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  • 1.
    Berg, Peter
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Koenigk, Torben
    SMHI, Research Department, Climate research - Rossby Centre.
    Impacts of using spectral nudging on regional climate model RCA4 simulations of the Arctic2013In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 6, no 3, p. 849-859Article in journal (Refereed)
    Abstract [en]

    The performance of the Rossby Centre regional climate model RCA4 is investigated for the Arctic CORDEX (COordinated Regional climate Downscaling EXperiment) region, with an emphasis on its suitability to be coupled to a regional ocean and sea ice model. Large biases in mean sea level pressure (MSLP) are identified, with pronounced too-high pressure centred over the North Pole in summer of over 5 hPa, and too-low pressure in winter of a similar magnitude. These lead to biases in the surface winds, which will potentially lead to strong sea ice biases in a future coupled system. The large-scale circulation is believed to be the major reason for the biases, and an implementation of spectral nudging is applied to remedy the problems by constraining the large-scale components of the driving fields within the interior domain. It is found that the spectral nudging generally corrects for the MSLP and wind biases, while not significantly affecting other variables, such as surface radiative components, two-metre temperature and precipitation.

  • 2.
    Berg, Peter
    et al.
    SMHI, Research Department, Hydrology.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Koenigk, Torben
    SMHI, Research Department, Climate research - Rossby Centre.
    On the effects of constraining atmospheric circulation in a coupled atmosphere-ocean Arctic regional climate model2016In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 46, no 11-12, p. 3499-3515Article in journal (Refereed)
  • 3.
    Caian, Mihaela
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Koenigk, Torben
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    An interannual link between Arctic sea-ice cover and the North Atlantic Oscillation2018In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 50, no 1-2, p. 423-441Article in journal (Refereed)
  • 4.
    Caian, Mihaela
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Koenigk, Torben
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    An interannual link between Arctic sea-ice cover and the North Atlantic Oscillation (vol 50, pg 423, 2017)2018In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 50, no 1-2, p. 443-443Article in journal (Refereed)
  • 5.
    Doescher, Ralf
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Beckmann, A
    Effects of a bottom boundary layer parameterization in a coarse-resolution model of the North Atlantic Ocean2000In: Journal of Atmospheric and Oceanic Technology, ISSN 0739-0572, E-ISSN 1520-0426, Vol. 17, no 5, p. 698-707Article in journal (Refereed)
    Abstract [en]

    The bottom boundary layer model approach of Beckmann and Doscher has been adopted for application in a coarse-resolution model of the North Atlantic Ocean. Both components of the approach (advective and conditional diffusive) are found to affect the deep water stratification and circulation. A significant deepening of the downward spreading North Atlantic Deep Water (NADW) is the major effect. This is associated with an enhanced spatial coverage of the NADW cell in the meridional circulation.

  • 6.
    Doescher, Ralf
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Koenigk, Torben
    SMHI, Research Department, Climate research - Rossby Centre.
    Arctic rapid sea ice loss events in regional coupled climate scenario experiments2013In: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 9, no 2, p. 217-248Article in journal (Refereed)
    Abstract [en]

    Rapid sea ice loss events (RILEs) in a mini-ensemble of regional Arctic coupled climate model scenario experiments are analyzed. Mechanisms of sudden ice loss are strongly related to atmospheric circulation conditions and preconditioning by sea ice thinning during the seasons and years before the event. Clustering of events in time suggests a strong control by large-scale atmospheric circulation. Anomalous atmospheric circulation is providing warm air anomalies of up to 5 K and is forcing ice flow, affecting winter ice growth. Even without a seasonal preconditioning during winter, ice drop events can be initiated by anomalous inflow of warm air during summer. It is shown that RILEs can be generated based on atmospheric circulation changes as a major driving force without major competing mechanisms, other than occasional longwave effects during spring and summer. Other anomalous seasonal radiative forcing or short-lived forcers (e.g., soot) play minor roles or no role at all in our model. RILEs initiated by ocean forcing do not occur in the model, although cannot be ruled out due to model limitations. Mechanisms found are qualitatively in line with observations of the 2007 RILE.

  • 7.
    Doescher, Ralf
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Simulated sea surface temperature and heat fluxes in different climates of the Baltic Sea2004In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 33, no 4-5, p. 242-248Article in journal (Refereed)
    Abstract [en]

    The physical state of the Baltic Sea in possible future climates is approached by numerical model experiments with a regional coupled ocean-atmosphere model driven by different global simulations. Scenarios and recent climate simulations are compared to estimate changes. The sea surface is clearly warmer by 2.9degreesC in the ensemble mean. The horizontal pattern of average annual mean warming can largely be explained in terms of ice-cover reduction. The transfer of heat from the atmosphere to the Baltic Sea shows a changed seasonal cycle: a reduced heat loss in fall, increased heat uptake in spring, and reduced heat uptake in summer. The interannual variability of surface temperature is generally increased. This is associated with a smoothed frequency distribution in northern basins. The overall heat budget shows increased solar radiation to the sea surface, which is balanced by changes of the other heat flux components.

