ALBERT

Description: The 1-way on-line coupled atmospheric chemistry model system MECO(n) – Part 1: The limited-area atmospheric chemistry model COSMO/MESSy Geoscientific Model Development Discussions, 4, 1305-1358, 2011 Author(s): A. Kerkweg and P. Jöckel The numerical weather prediction model of the Consortium for Small Scale Modelling (COSMO), maintained by the German weather service (DWD), is connected with the Modular Earth Submodel System (MESSy). This effort is undertaken in preparation of a~new, limited-area atmospheric chemistry model. This model is as consistent as possible, with respect to atmospheric chemistry and related processes, with a previously developed global atmospheric chemistry general circulation model: the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. The combined system constitutes a new research tool, bridging the global to the meso-γ scale for atmospheric chemistry research. MESSy provides the infrastructure and includes, among others, the process and diagnostic submodels for atmospheric chemistry simulations. Furthermore, MESSy is highly flexible allowing model setups with tailor made complexity, depending on the scientific question. Here, the connection of the MESSy infrastructure to the COSMO model is documented. Previously published prototype submodels for simplified tracer studies are generalised to be plugged-in and used in the global and the limited-area model. They are used to evaluate the tracer transport characteristics of the new COSMO/MESSy model system, an important prerequisite for future atmospheric chemistry applications. A supplementary document with further details on the technical implementation of the MESSy interface into COSMO with a complete list of modifications to the COSMO code is provided.

Description: Carbon monoxide as a tracer for tropical troposphere to stratosphere transport in the Chemical Lagrangian Model of the Stratosphere (CLaMS) Geoscientific Model Development Discussions, 4, 1185-1211, 2011 Author(s): R. Pommrich, R. Müller, J.-U. Grooß, P. Konopka, G. Günther, H.-C. Pumphrey, S. Viciani, F. D'Amato, and M. Riese Variations in the mixing ratio of trace gases of tropospheric origin entering the stratosphere in the tropics are of interest for assessing both troposphere to stratosphere transport fluxes in the tropics and the impact on the composition of the tropical lower stratosphere of quasi-horizontal in-mixing into the tropical tropopause layer from the mid-latitude stratosphere. Here, we present a simplified chemistry scheme for the Chemical Lagrangian Model of the Stratosphere (CLaMS) for the simulation, at comparatively low numerical cost, of CO, ozone, and long-lived trace substances (CH 4 , N 2 O, CCl 3 F, and CO 2 ) in the lower tropical stratosphere. The boundary conditions at the ground are represented for the long-lived trace substances CH 4 , N 2 O, CCl 3 F, and CO 2 based on ground-based measurements. The boundary condition for CO in the free troposphere is deduced from MOPITT measurements. We find that the zonally averaged tropical CO anomaly patterns simulated by this model version of CLaMS are in good agreement with observations. The introduction of a new scheme in the ECMWF integrated forecast system (Tompkins et al., 2007) for the ice supersaturation after September 2006, results in a somewhat less good agreement between observed and simulated CO patterns in the tropical lower stratosphere after this date.

Description: The Met Office Unified Model Global Atmosphere 3.0/3.1 and JULES Global Land 3.0/3.1 configurations Geoscientific Model Development Discussions, 4, 1213-1271, 2011 Author(s): D. N. Walters, M. J. Best, A. C. Bushell, D. Copsey, J. M. Edwards, P. D. Falloon, C. M. Harris, A. P. Lock, J. C. Manners, C. J. Morcrette, M. J. Roberts, R. A. Stratton, S. Webster, J. M. Wilkinson, M. R. Willett, I. A. Boutle, P. D. Earnshaw, P. G. Hill, C. MacLachlan, G. M. Martin, W. Moufouma-Okia, M. D. Palmer, J. C. Petch, G. G. Rooney, A. A. Scaife, and K. D. Williams We describe Global Atmosphere 3.0 (GA3.0): a configuration of the Met Office Unified Model (MetUM) developed for use across climate research and weather prediction activities. GA3.0 has been formulated by converging the development paths of the Met Office's weather and climate global atmospheric model components such that wherever possible, atmospheric processes are modelled or parametrized seamlessly across spatial resolutions and timescales. This unified development process will provide the Met Office and its collaborators with regular releases of a configuration that has been evaluated, and can hence be applied, over a variety of modelling régimes. We also describe Global Land 3.0 (GL3.0): a configuration of the JULES community land surface model developed for use with GA3.0. This paper provides a comprehensive technical and scientific description of the GA3.0 and GL3.0 (and related GA3.1 and GL3.1) configurations and presents the results of some initial evaluations of their performance in various applications. It is to be the first in a series of papers describing each subsequent Global Atmosphere release; this will provide a single source of reference for established users and developers as well as researchers requiring access to a current, but trusted, global MetUM setup.

