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  • 1. Ahlkrona, J.
    et al.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lotstedt, P.
    Accuracy of the zeroth- and second-order shallow-ice approximation - numerical and theoretical results2013In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 6, no 6, p. 2135-2152Article in journal (Refereed)
    Abstract [en]

    In ice sheet modelling, the shallow-ice approximation (SIA) and second-order shallow-ice approximation (SOSIA) schemes are approaches to approximate the solution of the full Stokes equations governing ice sheet dynamics. This is done by writing the solution to the full Stokes equations as an asymptotic expansion in the aspect ratio epsilon, i.e. the quotient between a characteristic height and a characteristic length of the ice sheet. SIA retains the zeroth-order terms and SOSIA the zeroth-, first-, and second-order terms in the expansion. Here, we evaluate the order of accuracy of SIA and SOSIA by numerically solving a two-dimensional model problem for different values of epsilon, and comparing the solutions with afinite element solution to the full Stokes equations obtained from Elmer/Ice. The SIA and SOSIA solutions are also derived analytically for the model problem. For decreasing epsilon, the computed errors in SIA and SOSIA decrease, but not always in the expected way. Moreover, they depend critically on a parameter introduced to avoid singularities in Glen's flow law in the ice model. This is because the assumptions behind the SIA and SOSIA neglect a thick, high-viscosity boundary layer near the ice surface. The sensitivity to the parameter is explained by the analytical solutions. As a verification of the comparison technique, the SIA and SOSIA solutions for a fluid with Newtonian rheology are compared to the solutions by Elmer/Ice, with results agreeing very well with theory.

  • 2. Baranizadeh, Elham
    et al.
    Murphy, Benjamin N.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Julin, Jan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. University of Eastern Finland, Finland.
    Falahat, Saeed
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Reddington, Carly L.
    Arola, Antti
    Ahlm, Lars
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mikkonen, Santtu
    Fountoukis, Christos
    Patoulias, David
    Minikin, Andreas
    Hamburger, Thomas
    Laaksonen, Ari
    Pandis, Spyros N.
    Vehkamäki, Hanna
    Lehtinen, Kari E. J.
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Implementation of state-of-the-art ternary new-particle formation scheme to the regional chemical transport model PMCAMx-UF in Europe2016In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 9, no 8, p. 2741-2754Article in journal (Refereed)
    Abstract [en]

    The particle formation scheme within PMCAMx-UF, a three-dimensional chemical transport model, was updated with particle formation rates for the ternary H2SO4-NH3-H2O pathway simulated by the Atmospheric Cluster Dynamics Code (ACDC) using quantum chemical input data. The model was applied over Europe for May 2008, during which the EUCAARI-LONGREX (European Aerosol Cloud Climate and Air Quality Interactions-Long-Range Experiment) campaign was carried out, providing aircraft vertical profiles of aerosol number concentrations. The updated model reproduces the observed number concentrations of particles larger than 4 nm within 1 order of magnitude throughout the atmospheric column. This agreement is encouraging considering the fact that no semi-empirical fitting was needed to obtain realistic particle formation rates. The cloud adjustment scheme for modifying the photolysis rate profiles within PMCAMx-UF was also updated with the TUV (Tropospheric Ultraviolet and Visible) radiative-transfer model. Results show that, although the effect of the new cloud adjustment scheme on total number concentrations is small, enhanced new-particle formation is predicted near cloudy regions. This is due to the enhanced radiation above and in the vicinity of the clouds, which in turn leads to higher production of sulfuric acid. The sensitivity of the results to including emissions from natural sources is also discussed.

  • 3.
    Döös, Kristofer
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Jönsson, Bror
    Kjellsson, Joakim
    Evaluation of oceanic and atmospheric trajectory schemes in the TRACMASS trajectory model v6.02017In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 10, no 4, p. 1733-1749Article in journal (Refereed)
    Abstract [en]

    Three different trajectory schemes for oceanic and atmospheric general circulation models are compared in two different experiments. The theories of the trajectory schemes are presented showing the differential equations they solve and why they are mass conserving. One scheme assumes that the velocity fields are stationary for set intervals of time between saved model outputs and solves the trajectory path from a differential equation only as a function of space, i.e. stepwise stationary. The second scheme is a special case of the stepwise-stationary scheme, where velocities are assumed constant between general circulation model (GCM) outputs; it uses hence a fixed GCM time step. The third scheme uses a continuous linear interpolation of the fields in time and solves the trajectory path from a differential equation as a function of both space and time, i.e. a time-dependent scheme. The trajectory schemes are tested offline, i.e. using the already integrated and stored velocity fields from a GCM. The first comparison of the schemes uses trajectories calculated using the velocity fields from a high-resolution ocean general circulation model in the Agulhas region. The second comparison uses trajectories calculated using the wind fields from an atmospheric reanalysis. The study shows that using the time-dependent scheme over the stepwise-stationary scheme greatly improves accuracy with only a small increase in computational time. It is also found that with decreasing time steps the stepwise-stationary scheme becomes increasingly more accurate but at increased computational cost. The time-dependent scheme is therefore preferred over the stepwise-stationary scheme. However, when averaging over large ensembles of trajectories, the two schemes are comparable, as intrinsic variability dominates over numerical errors. The fixed GCM time step scheme is found to be less accurate than the stepwisestationary scheme, even when considering averages over large ensembles.

  • 4. Ekici, A.
    et al.
    Beer, Christian
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Max Planck Society, Germany;.
    Hagemann, S.
    Boike, J.
    Langer, M.
    Hauck, C.
    Simulating high-latitude permafrost regions by the JSBACH terrestrial ecosystem model2014In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 7, no 2, p. 631-647Article in journal (Refereed)
    Abstract [en]

    The current version of JSBACH incorporates phenomena specific to high latitudes: freeze/thaw processes, coupling thermal and hydrological processes in a layered soil scheme, defining a multilayer snow representation and an insulating moss cover. Evaluations using comprehensive Arctic data sets show comparable results at the site, basin, continental and circumarctic scales. Such comparisons highlight the need to include processes relevant to high-latitude systems in order to capture the dynamics, and therefore realistically predict the evolution of this climatically critical biome.