  • 8.
    Doescher, Ralf
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Vihma, T.
    Maksimovich, E.
    Recent advances in understanding the Arctic climate system state and change from a sea ice perspective: a review2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 24, p. 13571-13600Article in journal (Refereed)
    Abstract [en]

    Sea ice is the central component and most sensitive indicator of the Arctic climate system. Both the depletion and areal decline of the Arctic sea ice cover, observed since the 1970s, have accelerated since the millennium. While the relationship of global warming to sea ice reduction is evident and underpinned statistically, it is the connecting mechanisms that are explored in detail in this review. Sea ice erodes both from the top and the bottom. Atmospheric, oceanic and sea ice processes interact in non-linear ways on various scales. Feedback mechanisms lead to an Arctic amplification of the global warming system: the amplification is both supported by the ice depletion and, at the same time, accelerates ice reduction. Knowledge of the mechanisms of sea ice decline grew during the 1990s and deepened when the acceleration became clear in the early 2000s. Record minimum summer sea ice extents in 2002, 2005, 2007 and 2012 provide additional information on the mechanisms. This article reviews recent progress in understanding the sea ice decline. Processes are revisited from atmospheric, oceanic and sea ice perspectives. There is strong evidence that decisive atmospheric changes are the major driver of sea ice change. Feedbacks due to reduced ice concentration, surface albedo, and ice thickness allow for additional local atmospheric and oceanic influences and self-supporting feedbacks. Large-scale ocean influences on Arctic Ocean hydrology and circulation are highly evident. Northward heat fluxes in the ocean are clearly impacting the ice margins, especially in the Atlantic sector of the Arctic. There is little indication of a direct and decisive influence of the warming ocean on the overall sea ice cover, due to an isolating layer of cold and fresh water underneath the sea ice.

  • 9.
    Doescher, Ralf
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Willen, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Rutgersson, Anna
    SMHI, Research Department, Climate research - Rossby Centre.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Graham, Phil
    SMHI, Research Department, Climate research - Rossby Centre.
    The development of the regional coupled ocean-atmosphere model RCAO2002In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 7, no 3, p. 183-192Article in journal (Refereed)
    Abstract [en]

    A regional coupled ocean-atmosphere-ice general circulation model for northern Europe is introduced for climate study purposes. The Baltic Sea is interactively coupled. The coupled model is validated in a 5-year hind-cast experiment with a focus on surface quantities and atmosphere-ocean heat fluxes. The coupled sea surface temperature matches observations well. The system is free of drift, does not need flux corrections and is suitable for multi-year climate runs. With flux forcing from the atmospheric model the regional ocean model gives sea surface temperatures statistically equivalent to the uncoupled ocean model forced by observations. Other oceanic surface quantities do not reach this quality in combination with the current atmosphere model. A strong dependence of sea ice extent on details of the atmospheric radiation scheme is found. Our standard scheme leads to an overestimation of ice, most likely due to a negative bias of long-wave radiation. There is indication that a latent heat flux bias in fall contributes to the ice problem. Other atmosphere-ocean heat fluxes are generally realistic in the long term mean.

  • 10.
    Doescher, Ralf
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Qian, Minwei
    Redler, Ren
    Quantifying Arctic contributions to climate predictability in a regional coupled ocean-ice-atmosphere model2010In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 34, no 7-8, p. 1157-1176Article in journal (Refereed)
    Abstract [en]

    The relative importance of regional processes inside the Arctic climate system and the large scale atmospheric circulation for Arctic interannual climate variability has been estimated with the help of a regional Arctic coupled ocean-ice-atmosphere model. The study focuses on sea ice and surface climate during the 1980s and 1990s. Simulations agree reasonably well with observations. Correlations between the winter North Atlantic Oscillation index and the summer Arctic sea ice thickness and summer sea ice extent are found. Spread of sea ice extent within an ensemble of model runs can be associated with a surface pressure gradient between the Nordic Seas and the Kara Sea. Trends in the sea ice thickness field are widely significant and can formally be attributed to large scale forcing outside the Arctic model domain. Concerning predictability, results indicate that the variability generated by the external forcing is more important in most regions than the internally generated variability. However, both are in the same order of magnitude. Local areas such as the Northern Greenland coast together with Fram Straits and parts of the Greenland Sea show a strong importance of internally generated variability, which is associated with wind direction variability due to interaction with atmospheric dynamics on the Greenland ice sheet. High predictability of sea ice extent is supported by north-easterly winds from the Arctic Ocean to Scandinavia.

  • 11. Doos, K
    et al.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    The Baltic haline conveyor belt or the overturning circulation and mixing in the Baltic2004In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 33, no 4-5, p. 261-266Article in journal (Refereed)
    Abstract [en]

    A study of the water-mass circulation of the Baltic has been undertaken by making use of a three dimensional Baltic Sea model simulation. The saline water from the North Atlantic is traced through the Danish Sounds into the Baltic where it upwells and mixes with the fresh water inflow from the rivers forming a Baltic haline conveyor belt. The mixing of the saline water from the Great Belt and Oresund with the fresh water is investigated making use of overturning stream functions and Lagrangian trajectories. The overturning stream function was calculated as a function of four different vertical coordinates (depth, salinity, temperature and density) in order to understand the path of the water and where it upwells and mixes. Evidence of a fictive depth overturning cell similar to the Deacon Cell in the Southern Ocean was found in the Baltic proper corresponding to the gyre circulation around Gotland, which vanishes when the overturning stream function is projected on density layers. A Lagrangian trajectory study was performed to obtain a better view of the circulation and mixing of the saline and fresh waters. The residence time of the water masses in the Baltic is calculated to be 26-29 years and the Lagrangian dispersion reaches basin saturation after 5 years.

