| 1. |
- Ferritsius, Rita, et al.
(författare)
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Water Absorption and Wet Strength in Hot-pressed Paper
- 2022
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Ingår i: Proceedings of the International Mechanical Pulping Conference. ; , s. 168-170
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Effects of hot-pressing on anisotropic sheets with less good formation was here investigated. The main objective was to study water absorption capacity in relation to the wet strength of hot-pressed paper. A pilot paper machine was used to produce papers from TMP and CTMP furnishes. The results indicate that it is not only the high dry content after wetting that contributes to the high wet strength of the paper hot-pressed at 200C. If it is required to have a paper with both low absorption of water and high wet strength, hot-pressing at 200C seems to be more desirable than using con-ventional drying and adding wet chemical agents to the furnish.
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| 2. |
- Jansson, Ulf, 1966-, et al.
(författare)
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Svenska forskares syn på hantering av rumsliga data - enkätundersökning 2021
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A survey, aimed at Swedish researchers in the field of spatial data, was conducted in 2021. 113 individuals responded to the questionnaire, which gives us insight into how researchers in the field view; sharing of data, how they work with data, which metadata they think are central and what support they ask for in order to be able to handle spatial data.According to the survey a majority of the researchers share and use data shared by others in their research. Central metadata that is emphasized are coordinate systems, projections, time of the information, data capture, data content and author. The question of how to make data available is very varied among the respondents. The questionnaire responses contain a wide range of individual solutions to make the information available. A majority of researchers believe that the work with data management and accessibility has increased over the past 5 years. As an obstacle to working more with this is time, but there are also other obstacles. The researchers are seeking additional support that can be summarized as: support, technical guidance, storage, information, time and money.
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| 3. |
- Lashgari, Katarina, 1974-, et al.
(författare)
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Evaluation of simulated responses to climate forcings : a flexible statistical framework using confirmatory factor analysis and structural equation modelling – Part 1: Theory
- 2022
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Ingår i: Advances in Statistical Climatology, Meteorology and Oceanography. - : Copernicus GmbH. - 2364-3587. ; 8:2, s. 225-248
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Tidskriftsartikel (refereegranskat)abstract
- Evaluation of climate model simulations is a crucial task in climate research. Here, a new statistical framework is proposed for evaluation of simulated temperature responses to climate forcings against temperature reconstructions derived from climate proxy data for the last millennium. The framework includes two types of statistical models, each of which is based on the concept of latent (unobservable) variables: confirmatory factor analysis (CFA) models and structural equation modelling (SEM) models. Each statistical model presented is developed for use with data from a single region, which can be of any size. The ideas behind the framework arose partly from a statistical model used in many detection and attribution (D&A) studies. Focusing on climatological characteristics of five specific forcings of natural and anthropogenic origin, the present work theoretically motivates an extension of the statistical model used in D&A studies to CFA and SEM models, which allow, for example, for non-climatic noise in observational data without assuming the additivity of the forcing effects. The application of the ideas of CFA is exemplified in a small numerical study, whose aim was to check the assumptions typically placed on ensembles of climate model simulations when constructing mean sequences. The result of this study indicated that some ensembles for some regions may not satisfy the assumptions in question.
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| 4. |
- Lashgari, Katarina, 1974-, et al.