  • 5.
    Gowan, Evan J.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. The Australian National University, Australia.
    Tregoning, Paul
    Purcell, Anthony
    Lea, James
    Stockholm University, Faculty of Science, Department of Physical Geography. University of Liverpool, UK.
    Fransner, Oscar J.
    Noormets, Riko
    Dowdeswell, J. A.
    ICESHEET 1.0: a program to produce paleo-ice sheet reconstructions with minimal assumptions2016In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 9, no 5, p. 1673-1682Article in journal (Refereed)
    Abstract [en]

    We describe a program that produces paleo-ice sheet reconstructions using an assumption of steady-state, perfectly plastic ice flow behaviour. It incorporates three input parameters: ice margin, basal shear stress and basal topography. Though it is unlikely that paleo-ice sheets were ever in complete steady-state conditions, this method can produce an ice sheet without relying on complicated and unconstrained parameters such as climate and ice dynamics. This makes it advantageous to use in glacial-isostatic adjustment ice sheet modelling, which are often used as input parameters in global climate modelling simulations. We test this program by applying it to the modern Greenland Ice Sheet and Last Glacial Maximum Barents Sea Ice Sheet and demonstrate the optimal parameters that balance computational time and accuracy.

  • 6.
    Grythe, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Norwegian Institute for Air Research (NILU), Norway; Finnish Meteorological Institute (FMI), Finland.
    Kristiansen, Nina I.
    Groot Zwaaftink, Christine D.
    Eckhardt, Sabine
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). University of Helsinki, Finland.
    Stohl, Andreas
    A new aerosol wet removal scheme for the Lagrangian particle model FLEXPART2017In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 10, no 4, p. 1447-1466Article in journal (Refereed)
    Abstract [en]

    A new and more physically based treatment of how removal by precipitation is calculated by FLEXPART is introduced, to take into account more aspects of aerosol diversity. Also new, is the definition of clouds and cloud properties. Results from simulations show good agreement with observed atmospheric concentrations for distinctly different aerosols. Atmospheric lifetimes were found to vary from a few hours (large aerosol particles) up to a month (small non-soluble).

  • 7.
    Hartung, Kerstin
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish e-Science Research Centre, Sweden.
    Svensson, Gunilla
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish e-Science Research Centre, Sweden.
    Struthers, Hamish
    Deppenmeier, Anna-Lena
    Hazeleger, Wilco
    An EC-Earth coupled atmosphere-ocean single-column model (AOSCM.v1_EC-Earth3) for studying coupled marine and polar processes2018In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 11, no 10, p. 4117-4137Article in journal (Refereed)
    Abstract [en]

    Single-column models (SCMs) have been used as tools to help develop numerical weather prediction and global climate models for several decades. SCMs decouple small-scale processes from large-scale forcing, which allows the testing of physical parameterisations in a controlled environment with reduced computational cost. Typically, either the ocean, sea ice or atmosphere is fully modelled and assumptions have to be made regarding the boundary conditions from other subsystems, adding a potential source of error. Here, we present a fully coupled atmosphere-ocean SCM (AOSCM), which is based on the global climate model EC-Earth3. The initial configuration of the AOSCM consists of the Nucleus for European Modelling of the Ocean (NEMO3.6) (ocean), the Louvain-la-Neuve Sea Ice Model (LIM3) (sea ice), the Open Integrated Forecasting System (OpenIFS) cycle 40r1 (atmosphere), and OASIS3-MCT (coupler). Results from the AOSCM are presented at three locations: the tropical Atlantic, the midlatitude Pacific and the Arctic. At all three locations, in situ observations are available for comparison. We find that the coupled AOSCM can capture the observed atmospheric and oceanic evolution based on comparisons with buoy data, soundings and ship-based observations. The model evolution is sensitive to the initial conditions and forcing data imposed on the column. Comparing coupled and uncoupled configurations of the model can help disentangle model feedbacks. We demonstrate that the AOSCM in the current set-up is a valuable tool to advance our understanding in marine and polar boundary layer processes and the interactions between the individual components of the system (atmosphere, sea ice and ocean).

  • 8. Hordoir, Robinson
    et al.
    Axell, Lars
    Höglund, Anders
    Dieterich, Christian
    Fransner, Filippa
    Stockholm University, Faculty of Science, Department of Meteorology . Bergen University, Norway; Bjerknes Centre for Climate Research, Norway.
    Gröger, Matthias
    Liu, Ye
    Pemberton, Per
    Schimanke, Semjon
    Andersson, Helen
    Ljungemyr, Patrik
    Nygren, Petter
    Falahat, Saeed
    Nord, Adam
    Jönsson, Anette
    Lake, Iréne
    Döös, Kristofer
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hieronymus, Magnus
    Dietze, Heiner
    Löptien, Ulrike
    Kuznetsov, Ivan
    Westerlund, Antti
    Tuomi, Laura
    Haapala, Jari
    Nemo-Nordic 1.0: a NEMO-based ocean model for the Baltic and North seas - research and operational applications2019In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 12, no 1, p. 363-386Article in journal (Refereed)
    Abstract [en]

    We present Nemo-Nordic, a Baltic and North Sea model based on the NEMO ocean engine. Surrounded by highly industrialized countries, the Baltic and North seas and their assets associated with shipping, fishing and tourism are vulnerable to anthropogenic pressure and climate change. Ocean models providing reliable forecasts and enabling climatic studies are important tools for the shipping infrastructure and to get a better understanding of the effects of climate change on the marine ecosystems. Nemo-Nordic is intended to be a tool for both short-term and long-term simulations and to be used for ocean forecasting as well as process and climatic studies. Here, the scientific and technical choices within Nemo-Nordic are introduced, and the reasons behind the design of the model and its domain and the inclusion of the two seas are explained. The model's ability to represent barotropic and baroclinic dynamics, as well as the vertical structure of the water column, is presented. Biases are shown and discussed. The short-term capabilities of the model are presented, especially its capabilities to represent sea level on an hourly timescale with a high degree of accuracy. We also show that the model can represent longer timescales, with a focus on the major Baltic inflows and the variability in deep-water salinity in the Baltic Sea.

