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  • 301. Conley, Daniel J.
    et al.
    Bjorck, Svante
    Bonsdorff, Erik
    Carstensen, Jacob
    Destouni, Georgia
    Gustafsson, Bo G.
    Hietanen, Susanna
    Kortekaas, Marloes
    Kuosa, Harri
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Mueller-Karulis, Baerbel
    Nordberg, Kjell
    Norkko, Alf
    Nuernberg, Gertrud
    Pitkanen, Heikki
    Rabalais, Nancy N.
    Rosenberg, Rutger
    Savchuk, Oleg P.
    Slomp, Caroline P.
    Voss, Maren
    Wulff, Fredrik
    Zillen, Lovisa
    Hypoxia-Related Processes in the Baltic Sea2009In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 43, no 10, p. 3412-3420Article, review/survey (Refereed)
    Abstract [en]

    Hypoxia, a growing worldwide problem, has been intermittently present in the modern Baltic Sea since its formation ca. 8000 cal. yr BP. However, both the spatial extent and intensity of hypoxia have increased with anthropogenic eutrophication due to nutrient inputs. Physical processes, which control stratification and the renewal of oxygen in bottom waters, are important constraints on the formation and maintenance of hypoxia. Climate controlled inflows of saline water from the North Sea through the Danish Straits is a critical controlling factor governing the spatial extent and duration of hypoxia. Hypoxia regulates the biogeochemical cycles of both phosphorus (P) and nitrogen (N) in the water column and sediments. Significant amounts of P are currently released from sediments, an order of magnitude larger than anthropogenic inputs. The Baltic Sea is unique for coastal marine ecosystems experiencing N losses in hypoxic waters below the halocline. Although benthic communities in the Baltic Sea are naturally constrained by salinity gradients, hypoxia has resulted in habitat loss over vast areas and the elimination of benthic fauna, and has severely disrupted benthic food webs. Nutrient load reductions are needed to reduce the extent, severity, and effects of hypoxia.

  • 302. Conley, Daniel J.
    et al.
    Carstensen, Jacob
    Aigars, Juris
    Axe, Philip
    SMHI, Research Department, Oceanography.
    Bonsdorff, Erik
    Eremina, Tatjana
    Haahti, Britt-Marie
    Humborg, Christoph
    Jonsson, Per
    Kotta, Jonne
    Lannegren, Christer
    Larsson, Ulf
    Maximov, Alexey
    Medina, Miguel Rodriguez
    Lysiak-Pastuszak, Elzbieta
    Remeikaite-Nikiene, Nijole
    Walve, Jakob
    Wilhelms, Sunhild
    Zillen, Lovisa
    Hypoxia Is Increasing in the Coastal Zone of the Baltic Sea2011In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 45, no 16, p. 6777-6783Article in journal (Refereed)
    Abstract [en]

    Hypoxia is a well-described phenomenon in the offshore waters of the Baltic Sea with both the spatial extent and intensity of hypoxia known to have increased due to anthropogenic eutrophication, however, an unknown amount of hypoxia is present in the coastal zone. Here we report on the widespread unprecedented occurrence of hypoxia across the coastal zone of the Baltic Sea. We have identified 115 sites that have experienced hypoxia during the period 1955-2009 increasing the global total to ca. 500 sites, with the Baltic Sea coastal zone containing over 20% of all known sites worldwide. Most sites experienced episodic hypoxia, which is a precursor to development of seasonal hypoxia. The Baltic Sea coastal zone displays an alarming trend with hypoxia steadily increasing with time since the 1950s effecting nutrient biogeochemical processes, ecosystem services, and coastal habitat.

  • 303. Corrales-Suastegui, Arturo
    et al.
    Fuentes Franco, Ramon
    SMHI, Research Department, Climate research - Rossby Centre.
    Pavia, Edgar G.
    The mid-summer drought over Mexico and Central America in the 21st century2019In: International Journal of Climatology, ISSN 0899-8418, E-ISSN 1097-0088Article in journal (Refereed)
    Abstract [en]

    The southern Mexico and Central America (SMCA) region shows a dominant well-defined precipitation annual cycle. The rainy season usually begins in May and ends in October, with a relatively dry period in July and August known as the mid-summer drought (MSD); notable exceptions are the Caribbean coast of Honduras and Costa Rica. This MSD phenomenon is expected to be affected as the SMCA experiences an enhanced differential warming between the Pacific and Atlantic Oceans (PO-AO) towards the end of the 21st century. Previous studies have suggested that this differential warming will induce a strengthening of the westward Caribbean low-level jet (CLLJ) and that this heightened CLLJ will shift precipitation westwards, falling on the PO instead that within the SMCA region causing a severe drought. In this work we examine this scenario with a new model, the Rossby Center Regional Climate Model (RCA4), for the COordinated Regional climate Downscaling EXperiment (CORDEX) Central America domain, forced with different general circulation models (GCMs) and for different representative concentration paths (RCPs). We consider 25-year periods as "present conditions" (1981-2005) and "future scenario" (2071-2095), focusing on the "extended summer" season (May-October). Results suggest that in the future the spatial extension of the MSD will decrease and that in certain areas the MSD will be more intense but less frequent compared to present conditions. Also, the oceanic differential warming, the intensification of the CLLJ, and the reduction in regional precipitation in the future scenario, suggested by previous works, were verified in this study.

  • 304. Couvreux, F.
    et al.
    Roehrig, R.
    Rio, C.
    Lefebvre, M. -P
    Caian, Mihaela
    SMHI, Research Department, Climate research - Rossby Centre.
    Komori, T.
    Derbyshire, S.
    Guichard, F.
    Favot, F.
    D'Andrea, F.
    Bechtold, P.
    Gentine, P.
    Representation of daytime moist convection over the semi-arid Tropics by parametrizations used in climate and meteorological models2015In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 141, no 691, p. 2220-2236Article in journal (Refereed)
    Abstract [en]

    A case of daytime development of deep convection over tropical semi-arid land is used to evaluate the representation of convection in global and regional models. The case is based on observations collected during the African Monsoon Multidisciplinary Analysis (AMMA) field campaign and includes two distinct transition phases, from clear sky to shallow cumulus and from cumulus to deep convection. Different types of models, run with identical initial and boundary conditions, are intercompared: a reference large-eddy simulation (LES), single-column model (SCM) version of four different Earth system models that participated in the Coupled Model Intercomparison Project 5 exercise, the SCM version of the European Centre for Medium-range Weather Forecasts operational forecast model, the SCM version of a mesoscale model and a bulk model. Surface fluxes and radiative heating are prescribed preventing any atmosphere-surface and cloud-radiation coupling in order to simplify the analyses so that it focuses only on convective processes. New physics packages are also evaluated within this framework. As the LES correctly reproduces the observed growth of the boundary layer, the gradual development of shallow clouds, the initiation of deep convection and the development of cold pools, it provides a basis to evaluate in detail the representation of the diurnal cycle of convection by the other models and to test the hypotheses underlying convective parametrizations. Most SCMs have difficulty in representing the timing of convective initiation and rain intensity, although substantial modifications to boundary-layer and deep-convection parametrizations lead to improvements. The SCMs also fail to represent the mid-level troposphere moistening during the shallow convection phase, which we analyse further. Nevertheless, beyond differences in timing of deep convection, the SCM models reproduce the sensitivity to initial and boundary conditions simulated in the LES regarding boundary-layer characteristics, and often the timing of convection triggering.

