| 1. |
- Podgrajsek, Eva, et al.
(author)
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Comparison of floating chamber and eddy covariance measurements of lake greenhouse gas fluxes
- 2014
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In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 11, s. 4225-4233
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Journal article (peer-reviewed)abstract
- Fluxes of carbon dioxide (CO2) and methane (CH4) from lakes may have a large impact on the magnitude of the terrestrial carbon sink. Traditionally lake fluxes have been measured using the floating chamber (FC) technique; however, several recent studies use the eddy covariance (EC) method. We present simultaneous flux measurements using both methods at lake Tämnaren in Sweden during field campaigns in 2011 and 2012. Only very few similar studies exist. For CO2 flux, the two methods agree relatively well during some periods, but deviate substantially at other times. The large discrepancies might be caused by heterogeneity of partial pressure of CO2 (pCO2w) in the EC flux footprint. The methods agree better for CH4 fluxes. It is, however, clear that short-term discontinuous FC measurements are likely to miss important high flux events.
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| 2. |
- Chen, Hans, 1988, et al.
(author)
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A robust mode of climate variability in the Arctic: The Barents Oscillation
- 2013
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 40:11, s. 2856-2861
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Journal article (peer-reviewed)abstract
- The Barents Oscillation (BO) is an anomalous wintertime atmospheric circulation pattern in the Northern Hemisphere that has been linked to the meridional flow over the Nordic Seas. There are speculations that the BO has important implications for the Arctic climate; however, it has also been suggested that the pattern is an artifact of Empirical Orthogonal Function (EOF) analysis due to an eastward shift of the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). In this study, EOF analyses are performed to show that a robust pattern resembling the BO can be found during different time periods, even when the AO/NAO is relatively stationary. This BO has a high and stable temporal correlation with the geostrophic zonal wind over the Barents Sea, while the contribution from the AO/NAO is small. The surface air temperature anomalies over the Barents Sea are closely associated with this mode of climate variability.
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| 3. |
- Hallquist, Åsa Marita, et al.
(author)
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On-board Measurements of Nanoparticles from a SCR-Equipped Marine Diesel Engine
- 2013
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In: Environmental Science & Technology. - : American Chemical Society. - 0013-936X .- 1520-5851. ; 47:2, s. 773-780
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Journal article (peer-reviewed)abstract
- In this study nanoparticle emissions have been characterised on-board a ship with focus on number, size and volatility. Measurements were conducted on one of the ship’s four main 12 600 kW medium–speed diesel engines which use low sulphur marine residual fuel and have a Selective Catalytic Reduction (SCR) system for NOX abatement. The particles were measured after the SCR with an engine exhaust particle sizer spectrometer (EEPS), giving particle number and mass distributions in the size range of 5.6-560 nm. The thermal characteristics of the particles were analysed using a volatility tandem DMA system (VTDMA). A dilution ratio of 450-520 was used which is similar to the initial real-world dilution. At a stable engine load of 75% of the maximum rated power, and after dilution and cooling of the exhaust gas, there was a bimodal number size distribution, with a major peak at ~10 nm and a smaller peak at around 30-40 nm. The mass distribution peaked around 20 nm and at 50-60 nm. The emission factor for particle number, EFPN, for an engine load of 75% in the open-sea was found to be 10.4 ± 1.6 × 1016 (kg fuel)-1 and about 50% of the particles by number were found to have a non-volatile core at 250 °C. Additionally, 20 nm particles consist of ~40% of non-volatile material by volume (evaporative temperature 250 °C) while the particles with a particle diameter <10 nm evaporate completely at a temperature of 130-150 °C. Emission factors for NOX, CO and CO2 for an engine load of 75% in the open-sea were determined to 4.06 ± 0.3 g (kg fuel)-1, 2.15 ± 0.06 g (kg fuel)-1 and 3.23 ± 0.08 kg (kg fuel)-1, respectively. This work contributes to an improved understanding of particle emissions from shipping using modern pollution reduction measures such as SCR and fuel with low sulphur content.
