high-performance computing facilities. Mk3L produces realistic simulations of the larger-scale features of the present-day climate, although with some biases on the regional scale. The model also produces reasonable representations of the leading modes of internal climate variability in both the tropics and extratropics. The control state of the model exhibits a high degree of stability, with only a weak cooling trend on millennial timescales. Ongoing development work aims to improve the model climatology and transform Mk3L into a comprehensive earth system model.

Description: Validation of modelled forest biomass in Germany using BETHY/DLR Geoscientific Model Development Discussions, 4, 1685-1722, 2011 Author(s): M. Tum, M. Buchhorn, K. P. Günther, and B. C. Haller 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 dynamic biomass model BETHY/DLR is used 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 derived 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.

Description: A subgrid parameterization scheme for precipitation Geoscientific Model Development Discussions, 4, 1643-1684, 2011 Author(s): S. Turner, J.-L. Brenguier, and C. Lac With increasing computing power, the horizontal resolution of numerical weather prediction (NWP) models is improving and today reaches 1 to 5 km. Nevertheless, clouds and precipitation are still subgrid scale processes for most cloud types, such as cumulus and stratocumulus. Subgrid scale parameterizations for water vapor condensation have been in use for many years and are based on a prescribed PDF of relative humidity spatial variability within the grid, thus providing a diagnosis of the cloud fraction. A similar scheme is developed and tested here. It is based on a prescribed PDF of cloud water variability and a threshold value of liquid water content for droplet collection to derive a rain fraction within the model grid. Precipitation of rainwater raises additional concerns relative to the overlap of cloud and rain fractions, however. The scheme is developed following an analysis of data collected during field campaigns in stratocumulus (DYCOMS-II) and fair weather cumulus (RICO) and tested in a 1-D framework against large eddy simulations of these observed cases. The new parameterization is then implemented in a 3-D NWP model with a horizontal resolution of 2.5 km to simulate real cases of precipitating cloud systems over France.

Description: The 1-way on-line coupled atmospheric chemistry model system MECO(n) – Part 3: Meteorological evaluation of the on-line coupled system Geoscientific Model Development Discussions, 4, 1533-1567, 2011 Author(s): C. Hofmann, A. Kerkweg, H. Wernli, and P. Jöckel Three detailed meteorological case studies are conducted with the global and regional atmospheric chemistry model system ECHAM5/MESSy(→COSMO/MESSy) n , shortly named MECO(n), in order 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: an intense cold frontal 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 in the near future to simulate atmospheric chemistry exploring the model's full capabilities during meteorologically challenging conditions.

Description: The CSIRO Mk3L climate system model v1.0 coupled to the CABLE land surface scheme v1.4b: evaluation of the control climatology Geoscientific Model Development Discussions, 4, 1611-1642, 2011 Author(s): J. Mao, S. J. Phipps, A. J. Pitman, Y. P. Wang, G. Abramowitz, and B. Pak 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.

Description: Improved convergence and stability properties in a three-dimensional higher-order ice sheet model Geoscientific Model Development Discussions, 4, 1569-1610, 2011 Author(s): J. J. Fürst, O. Rybak, H. Goelzer, B. De Smedt, P. de Groen, and P. Huybrechts We present a novel finite difference implementation of a three-dimensional higher-order ice sheet model that performs well both in terms of convergence rate and numerical stability. 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, an existing discretisation that operates exclusively on the regular grid serves as a reference. Participation in the ISMIP-HOM benchmark indicates that both discretisations are capable of reproducing the higher-order model inter-comparison results. This allows a direct comparison not only of the resultant velocity fields but also of the solver's convergence behaviour which holds main differences. 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 precision for the resultant velocity field can be chosen higher in the novel finite difference implementation. For high precisions, the old discretisation experiences difficulties to converge due to large variation in the velocity fields of consecutive Picard iterations. Finally, changing discretisation prevents build-up of local field irregularites that occasionally cause divergence of the solution for the reference discretisation. The improved behaviour makes the new discretisation more reliable for extensive application to real ice geometries. Higher precision 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. Transient applications also benefit from the increased computational efficiency.

Description: MIROC-ESM: model description and basic results of CMIP5-20c3m experiments Geoscientific Model Development Discussions, 4, 1063-1128, 2011 Author(s): S. Watanabe, T. Hajima, K. Sudo, T. Nagashima, T. Takemura, H. Okajima, T. Nozawa, H. Kawase, M. Abe, T. Yokohata, T. Ise, H. Sato, E. Kato, K. Takata, S. Emori, and M. Kawamiya An earth system model (MIROC-ESM) is fully described in terms of each model component and their interactions. Results for the CMIP5 (Coupled Model Intercomparison Project phase 5) historical simulation are presented to demonstrate the model's performance from several perspectives: atmosphere, ocean, sea-ice, land-surface, ocean and terrestrial biogeochemistry, and atmospheric chemistry and aerosols. An atmospheric chemistry coupled version of MIROC-ESM (MIROC-ESM-CHEM) reasonably reproduces transient variations in surface air temperatures for the period 1850–2005, as well as the present-day climatology for the zonal-mean zonal winds and temperatures from the surface to the mesosphere. The historical evolution and global distribution of column ozone and the amount of tropospheric aerosols are reasonably simulated in the model based on the Representative Concentration Pathways' (RCP) historical emissions of these precursors. The simulated distributions of the terrestrial and marine biogeochemistry parameters agree with recent observations, which is encouraging to use the model for future global change projections.

Description: A two-layer flow model to represent ice-ocean interactions beneath Antarctic ice shelves Geoscientific Model Development Discussions, 4, 65-136, 2011 Author(s): V. Lee, A. J. Payne, and J. M. Gregory We develop a two-dimensional two-layer flow model that can calculate melt rates beneath ice shelves from ocean temperature and salinity fields at the shelf front. The cavity motion is split into two layers where the upper plume layer represents buoyant meltwater-rich water rising along the underside of the ice to the shelf front, while the lower layer represents the ambient water connected to the open ocean circulating beneath the plume. Conservation of momentum has been reduced to a frictional geostrophic balance, which when linearized provides algebraic equations for the plume velocity. The turbulent exchange of heat and salt between the two layers is modelled through an entrainment rate which is directed into the faster flowing layer. The numerical model is tested using an idealized geometry based on the dimensions of Pine Island Ice Shelf. We find that the spatial distribution of melt rates is fairly robust. The rates are at least 2.5 times higher than the mean in fast flowing regions corresponding to the steepest section of the underside of the ice shelf close to the grounding line and to the converged geostrophic flow along the rigid lateral boundary. Precise values depend on a combination of entrainment and plume drag coefficients. The flow of the ambient is slow and the spread of ocean scalar properties is dominated by diffusion.

Description: Modeling and computation of effective emissions: a position paper Geoscientific Model Development Discussions, 4, 137-196, 2011 Author(s): R. Paoli, D. Cariolle, and R. Sausen An important issue in the evaluation of the environmental impact of emissions from concentrated sources such as transport modes, is to understand how processes occurring at the scales of exhaust plumes can influence the physical and chemical state of the atmosphere at regional and global scales. Indeed, three-dimensional global circulation models or chemistry transport models generally assume that emissions are instantaneously diluted into large-scale grid boxes, which may lead, for example, to overpredict the efficiency of NO x to produce ozone. In recent times, various methods have been developed to incorporate parameterizations of plume processes into global models that are based either on the correction of the original emissions or on the introduction of subgrid reaction rates in the models. This paper provides a review of the techniques proposed so far in the literature to account for local conversion of emissions in the plume, as well as the implementation of these techniques into atmospheric codes.

Description: The atmospheric chemistry box model CAABA/MECCA-3.0gmdd Geoscientific Model Development Discussions, 4, 197-217, 2011 Author(s): R. Sander, A. Baumgaertner, S. Gromov, H. Harder, P. Jöckel, A. Kerkweg, D. Kubistin, E. Regelin, H. Riede, A. Sandu, D. Taraborrelli, H. Tost, and Z.-Q. Xie We present version 3.0gmdd of the atmospheric chemistry box model CAABA/MECCA. In addition to a complete update of the rate coefficients to the most recent recommendations, a number of new features have been added: chemistry in multiple aerosol size bins; automatic multiple simulations reaching steady-state conditions; Monte-Carlo simulations with randomly varied rate coefficients within their experimental uncertainties; calculations along Lagrangian trajectories; mercury chemistry; more detailed isoprene chemistry; tagging of isotopically labeled species. Further changes have been implemented to make the code more user-friendly and to facilitate the analysis of the model results. Like earlier versions, CAABA/MECCA-3.0gmdd is a community model published under the GNU General Public License (GPL).