  • 305. Crewell, S
    et al.
    Bloemink, H
    Feijt, A
    Garcia, S G
    Jolivet, D
    Krasnov, O A
    van Lammeren, A
    Lohnert, J
    van Meijgaard, E
    Meywerk, J
    Quante, M
    Pfeilsticker, K
    Schmidt, S
    Scholl, T
    Simmer, C
    Schroder, M
    Trautmann, T
    Venema, V
    Wendisch, M
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    The BALTEX Bridge Campaign - An integrated approach for a better understanding of clouds2004In: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 85, no 10, p. 1565-+Article in journal (Refereed)
  • 306.
    Crochemore, Louise
    et al.
    SMHI, Research Department, Hydrology.
    Ramos, Maria-Helena
    Pappenberger, Florian
    Bias correcting precipitation forecasts to improve the skill of seasonal streamflow forecasts2016In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 20, no 9, p. 3601-3618Article in journal (Refereed)
  • 307.
    Crochemore, Louise
    et al.
    SMHI, Research Department, Hydrology.
    Ramos, Maria-Helena
    Pappenberger, Florian
    Perrin, Charles
    Seasonal streamflow forecasting by conditioning climatology with precipitation indices2017In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 21, no 3, p. 1573-1591Article in journal (Refereed)
  • 308. Cuxart, J
    et al.
    Holtslag, A A M
    Beare, R J
    Bazile, E
    Beljaars, A
    Cheng, A
    Conangla, L
    Ek, M
    Freedman, F
    Hamdi, R
    Kerstein, A
    Kitagawa, H
    Lenderink, G
    Lewellen, D
    Mailhot, J
    Mauritsen, T
    Perov, Veniamin
    SMHI, Research Department, Meteorology.
    Schayes, G
    Steeneveld, G J
    Svensson, G
    Taylor, P
    Weng, W
    Wunsch, S
    Xu, K M
    Single-column model intercomparison for a stably stratified atmospheric boundary layer2006In: Boundary-layer Meteorology, ISSN 0006-8314, E-ISSN 1573-1472, Vol. 118, no 2, p. 273-303Article in journal (Refereed)
    Abstract [en]

    The parameterization of the stably stratified atmospheric boundary layer is a difficult issue, having a significant impact on medium-range weather forecasts and climate integrations. To pursue this further, a moderately stratified Arctic case is simulated by nineteen single-column turbulence schemes. Statistics from a large-eddy simulation intercomparison made for the same case by eleven different models are used as a guiding reference. The single-column parameterizations include research and operational schemes from major forecast and climate research centres. Results from first-order schemes, a large number of turbulence kinetic energy closures, and other models were used. There is a large spread in the results; in general, the operational schemes mix over a deeper layer than the research schemes, and the turbulence kinetic energy and other higher-order closures give results closer to the statistics obtained from the large-eddy simulations. The sensitivities of the schemes to the parameters of their turbulence closures are partially explored.

  • 309. Dahl, M
    et al.
    Pers, Charlotta
    SMHI, Research Department, Hydrology.
    Comparison of four models simulating phosphorus dynamics in Lake Vanern, Sweden2004In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 8, no 6, p. 1153-1163Article in journal (Refereed)
    Abstract [en]

    This paper compares four water quality models applied to Lake Vanern, Sweden. The comparison is focused on phosphorus, the primary limiting nutrient in Lake Vanern. Two of the models, FYRISA and HBV-NP, are simple and were developed as parts of catchment models. Two other models, called LEEDS and MOM are more comprehensive lake models. The models were calibrated using data from the period 1985-1992 and validated using data from the period 1993-2000. The fit to calibration data is similar for the FYRISA, HBV-NP, and LEEDS models, and slightly worse for the BIOLA model. All models fit the validation data almost as well as the calibration data. The models behaviour was tested in two representative scenarios. An increase of emissions by 40% from a pulp and paper mill has a negligible effect on the water quality, while a decrease in phosphorus load by 14% (accomplished by better waste-water treatment in rural households) gives a considerable decrease in phosphorus concentration in the lake. Still, the results of the scenarios vary between the models.

  • 310.
    Dahlgren, Per
    et al.
    SMHI, Research Department, Meteorology.
    Gustafsson, Nils
    SMHI, Research Department, Meteorology.
    Assimilating host model information into a limited area model2012In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 64, article id 15836Article in journal (Refereed)
    Abstract [en]

    We propose to add an extra source of information to the data-assimilation of the regional HIgh Resolution Limited Area Model (HIRLAM) model, constraining larger scales to the host model providing the lateral boundary conditions. An extra term, J(k), measuring the distance to the large-scale vorticity of the host model, is added to the cost-function of the variational data-assimilation. Vorticity is chosen because it is a good representative of the large-scale flow and because vorticity is a basic control variable of the HIRLAM variational data-assimilation. Furthermore, by choosing only vorticity, the remaining model variables, divergence, temperature, surface pressure and specific humidity will be allowed to adapt to the modified vorticity field in accordance with the internal balance constraints of the regional model. The error characteristics of the J(k) term are described by the horizontal spectral densities and the vertical eigenmodes (eigenvectors and eigenvalues) of the host model vorticity forecast error fields, expressed in the regional model geometry. The vorticity field, provided by the European Centre for Medium-range Weather Forecasts (ECMWF) operational model, was assimilated into the HIRLAM model during an experiment period of 33 d in winter with positive impact on forecast verification statistics for upper air variables and mean sea level pressure.

  • 311.
    Dahlgren, Per
    et al.
    SMHI, Research Department, Meteorology.
    Landelius, Tomas
    SMHI, Research Department, Atmospheric remote sensing.
    Kållberg, Per
    SMHI, Research Department, Meteorology.
    Gollvik, Stefan
    SMHI, Research Department, Meteorology.
    A high-resolution regional reanalysis for Europe. Part 1: Three-dimensional reanalysis with the regional HIgh-Resolution Limited-Area Model (HIRLAM)2016In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 142, no 698, p. 2119-2131Article in journal (Refereed)
  • 312. Dahlke, Helen E.
    et al.
    Behrens, Thorsten
    Seibert, Jan
    Andersson, Lotta
    SMHI, Core Services.
    Test of statistical means for the extrapolation of soil depth point information using overlays of spatial environmental data and bootstrapping techniques2009In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 23, no 21, p. 3017-3029Article in journal (Refereed)
    Abstract [en]

    Hydrological modelling depends highly on the accuracy and uncertainty of model input parameters such as soil properties. Since most of these data are field Surveyed, geostatistical techniques Such as kriging, classification and regression trees or more sophisticated soil-landscape models need to be applied to interpolate point information to the area. Most of the existing interpolation techniques require a random or regular distribution of points Within the study area but are not adequate to satisfactorily interpolate soil catena or transect data. The soil landscape model presented in this study is predicting soil information from transect or catena point data using a statistical mean (arithmetic, geometric and harmonic mean) to calculate the soil information based on class means of merged spatial explanatory variables. A data set of 226 soil depth measurements covering a range of 0-6.5 m was used to test the model. The point data were sampled along four transects in the Stubbetorp catchment, SE-Sweden. We overlaid a geomorphology map (8 classes) with digital elevation model-derived topographic index maps (2-9 classes) to estimate the range of error the model produces with changing sample size and input maps. The accuracy of the soil depth predictions was estimated with the root mean square error (RMSE) based oil a testing and training data set. RMSE ranged generally between 0.73 and 0.83 m +/- 0.013 m depending on the amount of classes the merged layers had, but were smallest for a map combination with a low number of classes predicted with the harmonic mean (RMSE = 0.46 m). The results show that the prediction accuracy of this method depends oil the number of point values in the sample, the value range of the measured attribute and the initial correlations between point values and explanatory variables, but suggests that the model approach is in general scale invariant. Copyright (C) 2009 John Wiley & Sons, Ltd.

  • 313.
    Danelsson, Håkan
    et al.
    SMHI.
    Lindkvist, Torbjörn
    SMHI, Core Services.
    Sjökarte- och sjöuppgifter: Register 19871987Report (Other academic)
    Abstract [sv]

    Vid upprättandet av sjöregistret utgick SMHI från den aktuella topografiska kartan och tog i grundversionen med alla blå ytor större än 0.01 kmdvs 1 ha (1 ha= 100x100 m). Detta innebär att även tjärnar, gölar, vissa dammar mm är medtagna i sjöregistret. Det kan också innebära att vissa vattenytor idag är helt igenvuxna och egentligen bör betecknas som våtmark. En annan oklar gränsdragning är övergången mellan sjö och vattendrag som sammanhänger med inlopps- och utloppssektioner samt genomströmning.Många svenska sjöar är reglerade och i flera fall består nuvarande regleringsmagasin av flera sjöar. Dessa magasin är medtagna i sjöregistret.Sjösänkningsföretagen under 1800-talet och början av 1900-talet har på flera håll drastiskt minskat antalet sjöar. Genom naturliga processer sker också hela tiden förändringar av sjöarna. lgenväxning minskar sjöytan, många torvmarker har varit sjöar, sedimentation och erosion förändrar strand och bottenförhållanden, landhöjningen skapar nya sjöar osv.Av detta följer att antalet sjöar aldrig kan bli någon exakt siffra. I sjöregistret finns idag 54 000 sjöar.

