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  • 2051.
    Svensson, Urban
    et al.
    SMHI, Research Department, Oceanography.
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    SIMULATION OF SUPERCOOLING AND SIZE DISTRIBUTION IN FRAZIL ICE DYNAMICS1994In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 22, no 3, p. 221-233Article in journal (Refereed)
    Abstract [en]

    The objective of the work presented is to formulate a mathematical description of frazil ice dynamics. The formulation is to be in balance with the current knowledge of the physical processes, for example secondary nucleation. As the knowledge of some of these processes is fragmentary, this means that a conceptually simple formulation is sought. A number of processes are known to influence the supercooling rate and the frazil ice production. The present formulation accounts for the following processes: initial seeding, secondary nucleation, gravitational removal, growth due to cooling of water volume and flocculation/break up. Equations are formulated for these present considering a resolution in time and radius of particles but not in space (well-mixed jar). The equations are solved using a simple explicit numerical scheme. Preliminary results indicate that the model can be calibrated to describe the experimental results reported in the literature. It is mainly the supercooling curves that are used for comparison but some information about the crystal size distribution is also considered. It is to be noted that the model is calibrated to fit the experiments, due to the lack of detailed mathematical description of some of the physical processes. Sensitivity analysis is also used in order to establish that the model behaves according to experimental findings and expectations. The main conclusion of the study is that a fairly simple mathematical model can be formulated and calibrated, which fits the experimental data reported in the literature hitherto. It is further concluded that a resolution in radial space gives additional insight into the dynamics of the process. The evolution of the size distribution and its sensitivity to seeding and dissipation rate has been predicted with results that look physically plausible.

  • 2052.
    Svensson, Urban
    et al.
    SMHI, Research Department, Oceanography.
    Rahm, Lars
    SMHI, Research Department, Oceanography.
    MODELING THE NEAR-BOTTOM REGION OF THE BENTHIC BOUNDARY-LAYER1988In: JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, Vol. 93, no C6, p. 6909-6915Article in journal (Refereed)
  • 2053.
    Svensson, Urban
    et al.
    SMHI, Research Department, Oceanography.
    Sahlberg, Jörgen
    SMHI, Professional Services.
    FORMULAS FOR PRESSURE-GRADIENTS IN ONE-DIMENSIONAL LAKE MODELS1989In: JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, Vol. 94, no C4, p. 4939-4946Article in journal (Refereed)
  • 2054. Swap, R
    et al.
    Garstang, M
    Macko, S A
    Tyson, P D
    Maenhaut, W
    Artaxo, P
    Kållberg, Per
    SMHI, Research Department, Meteorology.
    Talbot, R
    The long-range transport of southern African aerosols the tropical South Atlantic1996In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 101, no D19, p. 23777-23791Article in journal (Refereed)
    Abstract [en]

    Two episodes of long-range aerosol transport (4000 km) from southern Africa into the central tropical South Atlantic are documented. Stable nitrogen isotope analysis, multielemental analysis, and meteorological observations on local and regional scales are used to describe the observed surface aerosol chemistry during these transport episodes. The chemical, kinematic, and thermodynamic analyses suggest that for the central tropical South Atlantic, west Africa between 0 degrees and 10 degrees S is the primary air mass source region (over 50%) during austral spring. Over 70% of all air arriving in the lower and middle troposphere in the central tropical South Atlantic comes from a broad latitudinal band extending from 20 degrees S to 10 degrees N. Air coming from the east subsides and is trapped below the midlevel and trade wind inversion layers. Air from the west originates at higher levels (500 hPa) and contributes less than 30% of the air masses arriving in the central tropical South Atlantic. The source types of aerosols and precursor trace gases extend over a broad range of biomes from desert and savanna to the rain forest. During austral spring, over this broad region, processes include production from vegetation, soils, and biomass burning. The aerosol composition of air masses over and the atmospheric chemistry of the central South Atlantic is a function of the supply of biogenic, biomass burning, and aeolian emissions from tropical Africa. Rainfall is a common controlling factor for all three sources. Rain, in turn, is governed by the large-scale circulations which show pronounced interannual variability. The field measurements were taken in an extremely dry year and reflect the circulation and transport fields typical of these conditions.

  • 2055.
    Södling, Johan
    et al.
    SMHI, Professional Services.
    Nerheim, Signild
    SMHI, Professional Services.
    Statistisk metodik för beräkning av extrema havsvattenstånd2018Report (Other academic)
    Abstract [sv]

    Som ett led i arbetet att förbättra metoderna för planeringsunderlag gällande extrema havsvattenstånd har SMHI gjort en inventering av statistiska metoder för extremvärdesanalys. Metoderna är vanligt förekommande när olika dimensioneringsunderlag tas fram. För att ta fram statistik med hög tillförlitlighet för händelser som har låg sannolikhet (hög återkomsttid) har dock metoderna begränsad användning.

    Tre huvudsakliga metoder har applicerats på SMHI:s havsvattenståndsdata. Den mest vanliga, Blockmaximum-metoden, används vanligtvis på årshögsta vattenstånd. POT – metoden (Peak Over Threshold), använder fler data och är inte lika vanlig. I Norge används en variant av POT – metoden, den så kallade ACER-metoden (Average Conditional Exceedance Rate). Den är mycket lämplig för att ta fram värden för lägre återkomsttider, och är förhållandevis robust när data läggs till vartefter.

    Metodernas lämplighet och känslighet utvärderades för extrema havsvattenstånd, alltså havsvattenstånd med höga återkomsttider(låg sannolikhet). Slutsatsen är att det inte går att välja en metod som överlägsen den andra, och att kunskap om den aktuella platsens oceanografiska förhållanden behövs för att utvärdera resultatens rimlighet. I alla analyser av extrema havsvattenstånd är det viktigt att beakta datakvalité och dataseriens längd. Resultat bör redovisas med konfidensintervall.

    Blockmaximum-metoden testades med olika fördelningar. Gumbel-fördelning visar sig kunna ge orimliga nivåer för vattenståndsextremer och rekommenderas därför inte. GEV (Generalized Extreme Value) och Log-normal fördelning används med fördel i kombination.POT-metoder tar till vara fler händelser än de riktigt extrema, men resultaten som ges har väldigt stora konfidensintervall som växer för låg sannolikhet. Om tröskeln sätts för låg är det inte extremvattenstånd som utvärderas.

    Som en följd av denna analys bestämdes att andra metoder behöver tas fram för att studera de högsta havsvattenstånden längs Sveriges kust. I Schöld m.fl. (2017) redovisas hur man kan gå till väga för att ta fram högsta beräknade havsvattenstånd utifrån befintliga data.

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  • 2056.
    Taesler, Roger
    SMHI, Research Department.
    CLIMATE AND BUILDING ENERGY MANAGEMENT1991In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 16, no 1-2, p. 599-608Article in journal (Refereed)
    Abstract [en]

    Indoor climate control is a major energy demand everywhere. Design and operation of buildings and HVAC systems crucially depend on climate data and real-time meteorological conditions. Energy-efficient buildings also contribute to reduce air pollution and climate change in urban areas as well as regionally and globally. However, the effects of climate and weather on building energy management are still largely overlooked in practice. A main reason for this is the lack of tools for translating meteorological conditions into energy requirements. The combined impact of temperature, solar irradiation, wind and humidity on the energy balance of a building depends on the building itself, i.e., its design, orientation, HVAC system, mode of operation, maintenance, etc. The paper discusses different approaches to model this complex interplay and associated problems at the design as well as in the operation stages. Recent developments in Sweden are reported, including applications to urban planning, building design and real-time operation of buildings and energy systems. The impact of solar irradiation and wind, in addition to that of temperature, is demonstrated. Further, the paper discusses the significance of local site condition versus building characteristics.