Description: Attribution of ozone changes to dynamical and chemical processes in CCMs and CTMs Geoscientific Model Development Discussions, 4, 1-43, 2011 Author(s): H. Garny, V. Grewe, M. Dameris, G. E. Bodeker, and A. Stenke Chemistry-climate models (CCMs) are commonly used to simulate the past and future development of Earth's ozone layer. The fully coupled chemistry schemes calculate the chemical production and destruction of ozone interactively and ozone is transported by the simulated atmospheric flow. Due to the complexity of the processes acting on ozone it is not straightforward to disentangle the influence of individual processes on the temporal development of ozone concentrations. A method is introduced here that quantifies the influence of chemistry and transport on ozone concentration changes and that is easily implemented in CCMs and chemistry-transport models (CTMs). In this method, ozone tendencies (i.e. the time rate of change of ozone) are partitioned into a contribution from ozone production and destruction (chemistry) and a contribution from transport of ozone (dynamics). The influence of transport on ozone in a specific region is further divided into export of ozone out of that region and import of ozone from elsewhere into that region. For this purpose, a diagnostic is used that disaggregates the ozone mixing ratio field into 9 separate fields according to in which of 9 predefined regions of the atmosphere the ozone originated. With this diagnostic the ozone mass fluxes between these regions are obtained. Furthermore, this method is used here to attribute long-term changes in ozone to chemistry and transport. The relative change in ozone from one period to another that is due to changes in production or destruction rates, or due to changes in import or export of ozone, are quantified. As such, the diagnostics introduced here can be used to attribute changes in ozone on monthly, interannual and long-term time-scales to the responsible mechanisms. Results from a CCM simulation are shown here as examples, with the main focus of the paper being on introducing the method.

Description: A pragmatic approach for the downscaling and bias correction of regional climate simulations – evaluation in hydrological modeling Geoscientific Model Development Discussions, 4, 45-63, 2011 Author(s): T. Marke, W. Mauser, A. Pfeiffer, and G. Zängl The present study investigates a statistical approach for the downscaling of climate simulations focusing on those meteorological parameters most commonly required as input for climate change impact models (temperature, precipitation, air humidity and wind speed), including the option to correct biases in the climate model simulations. The approach is evaluated by the utilization of a hydrometeorological model chain consisting of (i) the regional climate model MM5 (driven by reanalysis data at the boundaries of the model domain), (ii) the downscaling and model interface SCALMET, and (iii) the hydrological model PROMET. The results of four hydrological model runs are compared to discharge recordings at the gauge of the Upper Danube Watershed (Central Europe) for the historical period of 1972–2000 on a daily time basis. The comparison reveals that the presented approaches allow for a more accurate simulation of discharge for the catchment of the Upper Danube Watershed and the considered gauge at the outlet in Achleiten. The correction for subgrid-scale variability is shown to reduce biases in simulated discharge compared to the utilization of bilinear interpolation. Further enhancements in model performance could be achieved by a correction of biases in the RCM data within the downscaling process. Although the presented downscaling approach strongly improves the performance of the hydrological model, deviations from the observed discharge conditions persist that are not found when driving the hydrological model with spatially distributed meteorological observations.

Description: iGen: a program for the automated generation of models and parameterisations Geoscientific Model Development Discussions, 4, 843-868, 2011 Author(s): D. F. Tang and S. Dobbie Complex physical systems can often be simulated using very high-resolution models but this is not always practical because of computational restrictions. In this case the model must be simplified or parameterised, but this is a notoriously difficult process that often requires the introduction of "model assumptions" that are hard or impossible to justify. Here we introduce a new approach to parameterising models. The approach makes use of a newly developed computer program, which we call iGen, that analyses the source code of a high-resolution model and formally derives a much faster parameterised model that closely approximates the original, reporting bounds on the error introduced by any approximations. These error bounds can be used to formally justify use of the parameterised model in subsequent numerical experiments. Using increasingly complex physical systems as examples we illustrate that iGen has the ability to produce parameterisations that run typically orders of magnitude faster than the underlying, high-resolution models from which they are derived and show that iGen has the potential to become an important tool in model development.

Description: The JGrass-NewAge system for forecasting and managing the hydrological budgets at the basin scale: the models of flow generation, propagation, and aggregation Geoscientific Model Development Discussions, 4, 943-969, 2011 Author(s): G. Formetta, R. Mantilla, S. Franceschi, A. Antonello, and R. Rigon This paper presents a discussion of the predictive capacity of the first implementation of the semi-distributed hydrological modeling system JGrass-NewAge. This model focuses on the hydrological balance of medium scale to large scale basins, and considers statistics of the processes at the hillslope scale. The whole modeling system consists of six main parts: (i) estimation of energy balance; (ii) estimation of evapotranspiration; (iii) snow modelling; (iv) estimation of runoff production; (v) aggregation and propagation of flows in channel, and (vi) description of intakes, out-takes, and reservoirs. This paper details the processes, of runoff production, and aggregation/propagation of flows on a river network. The system is based on a hillslope-link geometrical partition of the landscape, so the basic unit, where the budget is evaluated, consists of hillslopes that drain into a single associated link rather than cells or pixels. To this conceptual partition corresponds an implementation of informatics that uses vectorial features for channels, and raster data for hillslopes. Runoff production at each channel link is estimated through a combination of the Duffy (1996) model and a GIUH model for estimating residence times in hillslope. Routing in channels uses equations integrated for any channels' link, and produces discharges at any link end, for any link in the river network. The model has been tested against measured discharges according to some indexes of goodness of fit such as RMSE and Nash Sutcliffe. The characteristic ability to reproduce discharge in any point of the river network is used to infer some statistics, and notably, the scaling properties of the modeled discharge.

Description: Modeling anthropogenically-controled secondary organic aerosols in a megacity: a simplified framework for global and climate models Geoscientific Model Development Discussions, 4, 869-905, 2011 Author(s): A. Hodzic and J. L. Jimenez A simplified parameterization for secondary organic aerosol (SOA) formation in polluted air and biomass burning smoke is tested and optimized in this work, towards the goal of a computationally inexpensive method to calculate pollution and biomass burning SOA in global and climate models. A regional chemistry-transport model is used as the testbed for the parameterization, which is compared against observations from the Mexico City metropolitan area during the MILAGRO 2006 field experiment. The empirical parameterization is based on the observed proportionality of SOA concentrations to excess CO and photochemical age of the airmass. The approach consists in emitting an organic gas as lumped SOA precursor surrogate proportional to anthropogenic or biomass burning CO emissions according to the observed ratio between SOA and CO in aged air, and reacting this surrogate with OH into a single non-volatile species that condenses to form SOA. An emission factor of 0.08 g of the lumped SOA precursor per g of CO and a rate constant with OH of 1.25 × 10 −11 cm 3 molecule −1 s −1 reproduce the observed average SOA mass within 30% in the urban area and downwind. When a 2.5 times slower rate is used (5 × 10 −12 cm 3 molecule −1 s −1 ) the predicted SOA amount and temporal evolution is nearly identical to the results obtained with SOA formation from semi-volatile and intermediate volatility primary organic vapors according to the Robinson et al. (2007) formulation. Our simplified method has the advantage of being much less computationally expensive than Robinson-type methods, and can be used in regions where the emissions of SOA precursors are not yet available. As the aged pollution SOA/ΔCO ratios are rather consistent globally, this parameterization could be reasonably tested in and applied to other regions. The potential enhancement of biogenic SOA by anthropogenic pollution, which has been suggested to play a major role in global SOA formation, is also tested using two simple parameterizations. Our results suggest that the pollution enhancement of biogenic SOA could provide several μg m −3 of additional SOA, but does not however explain the concentrations or especially the spatial and temporal variations of measured SOA mass in the vicinity of Mexico City, which appears to be controlled by anthropogenic sources. The contribution of the biomass burning to the predicted SOA is less than 10% during the study period.

Description: Evaluation of a Dynamic Global Vegetation Model using time series of satellite vegetation indices Geoscientific Model Development Discussions, 4, 907-941, 2011 Author(s): F. Maignan, F.-M. Bréon, F. Chevallier, N. Viovy, P. Ciais, C. Garrec, J. Trules, and M. Mancip Atmospheric CO 2 drives most of the greenhouse effect increase and one major uncertainty on the future rate of increase of CO 2 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 median correlation. 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.

Description: Coupled atmosphere-wildland fire modeling with WRF-Fire version 3.3 Geoscientific Model Development Discussions, 4, 497-545, 2011 Author(s): J. Mandel, J. D. Beezley, and A. K. Kochanski We describe the physical model, numerical algorithms, and software structure of WRF-Fire. WRF-Fire consists of a fire-spread model, implemented by the level-set method, coupled with the Weather Research and Forecasting model. In every time step, the fire model inputs the surface wind, which drives the fire, and outputs the heat flux from the fire into the atmosphere, which in turn influences the atmosphere. The level-set method allows submesh representation of the burning region and flexible implementation of various kinds of ignition. WRF-Fire is distributed as a part of WRF and it uses the WRF parallel infrastructure for parallel computing.

Description: Influence of the compiler on multi-CPU performance of WRFv3 Geoscientific Model Development Discussions, 4, 547-573, 2011 Author(s): T. Langkamp The Weather Research and Forecasting system version 3 (WRFv3) is an open source and state of the art numerical regional climate model used in climate related sciences. Over the years the model has been successfully optimized on a wide variety of clustered compute nodes connected with high speed interconnects. This is currently the most used hardware architecture for high-performance computing. As such, understanding WRFs dependency on the various hardware elements like the CPU, its interconnects, and the software is crucial for saving computing time. This is important because computing time in general is rare, resource intensive, and hence very expensive. This paper evaluates the influence of different compilers on WRFs performance, which was found to differ up to 26%. The paper also evaluates the performance of different message passing interface library versions, a software which is needed for multi CPU runs, and of different WRF versions. Both showed no significant influence on the performance for this test case on the used High Performance Cluster (HPC) hardware. Some emphasis is also laid on the applied non-standard method of performance measuring, which was required because of performance fluctuations between identical runs on the used HPC. Those are caused by contention for network resources, a phenomenon examined for many HPCs.