  • 9. Jungclaus, Johann H.
    et al.
    Bard, Edouard
    Baroni, Mélanie
    Braconnot, Pascale
    Cao, Jian
    Chini, Louise P.
    Egorova, Tania
    Evans, Michael
    González-Rouco, J. Fidel
    Goosse, Hugues
    Hurtt, George C.
    Joos, Fortunat
    Kaplan, Jed O.
    Khodri, Myriam
    Goldewijk, Kees Klein
    Krivova, Natalie
    LeGrande, Allegra N.
    Lorenz, Stephan J.
    Luterbacher, Jürg
    Man, Wenmin
    Maycock, Amanda C.
    Meinshausen, Malte
    Moberg, Anders
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Muscheler, Raimund
    Nehrbass-Ahles, Christoph
    Otto-Bliesner, Bette I.
    Phipps, Steven J.
    Pongratz, Julia
    Rozanov, Eugene
    Schmidt, Gavin A.
    Schmidt, Hauke
    Schmutz, Werner
    Schurer, Andrew
    Shapiro, Alexander I.
    Sigl, Michael
    Smerdon, Jason E.
    Solanki, Sami K.
    Timmreck, Claudia
    Toohey, Matthew
    Usoskin, Ilya G.
    Wagner, Sebastian
    Wu, Chi-Ju
    Yeo, Kok Leng
    Zanchettin, Davide
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Zorita, Eduardo
    The PMIP4 contribution to CMIP6-Part 3: The last millennium, scientific objective, and experimental design for the PMIP4 past1000 simulations2017In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 10, no 11, p. 4005-4033Article in journal (Refereed)
    Abstract [en]

    The pre-industrial millennium is among the periods selected by the Paleoclimate Model Intercomparison Project (PMIP) for experiments contributing to the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and the fourth phase of the PMIP (PMIP4). The past1000 transient simulations serve to investigate the response to (mainly) natural forcing under background conditions not too different from today, and to discriminate between forced and internally generated variability on interannual to centennial timescales. This paper describes the motivation and the experimental set-ups for the PMIP4-CMIP6 past1000 simulations, and discusses the forcing agents orbital, solar, volcanic, and land use/land cover changes, and variations in greenhouse gas concentrations. The past1000 simulations covering the pre-industrial millennium from 850 Common Era (CE) to 1849 CE have to be complemented by historical simulations (1850 to 2014 CE) following the CMIP6 protocol. The external forcings for the past1000 experiments have been adapted to provide a seamless transition across these time periods. Protocols for the past1000 simulations have been divided into three tiers. A default forcing data set has been defined for the Tier 1 (the CMIP6 past1000) experiment. However, the PMIP community has maintained the flexibility to conduct coordinated sensitivity experiments to explore uncertainty in forcing reconstructions as well as parameter uncertainty in dedicated Tier 2 simulations. Additional experiments (Tier 3) are defined to foster collaborative model experiments focusing on the early instrumental period and to extend the temporal range and the scope of the simulations. This paper outlines current and future research foci and common analyses for collaborative work between the PMIP and the observational communities (reconstructions, instrumental data).

  • 10. Kageyama, Masa
    et al.
    Albani, Samuel
    Braconnot, Pascale
    Harrison, Sandy P.
    Hopcroft, Peter O.
    Ivanovic, Ruza F.
    Lambert, Fabrice
    Marti, Olivier
    Peltier, W. Richard
    Peterschmitt, Jean-Yves
    Roche, Didier M.
    Tarasov, Lev
    Zhang, Xu
    Brady, Esther C.
    Haywood, Alan M.
    LeGrande, Allegra N.
    Lunt, Daniel J.
    Mahowald, Natalie M.
    Mikolajewicz, Uwe
    Nisancioglu, Kerim H.
    Otto-Bliesner, Bette L.
    Renssen, Hans
    Tomas, Robert A.
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Abe-Ouchi, Ayako
    Bartlein, Patrick J.
    Cao, Jian
    Li, Qiang
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Lohmann, Gerrit
    Ohgaito, Rumi
    Shi, Xiaoxu
    Volodin, Evgeny
    Yoshida, Kohei
    Zhang, Xiao
    Zheng, Weipeng
    The PMIP4 contribution to CMIP6-Part 4: Scientific objectives and experimental design of the PMIP4-CMIP6 Last Glacial Maximum experiments and PMIP4 sensitivity experiments2017In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 10, no 11, p. 4035-4055Article in journal (Refereed)
    Abstract [en]

    The Last Glacial Maximum (LGM, 21 000 years ago) is one of the suite of paleoclimate simulations included in the current phase of the Coupled Model Intercomparison Project (CMIP6). It is an interval when insolation was similar to the present, but global ice volume was at a maximum, eustatic sea level was at or close to a minimum, greenhouse gas concentrations were lower, atmospheric aerosol loadings were higher than today, and vegetation and land-surface characteristics were different from today. The LGM has been a focus for the Paleoclimate Modelling Intercomparison Project (PMIP) since its inception, and thus many of the problems that might be associated with simulating such a radically different climate are well documented. The LGM state provides an ideal case study for evaluating climate model performance because the changes in forcing and temperature between the LGM and pre-industrial are of the same order of magnitude as those projected for the end of the 21st century. Thus, the CMIP6 LGM experiment could provide additional information that can be used to constrain estimates of climate sensitivity. The design of the Tier 1 LGM experiment (lgm) includes an assessment of uncertainties in boundary conditions, in particular through the use of different reconstructions of the ice sheets and of the change in dust forcing. Additional (Tier 2) sensitivity experiments have been designed to quantify feedbacks associated with land-surface changes and aerosol loadings, and to isolate the role of individual forcings. Model analysis and evaluation will capitalize on the relative abundance of paleoenvironmental observations and quantitative climate reconstructions already available for the LGM.

  • 11. Kageyama, Masa
    et al.
    Braconnot, Pascale
    Harrison, Sandy P.
    Haywood, Alan M.
    Jungclaus, Johann H.
    Otto-Bliesner, Bette L.
    Peterschmitt, Jean-Yves
    Abe-Ouchi, Ayako
    Albani, Samuel
    Bartlein, Patrick J.
    Brierley, Chris
    Crucifix, Michel
    Dolan, Aisling
    Fernandez-Donado, Laura
    Fischer, Hubertus
    Hopcroft, Peter O.
    Ivanovic, Ruza F.
    Lambert, Fabrice
    Lunt, Daniel J.
    Mahowald, Natalie M.
    Peltier, W. Richard
    Phipps, Steven J.
    Roche, Didier M.
    Schmidt, Gavin A.
    Tarasov, Lev
    Valdes, Paul J.
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Zhou, Tianjun
    The PMIP4 contribution to CMIP6-Part 1: Overview and over-arching analysis plan2018In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 11, no 3, p. 1033-1057Article in journal (Refereed)
    Abstract [en]