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| 4. |
- Khosravi, Maryam, 1975
(author)
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Diurnal variation of stratospheric short-lived species
- 2012
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Licentiate thesis (other academic/artistic)abstract
- Diurnal variation of stratospheric short-lived speciesMaryam KhosraviChalmers University of TechnologyDepartment of Earth and Space SciencesAbstractThe depletion of ozone in the stratosphere has a direct impact on the amount of ultravioletradiation reaching the Earth’s surface. The ozone abundance and distributionis controlled by the photo-chemical reactions and catalytic cycles involving halogens(chlorine and bromine), odd hydrogen and odd nitrogen species as well as by atmospherictransport.An introduction to ozone related chemistry of the stratosphere and modelling ofshort-lived species using photo-chemical models is presented. A one dimensional (1D)atmospheric model is used in two distinct studies: modeling of short-lived species inthe Arctic lower stratosphere (paper I) and in the tropical mid to upper stratosphere(paper II).The first part of this thesis describes the diurnal variation of chlorine monoxide,ClO, which is the most important short-lived species controlling ozone in the polarlower stratosphere during winter and early-spring. The ClO-dimer cycle, involvingClO and its nighttime reservoir Cl2O2, contributes to about 75%of the polar ozone loss.ClO measurements from an airborne submillimeter radiometer in the Arctic twilighthave been compared with the results from a 1D photo-chemical model (MISU-1D), inorder to validate the model and to test the kinetics of the reactions controlling the partitioningof chlorine species during the course of a day. The results show that crosssections leading to faster photolysis rates of Cl2O2 match best with the ClO observations.This is consistent with the recent version of the chemical kinetics evaluation bythe Jet Propulsion Laboratory. Slower photolysis rates can not be reconciled with theobservations since active chlorine higher than the total available chlorine would be required.The model reproduces higher nighttime ClO than the observations, howeverthe nighttime ClOmodelled using recent JPL recommendations of the thermal equilibriumconstant agree within the uncertainty range of the observations. The sensitivityof the model to the assumed albedo and temperature are also tested. Neither the temperaturenor the albedo uncertainties allow us to reconcile the model with the lowerobserved nighttime ClO. Moreover, it is found that the ClO-BrO cycle decreases ClOmostly around sunrise and sunset.The second part of the thesis presents the partitioning and diurnal variation of chlorine,bromine, hydrogen, nitrogen and oxygen species in the tropics from the stratosphereto the lower mesosphere. Model results of the diurnal variation of HOCl (asone of the chlorine reservoirs), the related short-lived species ClO and HO2 and HCl(as the main chlorine reservoir) for the tropics and three altitudes (35, 45 and 55 km)are compared with measurements from five satellite instruments. The model resultsgenerally agree with the observations both in terms of the absolute values and the differencesbetween day and night.
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| 5. |
- Strandberg, Gustav, et al.
(author)
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Regional climate model simulations for Europe at 6 and 0.2 k BP : sensitivity to changes in anthropogenic deforestation
- 2014
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In: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 10:2, s. 661-680
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Journal article (peer-reviewed)abstract
- This study aims to evaluate the direct effects of anthropogenic deforestation on simulated climate at two contrasting periods in the Holocene, similar to 6 and similar to 0.2 k BP in Europe. We apply We apply the Rossby Centre regional climate model RCA3, a regional climate model with 50 km spatial resolution, for both time periods, considering three alternative descriptions of the past vegetation: (i) potential natural vegetation (V) simulated by the dynamic vegetation model LPJ-GUESS, (ii) potential vegetation with anthropogenic land use (deforestation) from the HYDE3.1 (History Database of the Global Environment) scenario (V + H3.1), and (iii) potential vegetation with anthropogenic land use from the KK10 scenario (V + KK10). The climate model results show that the simulated effects of deforestation depend on both local/regional climate and vegetation characteristics. At similar to 6 k BP the extent of simulated deforestation in Europe is generally small, but there are areas where deforestation is large enough to produce significant differences in summer temperatures of 0.5-1 degrees C. At similar to 0.2 k BP, extensive deforestation, particularly according to the KK10 model, leads to significant temperature differences in large parts of Europe in both winter and summer. In winter, deforestation leads to lower temperatures because of the differences in albedo between forested and unforested areas, particularly in the snow-covered regions. In summer, deforestation leads to higher temperatures in central and eastern Europe because evapotranspiration from unforested areas is lower than from forests. Summer evaporation is already limited in the southernmost parts of Europe under potential vegetation conditions and, therefore, cannot become much lower. Accordingly, the albedo effect dominates in southern Europe also in summer, which implies that deforestation causes a decrease in temperatures. Differences in summer temperature due to deforestation range from -1 degrees C in south-western Europe to +1 degrees C in eastern Europe. The choice of anthropogenic land-cover scenario has a significant influence on the simulated climate, but uncertainties in palaeoclimate proxy data for the two time periods do not allow for a definitive discrimination among climate model results.
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| 6. |
- Blennow, Kristina
(author)
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Evaluating the Local Climate Impacts Profile tool for assessing local impacts of extreme weather events
- 2014
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In: Journal of Geography and Natural Disasters. - : OMICS Publishing Group. - 2167-0587. ; 4
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Journal article (peer-reviewed)abstract
- The climate change adaptation tool Local Climate Impacts Profile (LCLIP), developed and previously widely usedin the UK, was systematically evaluated in terms of its transferability to Sweden and its usefulness as a catalyst forawareness-raising and action with respect to climate change adaptation. The tool includes scoping, media trawl,interviews and reporting and was applied in three Swedish municipalities. It was found that after some adjustment,the tool can be applied successfully under Swedish conditions. The municipalities involved found the results useful forstimulating local adaptation work. However, the municipalities concluded that LCLIP is primarily a beginner's tool thatcan be applied at a low cost and that other, more costly investigations on vulnerability to extreme weather typically needto be conducted for successful adaptation to climate change at municipal level. An advantage of the LCLIP tool is thatit involves civil servants from all departments in the municipality and thus the resulting vulnerability discussions alsoinvolve departments dealing with ‘soft' issues, such as administration and care.