  • 314. Danielssen, D S
    et al.
    Edler, Lars
    SMHI, Research Department, Oceanography.
    Fonselius, Stig
    SMHI, Research Department, Oceanography.
    Hernroth, L
    Ostrowski, M
    Svendsen, E
    Talpsepp, L
    Oceanographic variability in the Skagerrak and Northern Kattegat, May-June, 19901997In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 54, no 5, p. 753-773Article in journal (Refereed)
    Abstract [en]

    The Skagerrak Experiment (SKAGEX), was a large, international, ICES-supported joint venture, carried out in the Skagerrak-Kattegat area on four different surveys in the period 1990-1991. It involved some 20 institutes and, at times, up to 17 research vessels. The main aim of the Experiment was to identify and quantify the different water masses entering and leaving the Skagerrak area and their variation over lime. It also aimed to investigate the mechanisms that drive the circulation and to study their effects on biological processes. The aim was to be attained mostly through extensive synoptic observations. This paper focuses on the variability in physical, chemical and biological parameters during the first part of SKAGEX, 24 May-20 June 1990. During the first half of the period of investigation, the main outflow from the Skagerrak, represented by the Norwegian Coastal Current, was barotropic with daily mean velocities varying from 10-40 cm s(-1). During the second half a clear baroclinic current component developed, giving rise to near surface velocities of up to 100 cm s(-1). A pronounced feature in the Skagerrak during the study was the counter-clockwise circulation of the Norwegian Coastal Current at times of strong northwesterly winds. During such conditions this surface water reached as far as the Danish coast south of 57 degrees N and upwelling along the Norwegian coast was also found. During northerly winds upwelling also occurred along the Swedish coast. The nutrient-rich Jutland Coastal Water, originating from the German Eight, was never found to reach the inner part of the Skagerrak during this first part of SKAGEX. It was partly blocked or diluted by other water-masses. A large ''ridge'' of nutrient-rich Atlantic water was found in the central Skagerrak throughout the investigation. It is shown that this elongated ''ridge'' was associated with the deepest (>500 m) area of the Skagerrak. Within this area, high subsurface chlorophyll concentrations were always found and, due to the persistence of the supply of nutrients, it is concluded that this phenomenon could be one of the main reasons for the high productivity of the Skagerrak. (C) 1997 International Council for the Exploration of the Sea.

  • 315. Danielsson, A.
    et al.
    Jönsson, Anette
    SMHI, Core Services.
    Rahm, Lars
    SMHI, Research Department, Oceanography.
    Resuspension patterns in the Baltic proper2007In: Journal of Sea Research, ISSN 1385-1101, E-ISSN 1873-1414, Vol. 57, no 4, p. 257-269Article in journal (Refereed)
    Abstract [en]

    Waves induce resuspension of surface sediments and contribute to the long-term mobilisation of particulate matter from erosion to accumulation bottoms. This has a major impact on the nutrient cycle in shallow seas by enhancing degradation, microbial production and recycling. The Baltic Sea represents such an area. The aim of this work is to analyse the spatial and temporal resuspension patterns in the Baltic Sea. To estimate the bottom friction velocity, modelled wave data are used in combination with data on grain size. This new data set is compared to a resuspension threshold of friction velocity to estimate the events of resuspension. The variation in bottom friction velocity, resuspension frequency and duration are related to wind climate, fetch, water depth and sediment type. Substantial resuspension can be found down to 40-60 m, with durations from one day to as much as two weeks. The highest winds in the area are highly anisotropic with a dominance of S-SW-W winds and the highest resuspension frequencies are found along the shallow eastern coasts. A seasonal pattern is observed with relatively high friction velocities and high resuspension frequencies during winter. There is also a variation depending on grain size, where sediments with fine and medium sand have a considerably higher percentage of resuspension events than bottoms with other dominant grain sizes. Five sub-areas are identified, characterised by different sediment types, resuspension and wind characteristics. If, in the future, wind speed increases as predicted, resuspension of sediments will also increase with effects on the nutrient cycle. (c) 2006 Elsevier B.V. All rights reserved.

  • 316. de Brugh, J. M. J. Aan
    et al.
    Schaap, M.
    Vignati, E.
    Dentener, F.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Sofiev, M.
    Huijnen, V.
    Krol, M. C.
    The European aerosol budget in 20062011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 3, p. 1117-1139Article in journal (Refereed)
    Abstract [en]

    This paper presents the aerosol budget over Europe in 2006 calculated with the global transport model TM5 coupled to the size-resolved aerosol module M7. Comparison with ground observations indicates that the model reproduces the observed concentrations quite well with an expected slight underestimation of PM10 due to missing emissions (e.g. resuspension). We model that a little less than half of the anthropogenic aerosols emitted in Europe are exported and the rest is removed by deposition. The anthropogenic aerosols are removed mostly by rain (95%) and only 5% is removed by dry deposition. For the larger natural aerosols, especially sea salt, a larger fraction is removed by dry processes (sea salt: 70%, mineral dust: 35%). We model transport of aerosols in the jet stream in the higher atmosphere and an import of Sahara dust from the south at high altitudes. Comparison with optical measurements shows that the model reproduces the Angstrom parameter very well, which indicates a correct simulation of the aerosol size distribution. However, we underestimate the aerosol optical depth. Because the surface concentrations are close to the observations, the shortage of aerosol in the model is probably at higher altitudes. We show that the discrepancies are mainly caused by an overestimation of wet-removal rates. To match the observations, the wet-removal rates have to be scaled down by a factor of about 5. In that case the modelled ground-level concentrations of sulphate and sea salt increase by 50% (which deteriorates the match), while other components stay roughly the same. Finally, it is shown that in particular events, improved fire emission estimates may significantly improve the ability of the model to simulate the aerosol optical depth. We stress that discrepancies in aerosol models can be adequately analysed if all models would provide (regional) aerosol budgets, as presented in the current study.

  • 317. De Geer, Lars-Erik
    et al.
    Persson, Christer
    SMHI, Research Department, Air quality.
    Rodhe, Henning
    A Nuclear Jet at Chernobyl Around 21:23:45 UTC on April 25, 19862018In: Nuclear Technology, ISSN 0029-5450, E-ISSN 1943-7471, Vol. 201, no 1, p. 11-22Article in journal (Refereed)
  • 318. de la Vega, David
    et al.
    Matthews, James C. G.
    Norin, Lars
    SMHI, Research Department, Atmospheric remote sensing.
    Angulo, Itziar
    Mitigation Techniques to Reduce the Impact of Wind Turbines on Radar Services2013In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 6, no 6, p. 2859-2873Article, review/survey (Refereed)
    Abstract [en]

    Radar services are occasionally affected by wind farms. This paper presents a comprehensive description of the effects that a wind farm may cause on the different radar services, and it compiles a review of the recent research results regarding the mitigation techniques to minimize this impact. Mitigation techniques to be applied at the wind farm and on the radar systems are described. The development of thorough impact studies before the wind farm is installed is presented as the best way to analyze in advance the potential for interference, and subsequently identify the possible solutions to allow the coexistence of wind farms and radar services.

  • 319. De Lavenne, Alban
    et al.
    Cudennec, C.
    Assessment of freshwater discharge into a coastal bay through multi-basin ensemble hydrological modelling2019In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 669, p. 812-820Article in journal (Refereed)
  • 320. Deandreis, Celine
    et al.
    Page, Christian
    Braconnot, Pascale
    Bärring, Lars
    SMHI, Research Department, Climate research - Rossby Centre.
    Bucchignani, Edoardo
    de Cerff, Wim Som
    Hutjes, Ronald
    Joussaume, Sylvie
    Mares, Constantin
    Planton, Serge
    Plieger, Maarten
    Towards a dedicated impact portal to bridge the gap between the impact and climate communities: Lessons from use cases2014In: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 125, no 3-4, p. 333-347Article in journal (Refereed)
    Abstract [en]

    Future climate evolution is of primary importance for the societal, economical, political orientations and decision-making. It explains the increasing use of climate projections as input for quantitative impact studies, assessing vulnerability and defining adaptation strategies in different sectors. Here we analyse 17 national and representative use cases so as to identify the diversity of the demand for climate information depending on user profiles as well as the best practices, methods and tools that are needed to answer the different requests. A particular emphasis is put on the workflow that allows to translate climate data into suitable impact data, the way to deal with the different sources of uncertainty and to provide a suited product to users. We identified three complementary tools to close the gap between climate scientists and user needs: an efficient interface between users and providers; an optimized methodology to handle user requests and a portal to facilitate access to data and elaborated products. We detail in the paper how these three tools can limit the intervention of experts, educate users, and lead to the production of useful information. This work provides the basis on which the ENES (European Network for Earth System Modelling) Portal Interface for the Climate Impact Communities is built.