  • 2057.
    Taesler, Roger
    SMHI, Research Department.
    Köldperioden av olika längd och förekomst1986Report (Other academic)
  • 2058.
    Taesler, Roger
    SMHI, Research Department.
    THE BIOCLIMATE IN TEMPERATE AND NORTHERN CITIES1991In: International journal of biometeorology, ISSN 0020-7128, E-ISSN 1432-1254, Vol. 35, no 3, p. 161-168Article in journal (Refereed)
    Abstract [en]

    Climate is a basic component of the human environment. Developments in building design and indoor climate control have contributed greatly to improving human health and comfort. By contrast, the possibilities for improving urban climatic conditions by deliberate planning have been poorly exploited. The structure and processes of the urban atmosphere in extratropical regions are briefly described. The impact of certain selected urban climates on human health is summarized. The need for relevant bioclimatological "design tools" for applications in urban planning is stressed, followed by a brief review of some recent work on human thermal comfort. It is argued that the modification of present day comfort criteria to reflect human adaptation to climate may be important for further improvements of indoor climate. as well as for deducing the emissions of air pollutants and greenhouse gases.

  • 2059.
    Taesler, Roger
    et al.
    SMHI, Research Department.
    Andersson, C.
    SMHI.
    Wallentin, C.
    SMHI.
    Krieg, Roland
    SMHI, Research Department, Air quality.
    Klimatkorrigering för energiförbrukningen i ett eluppvärmt villaområde1987Report (Other academic)
  • 2060. Takano, Y.
    et al.
    Liou, K. N.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Yang, P.
    The single-scattering properties of black carbon aggregates determined from the geometric-optics surface-wave approach and the T-matrix method2013In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 125, p. 51-56Article in journal (Refereed)
    Abstract [en]

    The single-scattering properties of eight black carbon (BC, soot) fractal aggregates, composed of primary spheres from 7 to 600, computed by the geometric-optics surface-wave (GOS) approach coupled with the Rayleigh-Gans-Debye (RGD) adjustment for size parameters smaller than approximately 2, are compared with those determined from the superposition T-matrix method. We show that under the condition of random orientation, the results from GOS/RGD are in general agreement with those from T-matrix in terms of the extinction and absorption cross-sections, the single-scattering co-albedo, and the asymmetry factor. When compared with the specific absorption (m(2)/g) measured in the laboratory, we illustrate that using the observed radii of primary spheres ranging from 3.3 to 25 nm, the theoretical values determined from GOS/RGD for primary sphere numbers of 100-600 are within the range of measured values. The GOS approach can be effectively applied to aggregates composed of a large number of primary spheres (e.g., > 6000) and large size parameters (>> 2) in terms of computational efforts. (C) 2013 Elsevier Ltd. All rights reserved.

  • 2061. Tam, Jamie C.
    et al.
    Link, Jason S.
    Rossberg, Axel G.
    Rogers, Stuart I.
    Levin, Philip S.
    Rochet, Marie-Joelle
    Bundy, Alida
    Belgrano, Andrea
    Libralato, Simone
    Tomczak, Maciej
    van de Wolfshaar, Karen
    Pranovi, Fabio
    Gorokhova, Elena
    Large, Scott I.
    Niquil, Nathalie
    Greenstreet, Simon P. R.
    Druon, Jean-Noel
    Lesutiene, Jurate
    Johansen, Marie
    SMHI, Core Services.
    Preciado, Izaskun
    Patricio, Joana
    Palialexis, Andreas
    Tett, Paul
    Johansen, Geir O.
    Houle, Jennifer
    Rindorf, Anna
    Towards ecosystem-based management: identifying operational food-web indicators for marine ecosystems2017In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 74, no 7, p. 2040-2052Article in journal (Refereed)
  • 2062. Tamoffo, Alain T.
    et al.
    Moufouma-Okia, Wilfran
    Dosio, Alessandro
    James, Rachel
    Pokam, Wilfried M.
    Vondou, Derbetini A.
    Fotso-Nguemo, Thierry C.
    Guenang, Guy Merlin
    Kamsu-Tamo, Pierre H.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Longandjo, Georges-Noel
    Lennard, Christopher J.
    Bell, Jean-Pierre
    Takong, Roland R.
    Haensler, Andreas
    Tchotchou, Lucie A. Djiotang
    Nouayou, Robert
    Process-oriented assessment of RCA4 regional climate model projections over the Congo Basin under 1.5. C and 2. C global warming levels: influence of regional moisture fluxes2019In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 53, no 3-4, p. 1911-1935Article in journal (Refereed)
  • 2063. Tangang, Fredolin
    et al.
    Santisirisomboon, Jerasorn
    Juneng, Liew
    Salimun, Ester
    Chung, Jingxiang
    Supari, Supari
    Cruz, Faye
    Ngai, Sheau Tieh
    Ngo-Duc, Thanh
    Singhruck, Patama
    Narisma, Gemma
    Santisirisomboon, Jaruthat
    Wongsaree, Waranyu
    Promjirapawat, Kamphol
    Sukamongkol, Yod
    Srisawadwong, Ratchanan
    Setsirichok, Damrongrit
    Phan-Van, Tan
    Aldrian, Edvin
    Gunawan, Dodo
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Yang, Hongwei
    Projected future changes in mean precipitation over Thailand based on multi-model regional climate simulations of CORDEX Southeast Asia2019In: International Journal of Climatology, ISSN 0899-8418, E-ISSN 1097-0088, Vol. 39, no 14, p. 5413-5436Article in journal (Refereed)
  • 2064. Tanouchi, Hiroto
    et al.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Lindström, Göran
    SMHI, Research Department, Hydrology.
    Kawamura, Akira
    Amaguchi, Hideo
    Improving Urban Runoff in Multi-Basin Hydrological Simulation by the HYPE Model Using EEA Urban Atlas: A Case Study in the Sege River Basin, Sweden2019In: HYDROLOGY, ISSN 2306-5338, Vol. 6, no 1Article in journal (Refereed)
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  • 2065. Taubald, H.
    et al.
    Tonderski, K.
    Andersson, Lotta
    SMHI, Core Services.
    Ronnberg, R.
    Ahlgren, J.
    Oxygen isotopes in phosphate as a tracer for sources and pathways of catchment P in stream water2010In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 74, no 12, p. A1030-A1030Article in journal (Other academic)
  • 2066. Taylor, Christopher M.
    et al.
    Belusic, Danijel
    SMHI, Research Department, Climate research - Rossby Centre.
    Guichard, Francoise
    Arker, Douglas J. P.
    Vischel, Theo
    Bock, Olivier
    Harris, Phil P.
    Janicot, Serge
    Klein, Cornelia
    Panthou, Geremy
    Frequency of extreme Sahelian storms tripled since 1982 in satellite observations2017In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 544, no 7651, p. 475-+Article in journal (Refereed)
  • 2067. Taylor, Christopher M.
    et al.
    Birch, Cathryn E.
    Parker, Douglas J.
    Dixon, Nick
    Guichard, Francoise
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Lister, Grenville M. S.
    Modeling soil moisture-precipitation feedback in the Sahel: Importance of spatial scale versus convective parameterization2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 23, p. 6213-6218Article in journal (Refereed)
    Abstract [en]

    Feedback between soil moisture and precipitation influence climate variability in semiarid regions. However, serious concerns exist about the ability of coarse-scale global atmospheric models to depict one key aspect of the feedback loop, namely the sensitivity of daytime convection to soil moisture. Here we compare regional simulations using a single model, run at different spatial resolutions, and with convective parameterizations switched on or off against Sahelian observations. Convection-permitting simulations at 4 and 12 km capture the observed relationships between soil moisture and convective triggering, emphasizing the importance of surface-driven mesoscale dynamics. However, with the inclusion of the convection scheme at 12 km, the behavior of the model fundamentally alters, switching from negative to positive feedback. Similar positive feedback is found in 9 out of 10 Regional Climate Models run at 50 km. These results raise questions about the accuracy of the feedback in regional models based on current convective parameterizations.