Description: FAMOUS, faster: using parallel computing techniques to accelerate the FAMOUS/HadCM3 climate model with a focus on the radiative transfer algorithm Geoscientific Model Development Discussions, 4, 1273-1303, 2011 Author(s): P. Hanappe, A. Beurivé, F. Laguzet, L. Steels, N. Bellouin, O. Boucher, Y. H. Yamazaki, T. Aina, and M. Allen We have optimised the atmospheric radiation algorithm of the FAMOUS climate model on several hardware platforms. The optimisation involved translating the Fortran code to C and restructuring the algorithm around the computation of a single air column. A task queue and a thread pool are used to distribute the computation to several processors. Finally, four air columns are packed together in a single data structure and computed simultaneously using Single Instruction Multiple Data operations. The modified algorithm runs more than 50 times faster on the CELL's Synergistic Processing Elements than on its main PowerPC processing element. On Intel-compatible processors, the new radiation code runs 4 times faster and on graphics processors, using OpenCL, more than 2.5 times faster, as compared to the original code. Because the radiation code takes more than 60 % of the total CPU time, FAMOUS executes more than twice as fast. Our version of the algorithm returns bit-wise identical results, which demonstrates the robustness of our approach.

Description: Analyzing numerics of bulk microphysics schemes in Community models: warm rain processes Geoscientific Model Development Discussions, 4, 1403-1434, 2011 Author(s): I. Sednev and S. Menon In the last decade there has been only one study that discussed time integration scheme (TIS) applied to advance governing differential equations in bulk microphysics (BLK) schemes. Recently, Morrison and Gettelman (2008) examine numerical aspects of double-moment BLK scheme with diagnostic treatment of precipitating hydrometeors implemented into Community Atmosphere Model, version 3 (CAM) to find an acceptable level of accuracy and numerical stability. However, stability condition for their explicit non-positive definite TIS was not defined. It is conventionally thought that the Weather Research and Forecasting (WRF) model can be applied for a broad range of spatial scales from large eddy up to global scale simulations if time steps used for model integration satisfy to a certain limit imposed mainly by dynamics. However, numerics used in WRF BLK schemes has never been analyzed in detail. To improve creditability of BLK schemes we derive a general analytical stability and positive definiteness criteria for explicit Eulerian time integration scheme used to advanced finite-difference equations that govern warm rain formation processes in microphysics packages in Community models (CAM and WRF) and define well-behaved, conditionally well-behaved, and non-well-behaved Explicit Eulerian Bulk Microphysics Code (EEBMPC) classes. We highlight that source codes of BLK schemes, originally developed for use in cloud-resolving models, implemented in Community models belong to conditionally well-behaved EEBMPC class and exhibit better performance for finer spatial resolutions when time steps do not exceed seconds or tenths of seconds. For coarser spatial resolutions used in regional and global scale simulations time steps are usually increased from hundredths up to thousands of seconds. This might lead to a degradation of conditionally well-behaved EEBMPCs ability to calculate the amount of precipitation as well as its spatial and temporal distribution since both stability and positive definiteness conditions are not met in the TIS. The correction through the so called “mass conservation” technique commonly used in many models with bulk microphysics is a main characteristic of non-well-behaved EEBMPC, whose utilization leads to erroneous conclusions regarding relative importance of different microphysical processes. Moreover, surface boundary conditions for ocean, land, lake, and sea ice models are dependent on the precipitation and its spatial and temporal distribution. Uncertainties in calculations of temporal and spatial patterns of accumulated precipitation influence the global water cycle. In fact, numerics in non-well-behaved EEBMPCs, which are used in Community Earth System Model, act as a hidden climate forcing agent, if relatively long time steps are used for the host model integration. By analyzing numerics of warm rain processes in EEBMPCs implemented in Community models we provide general guidelines regarding appropriate choice of integration time steps for use in these models.