Description: LANL* V2.0: global modeling and validation Geoscientific Model Development Discussions, 4, 575-594, 2011 Author(s): J. Koller and S. Zaharia We describe in this paper the new version of LANL*. Just like the previous version, this new version V2.0 of LANL* is an artificial neural network (ANN) for calculating the magnetic drift invariant, L *, that is used for modeling radiation belt dynamics and for other space weather applications. We have implemented the following enhancements in the new version: (1) we have removed the limitation to geosynchronous orbit and the model can now be used for any type of orbit. (2) The new version is based on the improved magnetic field model by Tsyganenko and Sitnov (2005) (TS05) instead of the older model by Tsyganenko et al. (2003). We have validated the model and compared our results to L * calculations with the TS05 model based on ephemerides for CRRES, Polar, GPS, a LANL geosynchronous satellite, and a virtual RBSP type orbit. We find that the neural network performs very well for all these orbits with an error typically Δ L * 〈 0.2 which corresponds to an error of 3% at geosynchronous orbit. This new LANL-V2.0 artificial neural network is orders of magnitudes faster than traditional numerical field line integration techniques with the TS05 model. It has applications to real-time radiation belt forecasting, analysis of data sets involving decades of satellite of observations, and other problems in space weather.

Description: An improved non-iterative surface layer flux scheme for atmospheric stable stratification condition Geoscientific Model Development Discussions, 6, 6459-6492, 2013 Author(s): Y. Li, Z. Gao, D. Li, L. Wang, and H. Wang Parameterization of turbulent fluxes under stably stratified conditions has always been a challenge. Current surface fluxes calculation schemes either need iterations or suffer low accuracy. In this paper, a non-iteration scheme is proposed to approach the classic iterative computation results using multiple regressions. It can be applied to the full range of roughness status 10 ≤ z/z 0 ≤ 10 5 and −0.5 ≤ log( z 0 / z 0h ) ≤ 30 under stable conditions 0 〈 Ri B ≤ 2.5. The maximum (average) relative errors for the turbulent transfer coefficients for momentum and sensible heat are 12% (1%) and 9% (1%), respectively.

Description: A system of conservative regridding for ice/atmosphere coupling in a GCM Geoscientific Model Development Discussions, 6, 6493-6568, 2013 Author(s): R. Fischer, S. Nowicki, M. Kelley, and G. A. Schmidt The method of elevation classes has proven to be a useful way for a low-resolution general circulation model (GCM) to produce high-resolution downscaled surface mass balance fields, for use in one-way studies coupling GCMs and ice flow models. Past uses of elevation classes have been a cause of non-conservation of mass and energy, caused by inconsistency in regridding schemes chosen to regrid to the atmosphere vs. downscaling to the ice model. This causes problems for two-way coupling. A strategy that resolves this conservation issue has been designed and is presented here. The approach identifies three grids between which data must be regridded, and five transformations between those grids required by a typical coupled GCM–ice flow model. This paper shows how each of those transformations may be achieved in a consistent, conservative manner. These transformations are implemented in GLINT2, a library used to couple GCMs with ice models. Source code and documentation are available for download. Confounding real-world issues are discussed, including the use of projections for ice modeling, how to handle dynamically changing ice geometry, and modifications required for finite element ice models.

Description: A 24-variable low-order coupled ocean–atmosphere model: OA-QG-WS v2 Geoscientific Model Development Discussions, 6, 6569-6604, 2013 Author(s): S. Vannitsem and L. De Cruz A new low-order coupled ocean–atmosphere model for mid-latitudes is derived. It is based on quasi-geostrophic equations for both the ocean and the atmosphere, coupled through momentum transfer at the interface. The systematic reduction of the number of modes describing the dynamics leads to an atmospheric low-order component of 20 ordinary differential equations, already discussed in Reinhold and Pierrehumbert (1982), and an oceanic low-order component of 4 ordinary differential equations, as proposed by Pierini (2012). The coupling terms for both components are derived and all the coefficients of the ocean model are provided. Its dynamics is then briefly explored, through the analysis of its mean field, its variability and its instability properties. The wind-driven ocean displays a decadal variability induced by the atmospheric chaotic wind forcing. The chaotic behavior of the coupled system is highly sensitive to the ocean–atmosphere coupling, for low values of the thermal forcing affecting the atmosphere (corresponding to a weakly chaotic coupled system). But it is less sensitive for large values of the thermal forcing (corresponding to a highly chaotic coupled system). In all the cases explored, the number of positive exponents is increasing with the coupling. A Fortran code of the model integration is provided as Supplement.

Description: A variational data assimilation system for soil–atmosphere flux estimates for the Community Land Model (CLM3.5) Geoscientific Model Development Discussions, 6, 6605-6637, 2013 Author(s): C. M. Hoppe, H. Elbern, and J. Schwinger This article presents the development and implementation of a spatio–temporal variational data assimilation system (4D-var) for the soil–vegetation–atmosphere–transfer model "Community Land Model" (CLM3.5), along with the development of the adjoint code for the core soil-atmosphere transfer scheme of energy and soil moisture. The purpose of this work is to obtain an improved estimation technique for the energy fluxes (sensible and latent heat fluxes) between the soil and the atmosphere. Optimal assessments of these fluxes are neither available from model simulations nor measurements alone, while a 4D-var data assimilation has the potential to combine both information sources by a Best Linear Unbiased Estimate (BLUE). The 4D-var method requires the development of the adjoint model of the CLM which was established in this work. The new data assimilation algorithm is able to assimilate soil temperature and soil moisture measurements for one-dimensional columns of the model grid. Numerical experiments were first used to test the algorithm under idealised conditions. It was found that the analysis delivers improved results whenever there is a dependence between the initial values and the assimilated quantity. Furthermore, soil temperature and soil moisture from in situ field measurements were assimilated. These calculations demonstrate the improved performance of flux estimates, whenever soil property parameters are available of sufficient quality. Misspecifications could also be identified by the performance of the variational scheme.

Description: The Secondary Organic Aerosol Processor (SOAP v1.0) model: a unified model with different ranges of complexity based on the molecular surrogate approach Geoscientific Model Development Discussions, 7, 379-429, 2014 Author(s): F. Couvidat and K. Sartelet The Secondary Organic Aerosol Processor (SOAP v1.0) model is presented. This model is designed to be modular with different user options depending on the computing time and the complexity required by the user. This model is based on the molecular surrogate approach, in which each surrogate compound is associated with a molecular structure to estimate some properties and parameters (hygroscopicity, absorption on the aqueous phase of particles, activity coefficients, phase separation). Each surrogate can be hydrophilic (condenses only on the aqueous phase of particles), hydrophobic (condenses only on the organic phase of particles) or both (condenses on both the aqueous and the organic phases of particles). Activity coefficients are computed with the UNIFAC thermodynamic model for short-range interactions and with the AIOMFAC parameterization for medium and long-range interactions between electrolytes and organic compounds. Phase separation is determined by Gibbs energy minimization. The user can choose between an equilibrium and a dynamic representation of the organic aerosol. In the equilibrium representation, compounds in the particle phase are assumed to be at equilibrium with the gas phase. However, recent studies show that the organic aerosol (OA) is not at equilibrium with the gas phase because the organic phase could be semi-solid (very viscous liquid phase). The condensation or evaporation of organic compounds could then be limited by the diffusion in the organic phase due to the high viscosity. A dynamic representation of secondary organic aerosols (SOA) is used with OA divided into layers, the first layer at the center of the particle (slowly reaches equilibrium) and the final layer near the interface with the gas phase (quickly reaches equilibrium).

Description: Comparison of the ensemble Kalman filter and 4D-Var assimilation methods using a stratospheric tracer transport model Geoscientific Model Development Discussions, 7, 339-377, 2014 Author(s): S. Skachko, Q. Errera, R. Ménard, Y. Christophe, and S. Chabrillat The Ensemble Kalman filter (EnKF) assimilation method is applied to the tracer transport using the same stratospheric transport model as in the 4D-Var assimilation system BASCOE. This EnKF version of BASCOE was built primarily to avoid the large costs associated with the maintenance of an adjoint model. The EnKF developed in BASCOE accounts for two adjustable parameters: a parameter α controlling the model error term and a parameter r controlling the observational error. The EnKF system is shown to be markedly sensitive to these two parameters, which are adjusted based on the monitoring of a χ 2 -test measuring the misfit between the control variable and the observations. The performance of the EnKF and 4D-Var versions was estimated through the assimilation of Aura-MLS ozone observations during an 8 month period which includes the formation of the 2008 Antarctic ozone hole. To ensure a proper comparison, despite the fundamental differences between the two assimilation methods, both systems use identical and carefully calibrated input error statistics. We provide the detailed procedure for these calibrations, and compare the two sets of analyses with a focus on the lower and middle stratosphere where the ozone lifetime is much larger than the observational update frequency. Based on the Observation-minus-Forecast statistics, we show that the analyses provided by the two systems are markedly similar, with biases smaller than 5% and standard deviation errors smaller than 10% in most of the stratosphere. Since the biases are markedly similar, they have most probably the same causes: these can be deficiencies in the model and in the observation dataset, but not in the assimilation algorithm nor in the error calibration. The remarkably similar performance also shows that in the context of stratospheric transport, the choice of the assimilation method can be based on application-dependent factors, such as CPU cost or the ability to generate an ensemble of forecasts.