(författare)
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Evaluation of simulated responses to climate forcings : a flexible statistical framework using confirmatory factor analysis and structural equation modelling – Part 2: Numerical experiment
- 2022
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Ingår i: Advances in Statistical Climatology, Meteorology and Oceanography. - : Copernicus GmbH. - 2364-3587. ; 8:2, s. 249-271
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Tidskriftsartikel (refereegranskat)abstract
- The performance of a new statistical framework, developed for the evaluation of simulated temperature responses to climate forcings against temperature reconstructions derived from climate proxy data for the last millennium, is evaluated in a so-called pseudo-proxy experiment, where the true unobservable temperature is replaced with output data from a selected simulation with a climate model. Being an extension of the statistical model used in many detection and attribution (D&A) studies, the framework under study involves two main types of statistical models, each of which is based on the concept of latent (unobservable) variables: confirmatory factor analysis (CFA) models and structural equation modelling (SEM) models. Within the present pseudo-proxy experiment, each statistical model was fitted to seven continental-scale regional data sets. In addition, their performance for each defined region was compared to the performance of the corresponding statistical model used in D&A studies. The results of this experiment indicated that the SEM specification is the most appropriate one for describing the underlying latent structure of the simulated temperature data in question. The conclusions of the experiment have been confirmed in a cross-validation study, presuming the availability of several simulation data sets within each studied region. Since the experiment is performed only for zero noise level in the pseudo-proxy data, all statistical models, chosen as final regional models, await further investigation to thoroughly test their performance for realistic levels of added noise, similar to what is found in real proxy data for past temperature variations.
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| 5. |
- Rocha, Eva, 1985-
(författare)
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Trees and the environment : Possibilities and challenges in tree-ring research across spatial and temporal scales based on case studies in Sweden.
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The need to understand and quantify the magnitude and frequency of past and current environmental changes increased the demand for high-resolution proxy data across spatial and temporal scales. Due to their long lifespan and global distribution, trees provide a unique and continuous record of environmental variability. More specifically, trees can be used as proxies of environmental conditions since their physical and chemical characteristics reflect the conditions in which they have been growing.Focused on case studies from Sweden, this thesis presents a sample of applications where different tree-ring parameters were combined and compared with meteorological records, historical documents and soil profiles to provide information on natural and human-induced changes in the environment. Tree-ring width (TRW) measurements from living trees and subfossil wood from Jämtland, west-central Sweden, were combined to develop a two-millennia-long chronology from Norway spruce, a species that has been traditionally overlooked in dendroclimatic assessments in the region. This record enabled delivery of new perspectives on past regional climate variability and represents an important achievement for inter-and intraregional proxy analyses.A unique maximum latewood density (MXD) chronology was developed from trees growing in drought-prone environments in the Stockholm Archipelago and used to reconstruct past precipitation variability for east-central Sweden. The results showed that MXD provides a stronger climate–growth relationship than TRW and allows a broader target seasonal average (May - July) to be reconstructed.The resolution provided by ring width and density measurements is insufficient to understand growth responses to environmental stress at intra-annual scales. A pilot study using stem radial increment data retrieved from several dendrometers placed in the Stockholm area provided important insights into daily and seasonal growth dynamics in response to site-specific conditions. The main results show that short-term events, such as droughts, can significantly impact trees’ climate–growth relationship and their vegetative period.Annually resolved time-series of wood elemental composition were used to investigate environmental contamination at a glassworks site in southern Sweden. The dendrochemical signals showed large variability both between and within the species in analysis, suggesting a strong control of the soil properties and species-specific uptake on trees’ elemental composition.The findings presented in this thesis show that tree rings can be a highly suitable proxy to understand past and ongoing environmental changes and the link between ecosystems, climate and human activities. Overall, regionally developed networks of tree-ring data elucidated processes behind large-scale climate dynamics and provided new insights on past regional climate variability. In addition, locally-focused studies revealed fine-grained variations and the challenges of understanding the numerous physiological interactions between individual trees and the surrounding environment.
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| 6. |
- Wilcke, Renate Anna Irma, et al.