  • 12. Gascard, J. -C
    et al.
    Vihma, T.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    General introduction to the DAMOCLES special issue2015In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 15, no 10, p. 5377-5379Article in journal (Refereed)
  • 13.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Atmospheric response to different sea surface temperatures in the Baltic Sea: coupled versus uncoupled regional climate model experiments2005In: Nordic Hydrology, ISSN 0029-1277, E-ISSN 1996-9694, Vol. 36, no 4-5, p. 397-409Article in journal (Refereed)
    Abstract [en]

    A climate change experiment with a fully coupled high resolution regional atmosphere-ocean model for the Baltic Sea is compared to an experiment with a stand-alone regional atmospheric model. Both experiments simulate 30-yr periods with boundary data from the same global climate model system. This particular global model system simulates very high sea surface temperatures during summer for the Baltic Sea at the end of this century under the investigated emission scenario. We show that the sea surface temperatures are less warm in the coupled regional model compared to the global model system and that this difference is dependent on the atmospheric circulation. In summers with a high NAO index and thereby relatively strong westerly flow over the North Atlantic the differences between the two models are small, while in summers with a weaker, more northerly flow over the Baltic Sea the differences are very large. The higher sea surface temperatures in the uncoupled experiment lead to an intensified hydrological cycle over the Baltic Sea, with more than 30% additional precipitation in summer taken as an average over the full 30-yr period and over the entire Baltic Sea. The differences are mostly local, over the sea, but there are differences in surrounding land areas.

  • 14.
    Koenigk, Torben
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Beatty, Christof Konig
    Caian, Mihaela
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Potential decadal predictability and its sensitivity to sea ice albedo parameterization in a global coupled model2012In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 38, no 11-12, p. 2389-2408Article in journal (Refereed)
    Abstract [en]

    Decadal prediction is one focus of the upcoming 5th IPCC Assessment report. To be able to interpret the results and to further improve the decadal predictions it is important to investigate the potential predictability in the participating climate models. This study analyzes the upper limit of climate predictability on decadal time scales and its dependency on sea ice albedo parameterization by performing two perfect ensemble experiments with the global coupled climate model EC-Earth. In the first experiment, the standard albedo formulation of EC-Earth is used, in the second experiment sea ice albedo is reduced. The potential prognostic predictability is analyzed for a set of oceanic and atmospheric parameters. The decadal predictability of the atmospheric circulation is small. The highest potential predictability was found in air temperature at 2 m height over the northern North Atlantic and the southern South Atlantic. Over land, only a few areas are significantly predictable. The predictability for continental size averages of air temperature is relatively good in all northern hemisphere regions. Sea ice thickness is highly predictable along the ice edges in the North Atlantic Arctic Sector. The meridional overturning circulation is highly predictable in both experiments and governs most of the decadal climate predictability in the northern hemisphere. The experiments using reduced sea ice albedo show some important differences like a generally higher predictability of atmospheric variables in the Arctic or higher predictability of air temperature in Europe. Furthermore, decadal variations are substantially smaller in the simulations with reduced ice albedo, which can be explained by reduced sea ice thickness in these simulations.

  • 15.
    Koenigk, Torben
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Berg, Peter
    SMHI, Research Department, Hydrology.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Arctic climate change in an ensemble of regional CORDEX simulations2015In: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 34, article id 24603Article in journal (Refereed)
    Abstract [en]

    Fifth phase Climate Model Intercomparison Project historical and scenario simulations from four global climate models (GCMs) using the Representative Concentration Pathways greenhouse gas concentration trajectories RCP4.5 and RCP8.5 are downscaled over the Arctic with the regional Rossby Centre Atmosphere model (RCA). The regional model simulations largely reflect the circulation bias patterns of the driving global models in the historical period, indicating the importance of lateral and lower boundary conditions. However, local differences occur as a reduced winter 2-m air temperature bias over the Arctic Ocean and increased cold biases over land areas in RCA. The projected changes are dominated by a strong warming in the Arctic, exceeding 15 degrees K in autumn and winter over the Arctic Ocean in RCP8.5, strongly increased precipitation and reduced sea-level pressure. Near-surface temperature and precipitation are linearly related in the Arctic. The wintertime inversion strength is reduced, leading to a less stable stratification of the Arctic atmosphere. The diurnal temperature range is reduced in all seasons. The large-scale change patterns are dominated by the surface and lateral boundary conditions so future response is similar in RCA and the driving global models. However, the warming over the Arctic Ocean is smaller in RCA; the warming over land is larger in winter and spring but smaller in summer. The future response of winter cloud cover is opposite in RCA and the GCMs. Precipitation changes in RCA are much larger during summer than in the global models and more small-scale change patterns occur.

