Ole Einar Tveito

Classifications of Atmospheric Circulation Patterns

We review recent advances in classifications of circulation patterns as a specific research area within synoptic climatology. The review starts with a general description of goals of classification and the historical development in the field. We put circulation classifications into a broader context within climatology and systematize the varied methodologies and approaches. We characterize three basic groups of classifications: subjective (also called manual), mixed (hybrid), and objective (computer‐assisted, automated). The roles of cluster analysis and principal component analysis in the classification process are clarified. Several recent methodological developments in circulation classifications are identified and briefly described: the introduction of nonlinear methods, objectivization of subjective catalogs, efforts to optimize classifications, the need for intercomparisons of classifications, and the progress toward an optimum, if possible unified, classification method. Among the recent tendencies in the applications of circulation classifications, we mention a more extensive use in climate studies, both of past, present, and future climates, innovative applications in the ensemble forecasting, increasing variety of synoptic–climatological investigations, and steps above from the troposphere. After introducing the international activity within the field of circulation classifications, the COST733 Action, we briefly describe outputs of the inventory of classifications in Europe, which was carried out within the Action. Approaches to the evaluation of classifications and their mutual comparisons are also reviewed. A considerable part of the review is devoted to three examples of applications of circulation classifications: in historical climatology, in analyses of recent climate variations, and in analyses of outputs from global climate models.

A GIS-based agro-ecological decision system based on gridded climatology

The introduction of GIS has opened up new possibilities in combining different sources of geographical information. In Norway, an agro-meteorological decision system is under development which combines gridded weather information with soil and crop development data. The system is based on a daily scale soil moisture model driven by meteorological inputs. Weather information is based on in-situ observations, and spatial interpolation schemes are used to establish fine-mesh grids of these variables over the model domain. These interpolation schemes take advantage of geographical co-variables such as terrain information. The soil moisture model is used to estimate the soil water content, which is the determinant of soil suitability for tillage and sowing. The system also includes a phenological model for identification of suitable days when combine-harvesting of cereals can be satisfactorily undertaken. Spatial interpolation of the meteorological elements is based upon all available in-situ observations. The different elements are interpolated by different interpolation techniques. Snow depth, cloud cover, relative humidity and wind are in this first version, interpolated by using inverse distance weighting. Precipitation is determined by triangulation with elevation adjustment. Temperature is interpolated by using a residual kriging approach that includes five independent predictors in the trend equation. Evaporation is estimated by using the Penman2 formula based on the estimates of the meteorological elements. This approach is a good demonstration of the benefits of applying GIS and distributed geo-data in cross-disciplinary situations. The application is a valuable contribution to soil capability assessments. Copyright

Mapping temperatures in Norway applying terrain information, geostatistics and GIS

The spatial variation in monthly temperature normals (1961-90) from southern Norway was studied. Linear regression as well as an approach combining a deterministic and a geostatistical model were applied (residual kriging). The deterministic component describes the large-scale trend in the temperature, and in this study is defined as the vertical temperature gradient. The spatial variability caused by differences in elevation is removed by reducing the temperatures to sea level. The resulting temperature fields are more suited for spatial statistical analysis. These temperatures are closer to fulfilling the assumptions most statistical interpolation methods require, i.e. stationarity and isotropy. The reduced temperatures were interpolated applying kriging. It is shown that residual kriging gives better estimates than kriging on station level temperatures. Residual kriging is also more credible than the linear regression approach, which regionally gives large estimation errors.

THE EFFECT OF RADIATION SCREENS ON NORDIC TIME SERIES OF MEAN TEMPERATURE

A short survey of the historical development of temperature radiation screens is given based upon research in the archives of the Nordic meteorological institutes. In the middle of the nineteenth century most thermometer stands were open shelters, free-standing or fastened to a window or wall. Most of these were soon replaced by wall or window screens, i.e. small wooden or metal cages. Large free-standing screens were also introduced in the nineteenth century, but it took to the 1980s before they had replaced the wall screens completely in all Nordic countries. During recent years, small cylindrical screens suitable for automatic weather stations have been introduced. At some stations they have replaced the ordinary free-standing screen as part of a gradual move towards automation. The first free-standing screens used in the Nordic countries were single louvred. They were later improved by double louvres. Compared with observations from ventilated thermometers the monthly mean temperatures in the single louvred screens were 02‐04C higher during May‐August, whereas in the double louvred screens the temperatures were unbiased. Unless the series are adjusted, this improvement may lead to inhomogeneities in long climatic time series. The change from wall screen to free-standing screen also involved a relocation from the microclimatic influence of a house to a location free from obstacles. Tests to evaluate the effect of relocation by parallel measurements yielded variable results. However, the bulk of the tests showed no effect of the relocation in winter, whereas in summer the wall screen tended to be slightly warmer (00‐03C) than the double louvred screen. At two Norwegian sites situated on steep valley slopes, the wall screen was ca .0 5C colder in midwinter. The free-standing Swedish shelter, which was used at some stations up to 1960, seems to have been overheated in spring and summer (maximum overheating of about 04C in early summer). The new screen for automatic sensors appears to be unbiased compared with the ordinary free-standing screen concerning monthly mean temperature. # 1997 Royal Meteorological Society. Int. J. Climatol., 17, 1667‐1681

The use of geographic information systems in climatology and meteorology, COST719

No permission to reproduce or utilise the contents of this book by any means is necessary, other than in the case of images, diagrams or other material from other copyright holders. In such cases permission of the copyright holders is required ; European Co-operation in the field of Scientific and Technical Research.