  • 321. Dee, D. P.
    et al.
    Uppala, S. M.
    Simmons, A. J.
    Berrisford, P.
    Poli, P.
    Kobayashi, S.
    Andrae, U.
    Balmaseda, M. A.
    Balsamo, G.
    Bauer, P.
    Bechtold, P.
    Beljaars, A. C. M.
    van de Berg, L.
    Bidlot, J.
    Bormann, N.
    Delsol, C.
    Dragani, R.
    Fuentes, M.
    Geer, A. J.
    Haimberger, L.
    Healy, S. B.
    Hersbach, H.
    Holm, E. V.
    Isaksen, L.
    Kållberg, Per
    SMHI, Research Department, Meteorology.
    Koehler, M.
    Matricardi, M.
    McNally, A. P.
    Monge-Sanz, B. M.
    Morcrette, J. -J
    Park, B. -K
    Peubey, C.
    de Rosnay, P.
    Tavolato, C.
    Thepaut, J. -N
    Vitart, F.
    The ERA-Interim reanalysis: configuration and performance of the data assimilation system2011In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 137, no 656, p. 553-597Article, review/survey (Refereed)
    Abstract [en]

    ERA-Interim is the latest global atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). The ERA-Interim project was conducted in part to prepare for a new atmospheric reanalysis to replace ERA-40, which will extend back to the early part of the twentieth century. This article describes the forecast model, data assimilation method, and input datasets used to produce ERA-Interim, and discusses the performance of the system. Special emphasis is placed on various difficulties encountered in the production of ERA-40, including the representation of the hydrological cycle, the quality of the stratospheric circulation, and the consistency in time of the reanalysed fields. We provide evidence for substantial improvements in each of these aspects. We also identify areas where further work is needed and describe opportunities and objectives for future reanalysis projects at ECMWF. Copyright (C) 2011 Royal Meteorological Society

  • 322. den Outer, P. N.
    et al.
    Slaper, H.
    Kaurola, J.
    Lindfors, A.
    Kazantzidis, A.
    Bais, A. F.
    Feister, U.
    Junk, J.
    Janouch, M.
    Josefsson, Weine
    SMHI, Core Services.
    Reconstructing of erythemal ultraviolet radiation levels in Europe for the past 4 decades2010In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 115, article id D10102Article in journal (Refereed)
    Abstract [en]

    This paper is based on a comparative study on ultraviolet radiation (UV) measurements and UV reconstruction models for eight sites in Europe. Reconstruction models include neural network techniques and radiative transfer modeling combined with empirical relationships. The models have been validated against quality-controlled ground-based measurements, 8 to 20 years, on time scales ranging from daily to yearly UV sums. The standard deviations in the ratios of modeled to measured daily sums vary between 10 and 15%. The yearly sums agree within a 5% range. Depending on the availability of ancillary measurements, reconstructions have been carried out to the early 1960s. A method has been set up to educe one best estimate of the historical UV levels that takes into account the long-term stability and underlying agreement of the models, and the agreement with actual UV measurements. Using this best estimate, the yearly sums of erythemally weighted UV irradiance showed a range of 300 kJ/m(2) at 67 degrees N to 750 kJ/m(2) at 40 degrees N. The year-to-year variability was lowest at 40 degrees N with a relative variation of 4.3%; for central and northern European latitudes this year-to-year variation was 5.2 to 6.5%. With regard to the period 1980 to 2006, first-order trend lines range from 0.3 +/- 0.1 to 0.6 +/- 0.2% per year, approximately two thirds of which can be attributed to the diminishing of cloudiness and one third to ozone decline.

  • 323. den Outer, P. N.
    et al.
    van Dijk, A.
    Slaper, H.
    Lindfors, A. V.
    De Backer, H.
    Bais, A. F.
    Feister, U.
    Koskela, T.
    Josefsson, Weine
    SMHI, Core Services.
    Applying spaceborne reflectivity measurements for calculation of the solar ultraviolet radiation at ground level2012In: ATMOSPHERIC MEASUREMENT TECHNIQUES, ISSN 1867-1381, Vol. 5, no 12, p. 3041-3054Article in journal (Refereed)
    Abstract [en]

    Long-term analysis of cloud effects on ultraviolet (UV) radiation on the ground using spaceborne observations requires the use of instruments that have operated consecutively. The longest data record can be built from the reflectivity measurements produced by the instruments Total Ozone Mapping Spectrometers (TOMS) flown on Nimbus 7 from 1979 to 1992, TOMS on Earth Probe from 1996 to 2005, and the Ozone Monitoring Instrument (OMI) flown on EOS Aura since 2004. The reflectivity data produced by TOMS on Earth Probe is only included until 2002. A comparison is made with cloud effects inferred from ground-based pyranometer measurements at over 83 World Radiation Data Centre stations. Modelled UV irradiances utilizing the standard reflectivity are compared with measurements of UV irradiances at eight European low-elevation stations. The reflectivity data of the two TOMS instruments shows a consistent agreement, and the required corrections are of low percentage, i.e. 2-3%. In contrast, the reflectivity product of OMI requires correction of 7-10%, and a solar angle dependency therein is more pronounced. These corrections were inferred from a comparison with pyranometer data, and tested using the UV measurements. The average reduction of UV radiation due to clouds for all sites together indicates a small trend: a diminishing cloudiness, in line with ground-based UV observations. Uncorrected implementation of the reflectivity data would have indicated the opposite. An optimal area was established for reflectivity data for the calculation of daily sums of UV radiation. It measures approximately 1.25 degrees in latitudinal direction for square-shaped areas overhead the ground-based UV stations. Such an area can be traversed within 5 to 7 h at the average wind speeds found for the West European continent.

  • 324. Denby, B. R.
    et al.
    Sundvor, I.
    Johansson, C.
    Pirjola, L.
    Ketzel, M.
    Norman, M.
    Kupiainen, K.
    Gustafsson, M.
    Blomqvist, G.
    Kauhaniemi, M.
    Omstedt, Gunnar
    SMHI, Research Department, Air quality.
    A coupled road dust and surface moisture model to predict non-exhaust road traffic induced particle emissions (NORTRIP). Part 2: Surface moisture and salt impact modelling2013In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 81, p. 485-503Article in journal (Refereed)
    Abstract [en]

    Non-exhaust traffic induced emissions are a major source of airborne particulate matter in most European countries. This is particularly important in Nordic and Alpine countries where winter time road traction maintenance occurs, e.g. salting and sanding, and where studded tyres are used. Though the total mass generated by wear sources is a key factor in non-exhaust emissions, these emissions are also strongly controlled by surface moisture conditions. In this paper, Part 2, the road surface moisture submodel of a coupled road dust and surface moisture model (NORTRIP) is described. We present a description of the road surface moisture part of the model and apply the coupled model to seven sites in Stockholm, Oslo, Helsinki and Copenhagen over 18 separate periods, ranging from 3.5 to 24 months. At two sites surface moisture measurements are available and the moisture sub-model is compared directly to these observations. The model predicts the frequency of wet roads well at both sites, with an average fractional bias of -2.6%. The model is found to correctly predict the hourly surface state, wet or dry, 85% of the time. From the 18 periods modelled using the coupled model an average absolute fractional bias of 15% for PM10 concentrations was found. Similarly the model predicts the 90'th daily mean percentiles of PMio with an average absolute bias of 19% and an average correlation (R-2) of 0.49. When surface moisture is not included in the modelling then this average correlation is reduced to 0.16, demonstrating the importance of the surface moisture conditions. Tests have been carried out to assess the sensitivity of the model to model parameters and input data. The model provides a useful tool for air quality management and for improving our understanding of non-exhaust traffic emissions. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.

  • 325. Denby, B. R.
    et al.
    Sundvor, I.
    Johansson, C.
    Pirjola, L.
    Ketzel, M.
    Norman, M.
    Kupiainen, K.
    Gustafsson, M.
    Blomqvist, G.
    Omstedt, Gunnar
    SMHI, Research Department, Air quality.
    A coupled road dust and surface moisture model to predict non-exhaust road traffic induced particle emissions (NORTRIP). Part 1: Road dust loading and suspension modelling2013In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 77, p. 283-300Article in journal (Refereed)
    Abstract [en]

    Non-exhaust traffic induced emissions are a major source of particle mass in most European countries. This is particularly important in Nordic and Alpine countries where winter time road traction maintenance occurs, e.g. salting and sanding, and where studded tyres are used. In this paper, Part 1, the road dust sub-model of a coupled road dust and surface moisture model (NORTRIP) is described. The model provides a generalised process based formulation of the non-exhaust emissions, with emphasis on the contribution of road wear, suspension, surface dust loading and the effect of road surface moisture (retention of wear particles and suspended emissions). The model is intended for use as a tool for air quality managers to help study the impact of mitigation measures and policies. We present a description of the road dust sub-model and apply the model to two sites in Stockholm and Copenhagen where seven years of data with surface moisture measurements are available. For the site in Stockholm, where studded tyres are in use, the model predicts the PM10 concentrations very well with correlations (R-2) in the range of R-2 = 0.76-0.91 for daily mean PM10. The model also reproduces well the impact of a reduction in studded tyres at this site. For the site in Copenhagen the correlation is lower, in the range 0.44-0.51. The addition of salt is described in the model and at both sites this leads to improved correlations due to additional salt emissions. For future use of the model a number of model parameters, e.g. wear factors and suspension rates, still need to be refined. The effect of sanding on PM10 emissions is also presented but more information will be required before this can be confidently applied for management applications. (C) 2013 Elsevier Ltd. All rights reserved.