  • 16.
    Koenigk, Torben
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Arctic future scenario experiments with a coupled regional climate model2011In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 63, no 1, p. 69-86Article in journal (Refereed)
  • 17.
    Meier, Markus
    et al.
    SMHI, Research Department, Oceanography.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Simulated water and heat cycles of the Baltic Sea using a 3D coupled atmosphere-ice - ocean model2002In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 7, no 4, p. 327-334Article in journal (Refereed)
    Abstract [en]

    The heat and water cycles of the Baltic Sea are calculated utilizing multi-year model simulations. This is one of the major objectives of the BALTEX program. For the period 1988-1993, results of a 3D ice-ocean model forced with observed atmospheric surface fields are compared with results of a fully coupled atmosphere-ice-ocean model using re-analysis data at the lateral boundaries. The state-of-the-art coupled model system has been developed for climate study purposes in the Nordic countries. The model domain of the atmosphere model covers Scandinavia, Europe and parts of the North Atlantic whereas the ocean model is limited to the Baltic Sea. The annual and monthly mean heat budgets for the Baltic Sea are calculated from the dominating surface fluxes, i.e. sensible heat, latent heat, net longwave radiation and solar radiation to the open water or to the sea ice. The main part of the freshwater inflow to the Baltic is the river runoff. A smaller part of about 11 % is added from net precipitation. The heat and water cycles are compared with the results of a long-term simulation (1980-1993) using the stand-alone Baltic Sea model forced with observed atmospheric surface fields. In general, both approaches, using the uncoupled or coupled Baltic Sea model, give realistic estimates of the heat and water cycles and are in good agreement with results of other studies. However, in the coupled model the parameterizations of the latent heat flux and the incoming longwave radiation need to be improved.

  • 18.
    Meier, Markus
    et al.
    SMHI, Research Department, Oceanography.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Broman, Barry
    SMHI, Research Department, Climate research - Rossby Centre.
    Piechura, J
    The major Baltic inflow in January 2003 and preconditioning by smaller inflows in summer/autumn 2002: a model study2004In: Oceanologia, ISSN 0078-3234, Vol. 46, no 4, p. 557-579Article in journal (Refereed)
    Abstract [en]

    Using the results of the Rossby Centre Ocean model (RCO) the Baltic inflows in summer/autumn 2002 and January 2003 have been studied. The model results were extracted from a long simulation with observed atmospheric forcing Starting in May 1980. In RCO a bottom boundary layer model was embedded. Both the Smaller inflows and the major inflow in January 2003 are simulated in good agreement with observations. We found that a total of 222 km(3) water entered the Baltic in January: the salinity of 94 km(3) was greater than 17 PSU. In August/September 2002 the outflow through the Sound and inflow across the Darss Sill were simulated. The net inflow volume amounted to about 50 km(3).

  • 19.
    Meier, Markus
    et al.
    SMHI, Research Department, Oceanography.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Coward, Andrew C.
    James Renell Div,. Southhampton Oceanogr. Centre.
    Nycander, Jonas
    MISU.
    Döös, Kristofer
    MISU.
    RCO – Rossby Centre regional Ocean climate model: model description (version 1.0) and first results from the hindcast period 1992/931999Report (Other academic)
    Abstract [en]