  • 2068. Teixeira, J. C.
    et al.
    Fallmann, J.
    Carvalho, Ana
    SMHI, Research Department, Air quality.
    Rocha, A.
    Surface to boundary layer coupling in the urban area of Lisbon comparing different urban canopy models in WRF2019In: Urban Climate, ISSN 2212-0955, E-ISSN 2212-0955, Vol. 28, article id UNSP 100454Article in journal (Refereed)
  • 2069.
    Temnerud, Johan
    et al.
    SMHI, Research Department, Hydrology.
    Duker, A.
    Karlsson, S.
    Allard, B.
    Bishop, K.
    Folster, J.
    Kohler, S.
    Spatial patterns of some trace elements in four Swedish stream networks2013In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 10, no 3, p. 1407-1423Article in journal (Refereed)
    Abstract [en]

    Four river basins in southern Sweden, with catchment sizes from 0.3 to 127 km(2) (median 1.9), were sampled in October 2007. The 243 samples were analysed for 26 trace elements (Ag, As, Au, Ba, Be, Bi, Cd, Co, Cr, Cu, Ga, Ge, In, La, Li, Mo, Ni, Pb, Sb, Se, Sn, Tl, Ti, U, V and Zn) to identify spatial patterns within drainage networks. The range and median of each element were defined for different stream orders, and relationships to catchment characteristics, including deposition history, were explored. The sampling design made it possible to compare the differences along 40 stream reaches, above and below 53 stream junctions with 107 tributaries and between the 77 inlets and outlets of 36 lakes. The largest concentration differences (at reaches, junctions and lakes) were observed for lakes, with outlets usually having lower concentration compared to the inlets for As, Ba, Be, Bi, Cd, Co, Cr, Ga, Ge, Ni, Pb, Sn, Ti, Tl, U, V and Zn. Significantly lower concentrations were observed for Cd and Co when comparing headwaters with downstream sites in each catchment. Common factor analysis (FA) revealed that As, Bi, Cr, Ga, Ge, Tl and V co-vary positively with Al, Fe and total organic carbon (TOC) and negatively with La, Li and pH. The strong removal of a large number of trace elements when passing through lakes is evident though in the FA, where lake surface coverage plots opposite to many of those elements. Forest volume does not respond in a similar systematic fashion and, surprisingly, the amount of wetland does not relate strongly to either Fe or TOC at any of the rivers. A better understanding of the quantitative removal of organic carbon and iron will aid in understanding trace element fluxes from landscapes rich in organic matter and iron.

  • 2070.
    Temnerud, Johan
    et al.
    SMHI, Research Department, Hydrology.
    Foelster, J.
    Buffam, I.
    Laudon, H.
    Erlandsson, M.
    Bishop, K.
    Can the distribution of headwater stream chemistry be predicted from downstream observations?2010In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 24, no 16, p. 2269-2276Article in journal (Refereed)
    Abstract [en]

    Small streams with catchment areas <2 km(2) make up the majority of all stream length and are of great ecological importance. Surveys of first and second order streams reveal great spatial and temporal variability in the water chemistry of these headwaters, but their assessment presents a serious challenge since systematic, representative data are usually only collected in larger streams and rivers. Using low flow synoptic survey data from seven mesoscale Swedish catchments, this study tests the hypothesis that downstream monitoring data can be used to predict key features of the distribution of chemistry in headwater streams [median and interquartile range (IQR)]. Three ecologically relevant analytes were tested: pH, acid neutralizing capacity (ANC) and total organic carbon (TOC). For all seven catchments, the outlets (36-127 km(2)) were considerably less acid with lower TOC than the median of the headwaters (<2 km(2), N = 19-45). Among catchments, headwater median and IQR were positively correlated with the value at the outlet, for all three analytes. A univariate general linear model (GLM) was used to predict the headwater chemistry distribution for each catchment from its outlet chemistry, using the relationship established with the other six catchments. Headwater median pH and IQR of ANC were well predicted by a single downstream sample [median adj. R(2) similar to 0.7, normalized root mean squared error (NRMSE) <0.7]. Other response variables were not as well predicted, with median adj. R(2) ranging from 0.08 to 0.48, and NRMSE up to 1.1. A minority of models were significant at alpha = 0.05, in part due to the limited availability of catchments with such extensive survey data. However, the clear trends observed suggest that with additional model development, downstream chemistry could ultimately provide a valuable tool for characterizing the range of chemistry in the contributing headwaters. Copyright (C) 2010 John Wiley & Sons, Ltd.

  • 2071.
    Temnerud, Johan
    et al.
    SMHI, Research Department, Hydrology.
    von Bromssen, C.
    Folster, J.
    Buffam, I.
    Andersson, J. -O
    Nyberg, Leif
    SMHI, Research Department.
    Bishop, K.
    Map-based prediction of organic carbon in headwater streams improved by downstream observations from the river outlet2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 2, p. 399-413Article in journal (Refereed)
    Abstract [en]

    In spite of the great abundance and ecological importance of headwater streams, managers are usually limited by a lack of information about water chemistry in these headwaters. In this study we test whether river outlet chemistry can be used as an additional source of information to improve the prediction of the chemistry of upstream headwaters (size < 2 km(2)), relative to models based on map information alone. We use the concentration of total organic carbon (TOC), an important stream ecosystem parameter, as the target for our study. Between 2000 and 2008, we carried out 17 synoptic surveys in 9 mesoscale catchments (size 32-235 km(2)). Over 900 water samples were collected in total, primarily from headwater streams but also including each catchment's river outlet during every survey. First we used partial least square regression (PLS) to model the distribution (median, interquartile range (IQR)) of headwater stream TOC for a given catchment, based on a large number of candidate variables including sub-catchment characteristics from GIS, and measured river chemistry at the catchment outlet. The best candidate variables from the PLS models were then used in hierarchical linear mixed models (MM) to model TOC in individual headwater streams. Three predictor variables were consistently selected for the MM calibration sets: (1) proportion of forested wetlands in the sub-catchment (positively correlated with headwater stream TOC), (2) proportion of lake surface cover in the sub-catchment (negatively correlated with headwater stream TOC), and (3) river outlet TOC (positively correlated with headwater stream TOC). Including river outlet TOC improved predictions, with 5-15% lower prediction errors than when using map information alone. Thus, data on water chemistry measured at river outlets offer information which can complement GIS-based modelling of headwater stream chemistry.