Description: Regional climate modeling on European scales: a joint standard evaluation of the EURO-CORDEX RCM ensemble Geoscientific Model Development Discussions, 7, 217-293, 2014 Author(s): S. Kotlarski, K. Keuler, O. B. Christensen, A. Colette, M. Déqué, A. Gobiet, K. Goergen, D. Jacob, D. Lüthi, E. van Meijgaard, G. Nikulin, C. Schär, C. Teichmann, R. Vautard, K. Warrach-Sagi, and V. Wulfmeyer EURO-CORDEX is an international climate downscaling initiative that aims to provide high-resolution climate scenarios for Europe. Here an evaluation of the ERA-Interim-driven EURO-CORDEX regional climate model (RCM) ensemble is presented. The study documents the performance of the individual models in representing the basic spatio-temporal patterns of the European climate for the period 1989–2008. Model evaluation focuses on near-surface air temperature and precipitation, and uses the E-OBS dataset as observational reference. The ensemble consists of 17 simulations carried out by seven different models at grid resolutions of 12 km (nine experiments) and 50 km (eight experiments). Several performance metrics computed from monthly and seasonal mean values are used to assess model performance over eight sub-domains of the European continent. Results are compared to those for the ERA40-driven ENSEMBLES simulations. The analysis confirms the ability of RCMs to capture the basic features of the European climate, including its variability in space and time. But it also identifies non-negligible deficiencies of the simulations for selected metrics, regions and seasons. Seasonally and regionally averaged temperature biases are mostly smaller than 1.5 °C, while precipitation biases are typically located in the ±40% range. Some bias characteristics, such as a predominant cold and wet bias in most seasons and over most parts of Europe and a warm and dry summer bias over southern and south-eastern Europe reflect common model biases. For seasonal mean quantities averaged over large European sub-domains, no clear benefit of an increased spatial resolution (12 km vs. 50 km) can be identified. The bias ranges of the EURO-CORDEX ensemble mostly correspond to those of the ENSEMBLES simulations, but some improvements in model performance can be identified (e.g., a less pronounced southern European warm summer bias). The temperature bias spread across different configurations of one individual model can be of a similar magnitude as the spread across different models, demonstrating a strong influence of the specific choices in physical parameterizations and experimental setup on model performance. Based on a number of simply reproducible metrics, the present study quantifies the currently achievable accuracy of RCMs used for regional climate simulations over Europe and provides a quality standard for future model developments.

Description: Simulation of trace gases and aerosols over the Indian domain: evaluation of the WRF-Chem model Geoscientific Model Development Discussions, 7, 431-482, 2014 Author(s): M. Michael, A. Yadav, S. N. Tripathi, V. P. Kanawade, A. Gaur, P. Sadavarte, and C. Venkataraman The "online" meteorological and chemical transport Weather Research and Forecasting/Chemistry (WRF-Chem) model has been implemented over the Indian subcontinent for three consecutive summers in 2008, 2009 and 2010 to study the aerosol properties over the domain. The model simulated the meteorological parameters, trace gases and particulate matter. Predicted mixing ratios of trace gases (Ozone, carbon monoxide and sulfur dioxide) are compared with ground based observations over Kanpur. Simulated aerosol optical depth are compared with those observed at nine Aerosol Robotic Network stations (AERONET). The simulations show that the aerosol optical depth of the less polluted regions is better simulated compared to that of the locations where the aerosol loading is very high. The vertical profiles of extinction coefficient observed at the Kanpur Micropulse Lidar Network (MPLNET) station is underpredicted by the model by 10 to 50% for altitudes greater than 1.5 km and qualitatively simulate the elevated layers of aerosols. The simulated mass concentration of black carbon shows a correlation coefficient of 0.4 with observations. Vertical profiles of black carbon at various locations have also been compared with observations from an aircraft campaign held during pre-monsoon period of 2008 and 2009. This study shows that WRF-Chem model captures many important features of the observed atmospheric composition during the pre-monsoon season in India.

Description: Three-dimensional phase-field study of crack-seal microstructures – insights from innovative post-processing techniques Geoscientific Model Development Discussions, 7, 631-658, 2014 Author(s): K. Ankit, M. Selzer, and B. Nestler Numerical simulations of vein evolution contribute to a better understanding of processes involved in their formation and possess the potential to provide invaluable insights into the rock deformation history and fluid flow pathways. The primary aim of the present article is to investigate the influence of a "realistic" boundary condition, i.e. an algorithmically generated "fractal" surface, on the vein evolution in 3-D using a thermodynamically consistent approach, while explaining the benefits of accounting for an extra dimensionality. The 3-D simulation results are supplemented by innovative numerical post-processing and advanced visualization techniques. The new methodologies to measure the tracking efficiency demonstrate the importance of accounting the temporal evolution; no such information is usually accessible in field studies and notoriously difficult to obtain from laboratory experiments as well. The grain growth statistics obtained by numerically post-processing the 3-D computational microstructures explain the pinning mechanism which leads to arrest of grain boundaries/multi-junctions by crack peaks, thereby, enhancing the tracking behavior.

Description: A simple parameterization of the short-wave aerosol optical properties for surface direct and diffuse irradiances assessment in a numerical weather model Geoscientific Model Development Discussions, 7, 593-629, 2014 Author(s): J. A. Ruiz-Arias and J. Dudhia Broadband short-wave (SW) surface direct and diffuse irradiances are not typically within the set of output variables produced by numerical weather prediction (NWP) models. However, they are being more and more demanded in solar energy applications. A detailed representation of the aerosol optical properties is important to achieve an accurate assessment of these direct and diffuse irradiances. Nonetheless, NWP models typically oversimplify its representation or even neglect its effect. In this work, a flexible method to account for the SW aerosol optical properties in the computation of broadband SW surface direct and diffuse irradiances is presented. It only requires aerosol optical depth at 0.55 μm and the type of predominant aerosol. The rest of parameters needed to consider spectral aerosol extinction, namely, Angström exponent, aerosol single-scattering albedo and aerosol asymmetry factor, are parameterized. The parameterization has been tested in the RRTMG SW scheme of the Weather Research and Forecasting (WRF) NWP model. However, it can be adapted to any other SW radiative transfer band model. It has been verified against a control experiment along five radiometric stations in the contiguous US. The control experiment consisted of a clear-sky evaluation of the RRTMG solar radiation estimates obtained in WRF when RRTMG is driven with ground-observed aerosol optical properties. Overall, the verification has shown very satisfactory results for both broadband SW surface direct and diffuse irradiances. It has proven effective to significantly reduce the prediction error and constraint the seasonal bias in clear-sky conditions to within the typical observational error in well-maintained radiometers.

Description: High resolution global climate modelling; the UPSCALE project, a large simulation campaign Geoscientific Model Development Discussions, 7, 563-591, 2014 Author(s): M. S. Mizielinski, M. J. Roberts, P. L. Vidale, R. Schiemann, M.-E. Demory, J. Strachan, T. Edwards, A. Stephens, B. N. Lawrence, M. Pritchard, P. Chiu, A. Iwi, J. Churchill, C. del Cano Novales, J. Kettleborough, W. Roseblade, P. Selwood, M. Foster, M. Glover, and A. Malcolm The UPSCALE (UK on PRACE: weather-resolving Simulations of Climate for globAL Environmental risk) project constructed and ran an ensemble of HadGEM3 (Hadley centre Global Environment Model 3) atmosphere-only global climate simulations over the period 1985–2011, at resolutions of N512 (25 km), N216 (60 km) and N96 (130 km) as used in current global weather forecasting, seasonal prediction and climate modelling respectively. Alongside these present climate simulations a parallel ensemble looking at extremes of future climate was run, using a time-slice methodology to consider conditions at the end of this century. These simulations were primarily performed using a 144 million core hour, single year grant of computing time from PRACE (the Partnership for Advanced Computing in Europe) in 2012, with additional resources supplied by the Natural Environmental Research Council (NERC) and the Met Office. Almost 400 terabytes of simulation data were generated on the HERMIT supercomputer at the high performance computing center Stuttgart (HLRS), and transferred to the JASMIN super-data cluster provided by the Science and Technology Facilities Council Centre for Data Archival (STFC CEDA) for analysis and storage. In this paper we describe the implementation of the project, present the technical challenges in terms of optimisation, data output, transfer and storage that such a project involves and include details of the model configuration and the composition of the UPSCALE dataset. This dataset is available for scientific analysis to allow assessment of the value of model resolution in both present and potential future climate conditions.