(författare)
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The extremely warm summer of 2018 in Sweden - set in a historical context
- 2020
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Ingår i: Earth System Dynamics. - : Copernicus GmbH. - 2190-4979 .- 2190-4987. ; 11:4, s. 1107-1121
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Tidskriftsartikel (refereegranskat)abstract
- Two long-lasting high-pressure systems in summer 2018 led to persisting heatwaves over Scandinavia and other parts of Europe and an extended summer period with devastating impacts on agriculture, infrastructure, and human life. We use five climate model ensembles and the unique 263-year-long Stockholm temperature time series along with a composite 150-year-long time series for the whole of Sweden to set the latest heatwave in the summer of 2018 into historical perspective. With 263 years of data, we are able to grasp the pre-industrial period well and see a clear upward trend in temperature as well as upward trends in five heatwave indicators. With five climate model ensembles providing 20 580 simulated summers representing the latest 70 years, we analyse the likelihood of such a heat event and how unusual the 2018 Swedish summer actually was. We find that conditions such as those observed in summer 2018 are present in all climate model ensembles. An exception is the monthly mean temperature for May for which 2018 was warmer than any member in one of the five climate model ensembles. However, even if the ensembles generally contain individual years like 2018, the comparison shows that such conditions are rare. For the indices assessed here, anomalies such as those observed in 2018 occur in a maximum of 5 % of the ensemble members, sometimes even in less than 1 %. For all of the indices evaluated, we find that the probability of a summer such as that in 2018 has increased from relatively low values in the pre-industrial era (1861-1890, one ensemble) and the recent past (1951-1980, all five ensembles) to higher values in the most recent decades (1989-2018). An implication of this is that anthropogenic climate change has strongly increased the probability of a warm summer, such as the one observed 2018, occurring in Sweden. Despite this, we still find such summers in the pre-industrial climate in our simulations, albeit with a lower probability.
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| 7. |
- Brönnimann, Stefan, et al.
(författare)
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Unlocking Pre-1850 Instrumental Meteorological Records : A Global Inventory
- 2019
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Ingår i: Bulletin of The American Meteorological Society - (BAMS). - 0003-0007 .- 1520-0477. ; 100:12, s. ES389-ES413
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Tidskriftsartikel (refereegranskat)abstract
- Instrumental meteorological measurements from periods prior to the start of national weather services are designated early instrumental data. They have played an important role in climate research as they allow daily to decadal variability and changes of temperature, pressure, and precipitation, including extremes, to be addressed. Early instrumental data can also help place twenty-first century climatic changes into a historical context such as defining preindustrial climate and its variability. Until recently, the focus was on long, high-quality series, while the large number of shorter series (which together also cover long periods) received little to no attention. The shift in climate and climate impact research from mean climate characteristics toward weather variability and extremes, as well as the success of historical reanalyses that make use of short series, generates a need for locating and exploring further early instrumental measurements. However, information on early instrumental series has never been electronically compiled on a global scale. Here we attempt a worldwide compilation of metadata on early instrumental meteorological records prior to 1850 (1890 for Africa and the Arctic). Our global inventory comprises information on several thousand records, about half of which have not yet been digitized (not even as monthly means), and only approximately 20% of which have made it to global repositories. The inventory will help to prioritize data rescue efforts and can be used to analyze the potential feasibility of historical weather data products. The inventory will be maintained as a living document and is a first, critical, step toward the systematic rescue and reevaluation of these highly valuable early records. Additions to the inventory are welcome.
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| 8. |
- Charpentier Ljungqvist, Fredrik, et al.
(författare)
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Centennial-Scale Temperature Change in Last Millennium Simulations and Proxy-Based Reconstructions
- 2019
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Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 32:9, s. 2441-2482
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Tidskriftsartikel (refereegranskat)abstract
- Systematic comparisons of proxy-based reconstructions and climate model simulations of past millennium temperature variability offer insights into climate sensitivity and feedback mechanisms, besides allowing model evaluation independently from the period covered by instrumental data. Such simulation-reconstruction comparisons can help to distinguish more skillful models from less skillful ones, which may subsequently help to develop more reliable future projections. This study evaluates the low-frequency simulation-reconstruction agreement within the past millennium through assessing the amplitude of temperature change between the Medieval Climate Anomaly (here, 950-1250 CE) and the Little Ice Age (here, 1450-1850 CE) in PMIP3 model simulations compared to proxy-based local and continental-scale reconstructions. The simulations consistently show a smaller temperature change than the reconstructions for most regions in the Northern Hemisphere, but not in the Southern Hemisphere, as well as a partly different spatial pattern. A cost function analysis assesses how well the various simulations agree with reconstructions. Disregarding spatial correlation, significant differences are seen in the agreement with the local temperature reconstructions between groups of models, but insignificant differences are noted when compared to continental-scale reconstructions. This result points toward a limited possibility to rank models by means of their low-frequency temperature variability alone. The systematically lower amplitude of simulated versus reconstructed temperature change indicates either too-small simulated internal variability or that the analyzed models lack some critical forcing or have missing or too-weak feedback mechanisms. We hypothesize that too-cold initial ocean conditions in the models-in combination with too-weak internal variability and slow feedbacks over longer time scales-could account for much of the simulation-reconstruction disagreement.