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  • 2072. Teutschbein, Claudia
    et al.
    Wetterhall, Fredrik
    SMHI, Research Department, Hydrology.
    Seibert, Jan
    Evaluation of different downscaling techniques for hydrological climate-change impact studies at the catchment scale2011In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 37, no 9-10, p. 2087-2105Article in journal (Refereed)
    Abstract [en]

    Hydrological modeling for climate-change impact assessment implies using meteorological variables simulated by global climate models (GCMs). Due to mismatching scales, coarse-resolution GCM output cannot be used directly for hydrological impact studies but rather needs to be downscaled. In this study, we investigated the variability of seasonal streamflow and flood-peak projections caused by the use of three statistical approaches to downscale precipitation from two GCMs for a meso-scale catchment in southeastern Sweden: (1) an analog method (AM), (2) a multi-objective fuzzy-rule-based classification (MOFRBC) and (3) the Statistical DownScaling Model (SDSM). The obtained higher-resolution precipitation values were then used to simulate daily streamflow for a control period (1961-1990) and for two future emission scenarios (2071-2100) with the precipitation-streamflow model HBV. The choice of downscaled precipitation time series had a major impact on the streamflow simulations, which was directly related to the ability of the downscaling approaches to reproduce observed precipitation. Although SDSM was considered to be most suitable for downscaling precipitation in the studied river basin, we highlighted the importance of an ensemble approach. The climate and streamflow change signals indicated that the current flow regime with a snowmelt-driven spring flood in April will likely change to a flow regime that is rather dominated by large winter streamflows. Spring flood events are expected to decrease considerably and occur earlier, whereas autumn flood peaks are projected to increase slightly. The simulations demonstrated that projections of future streamflow regimes are highly variable and can even partly point towards different directions.

  • 2073. Theobald, Mark R.
    et al.
    Vivanco, Marta G.
    Aas, Wenche
    Andersson, Camilla
    SMHI, Research Department, Air quality.
    Ciarelli, Giancarlo
    Couvidat, Florian
    Cuvelier, Kees
    Manders, Astrid
    Mircea, Mihaela
    Pay, Maria-Teresa
    Tsyro, Svetlana
    Adani, Mario
    Bergström, Robert
    SMHI, Research Department, Air quality.
    Bessagnet, Bertrand
    Briganti, Gino
    Cappelletti, Andrea
    D'Isidoro, Massimo
    Fagerli, Hilde
    Mar, Kathleen
    Otero, Noelia
    Raffort, Valentin
    Roustan, Yelva
    Schaap, Martijn
    Wind, Peter
    Colette, Augustin
    An evaluation of European nitrogen and sulfur wet deposition and their trends estimated by six chemistry transport models for the period 1990-20102019In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 19, no 1, p. 379-405Article in journal (Refereed)
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  • 2074. Thirel, G.
    et al.
    Andreassian, V.
    Perrin, C.
    Audouy, J. -N
    Berthet, L.
    Edwards, P.
    Folton, N.
    Furusho, C.
    Kuentz, A.
    Lerat, J.
    Lindström, Göran
    SMHI, Research Department, Hydrology.
    Martin, E.
    Mathevet, T.
    Merz, R.
    Parajka, J.
    Ruelland, D.
    Vaze, J.
    Hydrology under change: an evaluation protocol to investigate how hydrological models deal with changing catchments2015In: Hydrological Sciences Journal, ISSN 0262-6667, E-ISSN 2150-3435, Vol. 60, no 7-8, p. 1184-1199Article in journal (Refereed)
    Abstract [en]

    Testing hydrological models under changing conditions is essential to evaluate their ability to cope with changing catchments and their suitability for impact studies. With this perspective in mind, a workshop dedicated to this issue was held at the 2013 General Assembly of the International Association of Hydrological Sciences (IAHS) in Goteborg, Sweden, in July 2013, during which the results of a common testing experiment were presented. Prior to the workshop, the participants had been invited to test their own models on a common set of basins showing varying conditions specifically set up for the workshop. All these basins experienced changes, either in physical characteristics (e.g. changes in land cover) or climate conditions (e.g. gradual temperature increase). This article presents the motivations and organization of this experimentthat isthe testing (calibration and evaluation) protocol and the common framework of statistical procedures and graphical tools used to assess the model performances. The basins datasets are also briefly introduced (a detailed description is provided in the associated Supplementary material).

  • 2075.
    Thomas, Manu Anna
    et al.
    SMHI, Research Department, Air quality.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    Sensitivity of free tropospheric carbon monoxide to atmospheric weather states and their persistency: an observational assessment over the Nordic countries2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 21, p. 11545-11555Article in journal (Refereed)
    Abstract [en]

    Among various factors that influence the long-range transport of pollutants in the free troposphere (FT), the prevailing atmospheric weather states probably play the most important role in governing characteristics and efficacy of such transport. The weather states, such as a particular wind pattern, cyclonic or anticyclonic conditions, and their degree of persistency determine the spatio-temporal distribution and the final fate of the pollutants. This is especially true in the case of Nordic countries, where baroclinic disturbances and associated weather fronts primarily regulate local meteorology, in contrast to the lower latitudes where a convective paradigm plays a similarly important role. Furthermore, the long-range transport of pollutants in the FT has significant contribution to the total column burden over the Nordic countries. However, there is insufficient knowledge on the large-scale co-variability of pollutants in the FT and atmospheric weather states based solely on observational data over this region. The present study attempts to quantify and understand this statistical co-variability while providing relevant meteorological background. To that end, we select eight weather states that predominantly occur over the Nordic countries and three periods of their persistency (3 days, 5 days, and 7 days), thus providing in total 24 cases to investigate sensitivity of free tropospheric carbon monoxide, an ideal tracer for studying pollutant transport, to these selected weather states. The eight states include four dominant wind directions (namely, NW, NE, SE and SW), cyclonic and anticyclonic conditions, and the enhanced positive and negative phases of the North Atlantic Oscillation (NAO). For our sensitivity analysis, we use recently released Version 6 retrievals of CO at 500 hPa from the Atmospheric Infrared Sounder (AIRS) onboard Aqua satellite covering the 11-year period from September 2002 through August 2013 and winds from the ECMWF's ERA-Interim project to classify weather states for the same 11-year period. We show that, among the various weather states studied here, southeasterly winds lead to highest observed CO anomalies (up to +8%) over the Nordic countries while transporting pollution from the central and eastern parts of Europe. The second (up to +4%) and third highest (up to +2.5%) CO anomalies are observed when winds are northwesterly (facilitating inter-continental transport from polluted North American regions) and during the enhanced positive phase of the NAO respectively. Higher than normal CO anomalies are observed during anticyclonic conditions (up to +1%) compared to cyclonic conditions. The cleanest conditions are observed when winds are northeasterly and during the enhanced negative phases of the NAO, when relatively clean Arctic air masses are transported over the Nordic regions in the both cases. In the case of nearly all weather states, the CO anomalies consistently continue to increase or decrease as the degree of persistency of a weather state is increased. The results of this sensitivity study further provide an observational basis for the process-oriented evaluation of chemistry transport models, especially with regard to the representation of large-scale coupling of chemistry and local weather states and its role in the long-range transport of pollutants in such models.