    Within SWECLIM a 3D fully coupled ice-ocean model has been developed based on the massively parallel OCCAM code from Southampton. Compared to the global OCCAM the model has to be adopted to Baltic Sea conditions with implementations of high-frequent atmospheric forcing fields in connection with adequate bulk formulae for wind stress, heat uxes and freshwater uxes, solar radiation, river runoff, active open boundary conditions, a second-order moment turbulence closure scheme and a dynamic-thermodynamic sea ice model. Thereby, state-of-the-art sub-models and parameterizations have been used. RCO is the first 3D coupled ice-ocean model for the Baltic Sea with the above mentioned specifications suitable for use on mpp computers like CRAY-T3E's. Thus, a milestone for 3D ocean model development has been set. No other model is as fast as RCO. The performance has been improved significantly using advanced algorithms to optimize processor maps. This guarantees work load balance between the different processors. From now on it is possible to perform longterm simulations (10 years) within SWECLIM using a sufficiently resolved 3D Baltic Sea model. The open boundary conditions have been tested. They allow waves to radiate out of the model domain and signals prescribed at the border to in uence the model interior. No significant trends (like emptying or filling) have been observed which might prevent longer integrations of the system. An option has been included in RCO for active open boundary conditions also for temperature and salinity. For the first time the turbulence closure model has been tested within a 3D model in all Baltic sub-basins. The new flux boundary conditions for turbulent kinetic energy parameterizing breaking surface waves perform well. First results for the hindcast period 1992/93 are presented. Therefor, realistic atmospheric, runoff and boundary data have been used. The model is initialized using observed profile temperature and salinity data. A spin-up period of 3 months starting in May is sufficient to smooth out artificial gradients from the initialization procedure and to turn in basin wide volume changes correctly. The model results have been compared to sea level, sea surface temperature, temperature/salinity profile and ice thickness/compactness data with good agreement. Basin wide volume changes as well as daily sea level oscillations are simulated surprisingly good. Sea surface temperatures follow the observed seasonal cycle. Up- and downwelling events in RCO occur as observed with the right frequency and area extent but the sst's tend to be colder in upwelling and warmer in downwelling regions compared to observations. Mixed layer depths, which are important for the ocean heat content, agree well with previous model studies which are validated against observations intensively (Meier, 1996). The water exchange between Baltic and North Sea crucial for multi-year integrations is modelled realistically. Especially the salt water inflow in January 1993 can be reproduced. The bottom water in Bornholm Basin is replaced by new water originating from the North Sea but maximum observed bottom salinities at Bornholm Deep are underestimated by 1-2 PSU. Freezing, breakup date and maximum ice extent are in good correspondence with observations. Improved parameterizations result in modelled ice thicknesses as observed whereas other authors report too large ice thicknesses and delayed ice melting (e.g., Haapala and Lepparanta,1996). Multi-year simulations including mild, normal and severe winters will be necessary to elucidate this problem further. A comparison between an experiment with full dynamic-thermodynamics and one without dynamic effects reveals the importance of ice advection under wind influence. A process study from the beginning of February 1993 showed that under strong wind conditions a hole in the ice coverage can open with the size of half of the Bothnian Bay. At the end of January 1993 the Bothnian Bay, the coastal area of the Bothnian Sea and the eastern parts of the Gulf of Finland are ice covered. A couple of days later westerly winds led to wide open areas in the western Bothnian Bay while ice piled up at the eastern coasts to a correct amount. This phenomenon can be modelled only with ice dynamics included. The aim of SWECLIM is to increase our knowledge of the effects of climate change in Sweden and the other Nordic countries. Therefor, it is necessary to understand the present climate. For the Baltic Sea even the knowledge about the present mean state and its transients is rather poor. Only a small number of long-time observations like sea level records (for example from Stockholm, see Ekman (1988)), maximum annual ice extent (e.g., Palosuo, 1953; Seina and Palosuo, 1993) or temperature and salinityprofiles from monitoring stations in some of the sub-basins (e.g., Matthaus and Frank,1992) are available. These informations are not enough to understand the driving mechanisms of mean horizontal and vertical transports of energy, momentum and matter. 3D Baltic Sea models like RCO will close this knowledge gap in future. Thereby, it will be possible to close the water and energy cycle of the Baltic catchment area, a final goal of BALTEX. By applying atmospheric forcing data from scenario simulations in one- or two-way coupled mode it will be possible to make predictions of climate change for the Baltic Sea. Impact studies of the future marine environment will be available using detailed highly resolved information from RCO. This report presents a powerful tool for solving these and other tasks.

  • 20.
    Meier, Markus
    et al.
    SMHI, Research Department, Oceanography.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Faxen, T
    A multiprocessor coupled ice-ocean model for the Baltic Sea: Application to salt inflow2003In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 108, no C8, article id 3273Article in journal (Refereed)
    Abstract [en]

    Within the Swedish Regional Climate Modeling Program, SWECLIM, a three-dimensional (3-D) coupled ice-ocean model for the Baltic Sea has been developed to simulate physical processes on timescales of hours to decades. The code has been developed based on the massively parallel version of the Ocean Circulation Climate Advanced Modeling (OCCAM) project of the Bryan-Cox-Semtner model. An elastic-viscous-plastic ice rheology is employed, resulting in a fully explicit numerical scheme that improves computational efficiency. An improved two-equation turbulence model has been embedded to simulate the seasonal cycle of surface mixed layer depths as well as deepwater mixing on decadal timescale. The model has open boundaries in the northern Kattegat and is forced with realistic atmospheric fields and river runoff. Optimized computational performance and advanced algorithms to calculate processor maps make the code fast and suitable for multi-year, high-resolution simulations. As test cases, the major salt water inflow event in January 1993 and the stagnation period 1980-1992, have been selected. The agreement between model results and observations is regarded as good. Especially, the time evolution of the halocline in the Baltic proper is realistically simulated also for the longer period without flux correction, data assimilation, or reinitialization. However, in particular, smaller salt water inflows into the Bornholm Basin are underestimated, independent of the horizontal model resolution used. It is suggested that the mixing parameterization still needs improvements. In addition, a series of process studies of the inflow period 1992/1993 have been performed to show the impact of river runoff, wind speed, and sea level in Kattegat. Natural interannual runoff variations control salt water inflows into the Bornholm Basin effectively. The effect of wind speed variation on the salt water flux from the Arkona Basin to the Bornholm Basin is minor.

  • 21.
    Meier, Markus
    et al.
    SMHI, Research Department, Oceanography.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Halkka, A
    Simulated distributions of Baltic Sea-ice in warming climate and consequences for the winter habitat of the Baltic ringed seal2004In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 33, no 4-5, p. 249-256Article in journal (Refereed)
    Abstract [en]

    Sea-ice in the Baltic Sea in present and future climates is investigated. The Rossby Centre Regional Atmosphere-Ocean model was used to perform a set of 30-year-long time slice experiments. For each of the two driving global models HadAM3H and ECHAM4/OPYC3, one control run (1961-1990) and two scenario runs (2071-2100) based upon the SIRES A2 and B2 emission scenarios were conducted. The future sea-ice volume in the Baltic Sea is reduced by 83% on average. The Bothnian Sea, large areas of the Gulf of Finland and Gulf of Riga, and the outer parts of the southwestern archipelago of Finland will become ice-free in the mean. The presented scenarios are used to study the impact of climate change on the Baltic ringed seal (Phoca hispida botnica). Climate change seems to be a major threat to all southern populations. The only fairly good winter sea-ice habitat is found to be confined to the Bay of Bothnia.