  • 326. Deng, Junjie
    et al.
    Harff, Jan
    Schimanke, Semjon
    SMHI, Research Department, Oceanography.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    A method for assessing the coastline recession due to the sea level rise by assuming stationary wind-wave climate2015In: OCEANOLOGICAL AND HYDROBIOLOGICAL STUDIES, ISSN 1730-413X, Vol. 44, no 3, p. 362-380Article in journal (Refereed)
    Abstract [en]

    The method introduced in this study for future projection of coastline changes hits the vital need of communicating the potential climate change impact on the coast in the 21th century. A quantitative method called the Dynamic Equilibrium Shore Model (DESM) has been developed to hindcast historical sediment mass budgets and to reconstruct a paleo Digital Elevation Model (DEM). The forward mode of the DESM model relies on paleo-scenarios reconstructed by the DESM model assuming stationary wind-wave climate. A linear relationship between the sea level, coastline changes and sediment budget is formulated and proven by the least square regression method. In addition to its forward prediction of coastline changes, this linear relationship can also estimate the sediment budget by using the information on the coastline and relative sea level changes. Wind climate change is examined based on regional climate model data. Our projections for the end of the 21st century suggest that the wind and wave climates in the southern Baltic Sea may not change compared to present conditions and that the investigated coastline along the Pomeranian Bay may retreat from 10 to 100 m depending on the location and on the sea level rise which was assumed to be in the range of 0.12 to 0.24 m.

  • 327. Deque, M
    et al.
    Jones, R G
    Wild, M
    Giorgi, F
    Christensen, J H
    Hassell, D C
    Vidale, P L
    Rockel, B
    Jacob, D
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    de Castro, M
    Kucharski, F
    van den Hurk, B
    Global high resolution versus Limited Area Model climate change projections over Europe: quantifying confidence level from PRUDENCE results2005In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 25, no 6, p. 653-670Article in journal (Refereed)
    Abstract [en]

    Four high resolution atmospheric general circulation models (GCMs) have been integrated with the standard forcings of the PRUDENCE experiment: IPCC-SRES A2 radiative forcing and Hadley Centre sea surface temperature and sea-ice extent. The response over Europe, calculated as the difference between the 2071-2100 and the 1961-1990 means is compared with the same diagnostic obtained with nine Regional Climate Models (RCM) all driven by the Hadley Centre atmospheric GCM. The seasonal mean response for 2m temperature and precipitation is investigated. For temperature, GCMs and RCMs behave similarly, except that GCMs exhibit a larger spread. However, during summer, the spread of the RCMs-in particular in terms of precipitation-is larger than that of the GCMs. This indicates that the European summer climate is strongly controlled by parameterized physics and/or high-resolution processes. The temperature response is larger than the systematic error. The situation is different for precipitation. The model bias is twice as large as the climate response. The confidence in PRUDENCE results comes from the fact that the models have a similar response to the IPCC-SRES A2 forcing, whereas their systematic errors are more spread. In addition, GCM precipitation response is slightly but significantly different from that of the RCMs.

  • 328. Deque, M.
    et al.
    Rowell, D. P.
    Luethi, D.
    Giorgi, F.
    Christensen, J. H.
    Rockel, B.
    Jacob, D.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    de Castro, M.
    van den Hurk, B.
    An intercomparison of regional climate simulations for Europe: assessing uncertainties in model projections2007In: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 81, p. 53-70Article in journal (Refereed)
    Abstract [en]

    Ten regional climate models (RCM) have been integrated with the standard forcings of the PRUDENCE experiment: IPCC-SRES A2 radiative forcing and Hadley Centre boundary conditions. The response over Europe, calculated as the difference between the 2071 2100and the 1961-1990 means can be viewed as an expected value about which various uncertainties exist. Uncertainties are measured here by variance in eight sub-European boxes. Four sources of uncertainty can be evaluated with the material provided by the PRUDENCE project. Sampling uncertainty is due to the fact that the model climate is estimated as an average over a finite number of years (30). Model uncertainty is due to the fact that the models use different techniques to discretize the equations and to represent sub-grid effects. Radiative uncertainty is due to the fact that IPCC-SRES A2 is merely one hypothesis. Some RCMs have been run with another scenario of greenhouse gas concentration (IPCC-SRES B2). Boundary uncertainty is due to the fact that the regional models have been run under the constraint of the same global model. Some RCMs have been run with other boundary forcings. The contribution of the different sources varies according to the field, the region and the season, but the role of boundary forcing is generally greater than the role of the RCM, in particular for temperature. Maps of minimum expected 2m temperature and precipitation responses for the IPCC-A2 scenario show that, despite the above mentioned uncertainties, the signal from the PRUDENCE ensemble is significant.

  • 329.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Fueglistaler, S.
    A climatological perspective of deep convection penetrating the TTL during the Indian summer monsoon from the AVHRR and MODIS instruments2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 10, p. 4573-4582Article in journal (Refereed)
    Abstract [en]

    The impact of very deep convection on the water budget and thermal structure of the tropical tropopause layer is still not well quantified, not least because of limitations imposed by the available observation techniques. Here, we present detailed analysis of the climatology of the cloud top brightness temperatures as indicators of deep convection during the Indian summer monsoon, and the variations therein due to active and break periods. We make use of the recently newly processed data from the Advanced Very High Resolution Radiometer (AVHRR) at a nominal spatial resolution of 4 km. Using temperature thresholds from the Atmospheric Infrared Sounder (AIRS), the AVHRR brightness temperatures are converted to climatological mean (2003-2008) maps of cloud amounts at 200, 150 and 100 hPa. Further, we relate the brightness temperatures to the level of zero radiative heating, which may allow a coarse identification of convective detrainment that will subsequently ascend into the stratosphere. The AVHRR data for the period 1982-2006 are used to document the differences in deep convection between active and break conditions of the monsoon. The analysis of AVHRR data is complemented with cloud top pressure and optical depth statistics (for the period 2003-2008) from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Aqua satellite. Generally, the two sensors provide a very similar description of deep convective clouds. Our analysis shows that most of the deep convection occurs over the Bay of Bengal and central northeast India. Very deep convection over the Tibetan plateau is comparatively weak, and may play only a secondary role in troposphere-to-stratosphere transport. The deep convection over the Indian monsoon region is most frequent in July/August, but the very highest convection (coldest tops, penetrating well into the TTL) occurs in May/June. Large variability in convection reaching the TTL is due to monsoon break/active periods. During the monsoon break period, deep convection reaching the TTL is almost entirely absent in the western part of the study area (i.e. 60 E-75 E), while the distribution over the Bay of Bengal and the Tibetan Plateau is less affected. Although the active conditions occur less frequently than the break conditions, they may have a larger bearing on the composition of the TTL within the monsoonal anticyclone, and tracer transport into the stratosphere because of deep convection occurring over anthropogenically more polluted regions.