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  • 2076.
    Thomas, Manu Anna
    et al.
    SMHI, Research Department, Air quality.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Exploiting the favourable alignment of CALIPSO's descending orbital tracks over Sweden to study aerosol characteristics2013In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 65, article id 21155Article in journal (Refereed)
    Abstract [en]

    One of the key knowledge gaps when estimating aerosol forcing and their role in air quality is our limited understanding of their vertical distribution. As an active lidar in space, the CALIOP-CALIPSO is helping to close this gap. The descending orbital track of CALIPSO follows elongated semi-major axis of Sweden, slicing its atmosphere every 2-3 d, thus providing a unique opportunity to characterise aerosols and their verticality in all seasons irrespective of solar conditions. This favourable orbital configuration of CALIPSO over Sweden is exploited in the present study. Using five years of night-time aerosol observations (2006-2011), we investigated the vertical distribution of aerosols. The role of temperature inversions and winds in governing this distribution is additionally investigated using collocated AIRS-Aqua and ERA-Interim Reanalysis data. It is found that the majority of aerosols (up to 70%) are located within 1 km above the surface in the lowermost troposphere, irrespective of the season. In summer, convection and stronger mixing lift aerosols to slightly higher levels, but their noticeable presence in the upper free troposphere is observed in the winter half of the year, when the boundary layer is decoupled due to strong temperature inversions separating local sources from the transport component. When southerly winds prevail, two or more aerosol layers are most frequent over southern Sweden and the polluted air masses have higher AOD values. The depolarisation ratio and integrated attenuated backscatter of these aerosol layers are also higher. About 30-50% of all aerosol layers are located below the level where temperature inversions peak. On the other hand, relatively cleaner conditions are observed when the winds have a northerly component.

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  • 2077.
    Thomas, Manu Anna
    et al.
    SMHI, Research Department, Air quality.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Andersson, Camilla
    SMHI, Research Department, Air quality.
    Kokkola, H.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Langner, Joakim
    SMHI, Research Department, Air quality.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    Integration of prognostic aerosol-cloud interactions in a chemistry transport model coupled offline to a regional climate model2015In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 8, no 6, p. 1885-1898Article in journal (Refereed)
    Abstract [en]

    To reduce uncertainties and hence to obtain a better estimate of aerosol (direct and indirect) radiative forcing, next generation climate models aim for a tighter coupling between chemistry transport models and regional climate models and a better representation of aerosol-cloud interactions. In this study, this coupling is done by first forcing the Rossby Center regional climate model (RCA4) with ERA-Interim lateral boundaries and sea surface temperature (SST) using the standard cloud droplet number concentration (CDNC) formulation (hereafter, referred to as the 'stand-alone RCA4 version' or 'CTRL' simulation). In the stand-alone RCA4 version, CDNCs are constants distinguishing only between land and ocean surface. The meteorology from this simulation is then used to drive the chemistry transport model, Multiple-scale Atmospheric Transport and Chemistry (MATCH), which is coupled online with the aerosol dynamics model, Sectional Aerosol module for Large Scale Applications (SALSA). CDNC fields obtained from MATCH-SALSA are then fed back into a new RCA4 simulation. In this new simulation (referred to as 'MOD' simulation), all parameters remain the same as in the first run except for the CDNCs provided by MATCH-SALSA. Simulations are carried out with this model setup for the period 2005-2012 over Europe, and the differences in cloud microphysical properties and radiative fluxes as a result of local CDNC changes and possible model responses are analysed. Our study shows substantial improvements in cloud microphysical properties with the input of the MATCH-SALSA derived 3-D CDNCs compared to the stand-alone RCA4 version. This model setup improves the spatial, seasonal and vertical distribution of CDNCs with a higher concentration observed over central Europe during boreal summer (JJA) and over eastern Europe and Russia during winter (DJF). Realistic cloud droplet radii (CD radii) values have been simulated with the maxima reaching 13 mu m, whereas in the stand-alone version the values reached only 5 mu m. A substantial improvement in the distribution of the cloud liquid-water paths (CLWP) was observed when compared to the satellite retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) for the boreal summer months. The median and standard deviation values from the 'MOD' simulation are closer to observations than those obtained using the stand-alone RCA4 version. These changes resulted in a significant decrease in the total annual mean net fluxes at the top of the atmosphere (TOA) by -5 W m(-2) over the domain selected in the study. The TOA net fluxes from the 'MOD' simulation show a better agreement with the retrievals from the Clouds and the Earth's Radiant Energy System (CERES) instrument. The aerosol indirect effects are estimated in the 'MOD' simulation in comparison to the pre-industrial aerosol emissions (1900). Our simulations estimated the domain averaged annual mean total radiative forcing of -0.64 W m(-2) with a larger contribution from the first indirect aerosol effect (-0.57 W m(-2)) than from the second indirect aerosol effect (-0.14 W m(-2)).

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  • 2078.
    Thomas, Manu Anna
    et al.
    SMHI, Research Department, Air quality.
    Suntharalingam, P.
    Pozzoli, L.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    Kloster, S.
    Rast, S.
    Feichter, J.
    Lenton, T. M.
    Rate of non-linearity in DMS aerosol-cloud-climate interactions2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 21, p. 11175-11183Article in journal (Refereed)
    Abstract [en]

    The degree of non-linearity in DMS-cloud-climate interactions is assessed using the ECHAM5-HAMMOZ model by taking into account end-to-end aerosol chemistry-cloud microphysics link. The evaluation is made over the Southern oceans in austral summer, a region of minimal anthropogenic influence. In this study, we compare the DMS-derived changes in the aerosol and cloud microphysical properties between a baseline simulation with the ocean DMS emissions from a prescribed climatology, and a scenario where the DMS emissions are doubled. Our results show that doubling the DMS emissions in the current climate results in a non-linear response in atmospheric DMS burden and subsequently, in SO2 and H2SO4 burdens due to inadequate OH oxidation. The aerosol optical depth increases by only similar to 20% in the 30 degrees S-75 degrees S belt in the SH summer months. This increases the vertically integrated cloud droplet number concentrations (CDNC) by 25 %. Since the vertically integrated liquid water vapor is constant in our model simulations, an increase in CDNC leads to a reduction in cloud droplet radius of 3.4 % over the Southern oceans in summer. The equivalent increase in cloud liquid water path is 10.7 %. The above changes in cloud microphysical properties result in a change in global annual mean radiative forcing at the TOA of -1.4 W m(-2). The results suggest that the DMS-cloud microphysics link is highly non-linear. This has implications for future studies investigating the DMS-cloud climate feedbacks in a warming world and for studies evaluating geoengineering options to counteract warming by modulating low level marine clouds.

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  • 2079.
    Thomas, Manu Anna
    et al.
    SMHI, Research Department, Air quality.
    Suntharalingam, P.
    Pozzoli, L.
    Rast, S.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    Kloster, S.
    Feichter, J.
    Lenton, T. M.
    Quantification of DMS aerosol-cloud-climate interactions using the ECHAM5-HAMMOZ model in a current climate scenario2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 15, p. 7425-7438Article in journal (Refereed)
    Abstract [en]

    The contribution of ocean dimethyl sulfide (DMS) emissions to changes in cloud microphysical properties is quantified seasonally and globally for present day climate conditions using an aerosol-chemistry-climate general circulation model, ECHAM5-HAMMOZ, coupled to a cloud microphysics scheme. We evaluate DMS aerosol-cloud-climate linkages over the southern oceans where anthropogenic influence is minimal. The changes in the number of activated particles, cloud droplet number concentration (CDNC), cloud droplet effective radius, cloud cover and the radiative forcing are examined by analyzing two simulations: a baseline simulation with ocean DMS emissions derived from a prescribed climatology and one in which the ocean DMS emissions are switched off. Our simulations show that the model realistically simulates the seasonality in the number of activated particles and CDNC, peaking during Southern Hemisphere (SH) summer coincident with increased phyto-plankton blooms and gradually declining with a minimum in SH winter. In comparison to a simulation with no DMS, the CDNC level over the southern oceans is 128% larger in the baseline simulation averaged over the austral summer months. Our results also show an increased number of smaller sized cloud droplets during this period. We estimate a maximum decrease of up to 15-18% in the droplet radius and a mean increase in cloud cover by around 2.5% over the southern oceans during SH summer in the simulation with ocean DMS compared to when the DMS emissions are switched off. The global annual mean top of the atmosphere DMS aerosol all sky radiative forcing is -2.03 W/m(2), whereas, over the southern oceans during SH summer, the mean DMS aerosol radiative forcing reaches -9.32 W/m(2).