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| 9. |
- Fetisova, Ekaterina, 1974-
(författare)
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Towards a flexible statistical modelling by latent factors for evaluation of simulated responses to climate forcings
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, using the principles of confirmatory factor analysis (CFA) and the cause-effect concept associated with structural equation modelling (SEM), a new flexible statistical framework for evaluation of climate model simulations against observational data is suggested. The design of the framework also makes it possible to investigate the magnitude of the influence of different forcings on the temperature as well as to investigate a general causal latent structure of temperature data. In terms of the questions of interest, the framework suggested here can be viewed as a natural extension of the statistical approach of 'optimal fingerprinting', employed in many Detection and Attribution (D&A) studies. Its flexibility means that it can be applied under different circumstances concerning such aspects as the availability of simulated data, the number of forcings in question, the climate-relevant properties of these forcings, and the properties of the climate model under study, in particular, those concerning the reconstructions of forcings and their implementation. It should also be added that although the framework involves the near-surface temperature as a climate variable of interest and focuses on the time period covering approximately the last millennium prior to the industrialisation period, the statistical models, included in the framework, can in principle be generalised to any period in the geological past as soon as simulations and proxy data on any continuous climate variable are available. Within the confines of this thesis, performance of some CFA- and SEM-models is evaluated in pseudo-proxy experiments, in which the true unobservable temperature series is replaced by temperature data from a selected climate model simulation. The results indicated that depending on the climate model and the region under consideration, the underlying latent structure of temperature data can be of varying complexity, thereby rendering our statistical framework, serving as a basis for a wide range of CFA- and SEM-models, a powerful and flexible tool. Thanks to these properties, its application ultimately may contribute to an increased confidence in the conclusions about the ability of the climate model in question to simulate observed climate changes.
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| 10. |
- Jungclaus, Johann H., et al.
(författare)
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The PMIP4 contribution to CMIP6 - Part 3 : The last millennium, scientific objective, and experimental design for the PMIP4 past1000 simulations
- 2017
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Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 10:11, s. 4005-4033
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Tidskriftsartikel (refereegranskat)abstract
- The pre-industrial millennium is among the periods selected by the Paleoclimate Model Intercomparison Project (PMIP) for experiments contributing to the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and the fourth phase of the PMIP (PMIP4). The past1000 transient simulations serve to investigate the response to (mainly) natural forcing under background conditions not too different from today, and to discriminate between forced and internally generated variability on interannual to centennial timescales. This paper describes the motivation and the experimental set-ups for the PMIP4-CMIP6 past1000 simulations, and discusses the forcing agents orbital, solar, volcanic, and land use/land cover changes, and variations in greenhouse gas concentrations. The past1000 simulations covering the pre-industrial millennium from 850 Common Era (CE) to 1849 CE have to be complemented by historical simulations (1850 to 2014 CE) following the CMIP6 protocol. The external forcings for the past1000 experiments have been adapted to provide a seamless transition across these time periods. Protocols for the past1000 simulations have been divided into three tiers. A default forcing data set has been defined for the Tier 1 (the CMIP6 past1000) experiment. However, the PMIP community has maintained the flexibility to conduct coordinated sensitivity experiments to explore uncertainty in forcing reconstructions as well as parameter uncertainty in dedicated Tier 2 simulations. Additional experiments (Tier 3) are defined to foster collaborative model experiments focusing on the early instrumental period and to extend the temporal range and the scope of the simulations. This paper outlines current and future research foci and common analyses for collaborative work between the PMIP and the observational communities (reconstructions, instrumental data).
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