Description: The 1-way on-line coupled atmospheric chemistry model system MECO(n) – Part 2: On-line coupling Geoscientific Model Development Discussions, 4, 1359-1402, 2011 Author(s): A. Kerkweg and P. Jöckel A new, highly flexible model system for the seamless dynamical down-scaling of meteorological and chemical processes from the global to the meso-γ scale is presented. A global model and a cascade of an arbitrary number of limited-area model instances run concurrently in the same parallel environment, in which the coarser grained instances provide the boundary data for the finer grained instances. Thus, disk-space intensive and time consuming intermediate and pre-processing steps are entirely avoided and the time interpolation errors of common off-line nesting approaches are minimised. More specifically, the regional model COSMO of the German Weather Service (DWD) is nested on-line into the atmospheric general circulation model ECHAM5 within the Modular Earth Submodel System (MESSy) framework. ECHAM5 and COSMO have previously been equipped with the MESSy infrastructure, implying that the same process formulations (MESSy submodels) are available for both models. This guarantees the highest degree of achievable consistency, between both, the meteorological and chemical conditions at the domain boundaries of the nested limited-area model, and between the process formulations on all scales. The on-line nesting of the different models is established by a client-server approach with the newly developed Multi-Model-Driver (MMD), an additional component of the MESSy infrastructure. With MMD an arbitrary number of model instances can be run concurrently within the same message passing interface (MPI) environment, the respective coarser model (either global or regional) is the server for the nested finer (regional) client model, i.e., it provides the data required to calculate the initial and boundary fields to the client model. On-line nesting means that the coupled (client-server) models exchange their data via the computer memory, in contrast to the data exchange via files on disk in common off-line nesting approaches. MMD consists of a library (Fortran95 and some parts in C) which is based on the MPI standard and two new MESSy submodels, MMDSERV and MMDCLNT (both Fortran95) for the server and client models, respectively. MMDCLNT contains a further sub-submodel, INT2COSMO, for the interpolation of the coarse grid data provided by the server models (either ECHAM5/MESSy or COSMO/MESSy) to the grid of the respective client model (COSMO/MESSy). INT2COSMO is based on the off-line pre-processing tool INT2LM provided by the DWD. The new achievements allow the setup of model cascades for zooming (down-scaling) from the global scale to the lower edge of the meso-γ scale (≈1 km) with a very high degree of consistency between the different models and between the chemical and meteorological boundary conditions.

Description: Development and evaluation of an Earth-system model – HadGEM2 Geoscientific Model Development Discussions, 4, 997-1062, 2011 Author(s): W. J. Collins, N. Bellouin, M. Doutriaux-Boucher, N. Gedney, P. Halloran, T. Hinton, J. Hughes, C. D. Jones, M. Joshi, S. Liddicoat, G. Martin, F. O'Connor, J. Rae, C. Senior, S. Sitch, I. Totterdell, A. Wiltshire, and S. Woodward We describe here the development and evaluation of an Earth system model suitable for centennial-scale climate prediction. The principal new components added to the physical climate model are the terrestrial and ocean ecosystems and gas-phase tropospheric chemistry, along with their coupled interactions. The individual Earth system components are described briefly and the relevant interactions between the components are explained. Because the multiple interactions could lead to unstable feedbacks, we go through a careful process of model spin up to ensure that all components are stable and the interactions balanced. This spun-up configuration is evaluated against observed data for the Earth system components and is generally found to perform very satisfactorily. The reason for the evaluation phase is that the model is to be used for the core climate simulations carried out by the Met Office Hadley Centre for the Coupled Model Intercomparison Project (CMIP5), so it is essential that addition of the extra complexity does not detract substantially from its climate performance. Localised changes in some specific meteorological variables can be identified, but the impacts on the overall simulation of present day climate are slight. This model is proving valuable both for climate predictions, and for investigating the strengths of biogeochemical feedbacks.

Description: iGen: the automated generation of a parameterisation of entrainment in marine stratocumulus Geoscientific Model Development Discussions, 4, 971-995, 2011 Author(s): D. F. Tang and S. Dobbie In a previous paper we described a new technique for automatically generating parameterisations using a program called iGen. iGen generates parameterisations by analysing the source code of a high resolution model that resolves the physics to be parameterised. In order to demonstrate that this technique scales up to deal with models of realistic complexity we have used iGen to generate a parameterisation of entrainment in marine stratocumulus. We present details of our technique in which iGen was used to analyse the source code of a cloud resolving model and generate a parameterisation of the mean and standard deviation of entrainment velocity in marine stratocumulus in terms of the large-scale state of the boundary layer. The parameterisation was tested against results from the DYCOMS-II intercomparison of cloud resolving models and iGen's parameterisation of mean entrainment velocity was found to be 5.27 × 10 −3 ± 0.62 × 10 −3 m s −1 compared to 5.2 × 10 −3 ± 0.8 × 10 −3 m s −1 for the DYCOMS-II ensemble of cloud resolving models.