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| 7. |
- Blennow, Kristina
(author)
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Simulating wind disturbance impacts on forest landscapes: Tree-level heterogeneity matters
- 2014
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In: Environmental Modelling and Software. - : Elsevier BV. - 1364-8152 .- 1873-6726. ; 51, s. 1-11
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Journal article (peer-reviewed)abstract
- Wind is the most detrimental disturbance agent in Europe's forest ecosystems. In recent years, disturbance frequency and severity have been increasing at continental scale, a trend that is expected to continue under future anthropogenic climate change. Disturbance management is thus increasingly important for sustainable stewardship of forests, and requires tools to evaluate the effects of management alternatives and climatic changes on disturbance risk and ecosystem services. We here present a process-based model of wind disturbance impacts on forest ecosystems, integrated into the dynamic landscape simulation model iLand. The model operates at the level of individual trees and simulates wind disturbance events iteratively, i.e., dynamically accounting for changes in forest structure and newly created edges during the course of a storm. Both upwind gap size and local shelter from neighboring trees are considered in this regard, and critical wind speeds for uprooting and stem breakage are distinguished. The simulated disturbance size, pattern, and severity are thus emergent properties of the model. We evaluated the new simulation tool against satellite-derived data on the impact of the storm Gudrun (January 2005) on a 1391 ha forest landscape in south central Sweden. Both the overall damage percentage (observation: 21.7%, simulation: 21.4%) as well as the comparison of spatial damage patterns showed good correspondence between observations and predictions (prediction accuracy: 60.4%) if the full satellite-derived structural and spatial heterogeneity of the landscape was taken into account. Neglecting within-stand heterogeneity in forest conditions, i.e., the state-of-the-art in many stand-level risk models, resulted in a considerable underestimation of simulated damage, supporting the notion that tree-level complexity matters for assessing and modeling large-scale disturbances. A sensitivity analysis further showed that changes in wind speed and soil freezing could have potentially large impacts on disturbed area and patch size. The model presented here is available as open source. It can be used to study the effects of different silvicultural systems and future climates on wind risk, as well as to quantify the impacts of wind disturbance on ecosystem services such as carbon sequestration. It thus contributes to improving our capacity to address changing disturbance regimes in ecosystem management. (C) 2013 Elsevier Ltd. All rights reserved.
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| 8. |
- Blennow, Kristina, et al.
(author)
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Societal impacts of storm damage
- 2013
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In: Living with Storm Damage to Forests. What science can tell us. - 9789525980097 ; :3, s. 70-77
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Book chapter (other academic/artistic)
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| 9. |
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| 10. |
- Matthes, Heidrun, et al.
(author)
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Sensitivity of high-resolution Arctic regional climate model projections to different implementations of land surface processes
- 2012
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In: Climatic Change. - : Springer Science and Business Media LLC. - 0165-0009 .- 1573-1480. ; 111:2, s. 197-214
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Journal article (peer-reviewed)abstract
- This paper discusses the effects of vegetation cover and soil parameters on the climate change projections of a regional climate model over the Arctic domain. Different setups of the land surface model of the regional climate model HIRHAM were realized to analyze differences in the atmospheric circulation caused by (1) the incorporation of freezing/thawing of soil moisture, (2) the consideration of top organic soil horizons typical for the Arctic and (3) a vegetation shift due to a changing climate. The largest direct thermal effect in 2 m air temperature was found for the vegetation shift, which ranged between −1.5 K and 3 K. The inclusion of a freeze/thaw scheme for soil moisture shows equally large sensitivities in spring over cool areas with high soil moisture content. Although the sensitivity signal in 2 m air temperature for the experiments differs in amplitude, all experiments show changes in mean sea level pressure (mslp) and geopotential height (z) throughout the troposphere of similar magnitude (mslp: −2 hPa to 1.5 hPa, z: −15 gpm to 5 gpm). This points to the importance of dynamical feedbacks within the atmosphere-land system. Land and soil processes have a distinct remote influence on large scale atmospheric circulation patterns in addition to their direct, regional effects. The assessment of induced uncertainties due to the changed implementations of land surface processes discussed in this study demonstrates the need to take all those processes for future Arctic climate projections into account, and demonstrates a clear need to include similar implementations in regional and global climate models.
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