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  • 2080.
    Thomas, Manu
    et al.
    SMHI, Research Department, Air quality.
    Brannstrom, Niklas
    Persson, Christer
    SMHI, Professional Services.
    Grahn, Hakan
    von Schoenberg, Pontus
    Robertson, Lennart
    SMHI, Research Department, Air quality.
    Surface air quality implications of volcanic injection heights2017In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 166, p. 510-518Article in journal (Refereed)
  • 2081.
    Thomas, Manu
    et al.
    SMHI, Research Department, Air quality.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    Typical meteorological conditions associated with extreme nitrogen dioxide (NO2) pollution events over Scandinavia2017In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 17, no 19, p. 12071-12080Article in journal (Refereed)
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  • 2082.
    Thomas, Manu
    et al.
    SMHI, Research Department, Air quality.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    Koenigk, Torben
    SMHI, Research Department, Climate research - Rossby Centre.
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Roberts, Malcolm
    Roberts, Christopher
    Lohmann, Katja
    A statistical and process-oriented evaluation of cloud radiative effects in high-resolution global models2019In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 12, no 4, p. 1679-1702Article in journal (Refereed)
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  • 2083.
    Thomas, Manu
    et al.
    SMHI, Research Department, Air quality.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    L'Ecuyer, Tristan
    Wang, Shiyu
    SMHI, Research Department, Climate research - Rossby Centre.
    Koenigk, Torben
    SMHI, Research Department, Climate research - Rossby Centre.
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Snowfall distribution and its response to the Arctic Oscillation: an evaluation of HighResMIP models in the Arctic using CPR/CloudSat observations2019In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 12, no 8, p. 3759-3772Article in journal (Refereed)
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  • 2084.
    Thomas, Manu
    et al.
    SMHI, Research Department, Air quality.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    Tjernstrom, Michael
    Ekman, Annica M. L.
    The Relation Between Aerosol Vertical Distribution and Temperature Inversions in the Arctic in Winter and Spring2019In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 5, p. 2836-2845Article in journal (Refereed)
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  • 2085.
    Thompson, Thomas
    SMHI.
    Ymer-80, satellites, arctic sea ice and weather1986Report (Other academic)
    Abstract [en]

    During the arctic expedition YMER-80 which took place in the area north of Svalbard between northeast Greenland and Frans Josephs Land satellite information was received onboard as an important aid in weather and sea ice surveillance. A satellits receiving station made it possible to receive images directly onboard from the NOAA weather satellrres. These APT images proved to be very valuable for the weather analyses but for sea ice mapping the resolution, geometrically as well as radiometrically, proved to be a little to coarce to be of real use in the the daily operations planning. High resolution LANDSAT images were received by radio from the receiving station in Kiruna but the limited areal coverage if these images together with the quality degradation in the transmission limited their operational usefullness.Multispectral processing of the full resolution NOAA, AVHRR data proved however that such data can give considerable details about the ice and therefore be of great value for the daily operetions of an expedition like YMER- 80. The report shows examples of NOAA and LANDSAT images received onboard as well as full resolution images processed after the the expedition was completed

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  • 2086.
    Thompson, Thomas
    et al.
    SMHI.
    Udin, Ingemar
    SMHI, Core Services.
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    Sea surface temperatures in waters surrounding Sweden1974Report (Other academic)
    Abstract [en]

    One of the sub-projects within the sea ice research programme carried out at SMHI deals with the thermodynamics of the sea and the ice. In these studies the sea surface temperature plays a fundamental r ole. During the latest years considerable efforts have been made in order to obtain more temperature observations, in particular from the open sea. Various vessels have been equipped with new instruments, the collection of observations improved, the sea surface temperature distribution analyzed every second day and all information stored in digital form.

    The instruments are discribed and their specifications given in the report. Various observational methods are compared and examples of sea surface temperature analyses for the period July 1973 - July 1974  illustrating yearly variations, tendency to circulation patterns, coastal effects, up-welling etc. are given.

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  • 2087.
    Thompson, Thomas
    et al.
    SMHI.
    Ulander, Lars
    SMHI.
    Håkansson, Bertil
    SMHI, Research Department, Oceanography.
    Brusmark, Bertil
    SMHI.
    Carlström, Anders
    SMHI.
    Gustavsson, Anders
    SMHI.
    BEERS -92: Final edition1992Report (Other academic)
  • 2088.
    Tiderman, Karin
    SMHI, Core Services.
    Sänkta och torrlagda sjöar: Svenskt Vattenarkiv1995Report (Other academic)
  • 2089. Tilmes, S
    et al.
    Brandt, J
    Flatoy, F
    Bergström, Robert
    SMHI, Research Department, Air quality.
    Flemming, J
    Langner, Joakim
    SMHI, Research Department, Air quality.
    Christensen, J H
    Frohn, L M
    Hov, O
    Jacobsen, I
    Reimer, E
    Stern, R
    Zimmermann, J
    Comparison of five eulerian air pollution forecasting systems for the summer of 1999 using the German ozone monitoring data2002In: Journal of Atmospheric Chemistry, ISSN 0167-7764, E-ISSN 1573-0662, Vol. 42, no 1, p. 91-121Article in journal (Refereed)
    Abstract [en]

    Eulerian state-of-the-art air pollution forecasting systems on the European scale are operated routinely by several countries in Europe. DWD and FUB, both Germany, NERI, Denmark, NILU, Norway, and SMHI, Sweden, operate some of these systems. To apply such modeling systems, e.g. for regulatory purposes according to new EU directives, an evaluation and comparison of the model systems is fundamental in order to assess their reliability. One step in this direction is presented in this study: The model forecasts from all five systems have been compared to measurements of ground level ozone in Germany. The outstanding point in this investigation is the availability of a huge amount of data - from forecasts by the different model systems and from observations. This allows for a thorough interpretation of the findings and assures the significance of the observed features. Data from more than 300 measurement stations for a 5-month period (May-September 1999) of the German monitoring networks have been used in this comparison. Different spatial and temporal statistical parameters were applied in the evaluation. Generally, it was found that the most comprehensive models gave the best results. However, the less comprehensive and computational cheaper models also produced good results. The extensive comparison made it possible to point out weak points in the different models and to describe the individual model behavior for a full summer period in a climatological sense. The comparison also gave valuable information for an assessment of individual measurement stations and complete monitoring networks in terms of the representativeness of the observation data.