The use of Geographic Information Systems in climatology and meteorology: COST 719

The COST Action 719 started in 2001 and presently 20 European countries are participating. The main objectives of the Action are to establish interfaces between GIS and meteorological data, assess the availability, contents and accessibility of meteorological and climatological data sets and encourage and foster European co-operation. The tasks are carried out within three working groups concentrated on issues such as data access and availability, methods of spatial interpolation and developing recommendations for standardised GIS applications. The applications that have been adopted mainly focus on three parameters, i.e. precipitation, temperature and energy balance for which three demonstration projects have been formulated. It is expected that the Action will result in recommendations for better and more cost-effective production of state-of-the-art meteorological and climatological information. Also an improvement of the co-operation between European countries in the application of GIS in the field of meteorology, climatology and environmental sciences should be achieved together with better-trained personnel within the operational and scientific divisions of national meteorological services. Additionally, the development of a visualisation system for climate data sets for internet applications is under preparation. This paper provides information concerning the work in progress on the demonstration projects made within COST 719.

CO2 emissions from cropland in Norway estimated by IPCC default and Tier 2 methods

Monitoring changes in soil organic carbon is linked not only to atmospheric CO2 dynamics, but also to the sustainability of agricultural systems, maintaining food security, reducing water pollution and soil erosion. In accordance with the Intergovernmental Panel on Climate Change (IPCC) methodology, a Tier 2 method for estimating CO2 emissions from cropland on mineral soils in Norway was developed and the results were compared with those of the default Tier 1 method. A soil C balance model, the introductory carbon balance model (ICBM) was used to calculate country-specific soil organic carbon (SOC) stock change factors for cropland management systems for the Tier 2 method. Annual CO2 emissions from cropland management were substantially higher when estimated by the default Tier 1 method (313 Gg CO2 per year) compared with Tier 2 (149 Gg CO2 per year). The differences between the results were mainly due to the default Tier 1 stock change factors for crop rotations without manure application, which led to greater CO2 emissions compared with the ICBM-based factors. Reduction in livestock numbers and reduced manure application to arable land were the main causes of net emissions from soil for both the methods. Policies to stabilize or increase livestock numbers could reduce soil CO2 emissions, although the impacts on other agricultural emissions sources, particularly methane from livestock, would need to be considered.

Novel Hydraulic Vulnerability Proxies for a Boreal Conifer Species Reveal That Opportunists May Have Lower Survival Prospects under Extreme Climatic Events

Top dieback in 40–60 years old forest stands of Norway spruce [Picea abies (L.) Karst.] in southern Norway is supposed to be associated with climatic extremes. Our intention was to learn more about the processes related to top dieback and in particular about the plasticity of possible predisposing factors. We aimed at (i) developing proxies for P50 based on anatomical data assessed by SilviScan technology and (ii) testing these proxies for their plasticity regarding climate, in order to (iii) analyze annual variations of hydraulic proxies of healthy looking trees and trees with top dieback upon their impact on tree survival. At two sites we selected 10 tree pairs, i.e., one healthy looking tree and one tree with visual signs of dieback such as dry tops, needle shortening and needle yellowing (n = 40 trees). Vulnerability to cavitation (P50) of the main trunk was assessed in a selected sample set (n = 19) and we thereafter applied SilviScan technology to measure cell dimensions (lumen (b) and cell wall thickness (t)) in these specimen and in all 40 trees in tree rings formed between 1990 and 2010. In a first analysis step, we searched for anatomical proxies for P50. The set of potential proxies included hydraulic lumen diameters and wall reinforcement parameters based on mean, radial, and tangential tracheid diameters. The conduit wall reinforcement based on tangential hydraulic lumen diameters ((t/bht)2) was the best estimate for P50. It was thus possible to relate climatic extremes to the potential vulnerability of single annual rings. Trees with top dieback had significantly lower (t/bht)2 and wider tangential (hydraulic) lumen diameters some years before a period of water deficit (2005–2006). Radial (hydraulic) lumen diameters showed however no significant differences between both tree groups. (t/bht)2 was influenced by annual climate variability; strongest correlations were found with precipitation in September of the previous growing season: high precipitation in previous September resulted in more vulnerable annual rings in the next season. The results are discussed with respect to an “opportunistic behavior” and genetic predisposition to drought sensitivity.

Observed Hydrological Cycle

The transition between the liquid and solid phase affects all processes in the Arctic. The solid phase is a special challenge to the instruments and the scientists who develop new instruments or analyze, correct, and interpret the observed data.

Farm specific natural resource base data for estimating greenhouse gas emissions

Abstract Models for an holistic analysis of a farms greenhouse gas (GHG) emissions are available, e.g. HolosNor. They require access to a farms management data and its soil and climatic conditions. The objective of this investigation was to demonstrate how available soil and climatic data can be used to provide the required inputs of a farms natural resource base. Soil type recordings from six municipalities representing main agroclimatic zones of Norway were used. By means of a soil moisture model a combined index of soil moisture and temperature was estimated for use in a carbon balance model, also taking crop species into account. Water filled pore space (Wfps) to saturation and soil temperature were estimated for calculation of emission of nitrous oxide. Input variables for calculation of GHG emissions varied considerably among municipalities and among farms therein.