    This paper is the first of a series of four GMD papers on the PMIP4-CMIP6 experiments. Part 2 (OttoBliesner et al., 2017) gives details about the two PMIP4-CMIP6 interglacial experiments, Part 3 (Jungclaus et al., 2017) about the last millennium experiment, and Part 4 (Kageyama et al., 2017) about the Last Glacial Maximum experiment. The mid-Pliocene Warm Period experiment is part of the Pliocene Model Intercomparison Project (PlioMIP) Phase 2, detailed in Haywood et al. (2016). The goal of the Paleoclimate Modelling Intercomparison Project (PMIP) is to understand the response of the climate system to different climate forcings for documented climatic states very different from the present and historical climates. Through comparison with observations of the environmental impact of these climate changes, or with climate reconstructions based on physical, chemical, or biological records, PMIP also addresses the issue of how well state-of-the-art numerical models simulate climate change. Climate models are usually developed using the present and historical climates as references, but climate projections show that future climates will lie well outside these conditions. Palaeoclimates very different from these reference states therefore provide stringent tests for state-of-the-art models and a way to assess whether their sensitivity to forcings is compatible with palaeoclimatic evidence. Simulations of five different periods have been designed to address the objectives of the sixth phase of the Coupled Model Intercomparison Project (CMIP6): the millennium prior to the industrial epoch (CMIP6 name: past1000); the mid-Holocene, 6000 years ago (midHolocene); the Last Glacial Maximum, 21 000 years ago (lgm); the Last Interglacial, 127 000 years ago (lig127k); and the mid-Pliocene Warm Period, 3.2 million years ago (midPliocene-eoi400). These climatic periods are well documented by palaeoclimatic and palaeoenvironmental records, with climate and environmental changes relevant for the study and projection of future climate changes. This paper describes the motivation for the choice of these periods and the design of the numerical experiments and database requests, with a focus on their novel features compared to the experiments performed in previous phases of PMIP and CMIP. It also outlines the analysis plan that takes advantage of the comparisons of the results across periods and across CMIP6 in collaboration with other MIPs.

  • 12. Kaiser, Sonja
    et al.
    Goeckede, Mathias
    Castro-Morales, Karel
    Knoblauch, Christian
    Ekici, Altug
    Kleinen, Thomas
    Zubrzycki, Sebastian
    Sachs, Torsten
    Wille, Christian
    Beer, Christian
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Process-based modelling of the methane balance in periglacial landscapes (JSBACH-methane)2017In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 10, no 1, p. 333-358Article in journal (Refereed)
    Abstract [en]

    A detailed process-based methane module for a global land surface scheme has been developed which is general enough to be applied in permafrost regions as well as wetlands outside permafrost areas. Methane production, oxidation and transport by ebullition, diffusion and plants are represented. In this model, oxygen has been explicitly incorporated into diffusion, transport by plants and two oxidation processes, of which one uses soil oxygen, while the other uses oxygen that is available via roots. Permafrost and wetland soils show special behaviour, such as variable soil pore space due to freezing and thawing or water table depths due to changing soil water content. This has been integrated directly into the methane-related processes. A detailed application at the Samoylov polygonal tundra site, Lena River Delta, Russia, is used for evaluation purposes. The application at Samoylov also shows differences in the importance of the several transport processes and in the methane dynamics under varying soil moisture, ice and temperature conditions during different seasons and on different microsites. These microsites are the elevated moist polygonal rim and the depressed wet polygonal centre. The evaluation shows sufficiently good agreement with field observations despite the fact that the module has not been specifically calibrated to these data. This methane module is designed such that the advanced land surface scheme is able to model recent and future methane fluxes from periglacial landscapes across scales. In addition, the methane contribution to carbon cycle-climate feedback mechanisms can be quantified when running coupled to an atmospheric model.

  • 13. Kirkevag, A.
    et al.
    Iversen, T.
    Seland, O.
    Hoose, C.
    Kristjansson, J. E.
    Struthers, Hamish
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Faculty of Science, Department of Meteorology .
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ghan, S.
    Griesfeller, J.
    Nilsson, E. Douglas
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Schulz, M.
    Aerosol-climate interactions in the Norwegian Earth System Model-NorESM1-M2013In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 6, no 1, p. 207-244Article in journal (Refereed)
    Abstract [en]

    The objective of this study is to document and evaluate recent changes and updates to the module for aerosols and aerosol-cloud-radiation interactions in the atmospheric module CAM4-Oslo of the core version of the Norwegian Earth System Model (NorESM), NorESM1-M. Particular attention is paid to the role of natural organics, sea salt, and mineral dust in determining the gross aerosol properties as well as the anthropogenic contribution to these properties and the associated direct and indirect radiative forcing. The aerosol module is extended from earlier versions that have been published, and includes life-cycling of sea salt, mineral dust, particulate sulphate, black carbon, and primary and secondary organics. The impacts of most of the numerous changes since previous versions are thoroughly explored by sensitivity experiments. The most important changes are: modified prognostic sea salt emissions; updated treatment of precipitation scavenging and gravitational settling; inclusion of biogenic primary organics and methane sulphonic acid (MSA) from oceans; almost doubled production of land-based biogenic secondary organic aerosols (SOA); and increased ratio of organic matter to organic carbon (OM/OC) for biomass burning aerosols from 1.4 to 2.6. Compared with in situ measurements and remotely sensed data, the new treatments of sea salt and dust aerosols give smaller biases in near-surface mass concentrations and aerosol optical depth than in the earlier model version. The model biases for mass concentrations are approximately unchanged for sulphate and BC. The enhanced levels of modeled OM yield improved overall statistics, even though OM is still underestimated in Europe and overestimated in North America. The global anthropogenic aerosol direct radiative forcing (DRF) at the top of the atmosphere has changed from a small positive value to -0.08 W m(-2) in CAM4-Oslo. The sensitivity tests suggest that this change can be attributed to the new treatment of biomass burning aerosols and gravitational settling. Although it has not been a goal in this study, the new DRF estimate is closer both to the median model estimate from the AeroCom intercomparison and the best estimate in IPCC AR4. Estimated DRF at the ground surface has increased by ca. 60 %, to -1.89 W m(-2). We show that this can be explained by new emission data and omitted mixing of constituents between updrafts and downdrafts in convective clouds. The increased abundance of natural OM and the introduction of a cloud droplet spectral dispersion formulation are the most important contributions to a considerably decreased estimate of the indirect radiative forcing (IndRF). The IndRF is also found to be sensitive to assumptions about the coating of insoluble aerosols by sulphate and OM. The IndRF of -1.2 W m(-2), which is closer to the IPCC AR4 estimates than the previous estimate of -1.9 W m(-2), has thus been obtained without imposing unrealistic artificial lower bounds on cloud droplet number concentrations.