  • 22.
    Meier, Markus
    et al.
    SMHI, Research Department, Oceanography.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Modelling the changing climate of the Baltic Sea.2006Report (Other academic)
  • 23. Paquin, Jean-Philippe
    et al.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Sushama, Laxmi
    Koenigk, Torben
    SMHI, Research Department, Climate research - Rossby Centre.
    Causes and consequences of mid-21st-century rapid ice loss events simulated by the Rossby centre regional atmosphere-ocean model2013In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 65, article id 19110Article in journal (Refereed)
    Abstract [en]

    Recent observations and modelling studies suggest that the Arctic climate is undergoing important transition. One manifestation of this change is seen in the rapid sea-ice cover decrease as experienced in 2007 and 2012. Although most numerical climate models cannot adequately reproduce the recent changes, some models produce similar Rapid Ice Loss Events (RILEs) during the mid-21st-century. This study presents an analysis of four specific RILEs clustered around 2040 in three transient climate projections performed with the coupled Rossby Centre regional Atmosphere-Ocean model (RCAO). The analysis shows that long-term thinning causes increased vulnerability of the Arctic Ocean sea-ice cover. In the Atlantic sector, pre-conditioning (thinning of sea ice) combined with anomalous atmospheric and oceanic heat transport causes large ice loss, while in the Pacific sector of the Arctic Ocean sea-ice albedo feedback appears important, particularly along the retreating sea-ice margin. Although maximum sea-ice loss occurs in the autumn, response in surface air temperature occurs in early winter, caused by strong increase in ocean-atmosphere surface energy fluxes, mainly the turbulent fluxes. Synchronicity of the events around 2040 in the projections is caused by a strong large-scale atmospheric circulation anomaly at the Atlantic lateral boundary of the regional model. The limited impact on land is caused by vertical propagation of the surface heat anomaly rather than horizontal, caused by the absence of low-level temperature inversion over the ocean.

  • 24.
    Rummukainen, Markku
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Johansson, Daniel J.A.
    Institutionen för energi och miljö, avdelningen för fysisk resursteori, Chalmers.
    Azar, Christian
    Institutionen för energi och miljö, avdelningen för fysisk resursteori, Chalmers.
    Langner, Joakim
    SMHI, Research Department, Air quality.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Smith, Henrik
    Centrum för miljö och klimatforskning, Lunds universitet.
    Uppdatering av den vetenskapliga grunden för klimatarbetet2011Report (Other academic)
    Abstract [sv]