  • 330.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Grassl, H.
    A daytime climatological distribution of high opaque ice cloud classes over the Indian summer monsoon region observed from 25-year AVHRR data2009In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 9, no 12, p. 4185-4196Article in journal (Refereed)
    Abstract [en]

    A daytime climatological spatio-temporal distribution of high opaque ice cloud (HOIC) classes over the Indian subcontinent (0-40 degrees N, 60 degrees E-100 degrees E) is presented using 25-year data from the Advanced Very High Resolution Radiometers (AVHRRs) for the summer monsoon months. The HOICs are important for regional radiative balance, precipitation and troposphere-stratosphere exchange. In this study, HOICs are sub-divided into three classes based on their cloud top brightness temperatures (BT). Class I represents very deep convection (BT < 220 K). Class II represents deep convection (220 K <=BT < 233 K) and Class III background convection (233 K <=BT < 253 K). Apart from presenting finest spatial resolution (0.1x0.1 degrees) and long-term climatology of such cloud classes from AVHRRs to date, this study for the first time illustrates on (1) how these three cloud classes are climatologically distributed during monsoon months, and (2) how their distribution changes during active and break monsoon conditions. It is also investigated that how many deep convective clouds reach the tropopause layer during individual monsoon months. It is seen that Class I and Class II clouds dominate the Indian subcontinent during monsoon. The movement of monsoon over continent is very well reflected in these cloud classes. During monsoon breaks strong suppression of convective activity is observed over the Arabian Sea and the western coast of India. On the other hand, the presence of such convective activity is crucial for active monsoon conditions and all-India rainfall. It is found that a significant fraction of HOICs (3-5%) reach the tropopause layer over the Bay of Bengal during June and over the north and northeast India during July and August. Many cases are observed when clouds penetrate the tropopause layer and reach the lower stratosphere. Such cases mostly occur during June compared to the other months.

  • 331.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Grassl, H.
    Comparison of low brightness temperatures derived from the AVHRR thermal channels with in situ measurements in Antarctica2009In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 30, no 2, p. 525-532Article in journal (Refereed)
    Abstract [en]

    Data from the National Oceanic and Atmospheric Administration (NOAA) satellites' Advanced Very High Resolution Radiometers (AVHRRs) represent the longest record (more than 25 years) of continuously available satellite-based thermal measurements, and have well-chosen spatial and spectral resolutions. As a consequence, these data are used extensively to develop cloud climatologies. However, for such applications, accurate calibration and intercalibration of both solar and thermal channels of the AVHRRs is necessary so as to homogenize the data obtained from the different AVHRR sensors. AVHRR thermal channels 4 and 5 are routinely used in threshold-based hierarchical decision-tree cloud detection and classification algorithms, and therefore an evaluation of the stability of these channels at low temperatures is important. In this letter, the AVHRR channel 4 and 5 brightness temperatures (BTs) are compared at five stations in Antarctica. The data for the period of June, July and August (the coldest months of every year and with minimal atmospheric influence) from 1982 to 2006 were used for the evaluations. The calibration and intercalibration of the thermal channels are found to be very robust. The root mean square errors (RMSEs) range from 2.2 to 3.4K and the correlation coefficients from 0.84 to 0.95. No apparent artefacts or artificial jumps in the BTs are visible in the data series after changes of sensors. The BTs from the thermal channels of the AVHRRs can be used for preparing cloud climatologies, as their intercalibration is found to be consistent across different afternoon satellites.

  • 332.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Karlsson, Karl-Göran
    SMHI, Research Department, Atmospheric remote sensing.
    Quaas, J.
    Grassl, H.
    Correcting orbital drift signal in the time series of AVHRR derived convective cloud fraction using rotated empirical orthogonal function2012In: ATMOSPHERIC MEASUREMENT TECHNIQUES, ISSN 1867-1381, Vol. 5, no 2, p. 267-273Article in journal (Refereed)
    Abstract [en]

    The Advanced Very High Resolution Radiometer (AVHRR) instruments onboard the series of National Oceanic and Atmospheric Administration (NOAA) satellites offer the longest available meteorological data records from space. These satellites have drifted in orbit resulting in shifts in the local time sampling during the life span of the sensors onboard. Depending upon the amplitude of the diurnal cycle of the geophysical parameters derived, orbital drift may cause spurious trends in their time series. We investigate tropical deep convective clouds, which show pronounced diurnal cycle amplitude, to estimate an upper bound of the impact of orbital drift on their time series. We carry out a rotated empirical orthogonal function analysis (REOF) and show that the REOFs are useful in delineating orbital drift signal and, more importantly, in subtracting this signal in the time series of convective cloud amount. These results will help facilitate the derivation of homogenized data series of cloud amount from NOAA satellite sensors and ultimately analyzing trends from them. However, we suggest detailed comparison of various methods and rigorous testing thereof applying final orbital drift corrections.

  • 333.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Norin, Lars
    SMHI, Research Department, Atmospheric remote sensing.
    The large-scale spatio-temporal variability of precipitation over Sweden observed from the weather radar network2014In: ATMOSPHERIC MEASUREMENT TECHNIQUES, ISSN 1867-1381, Vol. 7, no 6, p. 1605-1617Article in journal (Refereed)
    Abstract [en]

    Using measurements from the national network of 12 weather radar stations for the 11-year period 2000-2010, we investigate the large-scale spatio-temporal variability of precipitation over Sweden. These statistics provide useful information to evaluate regional climate models as well as for hydrology and energy applications. A strict quality control is applied to filter out noise and artifacts from the radar data. We focus on investigating four distinct aspects: the diurnal cycle of precipitation and its seasonality, the dominant timescale (diurnal versus seasonal) of variability, precipitation response to different wind directions, and the correlation of precipitation events with the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO). When classified based on their intensity, moderate-to high-intensity events (precipitation >0.34 mm/3 h) peak distinctly during late afternoon over the majority of radar stations in summer and during late night or early morning in winter. Precipitation variability is highest over the southwestern parts of Sweden. It is shown that the high-intensity events (precipitation >1.7 mm/3 h) are positively correlated with NAO and AO (esp. over northern Sweden), while the low intensity events are negatively correlated (esp. over southeastern parts). It is further observed that southeasterly winds often lead to intense precipitation events over central and northern Sweden, while southwesterly winds contribute most to the total accumulated precipitation for all radar stations. Apart from its operational applications, the present study demonstrates the potential of the weather radar data set for studying climatic features of precipitation over Sweden.

  • 334.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Sedlar, Joseph
    SMHI, Research Department, Atmospheric remote sensing.
    Kahn, Brian H.
    Tjernstrom, Michael
    Fetzer, Eric J.
    Tian, Baijun
    Teixeira, Joao
    Pagano, Thomas S.
    A DECADE OF SPACEBORNE OBSERVATIONS OF THE ARCTIC ATMOSPHERE Novel. Insights from NASA's AIRS Instrument2016In: BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY, ISSN 0003-0007, Vol. 97, no 11, p. 2163-2176Article in journal (Refereed)
  • 335.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Sedlar, Joseph
    SMHI, Research Department, Atmospheric remote sensing.
    Koenigk, Torben
    SMHI, Research Department, Climate research - Rossby Centre.
    Fetzer, E. J.
    The thermodynamic state of the Arctic atmosphere observed by AIRS: comparisons during the record minimum sea ice extents of 2007 and 20122013In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, no 15, p. 7441-7450Article in journal (Refereed)
    Abstract [en]

    The record sea ice minimum (SIM) extents observed during the summers of 2007 and 2012 in the Arctic are stark evidence of accelerated sea ice loss during the last decade. Improving our understanding of the Arctic atmosphere and accurate quantification of its characteristics becomes ever more crucial, not least to improve predictions of such extreme events in the future. In this context, the Atmospheric Infrared Sounder (AIRS) instrument onboard NASA's Aqua satellite provides crucial insights due to its ability to provide 3-D information on atmospheric thermodynamics. Here, we facilitate comparisons in the evolution of the thermodynamic state of the Arctic atmosphere during these two SIM events using a decade-long AIRS observational record (2003-2012). It is shown that the meteorological conditions during 2012 were not extreme, but three factors of preconditioning from winter through early summer played an important role in accelerating sea ice melt. First, the marginal sea ice zones along the central Eurasian and North Atlantic sectors remained warm throughout winter and early spring in 2012 preventing thicker ice build-up. Second, the circulation pattern favoured efficient sea ice transport out of the Arctic in the Atlantic sector during late spring and early summer in 2012 compared to 2007. Third, additional warming over the Canadian archipelago and southeast Beaufort Sea from May onward further contributed to accelerated sea ice melt. All these factors may have lead the already thin and declining sea ice cover to pass below the previous sea ice extent minimum of 2007. In sharp contrast to 2007, negative surface temperature anomalies and increased cloudiness were observed over the East Siberian and Chukchi seas in the summer of 2012. The results suggest that satellite-based monitoring of atmospheric preconditioning could be a critical source of information in predicting extreme sea ice melting events in the Arctic.