  • 14. Kirkevag, Alf
    et al.
    Grini, Alf
    Olivie, Dirk
    Seland, Oyvind
    Alterskjaer, Kari
    Hummel, Matthias
    Karset, Inger H. H.
    Lewinschal, Anna
    Stockholm University, Faculty of Science, Department of Meteorology .
    Liu, Xiaohong
    Makkonen, Risto
    Bethke, Ingo
    Griesfeller, Jan
    Schulz, Michael
    Iversen, Trond
    A production-tagged aerosol module for Earth system models, OsloAero5.3-extensions and updates for CAM5.3-Oslo2018In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 11, no 10, p. 3945-3982Article in journal (Refereed)
    Abstract [en]

    We document model updates and present and discuss modeling and validation results from a further developed production-tagged aerosol module, OsloAero5.3, for use in Earth system models. The aerosol module has in this study been implemented and applied in CAM5.3-Oslo. This model is based on CAM5.3-CESM1.2 and its own predecessor model version CAM4-Oslo. OsloAero5.3 has improved treatment of emissions, aerosol chemistry, particle life cycle, and aerosol-cloud interactions compared to its predecessor OsloAero4.0 in CAM4-Oslo. The main new features consist of improved aerosol sources; the module now explicitly accounts for aerosol particle nucleation and secondary organic aerosol production, with new emissions schemes also for sea salt, dimethyl sulfide (DMS), and marine primary organics. Mineral dust emissions are updated as well, adopting the formulation of CESM1.2. The improved model representation of aerosol-cloud interactions now resolves heterogeneous ice nucleation based on black carbon (BC) and mineral dust calculated by the model and treats the activation of cloud condensation nuclei (CCN) as in CAM5.3. Compared to OsloAero4.0 in CAM4-Oslo, the black carbon (BC) mass concentrations are less excessive aloft, with a better fit to observations. Near-surface mass concentrations of BC and sea salt aerosols are also less biased, while sulfate and mineral dust are slightly more biased. Although appearing quite similar for CAM5.3-Oslo and CAM4-Oslo, the validation results for organic matter (OM) are inconclusive, since both of the respective versions of OsloAero are equipped with a limited number of OM tracers for the sake of computational efficiency. Any information about the assumed mass ratios of OM to organic carbon (OC) for different types of OM sources is lost in the transport module. Assuming that observed OC concentrations scaled by 1.4 are representative for the modeled OM concentrations, CAM5.3-Oslo with OsloAero5.3 is slightly inferior for the very sparsely available observation data. Comparing clear-sky column-integrated optical properties with data from ground-based remote sensing, we find a negative bias in optical depth globally; however, it is not as strong as in CAM4-Oslo, but has positive biases in some areas typically dominated by mineral dust emissions. Aerosol absorption has a larger negative bias than the optical depth globally. This is reflected in a lower positive bias in areas where mineral dust is the main contributor to absorption. Globally, the low bias in absorption is smaller than in CAM4-Oslo. The Angstrom parameter exhibits small biases both globally and regionally, suggesting that the aerosol particle sizes are reasonably well represented. Cloud-top droplet number concentrations over oceans are generally underestimated compared to satellite retrievals, but seem to be overestimated downwind of major emissions of dust and biomass burning sources. Finally, we find small changes in direct radiative forcing at the top of the atmosphere, while the cloud radiative forcing due to anthropogenic aerosols is now more negative than in CAM4-Oslo, being on the strong side compared to the multi-model estimate in IPCC AR5. Although not all validation results in this study show improvement for the present CAM5.3-Oslo version, the extended and updated aerosol module OsloAero5.3 is more advanced and applicable than its predecessor OsloAero4.0, as it includes new parameterizations that more readily facilitate sensitivity and process studies and use in climate and Earth system model studies in general.

  • 15. Liu, X.
    et al.
    Easter, R. C.
    Ghan, S. J.
    Zaveri, R.
    Rasch, P.
    Shi, X.
    Lamarque, J. -F
    Gettelman, A.
    Morrison, H.
    Vitt, F.
    Conley, A.
    Park, S.
    Neale, R.
    Hannay, C.
    Ekman, Annica
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hess, P.
    Mahowald, N.
    Collins, W.
    Iacono, M. J.
    Bretherton, C. S.
    Flanner, M. G.
    Mitchell, D.
    Toward a minimal representation of aerosols in climate models: description and evaluation in the Community Atmosphere Model CAM52012In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 5, no 3, p. 709-739Article in journal (Refereed)
    Abstract [en]

    A modal aerosol module (MAM) has been developed for the Community Atmosphere Model version 5 (CAM5), the atmospheric component of the Community Earth System Model version 1 (CESM1). MAM is capable of simulating the aerosol size distribution and both internal and external mixing between aerosol components, treating numerous complicated aerosol processes and aerosol physical, chemical and optical properties in a physically-based manner. Two MAM versions were developed: a more complete version with seven lognormal modes (MAM7), and a version with three lognormal modes (MAM3) for the purpose of long-term (decades to centuries) simulations. In this paper a description and evaluation of the aerosol module and its two representations are provided. Sensitivity of the aerosol lifecycle to simplifications in the representation of aerosol is discussed. Simulated sulfate and secondary organic aerosol (SOA) mass concentrations are remarkably similar between MAM3 and MAM7. Differences in primary organic matter (POM) and black carbon (BC) concentrations between MAM3 and MAM7 are also small (mostly within 10 %). The mineral dust global burden differs by 10 % and sea salt burden by 30-40 % between MAM3 and MAM7, mainly due to the different size ranges for dust and sea salt modes and different standard deviations of the log-normal size distribution for sea salt modes between MAM3 and MAM7. The model is able to qualitatively capture the observed geographical and temporal variations of aerosol mass and number concentrations, size distributions, and aerosol optical properties. However, there are noticeable biases; e.g., simulated BC concentrations are significantly lower than measurements in the Arctic. There is a low bias in modeled aerosol optical depth on the global scale, especially in the developing countries. These biases in aerosol simulations clearly indicate the need for improvements of aerosol processes (e.g., emission fluxes of anthropogenic aerosols and precursor gases in developing countries, boundary layer nucleation) and properties (e.g., primary aerosol emission size, POM hygroscopicity). In addition, the critical role of cloud properties (e. g., liquid water content, cloud fraction) responsible for the wet scavenging of aerosol is highlighted.