Description: A suite of Early Eocene (~55 Ma) climate model boundary conditions Geoscientific Model Development Discussions, 7, 529-562, 2014 Author(s): N. Herold, J. Buzan, M. Seton, A. Goldner, J. A. M. Green, R. D. Müller, P. Markwick, and M. Huber We describe a set of Early Eocene (~55 Ma) climate model boundary conditions constructed in a self-consistent reference frame and incorporating recent data and methodologies. Given the growing need for uniform experimental design within the Eocene climate modelling community, we make publically available our datasets of Eocene topography, bathymetry, tidal dissipation, vegetation, aerosol distributions and river runoff. Particularly our Eocene topography and bathymetry has been significantly improved compared to previously utilized boundary conditions. Major improvements include the paleogeography of Antarctica, Australia, Europe, the Drake Passage and the Isthmus of Panama, and our boundary conditions include modelled estimates of Eocene aerosol distributions and tidal dissipation for the first time, both consistent with our paleotopography and paleobathymetry. The resolution of our datasets (1° × 1°) is also unprecedented and will facilitate high resolution climate simulations. In light of the inherent uncertainties involved in reconstructing global boundary conditions for past time periods these datasets should be considered as one interpretation of the available data. This paper marks the beginning of a process for reconstructing a set of accurate, open-access Eocene boundary conditions for use in climate models.

Description: Improved simulation of fire-vegetation interactions in the Land surface Processes and eXchanges dynamic global vegetation model (LPX-Mv1) Geoscientific Model Development Discussions, 7, 931-1000, 2014 Author(s): D. I. Kelley, S. P. Harrison, and I. C. Prentice The Land surface Processes and eXchanges (LPX) model is a fire-enabled dynamic global vegetation model that performs well globally but has problems representing fire regimes and vegetative mix in savannas. Here we focus on improving the fire module. To improve the representation of ignitions, we introduced a treatment of lightning that allows the fraction of ground strikes to vary spatially and seasonally, realistically partitions strike distribution between wet and dry days, and varies the number of dry-days with strikes. Fuel availability and moisture content were improved by implementing decomposition rates specific to individual plant functional types and litter classes, and litter drying rates driven by atmospheric water content. To improve water extraction by grasses, we use realistic plant-specific treatments of deep roots. To improve fire responses, we introduced adaptive bark thickness and post-fire resprouting for tropical and temperate broadleaf trees. All improvements are based on extensive analyses of relevant observational data sets. We test model performance for Australia, first evaluating parameterisations separately and then measuring overall behaviour against standard benchmarks. Changes to the lightning parameterisation produce a more realistic simulation of fires in southeastern and central Australia. Implementation of PFT-specific decomposition rates enhances performance in central Australia. Changes in fuel drying improve fire in northern Australia, while changes in rooting depth produce a more realistic simulation of fuel availability and structure in central and northern Australia. The introduction of adaptive bark thickness and resprouting produces more realistic fire regimes in savannas, including simulating biomass recovery rates consistent with observations. The new model (LPX-Mv1) improves Australian vegetation composition by 33% and burnt area by 19% compared to LPX.

Description: Estimation of uncertainties due to data scarcity in model upscaling: a case study of methane emissions from rice paddies in China Geoscientific Model Development Discussions, 7, 181-216, 2014 Author(s): W. Zhang, T. Li, Y. Huang, Q. Zhang, J. Bian, and P. Han Data scarcity is a major cause of substantial uncertainties in regional estimations conducted with model upscaling. To evaluate the impact of data scarcity on model upscaling, we introduce an approach for aggregating uncertainties in model estimations. A data sharing matrix was developed to aggregate the modeled uncertainties in divisions of a subject region. In a case study, the uncertainty in methane emissions from rice paddies on mainland China was calculated with a local-scale model CH4MOD. The data scarcities in five of the most sensitive model variables were included in the analysis. The national total methane emissions were 6.44–7.32 Tg, depending on the spatial resolution used for modeling, with a 95% confidence interval of 4.5–8.7 Tg. Based on the data sharing matrix, two numeral indices, I R and I ds , were also introduced to suggest the proper spatial resolution in model upscaling.

Description: A flexible three-dimensional stratocumulus, cumulus and cirrus cloud generator (3DCLOUD) based on drastically simplified atmospheric equations and Fourier transform framework Geoscientific Model Development Discussions, 7, 295-337, 2014 Author(s): F. Szczap, Y. Gour, T. Fauchez, C. Cornet, T. Faure, O. Jourdan, and P. Dubuisson The 3DCLOUD algorithm for generating stochastic three-dimensional (3-D) cloud fields is described in this paper. The generated outputs are 3-D optical depth (τ) for stratocumulus and cumulus fields and 3-D ice water content (IWC) for cirrus clouds. This model is designed to generate cloud fields that share some statistical properties observed in real clouds such as the inhomogeneity parameter ρ (standard deviation normalized by the mean of the studied quantity), the Fourier spectral slope β close to −5/3 between the smallest scale of the simulation to the outer L out (where the spectrum becomes flat). Firstly, 3DCLOUD assimilates meteorological profiles (humidity, pressure, temperature and wind velocity). The cloud coverage C , defined by the user, can also be assimilated, but only for stratocumulus and cumulus regime. 3DCLOUD solves drastically simplified basic atmospheric equations, in order to simulate 3-D cloud structures of liquid or ice water content. Secondly, Fourier filtering method is used to constrain intensity of ρ, β, L out and mean of τ or IWC of these 3-D cloud structures. 3DCLOUD model was developed to run on a personnel computer under Matlab environment with the Matlab statistics toolbox. It is used to study 3-D interactions between cloudy atmosphere and radiation.

Description: Global mass fixer algorithms for conservative tracer transport in the ECMWF model Geoscientific Model Development Discussions, 7, 777-814, 2014 Author(s): M. Diamantakis and J. Flemming Various mass fixer algorithms (MFA) have been implemented in the Integrated Forecasting System (IFS) of ECMWF to ensure mass conservation of atmospheric tracers within the Semi-Lagrangian (SL) advection scheme. Emphasis has been placed in implementing schemes that despite being primarily global in nature adjust the solution mostly in regions where the advected field has large gradients and therefore interpolation (transport) error is assumed larger. The MFA have been tested in weather forecast, idealised and atmospheric dispersion cases. Applying these fixers to specific humidity and cloud fields did not change the accuracy of 10 day forecasts. In other words, global mass tracer conservation is achieved without deteriorating the solution accuracy. However, for longer forecast timescales or for forecasts in which correlated species are transported, experiments suggest that MFA may improve IFS forecasts.

Description: Simultaneous parameterization of the two-source evapotranspiration model by Bayesian approach: application to spring maize in an arid region of northwest China Geoscientific Model Development Discussions, 7, 741-775, 2014 Author(s): G. F. Zhu, X. Li, Y. H. Su, K. Zhang, Y. Bai, J. Z. Ma, C. B. Li, X. L. Hu, and J. H. He Based on direct measurements of half-hourly canopy evapotranspiration (ET; W m −2 ) using the eddy covariance (EC) system and daily soil evaporation ( E ; mm d −1 ) using microlysimeters over a crop ecosystem in arid northwest China from 27 May to 14 September in 2013, a Bayesian method was used to simultaneously parameterize the soil surface and canopy resistances in the Shuttleworth–Wallace (S–W) model. The posterior distributions of the parameters in most cases were well updated by the multiple measuring dataset with relatively narrow high-probability intervals. There was a good agreement between measured and simulated values of half-hourly ET and daily E with a linear regression being y = 0.84 x +0.18 ( R 2 = 0.83) and y = 1.01 x + 0.01 ( R 2 = 0.82), respectively. The causes of underestimations of ET by the S–W model was mainly attributed to the micro-scale advection, which can contribute an added energy in the form of downward sensible heat fluxes to the ET process. Therefore, the advection process should be taken into accounted in simulating ET in heterogeneous land surface. Also, underestimations were observed on or shortly after rainy days due to direct evaporation of liquid water intercepted in the canopy. Thus, the canopy interception model should be coupled to the S–W model in the long-term ET simulation.

Description: The MESSy aerosol submodel MADE3 (v2.0b): description and a box model test Geoscientific Model Development Discussions, 7, 691-739, 2014 Author(s): J. C. Kaiser, J. Hendricks, M. Righi, N. Riemer, R. A. Zaveri, S. Metzger, and V. Aquila We introduce MADE3 (Modal Aerosol Dynamics model for Europe, adapted for global applications, 3rd generation), an aerosol dynamics submodel for application within the MESSy framework (Modular Earth Submodel System). MADE3 builds on the predecessor aerosol submodels MADE and MADE-in. Its main new features are the explicit representation of coarse particle interactions both with other particles and with condensable gases, and the inclusion of hydrochloric acid (HCl)/chloride (Cl) partitioning between the gas and condensed phases. The aerosol size distribution is represented in the new submodel as a superposition of nine lognormal modes: one for fully soluble particles, one for insoluble particles, and one for mixed particles in each of three size ranges (Aitken, accumulation, and coarse mode size ranges). In order to assess the performance of MADE3 we compare it to its predecessor MADE and to the much more detailed particle-resolved aerosol model PartMC-MOSAIC in a box model simulation of an idealised marine boundary layer test case. MADE3 and MADE results are very similar, except in the coarse mode, where the aerosol is dominated by sea spray particles. Cl is reduced in MADE3 with respect to MADE due to the HCl/Cl partitioning that leads to Cl removal from the sea spray aerosol in our test case. Additionally, aerosol nitrate concentration is higher in MADE3 due to the condensation of nitric acid on coarse particles. MADE3 and PartMC-MOSAIC show substantial differences in the fine particle size distributions (sizes ≲ 2 μm) that could be relevant when simulating climate effects on a global scale. Nevertheless, the agreement between MADE3 and PartMC-MOSAIC is very good when it comes to coarse particle size distribution, and also in terms of aerosol composition. Considering these results and the well-established ability of MADE in reproducing observed aerosol loadings and composition, MADE3 seems suitable for application within a global model.

