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| 2. |
- Lundin, Lars-Christer, et al.
(författare)
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Continuous long-term measurements of soil-plant-atmosphere variables at a forest site
- 1999
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Ingår i: Agricultural and Forest Meteorology. - 0168-1923 .- 1873-2240. ; 98-99, s. 53-73
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Tidskriftsartikel (refereegranskat)abstract
- It is a major challenge in modem science to decrease the uncertainty in predictions of global climate change. One of the largest uncertainties in present-day global climate models resides with the understanding of processes in the soil-vegetation-atmosphere-transfer (SVAT) system. Continuous, long-term data are needed in order to correctly quantify balances of water, energy and CO2 in this system and to correctly model it. It is the objective of this paper to demonstrate how a combined system of existing sensor, computer, and network technologies could be set up to provide continuous and reliable long-term SVAT-process data from a forested site under almost all environmental conditions. The Central Tower Site (CTS) system was set up in 1993-1994 in a 25 m high boreal forest growing on a highly heterogeneous till soil with a high content of stones and blocks. It has successfully monitored relevant states and fluxes in the system, such as atmospheric fluxes of momentum, heat, water vapour and CO2, atmospheric profiles of temperature, water vapour, CO2, short-and long-wave radiation, heat storage in soil and trees, sap-dow and a variety of ecophysiological properties, soil-water contents and tensions, and groundwater levels, rainfall and throughfall. System uptime has been more than 90% for most of its components during the first 5 years of operation. Results from the first 5 years of operation include e.g., budgets for energy, water and CO2, information on important but rarely occurring events such as evaporation from snow-covered canopies, and reactions of the forest to extreme drought. The carbon budget shows that the forest may be a sink of carbon although it is still growing. The completeness of the data has made it possible to test the internal consistency of SVAT models. The pioneering set-up at the CTS has been adopted by a large number of SVAT-monitoring sites around the world. Questions concerning tower maintenance, long-term calibration plans, maintenance of sensors and data-collection system, and continuous development of the computer network to keep it up to date are, however, only partly of interest as a research project in itself. It is thus difficult to get it funded from usual research-funding agencies. The full value of data generated by the CTS system can best be appreciated after a decade or more of continuous operation. Main uses of the data would be to evaluate how SVAT models handle the natural variability of climate conditions, quantification of water. carbon and energy budgets during various weather conditions, rind development of new parameterisation schemes in global and regional climate models.
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| 3. |
- Axelsson, B.O.M., et al.
(författare)
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Studies of the main cutting force at and near a cutting edge
- 1993
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Ingår i: European Journal of Wood and Wood Products. - 0018-3768 .- 1436-736X. ; 51:1, s. 43-48
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Tidskriftsartikel (refereegranskat)abstract
- The present work is a study of how various parameters affect the cutting forces at, and near a cutting edge when cutting wood at full speed and with all cutting edges of the tool. Statistical methods from experimental results are used to develop a model
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| 4. |
- Gustafsson, D., et al.
(författare)
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Multi-criteria parameterisation of a numerical forest snow processes model : analysis of parameter uncertainty and governing processes
- 2006
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Ingår i: Geophysical Research Abstracts. - : European Geosciences Union (EGU).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Forest snow processes such as snow interception evaporation and the influence of the canopy on snow cover melt are important for the land surface water and heat balance. Difficulties to model snow interception are due to both limitation in the understanding of the governing processes and in parameter estimations. In this study we parameterise a numerical simulation model (Alpine3D) using multiple calibration variables - snow water equivalent, snowmelt, throughfall, and runoff - through a Monte-Carlo procedure, which enables parameter uncertainty estimations and identification of the sensitivity in the model to different processes. The analysis is based on a data from a sub-alpine spruce forest in Alptal, Switzerland. Results show how the multi-criteria approach is able to reduce the number of parameter combinations that fulfil the critera. Further more, it is shown that parameters governing the turbulent exchange from the canopy and the snow cover were most important for the simulation of the snow cover evolution, whereas the runoff and throughfall was more sensitive to direct throughfall and interception capacity parameterisations.
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| 5. |
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| 6. |
- Kløve, Bjørn, et al.