  • 16. Lunt, Daniel J.
    et al.
    Huber, Matthew
    Anagnostou, Eleni
    Baatsen, Michiel L. J.
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology .
    DeConto, Rob
    Dijkstra, Henk A.
    Donnadieu, Yannick
    Evans, David
    Feng, Ran
    Foster, Gavin L.
    Gasson, Ed
    von der Heydt, Anna S.
    Hollis, Chris J.
    Inglis, Gordon N.
    Jones, Stephen M.
    Kiehl, Jeff
    Kirtland Turner, Sandy
    Korty, Robert L.
    Kozdon, Reinhardt
    Krishnan, Srinath
    Ladant, Jean-Baptiste
    Langebroek, Petra
    Lear, Caroline H.
    LeGrande, Allegra N.
    Littler, Kate
    Markwick, Paul
    Otto-Bliesner, Bette
    Pearson, Paul
    Poulsen, Christopher J.
    Salzmann, Ulrich
    Shields, Christine
    Snell, Kathryn
    Staerz, Michael
    Super, James
    Tabor, Clay
    Tierney, Jessica E.
    Tourte, Gregory J. L.
    Tripati, Aradhna
    Upchurch, Garland R.
    Wade, Bridget S.
    Wing, Scott L.
    Winguth, Arne M. E.
    Wright, Nicky M.
    Zachos, James C.
    Zeebe, Richard E.
    The DeepMIP contribution to PMIP4: experimental design for model simulations of the EECO, PETM, and pre-PETM (version 1.0)2017In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 10, no 2, p. 889-901Article in journal (Refereed)
    Abstract [en]

    Past warm periods provide an opportunity to evaluate climate models under extreme forcing scenarios, in particular high (>800 ppmv) atmospheric CO2 concentrations. Although a post hoc intercomparison of Eocene (similar to 50 Ma) climate model simulations and geological data has been carried out previously, models of past high-CO2 periods have never been evaluated in a consistent framework. Here, we present an experimental design for climate model simulations of three warm periods within the early Eocene and the latest Paleocene (the EECO, PETM, and pre-PETM). Together with the CMIP6 pre-industrial control and abrupt 4 x CO2 simulations, and additional sensitivity studies, these form the first phase of DeepMIP - the Deep-time Model Intercomparison Project, itself a group within the wider Paleo-climate Modelling Intercomparison Project (PMIP). The experimental design specifies and provides guidance on boundary conditions associated with palaeogeography, greenhouse gases, astronomical configuration, solar constant, land surface processes, and aerosols. Initial conditions, simulation length, and output variables are also specified. Finally, we explain how the geological data sets, which will be used to evaluate the simulations, will be developed.

  • 17.
    Merwin Monteiro, Joy
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    McGibbon, Jeremy
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology .
    sympl (v. 0.4.0) and climt (v. 0.15.3) - towards a flexible framework for building model hierarchies in Python2018In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 11, no 9, p. 3781-3794Article in journal (Refereed)
    Abstract [en]

    sympl (System for Modelling Planets) and climt (Climate Modelling and Diagnostics Toolkit) are an attempt to rethink climate modelling frameworks from the ground up. The aim is to use expressive data structures available in the scientific Python ecosystem along with best practices in software design to allow scientists to easily and reliably combine model components to represent the climate system at a desired level of complexity and to enable users to fully understand what the model is doing. sympl is a framework which formulates the model in terms of a state that gets evolved forward in time or modified within a specific time by well-defined components. sympl's design facilitates building models that are self-documenting, are highly interoperable, and provide fine-grained control over model components and behaviour. sympl components contain all relevant information about the input they expect and output that they provide. Components are designed to be easily interchanged, even when they rely on different units or array configurations. sympl provides basic functions and objects which could be used in any type of Earth system model. climt is an Earth system modelling toolkit that contains scientific components built using sympl base objects. These include both pure Python components and wrapped Fortran libraries. climt provides functionality requiring model-specific assumptions, such as state initialization and grid configuration. climt's programming interface designed to be easy to use and thus appealing to a wide audience. Model building, configuration and execution are performed through a Python script (or Jupyter Notebook), enabling researchers to build an end-to-end Python-based pipeline along with popular Python data analysis and visualization tools.

  • 18. Otto-Bliesner, Bette L.
    et al.
    Braconnot, Pascale
    Harrison, Sandy P.
    Lunt, Daniel J.
    Abe-Ouchi, Ayako
    Albani, Samuel
    Bartlein, Patrick J.
    Capron, Emilie
    Carlson, Anders E.
    Dutton, Andrea
    Fischer, Hubertus
    Goelzer, Heiko
    Govin, Aline
    Haywood, Alan
    Joos, Fortunat
    LeGrande, Allegra N.
    Lipscomb, William H.
    Lohmann, Gerrit
    Mahowald, Natalie
    Nehrbass-Ahles, Christoph
    Pausata, Francesco S. R.
    Peterschmitt, Jean-Yves
    Phipps, Steven J.
    Renssen, Hans
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    The PMIP4 contribution to CMIP6-Part 2: Two interglacials, scientific objective and experimental design for Holocene and Last Interglacial simulations2017In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 10, no 11, p. 3979-4003Article in journal (Refereed)
    Abstract [en]

    Two interglacial epochs are included in the suite of Paleoclimate Modeling Intercomparison Project (PMIP4) simulations in the Coupled Model Intercomparison Project (CMIP6). The experimental protocols for simulations of the mid-Holocene (midHolocene, 6000 years before present) and the Last Interglacial (lig127k, 127 000 years before present) are described here. These equilibrium simulations are designed to examine the impact of changes in orbital forcing at times when atmospheric greenhouse gas levels were similar to those of the preindustrial period and the continental configurations were almost identical to modern ones. These simulations test our understanding of the interplay between radiative forcing and atmospheric circulation, and the connections among large-scale and regional climate changes giving rise to phenomena such as land-sea contrast and high-latitude amplification in temperature changes, and responses of the monsoons, as compared to today. They also provide an opportunity, through carefully designed additional sensitivity experiments, to quantify the strength of atmosphere, ocean, cryosphere, and land-surface feedbacks. Sensitivity experiments are proposed to investigate the role of freshwater forcing in triggering abrupt climate changes within interglacial epochs. These feedback experiments naturally lead to a focus on climate evolution during interglacial periods, which will be examined through transient experiments. Analyses of the sensitivity simulations will also focus on interactions between extratropical and tropical circulation, and the relationship between changes in mean climate state and climate variability on annual to multi-decadal timescales. The comparative abundance of paleoenvironmental data and of quantitative climate reconstructions for the Holocene and Last Interglacial make these two epochs ideal candidates for systematic evaluation of model performance, and such comparisons will shed new light on the importance of external feedbacks (e.g., vegetation, dust) and the ability of state-of-the-art models to simulate climate changes realistically.