Description: Long residence times of rapidly decomposable soil organic matter: application of a multi-phase, multi-component, and vertically-resolved model (TOUGHREACTv1) to soil carbon dynamics Geoscientific Model Development Discussions, 7, 815-870, 2014 Author(s): W. J. Riley, F. M. Maggi, M. Kleber, M. S. Torn, J. Y. Tang, D. Dwivedi, and N. Guerry Accurate representation of soil organic matter (SOM) dynamics in Earth System Models is critical for future climate prediction, yet large uncertainties exist regarding how, and to what extent, the suite of proposed relevant mechanisms should be included. To investigate how various mechanisms interact to influence SOM storage and dynamics, we developed a SOM reaction network integrated in a one-dimensional, multi-phase, and multi-component reactive transport solver. The model includes representations of bacterial and fungal activity, multiple archetypal polymeric and monomeric carbon substrate groups, aqueous chemistry, aqueous advection and diffusion, gaseous diffusion, and adsorption (and protection) and desorption from the soil mineral phase. The model predictions reasonably matched observed depth-resolved SOM and dissolved organic carbon (DOC) stocks in grassland ecosystems as well as lignin content and fungi to aerobic bacteria ratios. We performed a suite of sensitivity analyses under equilibrium and dynamic conditions to examine the role of dynamic sorption, microbial assimilation rates, and carbon inputs. To our knowledge, observations do not exist to fully test such a complicated model structure or to test the hypotheses used to explain observations of substantial storage of very old SOM below the rooting depth. Nevertheless, we demonstrated that a reasonable combination of sorption parameters, microbial biomass and necromass dynamics, and advective transport can match observations without resorting to an arbitrary depth-dependent decline in SOM turnover rates, as is often done. We conclude that, contrary to assertions derived from existing turnover time based model formulations, observed carbon content and δ 14 C vertical profiles are consistent with a representation of SOM dynamics consisting of (1) carbon compounds without designated intrinsic turnover times, (2) vertical aqueous transport, and (3) dynamic protection on mineral surfaces.

Description: A novel model evaluation approach focussing on local and advected contributions to urban PM 2.5 levels – application to Paris, France Geoscientific Model Development Discussions, 6, 6391-6457, 2013 Author(s): H. Petetin, M. Beekmann, J. Sciare, M. Bressi, A. Rosso, O. Sanchez, and V. Ghersi Aerosol simulations in chemistry transport models (CTMs) still suffer from numerous uncertainties, and diagnostic evaluations are required to point out major error sources. This paper presents an original approach to evaluate CTMs based on local and imported contributions in a large megacity rather than urban background concentrations. The study is applied to the CHIMERE model in the Paris region (France) and considers the fine particulate matter (PM 2.5 ) and its main chemical constituents (elemental and organic carbon, nitrate, sulfate and ammonium), for which daily measurements are available during a whole year at various stations (PARTICULES project). Back-trajectory data are used to locate the upwind station, from which the concentration is identified as the import, the local production being deduced from the urban concentration by subtraction. Uncertainties on these contributions are quantified. Small biases in urban background PM 2.5 simulations (bias of +16%) hide significant error compensations between local and advected contributions, as well as in PM 2.5 chemical compounds. In particular, wintertime OM imports appear strongly underestimated while local OM and EC production are overestimated all along the year. Erroneous continental woodburning emissions and missing SOA pathways may explain errors on advected OM, while carbonaceous compounds overestimation is likely to be related to errors in emissions and dynamics. A statistically significant local formation of nitrate is also highlighted from observations, but missed by the model. Together with the overestimation of nitrate imports, it leads to a bias of +51% on the local PM 2.5 contribution. Such an evaluation finally gives more detailed insights on major gaps in current CTMs on which future efforts are needed.

Description: Adding a dynamical cryosphere into i LOVECLIM (version 1.0) – Part 1: Coupling with the GRISLI ice-sheet model Geoscientific Model Development Discussions, 6, 5215-5249, 2013 Author(s): D. M. Roche, C. Dumas, M. Bügelmayer, S. Charbit, and C. Ritz We present the coupling approach and the first results of the GRISLI ice-sheet model within the i LOVECLIM coupled climate model. The climate component is a relatively low resolution Earth System Model of Intermediate complexity, well suited for long-term integrations and thus for coupled climate–cryosphere studies. We describe the coupling procedure with emphasise on the downscaling scheme and the methods to compute the snow fraction from total precipitation fields. We then present results for the Northern Hemisphere ice sheet (Greenland) under pre-industrial climate conditions at the end of a 14 000 yr-long integration. The obtained simulated ice sheet presents a too large thickness in central Greenland owing to the overestimation of precipitation in the atmospheric component. We find that including downscaling procedures for temperature improves the temperature distributions over Greenland for both summer and annual mean temperatures. Overall, we find an ice-sheet areal extent in reasonnable agreement with the observed Greenland ice sheet given the simplicity of the chosen climate model.

Description: ADISM v.1.0: an adjoint of a thermomechanical ice-sheet model obtained using an algorithmic differentiation tool Geoscientific Model Development Discussions, 6, 5251-5288, 2013 Author(s): J. McGovern, I. Rutt, J. Utke, and T. Murray A number of problems in contemporary glaciology could benefit from the application of adjoint models. On a simple level, adjoint models can be used to calculate ice-sheet sensitivities with respect to spatially varying parameters such as the basal sliding coefficient. At a more sophisticated level, adjoint models may be used as components of variational data assimilation schemes, allowing problems of model initialization and data-constrained evolution to be tackled. Fundamentally, adjoint models calculate the sensitivity of a cost function to a suite of control parameters. Such model sensitivities can alternatively be obtained by running the model many times, perturbing each control parameter separately in turn, and calculating the resulting sensitivity in each case. For large numbers of control parameters, however, such as the case where a control parameter corresponds to each point in the model domain, the computational cost becomes prohibitive. The use of adjoint models allows sensitivities to be obtained more efficiently – adjoint model sensitivities are obtained in a single run – and more accurately, since the differentiation of the model is done with machine precision. We present a finite-difference shallow ice approximation (SIA), thermomechanical ice-sheet model (the forward model), and its adjoint, as generated by using the OpenAD algorithmic differentiation tool. We verify the ice-sheet model using standard SIA benchmark tests and check the consistency between derivatives computed by OpenAD and certain numerically approximated derivatives. Typical adjoint calculations are demonstrated by application to the Greenland ice sheet.

Description: Implementation of a soil albedo scheme in the CABLEv1.4b land surface model and evaluation against MODIS estimates over Australia Geoscientific Model Development Discussions, 7, 1671-1707, 2014 Author(s): J. Kala, J. P. Evans, A. J. Pitman, C. B. Schaaf, M. Decker, C. Carouge, D. Mocko, and Q. Sun Land surface albedo, the fraction of incoming solar radiation reflected by the land surface, is a key component of the earth system. This study evaluates snow-free surface albedo simulations by the Community Atmosphere Biosphere Land Exchange (CABLEv1.4b) model with the Moderate Resolution Imaging Spectroradiometer (MODIS) albedo. We compare results from two offline simulations over the Australian continent, one with prescribed background snow-free and vegetation-free soil albedo derived from MODIS (the control), and the other with a simple parameterisation based on soil moisture and colour. The control simulation shows that CABLE simulates albedo over Australia reasonably well, with differences with MODIS within an acceptable range. Inclusion of the parameterisation for soil albedo however introduced large errors for the near infra red albedo, especially for desert regions of central Australia. These large errors were not fully explained by errors in soil moisture or parameter uncertainties, but are similar to errors in albedo in other land surface models which use the same soil albedo scheme. Although this new parameterisation has introduced larger errors as compared to prescribing soil albedo, dynamic soil moisture-albedo feedbacks are now enabled in CABLE. Future directions for albedo parameterisations development in CABLE are discussed.

Description: Coupling the high complexity land surface model ACASA to the mesoscale model WRF Geoscientific Model Development Discussions, 7, 2829-2875, 2014 Author(s): L. Xu, R. D. Pyles, K. T. Paw U, S. H. Chen, and E. Monier In this study, the Weather Research and Forecasting Model (WRF) is coupled with the Advanced Canopy–Atmosphere–Soil Algorithm (ACASA), a high complexity land surface model. Although WRF is a state-of-the-art regional atmospheric model with high spatial and temporal resolutions, the land surface schemes available in WRF are simple and lack the capability to simulate carbon dioxide, for example, the popular NOAH LSM. ACASA is a complex multilayer land surface model with interactive canopy physiology and full surface hydrological processes. It allows microenvironmental variables such as air and surface temperatures, wind speed, humidity, and carbon dioxide concentration to vary vertically. Simulations of surface conditions such as air temperature, dew point temperature, and relative humidity from WRF–ACASA and WRF–NOAH are compared with surface observation from over 700 meteorological stations in California. Results show that the increase in complexity in the WRF–ACASA model not only maintains model accuracy, it also properly accounts for the dominant biological and physical processes describing ecosystem-atmosphere interactions that are scientifically valuable. The different complexities of physical and physiological processes in the WRF–ACASA and WRF–NOAH models also highlight the impacts of different land surface and model components on atmospheric and surface conditions.