  • 2090. Tiselius, Peter
    et al.
    Belgrano, Andrea
    Andersson, Lars
    SMHI, Core Services.
    Lindahl, Odd
    Contribution to the Themed Section: Scaling from individual Plankton to marine ecosystems Primary productivity in a coastal ecosystem: a trophic perspective on a long-term time series2016In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 38, no 4, p. 1092-1102Article in journal (Refereed)
  • 2091. Tjernstrom, M.
    et al.
    Birch, C. E.
    Brooks, I. M.
    Shupe, M. D.
    Persson, P. O. G.
    Sedlar, Joseph
    SMHI, Research Department, Atmospheric remote sensing.
    Mauritsen, T.
    Leck, C.
    Paatero, J.
    Szczodrak, M.
    Wheeler, C. R.
    Meteorological conditions in the central Arctic summer during the Arctic Summer Cloud Ocean Study (ASCOS)2012In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 12, no 15, p. 6863-6889Article in journal (Refereed)
    Abstract [en]

    Understanding the rapidly changing climate in the Arctic is limited by a lack of understanding of underlying strong feedback mechanisms that are specific to the Arctic. Progress in this field can only be obtained by process-level observations; this is the motivation for intensive ice-breaker-based campaigns such as the Arctic Summer Cloud-Ocean Study (ASCOS), described here. However, detailed field observations also have to be put in the context of the larger-scale meteorology, and short field campaigns have to be analysed within the context of the underlying climate state and temporal anomalies from this. To aid in the analysis of other parameters or processes observed during this campaign, this paper provides an overview of the synoptic-scale meteorology and its climatic anomaly during the ASCOS field deployment. It also provides a statistical analysis of key features during the campaign, such as key meteorological variables, the vertical structure of the lower troposphere and clouds, and energy fluxes at the surface. In order to assess the representativity of the ASCOS results, we also compare these features to similar observations obtained during three earlier summer experiments in the Arctic Ocean: the AOE-96, SHEBA and AOE-2001 expeditions. We find that these expeditions share many key features of the summertime lower troposphere. Taking ASCOS and the previous expeditions together, a common picture emerges with a large amount of low-level cloud in a well-mixed shallow boundary layer, capped by a weak to moderately strong inversion where moisture, and sometimes also cloud top, penetrate into the lower parts of the inversion. Much of the boundary-layer mixing is due to cloud-top cooling and subsequent buoyant overturning of the cloud. The cloud layer may, or may not, be connected with surface processes depending on the depths of the cloud and surface-based boundary layers and on the relative strengths of surface-shear and cloud-generated turbulence. The latter also implies a connection between the cloud layer and the free troposphere through entrainment at cloud top.

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  • 2092. Tjernstrom, M.
    et al.
    Leck, C.
    Birch, C. E.
    Bottenheim, J. W.
    Brooks, B. J.
    Brooks, I. M.
    Backlin, L.
    Chang, Y. -W
    de Leeuw, G.
    Di Liberto, L.
    de la Rosa, S.
    Granath, E.
    Graus, M.
    Hansel, A.
    Heintzenberg, J.
    Held, A.
    Hind, A.
    Johnston, P.
    Knulst, J.
    Martin, M.
    Matrai, P. A.
    Mauritsen, T.
    Mueller, M.
    Norris, S. J.
    Orellana, M. V.
    Orsini, D. A.
    Paatero, J.
    Persson, P. O. G.
    Gao, Q.
    Rauschenberg, C.
    Ristovski, Z.
    Sedlar, Joseph
    SMHI, Research Department, Atmospheric remote sensing.
    Shupe, M. D.
    Sierau, B.
    Sirevaag, A.
    Sjogren, S.
    Stetzer, O.
    Swietlicki, E.
    Szczodrak, M.
    Vaattovaara, P.
    Wahlberg, N.
    Westberg, M.
    Wheeler, C. R.
    The Arctic Summer Cloud Ocean Study (ASCOS): overview and experimental design2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 6, p. 2823-2869Article in journal (Refereed)
    Abstract [en]

    The climate in the Arctic is changing faster than anywhere else on earth. Poorly understood feedback processes relating to Arctic clouds and aerosol-cloud interactions contribute to a poor understanding of the present changes in the Arctic climate system, and also to a large spread in projections of future climate in the Arctic. The problem is exacerbated by the paucity of research-quality observations in the central Arctic. Improved formulations in climate models require such observations, which can only come from measurements in situ in this difficult-to-reach region with logistically demanding environmental conditions. The Arctic Summer Cloud Ocean Study (ASCOS) was the most extensive central Arctic Ocean expedition with an atmospheric focus during the International Polar Year (IPY) 2007-2008. ASCOS focused on the study of the formation and life cycle of low-level Arctic clouds. ASCOS departed from Longyearbyen on Svalbard on 2 August and returned on 9 September 2008. In transit into and out of the pack ice, four short research stations were undertaken in the Fram Strait: two in open water and two in the marginal ice zone. After traversing the pack ice northward, an ice camp was set up on 12 August at 87 degrees 21' N, 01 degrees 29' W and remained in operation through 1 September, drifting with the ice. During this time, extensive measurements were taken of atmospheric gas and particle chemistry and physics, mesoscale and boundary-layer meteorology, marine biology and chemistry, and upper ocean physics. ASCOS provides a unique interdisciplinary data set for development and testing of new hypotheses on cloud processes, their interactions with the sea ice and ocean and associated physical, chemical, and biological processes and interactions. For example, the first-ever quantitative observation of bubbles in Arctic leads, combined with the unique discovery of marine organic material, polymer gels with an origin in the ocean, inside cloud droplets suggests the possibility of primary marine organically derived cloud condensation nuclei in Arctic stratocumulus clouds. Direct observations of surface fluxes of aerosols could, however, not explain observed variability in aerosol concentrations, and the balance between local and remote aerosols sources remains open. Lack of cloud condensation nuclei (CCN) was at times a controlling factor in low-level cloud formation, and hence for the impact of clouds on the surface energy budget. ASCOS provided detailed measurements of the surface energy balance from late summer melt into the initial autumn freeze-up, and documented the effects of clouds and storms on the surface energy balance during this transition. In addition to such process-level studies, the unique, independent ASCOS data set can and is being used for validation of satellite retrievals, operational models, and reanalysis data sets.

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  • 2093. Tjernstrom, M
    et al.
    Zagar, M
    Svensson, G
    Cassano, J J
    Pfeifer, S
    Rinke, A
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Dethloff, K
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Semmler, T
    Shaw, M
    Modelling the arctic boundary layer: An evaluation of six arcmip regional-scale models using data from the Sheba project2005In: Boundary-layer Meteorology, ISSN 0006-8314, E-ISSN 1573-1472, Vol. 117, no 2, p. 337-381Article in journal (Refereed)
    Abstract [en]

    A primary climate change signal in the central Arctic is the melting of sea ice. This is dependent on the interplay between the atmosphere and the sea ice, which is critically dependent on the exchange of momentum, heat and moisture at the surface. In assessing the realism of climate change scenarios it is vital to know the quality by which these exchanges are modelled in climate simulations. Six state-of-the-art regional-climate models are run for one year in the western Arctic, on a common domain that encompasses the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment ice-drift track. Surface variables, surface fluxes and the vertical structure of the lower troposphere are evaluated using data from the SHEBA experiment. All the models are driven by the same lateral boundary conditions, sea-ice fraction and sea and sea-ice surface temperatures. Surface pressure, near-surface air temperature, specific humidity and wind speed agree well with observations, with a falling degree of accuracy in that order. Wind speeds have systematic biases in some models, by as much as a few metres per second. The surface radiation fluxes are also surprisingly accurate, given the complexity of the problem. The turbulent momentum flux is acceptable, on average, in most models, but the turbulent heat fluxes are, however, mostly unreliable. Their correlation with observed fluxes is, in principle, insignificant, and they accumulate over a year to values an order of magnitude larger than observed. Typical instantaneous errors are easily of the same order of magnitude as the observed net atmospheric heat flux. In the light of the sensitivity of the atmosphere-ice interaction to errors in these fluxes, the ice-melt in climate change scenarios must be viewed with considerable caution.