  • 336.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Sedlar, Joseph
    SMHI, Research Department, Atmospheric remote sensing.
    Tjernstrom, M.
    Characteristics of water-vapour inversions observed over the Arctic by Atmospheric Infrared Sounder (AIRS) and radiosondes2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 18, p. 9813-9823Article in journal (Refereed)
    Abstract [en]

    An accurate characterization of the vertical structure of the Arctic atmosphere is useful in climate change and attribution studies as well as for the climate modelling community to improve projections of future climate over this highly sensitive region. Here, we investigate one of the dominant features of the vertical structure of the Arctic atmosphere, i.e. water-vapour inversions, using eight years of Atmospheric Infrared Sounder data (2002-2010) and radiosounding profiles released from the two Arctic locations (North Slope of Alaska at Barrow and during SHEBA). We quantify the characteristics of clear-sky water vapour inversions in terms of their frequency of occurrence, strength and height covering the entire Arctic for the first time. We found that the frequency of occurrence of water-vapour inversions is highest during winter and lowest during summer. The inversion strength is, however, higher during summer. The observed peaks in the median inversion-layer heights are higher during the winter half of the year, at around 850 hPa over most of the Arctic Ocean, Siberia and the Canadian Archipelago, while being around 925 hPa during most of the summer half of the year over the Arctic Ocean. The radiosounding profiles agree with the frequency, location and strength of water-vapour inversions in the Pacific sector of the Arctic. In addition, the radiosoundings indicate that multiple inversions are the norm with relatively few cases without inversions. The amount of precipitable water within the water-vapour inversion structures is estimated and we find a distinct, two-mode contribution to the total column precipitable water. These results suggest that water-vapour inversions are a significant source to the column thermodynamics, especially during the colder winter and spring seasons. We argue that these inversions are a robust metric to test the reproducibility of thermodynamics within climate models. An accurate statistical representation of water-vapour inversions in models would mean that the large-scale coupling of moisture transport, precipitation, temperature and water-vapour vertical structure and radiation are essentially captured well in such models.

  • 337.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Thomas, Manu Anna
    SMHI, Research Department, Air quality.
    A global survey of aerosol-liquid water cloud overlap based on four years of CALIPSO-CALIOP data2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 3, p. 1143-1154Article in journal (Refereed)
    Abstract [en]

    Simulating the radiative impacts of aerosols located above liquid water clouds presents a significant challenge. In particular, absorbing aerosols, such as smoke, may have significant impact in such situations and even change the sign of net radiative forcing. It is not possible to reliably obtain information on such overlap events from existing passive satellite sensors. However, the CALIOP instrument onboard NASA's CALIPSO satellite allows us to examine these events with unprecedented accuracy. Using four years of collocated CALIPSO 5 km Aerosol and Cloud Layer Version 3 Products (June 2006 May 2010), we quantify, for the first time, the characteristics of overlapping aerosol and water cloud layers globally. We investigate seasonal variability in these characteristics over six latitude bands to understand the hemispheric differences when all aerosol types are included in the analysis (the AAO case). We also investigate frequency of smoke aerosol-cloud overlap (the SAO case). Globally, the frequency is highest during the JJA months in the AAO case, while for the SAO case, it is highest in the SON months. The seasonal mean overlap frequency can regionally exceed 20% in the AAO case and 10% in the SAO case. In about 5-10% cases the vertical distance between aerosol and cloud layers is less than 100 m, while about in 45-60% cases it less than a kilometer in the annual means for different latitudinal bands. In about 70-80% cases, aerosol layers are less than a kilometer thick, while in about 18-22% cases they are 1-2 km thick. The frequency of aerosol layers 2-3 km thick is about 4-5% in the tropical belts during overlap events. Over the regions where high aerosol loadings are present, the overlap frequency can be up to 50% higher when quality criteria on aerosol/cloud feature detection are relaxed. Over the polar regions, more than 50% of the overlapping aerosol layers have optical thickness less than 0.02, but the contribution from the relatively optically thicker aerosol layers increases towards the equatorial regions in both hemispheres. The results suggest that the frequency of occurrence of overlap events is far from being negligible globally.

  • 338.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Thomas, Manu Anna
    SMHI, Research Department, Air quality.
    An investigation of statistical link between inversion strength and carbon monoxide over Scandinavia in winter using AIRS data2012In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 56, p. 109-114Article in journal (Refereed)
    Abstract [en]

    Temperature inversions influence the local air quality at smaller scales and the pollution transport at larger spatio-temporal scales and are one of the most commonly observed meteorological phenomena over Scandinavia (54 degrees N-70 degrees N, 0-30 degrees E) during winter. Here, apart from presenting key statistics on temperature inversions, a large-scale co-variation of inversion strength and carbon monoxide (CO), an ideal pollution tracer, is further quantified at six vertical levels in the free troposphere during three distinct meteorological regimes that are identified based on inversion strength. Collocated temperature and CO profiles from Atmospheric Infrared Sounder (AIRS) are used for this purpose. Higher values of CO (up to 15%) are observed over Scandinavia during weakly stable regimes at all vertical levels studied, whereas lower CO values (up to 10%) are observed when inversions become stronger and elevated. The observed systematic co-variation between CO and inversion strength in three meteorological regimes is most likely explained by the efficacy of long-range transport to influence tropospheric composition over Scandinavia. We argue that this large-scale co-variation of temperature inversions and CO would be a robust metric to test coupling of large-scale meteorology and chemistry in transport models. (C) 2012 Elsevier Ltd. All rights reserved.

  • 339.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Thomas, Manu Anna
    SMHI, Research Department, Air quality.
    Sensitivity of Cloud Liquid Water Content Estimates to the Temperature-Dependent Thermodynamic Phase: A Global Study Using CloudSat Data2012In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 25, no 20, p. 7297-7307Article in journal (Refereed)
    Abstract [en]

    The main purpose of this study is to underline the sensitivity of cloud liquid water content (LWC) estimates purely to 1) the shape of computationally simplified temperature-dependent thermodynamic phase and 2) the range of subzero temperatures covered to partition total cloud condensate into liquid and ice fractions. Linear, quadratic, or sigmoid-shaped functions for subfreezing temperatures (down to -20 degrees or -40 degrees C) are often used in climate models and reanalysis datasets for partitioning total condensate. The global vertical profiles of clouds obtained from CloudSat for the 4-yr period June 2006-May 2010 are used for sensitivity analysis and the quantitative estimates of sensitivities based on these realistic cloud profiles are provided. It is found that three cloud regimes in particular-convective clouds in the tropics, low-level clouds in the northern high latitudes, and middle-level clouds over the midlatitudes and Southern Ocean-are most sensitive to assumptions on thermodynamic phase. In these clouds, the LWC estimates based purely on quadratic or sigmoid-shaped functions with a temperature range down to -20 degrees C can differ by up to 20%-40% over the tropics (in seasonal means). 10%-30% over the midlatitudes, and up to 50% over high latitudes compared to a linear assumption. When the temperature range is extended down to -40 degrees C. LWC estimates in the sigmoid case can be much higher than the above values over high-latitude regions compared to the commonly used case with quadratic dependency down to -20 C. This sensitivity study emphasizes the need to critically investigate radiative impacts of cloud thermodynamic phase assumptions in simplified climate models and reanalysis datasets.

  • 340.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Tjernstrom, M.
    Caian, Mihaela
    SMHI, Research Department, Climate research - Rossby Centre.
    Thomas, Manu Anna
    SMHI, Research Department, Air quality.
    Kahn, B. H.
    Fetzer, E. J.
    Influence of the Arctic Oscillation on the vertical distribution of clouds as observed by the A-Train constellation of satellites2012In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 12, no 21, p. 10535-10544Article in journal (Refereed)
    Abstract [en]

    The main purpose of this study is to investigate the influence of the Arctic Oscillation (AO), the dominant mode of natural variability over the northerly high latitudes, on the spatial (horizontal and vertical) distribution of clouds in the Arctic. To that end, we use a suite of sensors on-board NASA's A-Train satellites that provide accurate observations of the distribution of clouds along with information on atmospheric thermodynamics. Data from three independent sensors are used (AQUA-AIRS, CALIOP-CALIPSO and CPR-CloudSat) covering two time periods (winter half years, November through March, of 2002-2011 and 2006-2011, respectively) along with data from the ERA-Interim reanalysis. We show that the zonal vertical distribution of cloud fraction anomalies averaged over 67-82 degrees N to a first approximation follows a dipole structure (referred to as "Greenland cloud dipole anomaly", GCDA), such that during the positive phase of the AO, positive and negative cloud anomalies are observed eastwards and westward of Greenland respectively, while the opposite is true for the negative phase of AO. By investigating the concurrent meteorological conditions (temperature, humidity and winds), we show that differences in the meridional energy and moisture transport during the positive and negative phases of the AO and the associated thermodynamics are responsible for the conditions that are conducive for the formation of this dipole structure. All three satellite sensors broadly observe this large-scale GCDA despite differences in their sensitivities, spatio-temporal and vertical resolutions, and the available lengths of data records, indicating the robustness of the results. The present study also provides a compelling case to carry out process-based evaluation of global and regional climate models.