Description: Improved routines to model the ocean carbonate system: mocsy 1.0 Geoscientific Model Development Discussions, 7, 2877-2902, 2014 Author(s): J. C. Orr and J.-M. Epitalon Software used by modelers to compute ocean carbonate chemistry is often based on code from the Ocean Carbon Cycle Model Intercomparison Project (OCMIP), last revised in 2005. As an update, we offer here new publicly available Fortran 95 routines to model the ocean carbonate system (mocsy). Both codes take as input dissolved inorganic carbon C T and total alkalinity A T , the only two tracers of the ocean carbonate system that are unaffected by changes in temperature and salinity and conservative with respect to mixing, properties that make them ideally suited for ocean carbon models. With the same basic thermodynamic equilibria, both codes compute surface-ocean p CO 2 in order to simulate air–sea CO 2 fluxes. The mocsy package goes beyond the OCMIP code by computing all other carbonate system variables (e.g., pH, CO 3 2− , and CaCO 3 saturation states) and by doing so throughout the water column. Moreover, it avoids three common model approximations: that density is constant, that modeled potential temperature is equivalent to in situ temperature, and that depth is equivalent to pressure. These approximations work well at the surface, but total errors in computed variables grow with depth, e.g., reaching −8 μatm in p CO 2 , +0.010 in pH, and +0.01 in Ω A at 5000 m. Besides the equilibrium constants recommended for best practices, mocsy also offers users three new options: (1) a recent formulation for total boron that increases its ocean content by 4%, (2) an older formulation for K F common to all other such software, and (3) recent formulations for K 1 and K 2 designed to also include low-salinity waters. More total boron increases borate alkalinity and reduces carbonate alkalinity, which is calculated as a difference from total alkalinity. As a result, the computed surface p CO 2 increases by 4 to 6 μatm, while the computed aragonite saturation horizon (ASH) shallows by 60 m in the North Atlantic and by up to 90 m in the Southern Ocean. Changes due to the new formulation for K 1 and K 2 enhance p CO 2 by up to 8 μatm in the deep ocean and in high-latitude surface waters. These changes are comparable in magnitude to errors in the same regions associated with neglecting nutrient contributions to total alkalinity, a common practice in ocean biogeochemical modeling. The mocsy code with the standard options for best practices and none of the 3 approximations agrees with results from the CO2SYS package generally within 0.005%.

Description: Droplet activation parameterization: the population splitting concept revisited Geoscientific Model Development Discussions, 7, 2903-2932, 2014 Author(s): R. Morales Betancourt and A. Nenes In this work we postulate, implement and evaluate modifications to the "population splitting" concept introduced by Nenes and Seinfeld (2003) for calculation of water condensation rates in droplet activation parameterizations. The modifications introduced here lead to an improved accuracy and precision of the parameterization-derived maximum supersaturation, s max , and droplet number concentration, N d , as determined by comparing against those of detailed numerical simulations of the activation process. A numerical computation of the first-order derivatives ∂ N d /∂ χ j of the parameterized N d to input variables χ j was performed, and compared against the corresponding parcel model derived sensitivities, providing a thorough evaluation of the impacts of the introduced modifications in the parameterization ability to respond to aerosol characteristics. The proposed modifications require only minor changes for their numerical implementation in existing codes based on the population splitting concept.

Description: SEHR-ECHO v1.0: a Spatially-Explicit Hydrologic Response model for ecohydrologic applications Geoscientific Model Development Discussions, 7, 1865-1904, 2014 Author(s): B. Schaefli, L. Nicótina, C. Imfeld, P. Da Ronco, E. Bertuzzo, and A. Rinaldo This paper presents the Spatially-Explicit Hydrologic Response (SEHR) model developed at the Laboratory of Ecohydrology of the Ecole Polytechnique Fédérale de Lausanne for the simulation of hydrological processes at the catchment scale. The key concept of the model is the formulation of water transport by geomorphologic travel time distributions through gravity-driven transitions among geomorphic states: the mobilization of water (and possibly dissolved solutes) is simulated at the sub-catchment scale and the resulting responses are convolved with the travel paths distribution within the river network to obtain the hydrologic response at the catchment outlet. The model thus breaks down the complexity of the hydrologic response into an explicit geomorphological combination of dominant spatial patterns of precipitation input and of hydrologic process controls. Nonstationarity and nonlinearity effects are tackled through soil moisture dynamics in the active soil layer. We present here the basic model set-up for precipitation–runoff simulation. The performance of the model is illustrated for a snow-dominated catchment in Switzerland with a small glacier cover.

Description: Modelling of primary aerosols in the chemical transport model MOCAGE: development and evaluation of aerosol physical parameterizations Geoscientific Model Development Discussions, 7, 2745-2796, 2014 Author(s): B. Sič, L. El Amraoui, V. Marécal, B. Josse, J. Arteta, J. Guth, M. Joly, and P. Hamer This paper deals with recent improvements to the chemical transport model of Météo-France MOCAGE that consists of updates to different aerosol parameterizations. MOCAGE only contains primary aerosol species. We introduced important changes to the aerosol parameterization concerning emissions, wet deposition and sedimentation. For the emissions, size distribution and wind calculations are modified for desert dust aerosols, and a surface sea temperature dependant source function is introduced for sea salt aerosols. Wet deposition is modified toward a more physically realistic representation by introducing re-evaporation of falling rain and snowfall scavenging, and by changing in-cloud scavenging scheme along with calculations of precipitation cloud cover and rain properties. The sedimentation scheme update includes changes regarding the stability and viscosity calculations. Independent data from satellites (MODIS, SEVIRI), the ground (AERONET), and a model inter-comparison project (AeroCom) is compared with MOCAGE simulations and showed that the introduced changes brought a significant improvement on aerosol representation, properties and global distribution. Emitted quantities of desert dust and sea salt, as well their lifetimes, moved closer towards values of AeroCom estimates and the multi-model average. When comparing the model simulations with MODIS aerosol optical depth (AOD) observations over the oceans, the updated model configuration shows a decrease in the bias (from 0.032 to 0.002) and a better correlation (from 0.062 to 0.322) in terms of the geographical distribution and the temporal variability. The updates corrected a strong positive bias in the sea salt representation at high latitudes (from 0.153 to 0.026), and a negative bias in the desert dust representation in the African dust outflow region (from −0.179 to −0.051). The updates in sedimentation produced a modest difference; the bias with MODIS data from 0.002 in the updated configuration went to 0.003 in the updated configuration only without the sedimentation updates. Yet, the updates in the emissions and the wet deposition made a stronger impact on the results; the bias was 0.041 and 0.032 in updated configurations only without emission, and wet deposition updates, respectively. Also, the lifetime, the extent, and the strength of the episodic aerosol events are better reproduced in the updated configuration. The wet deposition processes and the differences between the various configurations that were tested greatly influence the representation of the episodic events. However, wet deposition is not a continuous process; it has a local and episodic signature and its representation depends strongly on the precipitation regime in the model.

Description: MM5 v3.6.1 and WRF v3.2.1 model comparison of standard and surface energy variables in the development of the planetary boundary layer Geoscientific Model Development Discussions, 7, 2705-2743, 2014 Author(s): C.-S. M. Wilmot, B. Rappenglück, and X. Li Air quality forecasting requires atmospheric weather models to generate accurate meteorological conditions, one of which is the development of the planetary boundary layer (PBL). An important contributor to the development of the PBL is the land-air exchange captured in the energy budget as well as turbulence parameters. Standard and surface energy variables were modeled using the fifth-generation Penn State/National Center for Atmospheric Research mesoscale model (MM5), version 3.6.1, and the Weather Research and Forecasting (WRF) model, version 3.2.1, and compared to measurements for a southeastern Texas coastal region. The study period was 28 August–1 September 2006. It also included a frontal passage. The results of the study are ambiguous. Although WRF does not perform as well as MM5 in predicting PBL heights, it better simulates most of the general and energy budget variables. Both models overestimate incoming solar radiation, which implies a surplus of energy that could be redistributed in either the partitioning of the surface energy variables or in some other aspect of the meteorological modeling not examined here. The MM5 model consistently had much drier conditions than the WRF model, which could lead to more energy available to other parts of the meteorological system. On the clearest day of the study period MM5 had increased latent heat flux, which could lead to higher evaporation rates and lower moisture in the model. However, this latent heat disparity between the two models is not visible during any other part of the study. The observed frontal passage affected the performance of most of the variables, including the radiation, flux, and turbulence variables, at times creating dramatic differences in the r 2 values.