  • 2094. Tjernström, M
    et al.
    Rummukainen, Markku
    SMHI, Research Department, Climate research - Rossby Centre.
    Bergström, Sten
    SMHI, Research Department, Hydrology.
    Rodhe, J.
    SMHI.
    Persson, Gunn
    SMHI, Professional Services.
    Klimatmodellering och klimatscenarier ur SWECLIMs perspektiv2003Report (Other academic)
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  • 2095. Tjernström, M.
    et al.
    Zagar, M.
    Svensson, G.
    Dethloff, K.
    Rinke, A.
    Cassano, J.
    Pfeifer, S.
    Semmler, T.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    The Arctic boundary-layer in six different RCM compared to SHEBA observations (ARCMIP).2005In: Extended abstracts of a WMO/WCRP-sponsored Regional-Scale Climate Modelling Workshop [Elektronisk resurs] : high-resolution climate modelling : assessment, added value and applications, Lund, Sweden, 29 March-2 April 2004 / [ed] Lars Bärring & René Laprise, Lund: Department of Physical Geography & Ecosystems Analysis, Lund University , 2005, p. 44-45Conference paper (Other academic)
  • 2096. Tobin, Isabelle
    et al.
    Jerez, Sonia
    Vautard, Robert
    Thais, Francoise
    van Meijgaard, Erik
    Prein, Andreas
    Deque, Michel
    Kotlarski, Sven
    Maule, Cathrine Fox
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Noel, Thomas
    Teichmann, Claas
    Climate change impacts on the power generation potential of a European mid-century wind farms scenario2016In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 11, no 3, article id 034013Article in journal (Refereed)
    Abstract [en]

    Wind energy resource is subject to changes in climate. To investigate the impacts of climate change on future European wind power generation potential, we analyze a multi-model ensemble of the most recent EURO-CORDEX regional climate simulations at the 12 km grid resolution. We developed a mid-century wind power plant scenario to focus the impact assessment on relevant locations for future wind power industry. We found that, under two greenhouse gas concentration scenarios, changes in the annual energy yield of the future European wind farms fleet as a whole will remain within +/- 5% across the 21st century. At country to local scales, wind farm yields will undergo changes up to 15% in magnitude, according to the large majority of models, but smaller than 5% in magnitude for most regions and models. The southern fleets such as the Iberian and Italian fleets are likely to be the most affected. With regard to variability, changes are essentially small or poorly significant from subdaily to interannual time scales.

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  • 2097. Toledano, C.
    et al.
    Cachorro, V. E.
    Gausa, M.
    Stebel, K.
    Aaltonen, V.
    Berjon, A.
    Ortiz de Galisteo, J. P.
    de Frutos, A. M.
    Bennouna, Y.
    Blindheim, S.
    Myhre, C. L.
    Zibordi, G.
    Wehrli, C.
    Kratzer, S.
    Håkansson, Bertil
    SMHI, Research Department, Oceanography.
    Carlund, Thomas
    SMHI, Core Services.
    de Leeuw, G.
    Herber, A.
    Torres, B.
    Overview of sun photometer measurements of aerosol properties in Scandinavia and Svalbard2012In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 52, p. 18-28Article in journal (Refereed)
    Abstract [en]

    An overview on the data of columnar aerosol properties measured in Northern Europe is provided. Apart from the necessary data gathered in the Arctic, the knowledge of the aerosol loading in nearby areas (e.g. sub-Arctic) is of maximum interest to achieve a correct analysis of the Arctic aerosols and transport patterns. This work evaluates data from operational sites with sun photometer measurements belonging either to national or international networks (AERONET, GAW-PFR) and programs conducted in Scandinavia and Svalbard. We enumerate a list of sites, measurement type and periods together with observed aerosol properties. An evaluation and analysis of aerosol data was carried out with a review of previous results as well. Aerosol optical depth (AOD) and Angstrom exponent (AE) are the current parameters with sufficient long-term records for a first evaluation of aerosol properties. AOD (500 nm) ranges from 0.08 to 0.10 in Arctic and sub-Arctic sites (Ny-Alesund: 0.09; Andenes: 0.10; Sodankyla: 0.08), and it is somewhat higher in more populated areas in Southern Scandinavia (AOD about 0.10-0.12 at 500 nm). On the Norwegian coast, aerosols show larger mean size (AE = 1.2 at Andenes) than in Finland, with continental climate (AE = 1.5 at Sodankyla). Columnar particle size distributions and related parameters derived from inversion of sun/sky radiances were also investigated. This work makes special emphasis in the joint and collaborative effort of the various groups from different countries involved in this study. Part of the measurements presented here were involved in the IPY projects Polar-AOD and POLARCAT. (C) 2011 Elsevier Ltd. All rights reserved.

  • 2098. Tonderski, K S
    et al.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    Pers, Charlotta
    SMHI, Research Department, Hydrology.
    Modeling the impact of potential wetlands on phosphorus retention in a Swedish catchment2005In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 34, no 7, p. 544-551Article in journal (Refereed)
    Abstract [en]

    In southern Sweden, wetlands are constructed to remove nitrogen (N) in agricultural catchments. The possible effects of such wetlands on riverine phosphorus (P) were also estimated using input-output data from three well-monitored wetlands. This was done to formulate a simple model for removal of P that is dependent on inflow characteristics. Next, the N- and P-reducing effects of wetlands were modeled on a catchment scale (1900 km 2) using the HBV-NP model and various assumptions about the wetland area and location. All three wetlands functioned as sinks for total P (tot-P) and for total suspended solids (TSS) with a removal of 10% to 31% and 28% to 50%, respectively. Mean P-removal rates of 17-49 kg ha(-1) yr(-1) were well simulated with the model. Catchment scale simulations indicated that wetlands were more efficient (in percentage of load) as traps for P than for N and that this may motivate the construction of wetlands for P removal far upstream from the catchment outlet.

  • 2099. Tonderski, Karin
    et al.
    Andersson, Lotta
    SMHI, Research Department, Hydrology.
    Lindström, Göran
    SMHI, Research Department, Hydrology.
    St Cyr, Rasmus
    Schoenberg, Ronny
    Taubald, Heinrich
    Assessing the use of delta O-18 in phosphate as a tracer for catchment phosphorus sources2017In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 607, p. 1-10Article in journal (Refereed)
  • 2100. Tourigny, Etienne
    et al.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    An analysis of regional climate model performance over the tropical Americas. Part I: simulating seasonal variability of precipitation associated with ENSO forcing2009In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 61, no 3, p. 323-342Article in journal (Refereed)
    Abstract [en]

    Sea surface temperature (SST) anomalies associated with El Nino/Southern Oscillation (ENSO) constitute a major source of predictability in the tropics. We evaluate the ability of a regional climate model (the Rossby Centre Atmospheric Model; RCA) to downscale SST and large-scale atmospheric anomalies associated with ENSO. RCA is configured over the tropical east Pacific and tropical Americas and runs for the period 1979-2005, using European Centre for Medium-Range Weather Forecasts (ECMWF) lateral and surface boundary conditions. We study the ability of RCA to represent regional patterns of precipitation, with respect to both the climatology and interannual variability associated with ENSO. The latter is achieved by grouping the simulations into El Nino and La Nina composites and studying the delayed response of precipitation to SST forcing in four regions of Central and South America. In this paper, we concentrate on seasonal mean timescales. We find that RCA accurately simulates the main features of the precipitation climatology over the four regions and also reproduces the majority of the documented regional responses to ENSO forcing. Furthermore, the model captures the variability in precipitation anomalies between different ENSO events. The model exhibits a wet bias over the northern Amazon and slightly overestimates the magnitude of ENSO anomalies over Central America.

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