  • 19. Ottosen, T. -B.
    et al.
    Kakosimos, K. E.
    Johansson, Christer
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Environment and Health Administration, Stockholm, Sweden.
    Hertel, O.
    Brandt, J.
    Skov, H.
    Berkowicz, R.
    Ellermann, T.
    Jensen, S. S.
    Ketzel, M.
    Analysis of the impact of inhomogeneous emissions in the Operational Street Pollution Model (OSPM)2015In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 8, no 10, p. 3231-3245Article in journal (Refereed)
    Abstract [en]

    Semi-parameterized street canyon models, as e.g. the Operational Street Pollution Model (OSPM (R)), have been frequently applied for the last two decades to analyse levels and consequences of air pollution in streets. These models are popular due to their speed and low input requirements. One often-used simplification is the assumption that emissions are homogeneously distributed in the entire length and width of the street canyon. It is thus the aim of the present study to analyse the impact of this assumption by implementing an inhomogeneous emission geometry scheme in OSPM. The homogeneous and the inhomogeneous emission geometry schemes are validated against two real-world cases: Hornsgatan, Stockholm, a sloping street canyon; and Jagtvej, Copenhagen; where the morning rush hour has more traffic on one lane compared to the other. The two cases are supplemented with a theoretical calculation of the impact of street aspect (height / width) ratio and emission inhomogeneity on the concentrations resulting from inhomogeneous emissions. The results show an improved performance for the inhomogeneous emission geometry over the homogeneous emission geometry. Moreover, it is shown that the impact of inhomogeneous emissions is largest for near-parallel wind directions and for high aspect ratio canyons. The results from the real-world cases are however confounded by challenges estimating the emissions accurately.

  • 20.
    Scher, Sebastian
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Messori, Gabriele
    Stockholm University, Faculty of Science, Department of Meteorology . Uppsala University, Sweden.
    Weather and climate forecasting with neural networks: using general circulation models (GCMs) with different complexity as a study ground2019In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 12, no 7, p. 2797-2809Article in journal (Refereed)
    Abstract [en]

    Recently, there has been growing interest in the possibility of using neural networks for both weather forecasting and the generation of climate datasets. We use a bottom-up approach for assessing whether it should, in principle, be possible to do this. We use the relatively simple general circulation models (GCMs) PUMA and PLASIM as a simplified reality on which we train deep neural networks, which we then use for predicting the model weather at lead times of a few days. We specifically assess how the complexity of the climate model affects the neural network's forecast skill and how dependent the skill is on the length of the provided training period. Additionally, we show that using the neural networks to reproduce the climate of general circulation models including a seasonal cycle remains challenging - in contrast to earlier promising results on a model without seasonal cycle.

  • 21. Thomas, Manu Anna
    et al.
    Devasthale, Abhay
    L'Ecuyer, Tristan
    Wang, Shiyu
    Koenigk, Torben
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish Meteorological and Hydrological Institute, Sweden.
    Wyser, Klaus
    Snowfall distribution and its response to the Arctic Oscillation: an evaluation of HighResMIP models in the Arctic using CPR/CloudSat observations2019In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 12, no 8, p. 3759-3772Article in journal (Refereed)
    Abstract [en]

    A realistic representation of snowfall in general circulation models (GCMs) of global climate is important to accurately simulate snow cover, surface albedo, high-latitude precipitation and thus the surface radiation budget. Hence, in this study, we evaluate snowfall in a range of climate models run at two different resolutions by comparing to the latest estimates of snowfall from the CloudSat Cloud Profiling Radar over the northern latitudes. We also evaluate whether the finer-resolution versions of the GCMs simulate the accumulated snowfall better than their coarse-resolution counterparts. As the Arctic Oscillation (AO) is the prominent mode of natural variability in the polar latitudes, the snowfall variability associated with the different phases of the AO is examined in both models and in our observational reference. We report that the statistical distributions of snowfall differ considerably between the models and CloudSat observations. While CloudSat shows an exponential distribution of snowfall, the models show a Gaussian distribution that is heavily positively skewed. As a result, the 10th and 50th percentiles, representing the light and median snowfall, are overestimated by up to factors of 3 and 1.5, respectively, in the models investigated here. The overestimations are strongest during the winter months compared to autumn and spring. The extreme snowfall represented by the 90th percentiles, on the other hand, is positively skewed, underestimating the snowfall estimates by up to a factor of 2 in the models in winter compared to the CloudSat estimates. Though some regional improvements can be seen with increased spatial resolution within a particular model, it is not easy to identify a specific pattern that holds across all models. The characteristic snow- fall variability associated with the positive phase of AO over Greenland Sea and central Eurasian Arctic is well captured by the models.

  • 22. Tittensor, Derek P.
    et al.
    Eddy, Tyler D.
    Lotze, Heike K.
    Galbraith, Eric D.
    Cheung, William
    Barange, Manuel
    Blanchard, Julia L.
    Bopp, Laurent
    Bryndum-Buchholz, Andrea
    Buechner, Matthias
    Bulman, Catherine
    Carozza, David A.
    Christensen, Villy
    Coll, Marta
    Dunne, John P.
    Fernandes, Jose A.
    Fulton, Elizabeth A.
    Hobday, Alistair J.
    Huber, Veronika
    Jennings, Simon
    Jones, Miranda
    Lehodey, Patrick
    Link, Jason S.
    Mackinson, Steve
    Maury, Olivier
    Niiranen, Susa
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Oliveros-Ramos, Ricardo
    Roy, Tilla
    Schewe, Jacob
    Shin, Yunne-Jai
    Silva, Tiago
    Stock, Charles A.
    Steenbeek, Jeroen
    Underwood, Philip J.
    Volkholz, Jan
    Watson, James R.
    Walker, Nicola D.
    A protocol for the intercomparison of marine fishery and ecosystem models: Fish-MIP v1.02018In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 11, no 4, p. 1421-1442Article in journal (Refereed)
    Abstract [en]