    Det naturvetenskapliga kunskapsläget om klimatförändringarna förbättrats ständigt genom forskningen om klimatsystemet, klimatpåverkan, klimatets variationer och förändringar samt klimateffekter. Kunskapsläget är väletablerat när det gäller den grundläggande fysiken bakom växthuseffekten, liksom att genomsnittstemperaturen vid jordytan stigit de senaste femtio åren. Det är också mycket sannolikt att det mesta av den observerade uppvärmningen beror på mänsklig klimatpåverkan. Samtidigt finns det betydande osäkerheter när det gäller konsekvenserna av klimatförändringarna samt hur mycket utsläppen behöver minska för att man ska nå ett givet klimatmål. Värdet på klimatkänsligheten är den viktigaste faktorn för beräkningar av hur mycket växthusgaser vi kan släppa ut, givet ett visst temperaturmål. Forskningen visar att det behövs stora och snabba utsläppsminskningar för att uppnå tvågradersmålet. För att nå ett lägre temperaturmål, till exempel ett 1,5-gradersmål, är de nödvändiga utsläppsminskningarna än mer omfattande.  För att nå tvågradersmålet med en sannolikhet runt 70 % krävs uppskattningsvis att de globala växthusgasutsläppen minskar i storleksordningen 50‒60 % från år 2000 till 2050, och minskar med nära 100 % till 2100.  För att nå ett 1,5-gradersmål med en sannolikhet runt 70 % krävs globala nollutsläpp redan runt år 2050.  För att nå ett 1,5-gradersmål med en sannolikhet runt 50 % krävs uppskattningsvis att de globala växthusgasutsläppen minskar i storleksordningen 80 % från år 2000 till 2050, och med nära 100 % till 2100. Det är framför allt de kumulativa utsläppen av koldioxid och andra långlivade växthusgaser som räknas när det gäller hur stora klimatförändringarna blir bortom 2100. Ju senare de globala utsläppen kulminerar, och ju högre nivå de då är på, desto större blir utmaningen för att åstadkomma en tillräckligt snabb påföljande utsläppsminskningstakt. Reducerade utsläpp av kortlivade klimatpåverkande ämnen är viktigt främst i ett kortare perspektiv. Det finns olika modeller för hur de globala utsläppsminskningarna kan fördelas mellan olika regioner och länder. Dessa baseras inte på naturvetenskapliga principer utan är beroende av politiska och andra ställningstaganden. För en del länder skiljer sig resultaten mycket beroende på valet av fördelningsmodell. För de flesta industriländer är slutsatsen dock generellt sett densamma: jämfört med idag behöver deras utsläpp minska mycket kraftigt.  För att nå tvågradersmålet med i storleksordningen 70 % sannolikhet krävs, givet en globalt lika per capita fördelning av utsläppen från och med 2050, att utsläppen i Sverige minskar med cirka 70 % från år 2005 till 2050. Den motsvarande siffran för EU är cirka 80 %.  För att nå ett 1,5-gradersmål med i storleksordningen 70 % sannolikhet krävs, givet en globalt lika per capita fördelning av utsläppen från och med 2050, att utsläppen minskar från år 2005 till år 2050 med runt 100 % i Sverige och i EU, och i andra länder.  För att nå ett 1,5-gradersmål med i storleksordningen 50 % sannolikhet krävs, givet en globalt lika per capita fördelning av utsläppen från och med 2050, att utsläppen i Sverige och EU minskar med drygt 90 % från år 2005 till 2050. Nettoutsläpp av koldioxid från avskogning och utrikes luft- och sjöfart ingår inte i dessa uppskattningar. Generellt blir riskerna för allvarliga klimateffekter mindre ju mer ambitiöst temperaturmål som väljs, men riskerna försvinner inte med tvågradersmålet, och inte ens med ett 1,5-gradersmål. Jämfört med IPCC:s AR4 från 2007, har nya forskningsresultat publicerats om klimateffekter. I denna rapport har vi fokuserat på havsnivåhöjningen, havsförsurningen, den biologiska mångfalden samt klimateffekter i Arktis. Jämfört med genomgången av kunskapsläget i AR4 visar nya resultat att den framtida havsnivåhöjningen kan bli större, havsförsurningens effekter på marina ekosystem omfattande och även om en del arter kan vara anpassningsbara, kan världens ekosystem påverkas av skillnader i olika arters sårbarhet för klimatförändringarna. I Arktis sker snabba förändringar. Sammantaget ter sig riskerna för allvarliga klimateffekter större jämfört med AR4. Denna rapport utgår från naturvetenskaplig klimatforskning sedan 2007. Rapporten förordar inte något specifikt temperaturmål, någon specifik utsläppsbana eller specifika policybeslut. Dessa är föremål för politiska avgöranden.

  • 25.
    Räisänen, Jouni
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Simulation of present-day climate in Northen Europé in the HadCM2 OAGCM1998Report (Other academic)
  • 26.
    Räisänen, Jouni
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, U
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Graham, Phil
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Willen, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    European climate in the late twenty-first century: regional simulations with two driving global models and two forcing scenarios2004In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 22, no 1, p. 13-31Article in journal (Refereed)
    Abstract [en]

    A basic analysis is presented for a series of regional climate change simulations that were conducted by the Swedish Rossby Centre and contribute to the PRUDENCE (Prediction of Regional scenarios and Uncertainties for Defining EuropeaN Climate change risks and Effects) project. For each of the two driving global models HadAM3H and ECHAM4/OPYC3, a 30-year control run and two 30-year scenario runs (based on the SRES A2 and B2 emission scenarios) were made with the regional model. In this way, four realizations of climate change from 1961-1990 to 2071-2100 were obtained. The simulated changes are larger for the A2 than the B2 scenario (although with few qualitative differences) and in most cases in the ECHAM4/OPYC3-driven (RE) than in the HadAM3H-driven (RH) regional simulations. In all the scenario runs, the warming in northern Europe is largest in winter or late autumn. In central and southern Europe, the warming peaks in summer when it locally reaches 10 degreesC in the RE-A2 simulation and 6-7 degreesC in the RH-A2 and RE-B2 simulations. The four simulations agree on a general increase in precipitation in northern Europe especially in winter and on a general decrease in precipitation in southern and central Europe in summer, but the magnitude and the geographical patterns of the change differ markedly between RH and RE. This reflects very different changes in the atmospheric circulation during the winter half-year, which also lead to quite different simulated changes in windiness. All four simulations show a large increase in the lowest minimum temperatures in northern, central and eastern Europe, most likely due to reduced snow cover. Extreme daily precipitation increases even in most of those areas where the mean annual precipitation decreases.