Description: A new WRF-Chem treatment for studying regional scale impacts of cloud-aerosol interactions in parameterized cumuli Geoscientific Model Development Discussions, 7, 2651-2704, 2014 Author(s): L. K. Berg, M. Shrivastava, R. C. Easter, J. D. Fast, E. G. Chapman, and Y. Liu A new treatment of cloud-aerosol interactions within parameterized shallow and deep convection has been implemented in WRF-Chem that can be used to better understand the aerosol lifecycle over regional to synoptic scales. The modifications to the model to represent cloud-aerosol interactions include treatment of the cloud droplet number mixing ratio; key cloud microphysical and macrophysical parameters (including the updraft fractional area, updraft and downdraft mass fluxes, and entrainment) averaged over the population of shallow clouds, or a single deep convective cloud; and vertical transport, activation/resuspension, aqueous chemistry, and wet removal of aerosol and trace gases in warm clouds. These changes have been implemented in both the WRF-Chem chemistry packages as well as the Kain–Fritsch cumulus parameterization that has been modified to better represent shallow convective clouds. Preliminary testing of the modified WRF-Chem has been completed using observations from the Cumulus Humilis Aerosol Processing Study (CHAPS) as well as a high-resolution simulation that does not include parameterized convection. The simulation results are used to investigate the impact of cloud-aerosol interactions on regional scale transport of black carbon (BC), organic aerosol (OA), and sulfate aerosol. Based on the simulations presented here, changes in the column integrated BC can be as large as −50% when cloud-aerosol interactions are considered (due largely to wet removal), or as large as +40% for sulfate in non-precipitating conditions due to the sulfate production in the parameterized clouds. The modifications to WRF-Chem version 3.2.1 are found to account for changes in the cloud drop number concentration (CDNC) and changes in the chemical composition of cloud-drop residuals in a way that is consistent with observations collected during CHAPS. Efforts are currently underway to port the changes described here to WRF-Chem version 3.5, and it is anticipated that they will be included in a future public release of WRF-Chem.

Description: IL-GLOBO (1.0) – integrated Lagrangian particle model and Eulerian general circulation model GLOBO: development of the vertical diffusion module Geoscientific Model Development Discussions, 7, 2797-2828, 2014 Author(s): D. Rossi and A. Maurizi The development and validation of the vertical diffusion module of IL-GLOBO, a Lagrangian transport model coupled online with the Eulerian General Circulation Model GLOBO, is described. The module simulates the effects of turbulence on particle motion by means of a Lagrangian Stochastic Model (LSM) consistent with the turbulent diffusion equation used in GLOBO. The implemented LSM integrates particle trajectories, using the native σ-hybrid coordinates of the Eulerian component, and fulfills the Well Mixed Condition (WMC) in the general case of a variable density profile. The module is validated through a series of 1-D numerical experiments by assessing its accuracy in maintaining an initially well mixed distribution. A dynamical time-step selection algorithm with constraints related to the shape of the diffusion coefficient profile is developed and gives accurate results, even for strongly peaked diffusivity profiles. Finally, the skills of a linear interpolation and a modified Akima spline interpolation method are compared, showing that the former generally introduces deviations from the WMC, due to the inconsistency between the local value of the diffusion coefficient and its derivatives. The Akima interpolation algorithm, for which the model satisfies the WMC rigorously, has a computational cost within 120% of the linear interpolation algorithm, making it a reasonable option for implementation in the 3-D model.

Description: A model using marginal efficiency of investment to analyse carbon and nitrogen interactions in terrestrial ecosystems (ACONITE Version 1) Geoscientific Model Development Discussions, 7, 2525-2580, 2014 Author(s): R. Q. Thomas and M. Williams Carbon (C) and nitrogen (N) cycles are coupled in terrestrial ecosystems through multiple processes including photosynthesis, tissue allocation, respiration, N fixation, N uptake, and decomposition of litter and soil organic matter. Capturing the constraint of N on terrestrial C uptake and storage has been a focus of the Earth System modelling community. However there is little understanding of the trade-offs and sensitivities of allocating C and N to different tissues in order to optimize the productivity of plants. Here we describe a new, simple model of ecosystem C–N cycling and interactions (ACONITE), that builds on theory related to plant economics in order to predict key ecosystem properties (leaf area index, leaf C : N, N fixation, and plant C use efficiency) using emergent constraints provided by marginal returns on investment for C and/or N allocation. We simulated and evaluated steady-state ecosystem stocks and fluxes in three different forest ecosystems types (tropical evergreen, temperate deciduous, and temperate evergreen). Leaf C : N differed among the three ecosystem types (temperate deciduous 〈 tropical evergreen 〈 temperature evergreen), a result that compared well to observations from a global database describing plant traits. Gross primary productivity (GPP) and net primary productivity (NPP) estimates compared well to observed fluxes at the simulation sites. Simulated N fixation at steady-state, calculated based on relative demand for N and the marginal return on C investment to acquire N, was an order of magnitude higher in the tropical forest than in the temperate forest, consistent with observations. A sensitivity analysis revealed that parameterization of the relationship between leaf N and leaf respiration had the largest influence on leaf area index and leaf C : N. Also, a widely used linear leaf N-respiration relationship did not yield a realistic leaf C : N, while a more recently reported non-linear relationship performed better. A parameter governing how photosynthesis scales with day length had the largest influence on total vegetation C, GPP, and NPP. Multiple parameters associated with photosynthesis, respiration, and N uptake influenced the rate of N fixation. Overall, our ability to constrain leaf area index and have spatially and temporally variable leaf C : N helps address challenges for ecosystem and Earth System models. Furthermore, the simple approach with emergent properties based on coupled C–N dynamics has potential for use in research that uses data-assimilation methods to integrate data on both the C and N cycles to improve C flux forecasts.

Description: Description and basic evaluation of BNU-ESM version 1 Geoscientific Model Development Discussions, 7, 1601-1647, 2014 Author(s): D. Ji, L. Wang, J. Feng, Q. Wu, H. Cheng, Q. Zhang, J. Yang, W. Dong, Y. Dai, D. Gong, R.-H. Zhang, X. Wang, J. Liu, J. C. Moore, D. Chen, and M. Zhou An earth system model has been developed at Beijing Normal University (Beijing Normal University Earth System Model, BNU-ESM); the model is based on several widely evaluated climate model components and is used to study mechanisms of ocean–atmosphere interactions, natural climate variability and carbon-climate feedbacks at interannual to interdecadal time scales. In this paper, the model structure and individual components are described briefly. Further, results for the CMIP5 (Coupled Model Intercomparison Project phase 5) pre-industrial control and historical simulations are presented to demonstrate the model's performance in terms of the mean model state and the internal variability. It is illustrated that BNU-ESM can simulate many observed features of the earth climate system, such as the climatological annual cycle of surface air temperature and precipitation, annual cycle of tropical Pacific sea surface temperature (SST), the overall patterns and positions of cells in global ocean meridional overturning circulation. For example, the El Niño-Southern Oscillation (ENSO) simulated in BNU-ESM exhibits an irregular oscillation between 2 and 5 years with the seasonal phase locking feature of ENSO. Important biases with regard to observations are presented and discussed, including warm SST discrepancies in the major upwelling regions, an equatorward drift of midlatitude westerly wind bands, and tropical precipitation bias over the ocean that is related to the double Intertropical Convergence Zone (ITCZ).

Description: Towards a representation of halogen chemistry within volcanic plumes in a chemistry transport model Geoscientific Model Development Discussions, 7, 2581-2650, 2014 Author(s): L. Grellier, V. Marécal, B. Josse, P. D. Hamer, T. J. Roberts, A. Aiuppa, and M. Pirre Volcanoes are a known source of halogens to the atmosphere. HBr volcanic emissions lead rapidly to the formation of BrO within volcanic plumes as shown by recent work based on observations and models. BrO, having a longer residence time in the atmosphere than HBr, is expected to have a significant impact on tropospheric chemistry, at least at the local and regional scales. The objective of this paper is to prepare a framework that will allow 3-D modelling of volcanic halogen emissions in order to determine their fate within the volcanic plume and then in the atmosphere at the regional and global scales. This work is based on a 1-D configuration of the chemistry transport model MOCAGE whose low computational cost allows us to perform a large set of sensitivity studies. This paper studies the Etna eruption on the 10 May 2008 that took place just before night time. Adaptations are made to MOCAGE to be able to produce the chemistry occurring within the volcanic plume. A simple sub-grid scale parameterization of the volcanic plume is implemented and tested. The use of this parameterization in a 0.5° × 0.5° configuration (typical regional resolution) has an influence on the partitioning between the various bromine compounds both during the eruption period and also during the night period immediately afterwards. During the day after the eruption, simulations both with and without parameterizations give very similar results that are consistent with the tropospheric column of BrO and SO 2 in the volcanic plume derived from GOME-2 observations. Tests have been performed to evaluate the sensitivity of the results to the mixing between ambient air and the magmatic air at very high temperature at the crater vent that modifies the composition of the emission, and in particular the sulphate aerosol content that is key compound in the BrO production. Simulations show that the plume chemistry is not very sensitive to the assumptions used for the mixing parameter (relative quantity of ambient air mixed with magmatic air in the mixture) that is not well known. This is because there is no large change in the compounds limiting/favouring the BrO production in the plume. The impact of the model grid resolution is also tested in view of future 3-D-simulations at the global scale. A dilution of the emitted gases and aerosols is observed when using the typical global resolution (2°) as compared to a typical regional resolution (0.5°), as expected. Taking this into account, the results of the 2° resolution simulations are consistent with the GOME-2 observations. In general the simulations at 2° resolution are less efficient at producing BrO after the emission both with and without the subgrid-scale parameterization. The differences are mainly due to an interaction between concentration effects than stem from using a reduced volume in the 0.5° resolution combined with second order rate kinetics. The last series of tests were on the mean radius assumed for the sulphate aerosols that indirectly impacts the production of BrO by heterogeneous reactions. The simulations show that the BrO production is sensitive to this parameter with a stronger production when smaller aerosols are assumed. These results will be used to guide the implementation of volcanic halogen emissions in the 3-D configuration of MOCAGE.