    Model intercomparison studies in the climate and Earth sciences communities have been crucial to building credibility and coherence for future projections. They have quantified variability among models, spurred model development, contrasted within- and among-model uncertainty, assessed model fits to historical data, and provided ensemble projections of future change under specified scenarios. Given the speed and magnitude of anthropogenic change in the marine environment and the consequent effects on food security, biodiversity, marine industries, and society, the time is ripe for similar comparisons among models of fisheries and marine ecosystems. Here, we describe the Fisheries and Marine Ecosystem Model Intercomparison Project protocol version 1.0 (Fish-MIP v1.0), part of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP), which is a cross-sectoral network of climate impact modellers. Given the complexity of the marine ecosystem, this class of models has substantial heterogeneity of purpose, scope, theoretical underpinning, processes considered, parameterizations, resolution (grain size), and spatial extent. This heterogeneity reflects the lack of a unified understanding of the marine ecosystem and implies that the assemblage of all models is more likely to include a greater number of relevant processes than any single model. The current Fish-MIP protocol is designed to allow these heterogeneous models to be forced with common Earth System Model (ESM) Coupled Model Intercomparison Project Phase 5 (CMIP5) outputs under prescribed scenarios for historic (from the 1950s) and future (to 2100) time periods; it will be adapted to CMIP phase 6 (CMIP6) in future iterations. It also describes a standardized set of outputs for each participating Fish-MIP model to produce. This enables the broad characterization of differences between and uncertainties within models and projections when assessing climate and fisheries impacts on marine ecosystems and the services they provide. The systematic generation, collation, and comparison of results from Fish-MIP will inform an understanding of the range of plausible changes in marine ecosystems and improve our capacity to define and convey the strengths and weaknesses of model-based advice on future states of marine ecosystems and fisheries. Ultimately, Fish-MIP represents a step towards bringing together the marine ecosystem modelling community to produce consistent ensemble medium- and long-term projections of marine ecosystems.

  • 23.
    van Dongen, Eef C. H.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. ETHZ, Switzerland; Delft University of Technology, the Netherlands; Utrecht University, the Netherlands.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    van Gijzen, Martin B.
    van de Wal, Roderik S. W.
    Zwinger, Thomas
    Cheng, Gong
    Lötstedt, Per
    von Sydow, Lina
    Dynamically coupling full Stokes and shallow shelf approximation for marine ice sheet flow using Elmer/Ice (v8.3)2018In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 11, no 11, p. 4563-4576Article in journal (Refereed)
    Abstract [en]

    Ice flow forced by gravity is governed by the full Stokes (FS) equations, which are computationally expensive to solve due to the nonlinearity introduced by the rheology. Therefore, approximations to the FS equations are commonly used, especially when modeling a marine ice sheet (ice sheet, ice shelf, and/or ice stream) for 103 years or longer. The shallow ice approximation (SIA) and shallow shelf approximation (SSA) are commonly used but are accurate only for certain parts of an ice sheet. Here, we report a novel way of iteratively coupling FS and SSA that has been implemented in Elmer/Ice and applied to conceptual marine ice sheets. The FS-SSA coupling appears to be very accurate; the relative error in velocity compared to FS is below 0.5% for diagnostic runs and below 5% for prognostic runs. Results for grounding line dynamics obtained with the FS-SSA coupling are similar to those obtained from an FS model in an experiment with a periodical temperature forcing over 3000 years that induces grounding line advance and retreat. The rapid convergence of the FS-SSA coupling shows a large potential for reducing computation time, such that modeling a marine ice sheet for thousands of years should become feasible in the near future. Despite inefficient matrix assembly in the current implementation, computation time is reduced by 32 %, when the coupling is applied to a 3-D ice shelf.

  • 24. Zanchettin, Davide
    et al.
    Khodri, Myriam
    Timmreck, Claudia
    Toohey, Matthew
    Schmidt, Anja
    Gerber, Edwin P.
    Hegerl, Gabriele
    Robock, Alan
    Pausata, Francesco S. R.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ball, William T.
    Bauer, Susanne E.
    Bekki, Slimane
    Dhomse, Sandip S.
    LeGrande, Allegra N.
    Mann, Graham W.
    Marshall, Lauren
    Mills, Michael
    Marchand, Marion
    Niemeier, Ulrike
    Poulain, Virginie
    Rozanov, Eugene
    Rubino, Angelo
    Stenke, Andrea
    Tsigaridis, Kostas
    Tummon, Fiona
    The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP): experimental design and forcing input data for CMIP62016In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 9, no 8, p. 2701-2719Article in journal (Refereed)
    Abstract [en]

    The enhancement of the stratospheric aerosol layer by volcanic eruptions induces a complex set of responses causing global and regional climate effects on a broad range of timescales. Uncertainties exist regarding the climatic response to strong volcanic forcing identified in coupled climate simulations that contributed to the fifth phase of the Coupled Model Intercomparison Project (CMIP5). In order to better understand the sources of these model diversities, the Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP) has defined a coordinated set of idealized volcanic perturbation experiments to be carried out in alignment with the CMIP6 protocol. VolMIP provides a common stratospheric aerosol data set for each experiment to minimize differences in the applied volcanic forcing. It defines a set of initial conditions to assess how internal climate variability contributes to determining the response. VolMIP will assess to what extent volcanically forced responses of the coupled ocean-atmosphere system are robustly simulated by state-of-the-art coupled climate models and identify the causes that limit robust simulated behavior, especially differences in the treatment of physical processes. This paper illustrates the design of the idealized volcanic perturbation experiments in the VolMIP protocol and describes the common aerosol forcing input data sets to be used.

  • 25. Zhang, Haicheng
    et al.
    Goll, Daniel S.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Ciais, Philippe
    Guenet, Bertrand
    Huang, Yuanyuan
    Modeling the effects of litter stoichiometry and soil mineral N availability on soil organic matter formation using CENTURY-CUE (v1.0)2018In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 11, no 12, p. 4779-4796Article in journal (Refereed)
    Abstract [en]

    Microbial decomposition of plant litter is a crucial process for the land carbon (C) cycle, as it directly controls the partitioning of litter C between CO2 released to the atmosphere versus the formation of new soil organic matter (SOM). Land surface models used to study the C cycle rarely considered flexibility in the decomposer C use efficiency (CUEd) defined by the fraction of decomposed litter C that is retained as SOM (as opposed to be respired). In this study, we adapted a conceptual formulation of CUEd based on assumption that litter decomposers optimally adjust their CUEd as a function of litter substrate C to nitrogen (N) stoichiometry to maximize their growth rates. This formulation was incorporated into the widely used CENTURY soil biogeochemical model and evaluated based on data from laboratory litter incubation experiments. Results indicated that the CENTURY model with new CUEd formulation was able to reproduce differences in respiration rate of litter with contrasting C: N ratios and under different levels of mineral N availability, whereas the default model with fixed CUEd could not. Using the model with flexible CUEd, we also illustrated that litter quality affected the long-term SOM formation. Litter with a small C: N ratio tended to form a larger SOM pool than litter with larger C: N ratios, as it could be more efficiently incorporated into SOM by microorganisms. This study provided a simple but effective formulation to quantify the effect of varying litter quality (N content) on SOM formation across temporal scales. Optimality theory appears to be suitable to predict complex processes of litter decomposition into soil C and to quantify how plant residues and manure can be harnessed to improve soil C sequestration for climate mitigation.

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