  • 27.
    Räisänen, Jouni
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Graham, Phil
    SMHI, Professional Services.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    GCM driven simulations of recent and future climate with the Rossby Centre coupled atmosphere - Baltic Sea regional climate model RCAO2003Report (Other academic)
    Abstract [en]

    A series of six general circulation model (GCM) driven regional climate simulations made at the Rossby Centre, SMHI, during the year 2002 are documented. For both the two driving GCMs HadAM3H andECHAM4/OPYC3, a 30-year (1961-1990) control run and two 30-year (2071-2100) scenario runs have been made. The scenario runs are based on the IPCC SRES A2 and B2 forcing scenarios. These simulations were made at 49 km atmospheric resolution and they are part of the European PRUDENCE project.Many aspects of the simulated control climates compare favourably with observations, but some problems are also evident. For example, the simulated cloudiness and precipitation appear generally too abundant in northern Europe (although biases in precipitation measurements complicate the interpretation), whereas too clear and dry conditions prevail in southern Europe. There is a lot of similarity between the HadAM3Hdriven (RCAO-H) and ECHAM4/OPYC3-driven (RCAO-E) control simulations, although the problems associated with the hydrological cycle and cloudiness are somewhat larger in the latter.The simulated climate changes (2071-2100 minus 1961-1990) depend on both the forcing scenario (the changes are generally larger for A2 than B2) and the driving global model (the largest changes tend to occur in RCAO-E). In all the scenario simulations, the warming in northern Europe is largest in winter or autumn. In central and southern Europe, the warming peaks in summer and reaches in the RCAO-E A2 simulation locally 10°C. The four simulations agree on a general increase in precipitation in northern Europe especiallyin winter and on a general decrease in precipitation in southern and central Europe in summer, but the magnitude and the geographical patterns of the change differ a lot between RCAO-H and RCAO-E. Thisreflects very different changes in the atmospheric circulation during the winter half-year, which also have a large impact on the simulated changes in windiness. A very large increase in the lowest minimumtemperatures occurs in a large part of Europe, most probably due to reduced snow cover. Extreme daily precipitation increases even in most of those areas where the mean annual precipitation decreases.

  • 28.
    Wang, Shiyu
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Dieterich, Christian
    SMHI, Research Department, Oceanography.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Höglund, Anders
    SMHI, Research Department, Oceanography.
    Hordoir, Robinson
    SMHI, Research Department, Oceanography.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Schimanke, Semjon
    SMHI, Research Department, Oceanography.
    Development and evaluation of a new regional coupled atmosphere-ocean model in the North Sea and Baltic Sea2015In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 67, article id 24284Article in journal (Refereed)
    Abstract [en]

    A new regional coupled model system for the North Sea and the Baltic Sea is developed, which is composed of the regional setup of ocean model NEMO, the Rossby Centre regional climate model RCA4, the sea ice model LIM3 and the river routing model CaMa-Flood. The performance of this coupled model system is assessed using a simulation forced with ERA-Interim reanalysis data at the lateral boundaries during the period 1979-2010. Compared to observations, this coupled model system can realistically simulate the present climate. Since the active coupling area covers the North Sea and Baltic Sea only, the impact of the ocean on the atmosphere over Europe is small. However, we found some local, statistically significant impacts on surface parameters like 2m air temperature and sea surface temperature (SST). A precipitation-SST correlation analysis indicates that both coupled and uncoupled models can reproduce the air-sea relationship reasonably well. However, the coupled simulation gives slightly better correlations even when all seasons are taken into account. The seasonal correlation analysis shows that the air-sea interaction has a strong seasonal dependence. Strongest discrepancies between the coupled and the uncoupled simulations occur during summer. Due to lack of air-sea interaction, in the Baltic Sea in the uncoupled atmosphere-standalone run the correlation between precipitation and SST is too small compared to observations, whereas the coupled run is more realistic. Further, the correlation analysis between heat flux components and SST tendency suggests that the coupled model has a stronger correlation. Our analyses show that this coupled model system is stable and suitable for different climate change studies.

  • 29. Wormbs, N.
    et al.
    Nilsson, A.E.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Sörlin, S.
    The History of Emerging Arctic Climate Modelling, poster presented at the IPY final conference in Oslo2010Conference paper (Other academic)
  • 30. Zhang, Wenxin
    et al.
    Miller, Paul A.
    Smith, Benjamin
    Wania, Rita
    Koenigk, Torben
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Tundra shrubification and tree-line advance amplify arctic climate warming: results from an individual-based dynamic vegetation model2013In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 8, no 3, article id 034023Article in journal (Refereed)
    Abstract [en]

    One major challenge to the improvement of regional climate scenarios for the northern high latitudes is to understand land surface feedbacks associated with vegetation shifts and ecosystem biogeochemical cycling. We employed a customized, Arctic version of the individual-based dynamic vegetation model LPJ-GUESS to simulate the dynamics of upland and wetland ecosystems under a regional climate model-downscaled future climate projection for the Arctic and Subarctic. The simulated vegetation distribution (1961-1990) agreed well with a composite map of actual arctic vegetation. In the future (2051-2080), a poleward advance of the forest-tundra boundary, an expansion of tall shrub tundra, and a dominance shift from deciduous to evergreen boreal conifer forest over northern Eurasia were simulated. Ecosystems continued to sink carbon for the next few decades, although the size of these sinks diminished by the late 21st century. Hot spots of increased CH4 emission were identified in the peatlands near Hudson Bay and western Siberia. In terms of their net impact on regional climate forcing, positive feedbacks associated with the negative effects of tree-line, shrub cover and forest phenology changes on snow-season albedo, as well as the larger sources of CH4, may potentially dominate over negative feedbacks due to increased carbon sequestration and increased latent heat flux.

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