Description: The HadGEM2-ES implementation of CMIP5 centennial simulations Geoscientific Model Development Discussions, 4, 689-763, 2011 Author(s): C. D. Jones, J. K. Hughes, N. Bellouin, S. C. Hardiman, G. S. Jones, J. Knight, S. Liddicoat, F. M. O'Connor, R. J. Andres, C. Bell, K.-O. Boo, A. Bozzo, N. Butchart, P. Cadule, K. D. Corbin, M. Doutriaux-Boucher, P. Friedlingstein, J. Gornall, L. Gray, P. R. Halloran, G. Hurtt, W. Ingram, J.-F. Lamarque, R. M. Law, M. Meinshausen, S. Osprey, E. J. Palin, L. Parsons Chini, T. Raddatz, M. Sanderson, A. A. Sellar, A. Schurer, P. Valdes, N. Wood, S. Woodward, M. Yoshioka, and M. Zerroukat The scientific understanding of the Earth's climate system, including the central question of how the climate system is likely to respond to human-induced perturbations, is comprehensively captured in GCMs and Earth System Models(ESM). Diagnosing the simulated climate response, and comparing responses across different models, is crucially dependent on transparent assumptions of how the GCM/ESM has been driven – especially because the implementation can involve subjective decisions and may differ between modelling groups performing the same experiment. This paper outlines the climate forcings and setup of the Met Office Hadley Centre ESM, HadGEM2-ES for the CMIP5 set of centennial experiments. We document the prescribed greenhouse gas concentrations, aerosol precursors, stratospheric and tropospheric ozone assumptions, as well as implementation of land-use change and natural forcings for the HadGEM2-ES historical and future experiments following the Representative Concentration Pathways. In addition, we provide details of how HadGEM2-ES ensemble members were initialised from the control run and how the palaeoclimate and AMIP experiments, as well as the "emission-driven" RCP experiments were performed.

Description: The HadGEM2 family of Met Office Unified Model Climate configurations Geoscientific Model Development Discussions, 4, 765-841, 2011 Author(s): The HadGEM2 Development Team: Martin, G. M., N. Bellouin, W. J. Collins, I. D. Culverwell, P. R. Halloran, S. C. Hardiman, T. J. Hinton, C. D. Jones, R. E. McDonald, A. J. McLaren, F. M. O'Connor, M. J. Roberts, J. M. Rodriguez, S. Woodward, M. J. Best, M. E. Brooks, A. R. Brown, N. Butchart, C. Dearden, S. H. Derbyshire, I. Dharssi, M. Doutriaux-Boucher, J. M. Edwards, P. D. Falloon, N. Gedney, L. J. Gray, H. T. Hewitt, M. Hobson, M. R. Huddleston, J. Hughes, S. Ineson, W. J. Ingram, P. M. James, T. C. Johns, C. E. Johnson, A. Jones, C. P. Jones, M. M. Joshi, A. B. Keen, S. Liddicoat, A. P. Lock, A. V. Maidens, J. C. Manners, S. F. Milton, J. G. L. Rae, J. K. Ridley, A. Sellar, C. A. Senior, I. J. Totterdell, A. Verhoef, P. L. Vidale, and A. Wiltshire We describe the HadGEM2 family of climate configurations of the Met Office Unified Model, MetUM. The concept of a model "family" comprises a range of specific model configurations incorporating different levels of complexity but with a common physical framework. The HadGEM2 family of configurations includes atmosphere and ocean components, with and without a vertical extension to include a well-resolved stratosphere, and an Earth-System (ES) component which includes dynamic vegetation, ocean biology and atmospheric chemistry. The HadGEM2 physical model includes improvements designed to address specific systematic errors encountered in the previous climate configuration, HadGEM1, namely Northern Hemisphere continental temperature biases and tropical sea surface temperature biases and poor variability. Targeting these biases was crucial in order that the ES configuration could represent important biogeochemical climate feedbacks. Detailed descriptions and evaluations of particular HadGEM2 family members are included in a number of other publications, and the discussion here is limited to a summary of the overall performance using a set of model metrics which compare the way in which the various configurations simulate present-day climate and its variability.