(författare)
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Groundwater surface water interaction in GDE
- 2012
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Rapport (populärvet., debatt m.m.)abstract
- This report reviews and discussed the interaction of groundwaterin GDEs. The report presents and integrates past and new results.Different methods used to measure groundwater interaction withecosystems are presented. Various GENESIS case studies acrossEurope to demonstrate the variable and complex role ofgroundwater in GDEs. The basis for developing conceptual for GDEsis presented. Various methods to model GDEs are discussed.
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| 7. |
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| 8. |
- Lundberg, Angela, et al.
(författare)
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New approach to the measurement of interception evaporation
- 1997
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Ingår i: Journal of Atmospheric and Oceanic Technology. - 0739-0572 .- 1520-0426. ; 14:5, s. 1023-1035
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Tidskriftsartikel (refereegranskat)abstract
- Evaporation of water intercepted by vegetation represents an important (sometimes major) part of evapotranspiration in temperate regions. Interception evaporation is an important process where insufficient measurement techniques hamper progress in knowledge and modeling. An ideal technique to study the interception evaporation process should monitor intercepted mass (and its vertical distribution) and interception loss with high accuracy (0.1 mm) and time resolution (1 min), and give correct area estimates. The method should be inexpensive, require minor supervision during extended periods, and work in dense forests. Net precipitation techniques, in which interception evaporation is determined from the difference between gross precipitation (measured with funnels) and throughfall (measured with funnels, troughs, or plastic sheet net-rainfall gauges) fulfill many of the requirements but usually have a too-low accuracy and time resolution for process studies. Precipitation measurements are normally affected by distortion of the wind field around gauges as well as by adhesive and evaporative losses. Throughfall measurements with precipitation funnels, troughs, or plastic sheet net-rainfall gauges, manually emptied or combined with tipping buckets, usually have too-low accuracy and time resolution for process studies and are impaired by adhesive losses. A new loadcell-based system to determine interception evaporation from gross and net precipitation is presented. A weighing gauge with minimal wind loss is used for precipitation, and weighing troughs are used for throughfall measurements. The weighing troughs minimize adhesive-loss errors and react instantaneously. Preliminary results with the method confirm that it can be used for process studies with a high accuracy (0.1 mm) and a high time resolution (1 min).
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| 9. |
- Lundberg, Angela, et al.
(författare)
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Optical Precipitation Gauge : Determination of Precipitation Type and Intensity by Ligth Attenuation Technique
- 1994
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Ingår i: Nordic Hydrology. - : IWA Publishing. - 0029-1277 .- 1996-9694. ; 25:5, s. 359-370
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Tidskriftsartikel (refereegranskat)abstract
- There exists a great need for automatic precipitation gauges for effective road maintenance during the winter period. These gauges should be inexpensive, not require mains supply, need little attendance, give information about presence of precipitation and determine type (snow, rain or sleet) while there is no need for high accuracy of the precipitation intensity. Light attenuation precipitation sensors (optical gauges) fulfil several of these requirements and are used in the Swedish National Road Administration Road Weather System. The optical gauges measure the time it takes of particles of snow etc. to pass (attenuate) a light beam and relate this time to precipitation type and intensity. The rain precipitation mass is approximately proportional to the accumulated attenuation time. To investigate whether or not optical gauges could also be used for solid precipitation, the precipitation mass for snow, rain and sleet was measured with a reference gauge and compared to the attenuation time. The passage time of individual hydrometeorologic particles (snow, rain and sleet) was compared with precipitation type and wind speed. Air temperature could be used as a rough guide a distinguish three precipitation categories for the following temperatures: rain (> +2-degrees-C), sleet (0 to +2-degrees-C) and snow (less-than-or-equal-to 0-degree-C). At low wind speeds (< 3 m/s) the passage time of individual particles could be used to distinguish between rain and snow. The accumulated attenuation time for the same precipitation mass was approximately 25 and 5 times greater for snow and sleet respectively compared to rain. With the attenuation time for the snow-fall corrected for wind influence the quotient between the attenuation time for snow and rain is decreased from approximately 25 to approximately 12 times.
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