  • 341.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Tjernstrom, Michael
    Karlsson, Karl-Göran
    SMHI, Research Department, Atmospheric remote sensing.
    Thomas, Manu Anna
    SMHI, Research Department, Air quality.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Sedlar, Joseph
    SMHI, Research Department, Atmospheric remote sensing.
    Omar, Ali H.
    The vertical distribution of thin features over the Arctic analysed from CALIPSO observations2011In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 63, no 1, p. 77-85Article in journal (Refereed)
    Abstract [en]

    Clouds play a crucial role in the Arctic climate system. Therefore, it is essential to accurately and reliably quantify and understand cloud properties over the Arctic. It is also important to monitor and attribute changes in Arctic clouds. Here, we exploit the capability of the CALIPSO-CALIOP instrument and provide comprehensive statistics of tropospheric thin clouds, otherwise extremely difficult to monitor from passive satellite sensors. We use 4 yr of data (June 2006-May 2010) over the circumpolar Arctic, here defined as 67-82 degrees N, and characterize probability density functions of cloud base and top heights, geometrical thickness and zonal distribution of such cloud layers, separately for water and ice phases, and discuss seasonal variability of these properties. When computed for the entire study area, probability density functions of cloud base and top heights and geometrical thickness peak at 200-400, 1000-2000 and 400-800 m, respectively, for thin water clouds, while for ice clouds they peak at 6-8, 7-9 and 400-1000 m, respectively. In general, liquid clouds were often identified below 2 km during all seasons, whereas ice clouds were sensed throughout the majority of the upper troposphere and also, but to a smaller extent, below 2 km for all seasons.

  • 342.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Tjernstrom, Michael
    Omar, Ali H.
    The vertical distribution of thin features over the Arctic analysed from CALIPSO observations2011In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 63, no 1, p. 86-95Article in journal (Refereed)
    Abstract [en]

    Influx of aerosols from the mid-latitudes has a wide range of impacts on the Arctic atmosphere. In this study, the capability of the CALIPSO-CALIOP instrument to provide accurate observations of aerosol layers is exploited to characterize their vertical distribution, probability density functions (PDFs) of aerosol layer thickness, base and top heights, and optical depths over the Arctic for the 4-yr period from June 2006 to May 2010. It is shown that the bulk of aerosols, from about 65% in winter to 45% in summer, are confined below the lowermost kilometer of the troposphere. In the middle troposphere (3-5 km), spring and autumn seasons show slightly higher aerosol amounts compared to other two seasons. The relative vertical distribution of aerosols shows that clean continental aerosol is the largest contributor in all seasons except in summer, when layers of polluted continental aerosols are almost as large. In winter and spring, polluted continental aerosols are the second largest contributor to the total number of observed aerosol layers, whereas clean marine aerosol is the second largest contributor in summer and autumn. The PDFs of the geometrical thickness of the observed aerosol layers peak about 400-700 m. Polluted continental and smoke aerosols, which are associated with the intrusions from mid-latitudes, have much broader distributions of optical and geometrical thicknesses, suggesting that they appear more often optically thicker and higher up in the troposphere.

  • 343.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Karlsson, Karl-Göran
    SMHI, Research Department, Atmospheric remote sensing.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Quantifying the clear-sky temperature inversion frequency and strength over the Arctic Ocean during summer and winter seasons from AIRS profiles2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 12, p. 5565-5572Article in journal (Refereed)
    Abstract [en]

    Temperature inversions are one of the dominant features of the Arctic atmosphere and play a crucial role in various processes by controlling the transfer of mass and moisture fluxes through the lower troposphere. It is therefore essential that they are accurately quantified, monitored and simulated as realistically as possible over the Arctic regions. In the present study, the characteristics of inversions in terms of frequency and strength are quantified for the entire Arctic Ocean for summer and winter seasons of 2003 to 2008 using the AIRS data for the clear-sky conditions. The probability density functions (PDFs) of the inversion strength are also presented for every summer and winter month. Our analysis shows that although the inversion frequency along the coastal regions of Arctic decreases from June to August, inversions are still seen in almost each profile retrieved over the inner Arctic region. In winter, inversions are ubiquitous and are also present in every profile analysed over the inner Arctic region. When averaged over the entire study area (70 degrees N-90 degrees N), the inversion frequency in summer ranges from 69 to 86% for the ascending passes and 72-86% for the descending passes. For winter, the frequency values are 88-91% for the ascending passes and 89-92% for the descending passes of AIRS/AQUA. The PDFs of inversion strength for the summer months are narrow and right-skewed (or positively skewed), while in winter, they are much broader. In summer months, the mean values of inversion strength for the entire study area range from 2.5 to 3.9 K, while in winter, they range from 7.8 to 8.9 K. The standard deviation of the inversion strength is double in winter compared to summer. The inversions in the summer months of 2007 were very strong compared to other years. The warming in the troposphere of about 1.5-3.0K vertically extending up to 400 hPa was observed in the summer months of 2007.

  • 344. Dias, Daniela
    et al.
    Amorim, Jorge Humberto
    SMHI, Research Department, Air quality.
    Sa, Elisa
    Borrego, Carlos
    Fontes, Tania
    Fernandes, Paulo
    Pereira, Sergio Ramos
    Bandeira, Jorge
    Coelho, Margarida C.
    Tchepel, Oxana
    Assessing the importance of transportation activity data for urban emission inventories2018In: Transportation Research Part D: Transport and Environment, ISSN 1361-9209, E-ISSN 1879-2340, Vol. 62, p. 27-35Article in journal (Refereed)
  • 345. Dienst, Manuel
    et al.
    Linden, Jenny
    Engström, Erik
    SMHI, Core Services.
    Esper, Jan
    Removing the relocation bias from the 155-year Haparanda temperature record in Northern Europe2017In: International Journal of Climatology, ISSN 0899-8418, E-ISSN 1097-0088, Vol. 37, no 11, p. 4015-4026Article in journal (Refereed)
  • 346.
    Dieterich, Christian
    et al.
    SMHI, Research Department, Oceanography.
    Wang, Shiyu
    SMHI, Research Department, Climate research - Rossby Centre.
    Schimanke, Semjon
    SMHI, Research Department, Oceanography.
    Groger, Matthias
    SMHI, Research Department, Oceanography.
    Klein, Birgit
    Hordoir, Robinson
    SMHI, Research Department, Oceanography.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Liu, Ye
    SMHI, Research Department, Oceanography.
    Axell, Lars
    SMHI, Research Department, Oceanography.
    Höglund, Anders
    SMHI, Research Department, Oceanography.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Surface Heat Budget over the North Sea in Climate Change Simulations2019In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 10, no 5, article id 272Article in journal (Refereed)
  • 347. Dietze, H.
    et al.
    Löptien, Ulrike
    SMHI, Research Department, Oceanography.
    Revisiting "nutrient trapping" in global coupled biogeochemical ocean circulation models2013In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 27, no 2, p. 265-284Article in journal (Refereed)
    Abstract [en]

    We analyze an extensive set of global coupled biogeochemical ocean circulation models. The focus is on the equatorial Pacific. In all simulations, which are consistent with observed standing stocks of relevant biogeochemical species at the surface, we find spuriously enhanced (reduced) macronutrient (oxygen) concentrations in the deep eastern equatorial Pacific. This modeling problem, apparently endemic to global coupled biogeochemical ocean circulation models, was coined " nutrient trapping" by Najjar et al. (1992). In contrast to Aumont et al. (1999), we argue that " nutrient trapping" is still a persistent problem, even in eddy-permitting models and, further, that the scale of the problem retards model projections of nitrogen cycling. In line with previous work, our results indicate that a deficient circulation is at the core of the problem rather than an admittedly poor quantitative understanding of biogeochemical cycles. More specifically, we present indications that " nutrient trapping" in models is a result of a spuriously damped Equatorial Intermediate (zonal) Current System and Equatorial Deep Jets-phenomenon which await a comprehensive understanding and have, to date, not been successfully simulated.

  • 348.
    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.

  • 349.
    Doescher, Ralf
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Rutgersson, Anna
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    The development of the coupled ocean-atmosphere model RCAO2001In: Third study conference on BALTEX / [ed] J. Meywerk, 2001, p. 45-46Conference paper (Other academic)
  • 350.
    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.

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