| 1. |
- Olafsson, Haraldur
(författare)
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Nordisk kulturhistoria
- 1985
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Ingår i: Kulturminnesvård. - Stockholm : Riksantikvarieämbetet. - 0346-9077. ; :3-4, s. 7-11
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- På Island, där naturen är överväldigande men kulturminnena få, kan det vara svårt att för turister peka ut den historia som mest ryms i sagor och diktning. Haraldur Olafsson, som är docent i kulturantropologi vid Islands universitet, vet hur det går till! Som medlem av isländska riksdagen och verksam i föreningen Norden har han också synpunkter på de särdrag i nordisk kulturhistoria som är viktiga för turismen.
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| 2. |
- Parmhed, Oskar, 1973-
(författare)
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Near surface atmospheric flow over high latitude glaciers
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis various descriptions of the near surface atmospheric flow over a high latitude glacier is used in an effort to increase our understanding of the basic flow dynamics there. Through their contribution to sea-level change, mountain glaciers play a significant role in Earth’s climate system. Properties of the near surface atmospheric flow are important for understanding glacier response to climate change. Here, the near surface atmospheric flow is studied from several perspectives including the effects of both rotation and slope. Rotation is an important aspect of most atmospheric flows and its significance for mesoscale flows have gained recognition over the last years. Similarly, the very stable boundary layer (VSBL) has lately gained interest. Within a VSBL over sloping terrain katabatic flow is known to be usual and persistent. For the present thesis a combination of numerical and simple analytical models as well as observations from the Vatnajökull glacier on Iceland have been used. The models have continuously been compared to available observations. Three different approaches have been used: linear wave modeling, analytic modeling of katabatic flow and of the Ekman layer, and numerical simulations of the katabatic flow using a state of the art mesoscale model. The analytic models for the katabatic flow and the Ekman layer used in this thesis both utilizes the WKB method to allow the eddy diffusivity to vary with height. This considerably improves the results of the models. Among other findings it is concluded that: a large part of the flow can be explained by linear theory, that good results can be obtained for surface energy flux using simple models, and that the very simple analytic models for the katabatic flow and the Ekman layer can perform adequately if the restraint of constant eddy diffusivity is relieved.
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| 3. |
- Renard, Jean-Baptiste, et al.
(författare)
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LOAC : a small aerosol optical counter/sizer for ground-based and balloon measurements of the size distribution and nature of atmospheric particles - Part 1
- 2016
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 9:4, s. 1721-1742
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Tidskriftsartikel (refereegranskat)abstract
- The study of aerosols in the troposphere and in the stratosphere is of major importance both for climate and air quality studies. Among the numerous instruments available, optical aerosol particles counters (OPCs) provide the size distribution in diameter range from about 100 nm to a few tens of mu m. Most of them are very sensitive to the nature of aerosols, and this can result in significant biases in the retrieved size distribution. We describe here a new versatile optical particle/sizer counter named LOAC (Light Optical Aerosol Counter), which is light and compact enough to perform measurements not only at the surface but under all kinds of balloons in the troposphere and in the stratosphere. LOAC is an original OPC performing observations at two scattering angles. The first one is around 12 degrees, and is almost insensitive to the refractive index of the particles; the second one is around 60 degrees and is strongly sensitive to the refractive index of the particles. By combining measurement at the two angles, it is possible to retrieve the size distribution between 0.2 and 100 mu m and to estimate the nature of the dominant particles (droplets, carbonaceous, salts and mineral particles) when the aerosol is relatively homogeneous. This typology is based on calibration charts obtained in the laboratory. The uncertainty for total concentrations measurements is +/- 20% when concentrations are higher than 1 particle cm 3 (for a 10 min integration time). For lower concentrations, the uncertainty is up to about +/- 60% for concentrations smaller than 10 2 particle cm(-3). Also, the uncertainties in size calibration are +/- 0.025 mu m for particles smaller than 0.6 mu m, 5% for particles in the 0.7-2 mu m range, and 10% for particles greater than 2 mu m. The measurement accuracy of sub-micronic particles could be reduced in a strongly turbid case when concentration of particles > 3 mu m exceeds a few particles cm(-3). Several campaigns of cross-comparison of LOAC with other particle counting instruments and remote sensing photometers have been conducted to validate both the size distribution derived by LOAC and the retrieved particle number density. The typology of the aerosols has been validated in well-defined conditions including urban pollution, desert dust episodes, sea spray, fog, and cloud. Comparison with reference aerosol mass monitoring instruments also shows that the LOAC measurements can be successfully converted to mass concentrations.
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| 4. |
- Renard, Jean-Baptiste, et al.
(författare)
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LOAC : a small aerosol optical counter/sizer for ground-based and balloon measurements of the size distribution and nature of atmospheric particles - Part 2
- 2016
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 9:8, s. 3673-3686
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Tidskriftsartikel (refereegranskat)abstract
- In the companion (Part I) paper, we have described and evaluated a new versatile optical particle counter/sizer named LOAC (Light Optical Aerosol Counter), based on scattering measurements at angles of 12 and 60A degrees. That allows for some typology identification of particles (droplets, carbonaceous, salts, and mineral dust) in addition to size-segregated counting in a large diameter range from 0.2aEuro-A mu m up to possibly more than 100aEuro-A mu m depending on sampling conditions (Renard et al., 2016). Its capabilities overpass those of preceding optical particle counters (OPCs) allowing the characterization of all kind of aerosols from submicronic-sized absorbing carbonaceous particles in polluted air to very coarse particles (> 10-20aEuro-A mu m in diameter) in desert dust plumes or fog and clouds. LOAC's light and compact design allows measurements under all kinds of balloons, on-board unmanned aerial vehicles (UAVs) and at ground level. We illustrate here the first LOAC airborne results obtained from a UAV and a variety of scientific balloons. The UAV was deployed in a peri-urban environment near Bordeaux in France. Balloon operations include (i) tethered balloons deployed in urban environments in Vienna (Austria) and Paris (France), (ii) pressurized balloons drifting in the lower troposphere over the western Mediterranean (during the Chemistry-Aerosol Mediterranean Experiment - ChArMEx campaigns), (iii) meteorological sounding balloons launched in the western Mediterranean region (ChArMEx) and from Aire-sur-l'Adour in south-western France (VOLTAIRE-LOAC campaign). More focus is put on measurements performed in the Mediterranean during (ChArMEx) and especially during African dust transport events to illustrate the original capability of balloon-borne LOAC to monitor in situ coarse mineral dust particles. In particular, LOAC has detected unexpected large particles in desert sand plumes.
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| 5. |
- Roegnvaldsson, Olafur, et al.
(författare)
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Numerical simulations of precipitation in the complex terrain of Iceland - Comparison with glaciological and hydrological data
- 2007
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Ingår i: Meteorologische Zeitschrift. - : Schweizerbart. - 1610-1227 .- 0941-2948. ; 16:1, s. 71-85
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric flow over Iceland has been simulated for the period September 1987 through June 2003, using the PSU/NCAR MM5 mesoscale model driven by initial and boundary data from the European Centre for Medium-range Weather Forecasts (ECMWF). The simulated precipitation is compared with two types of indirect precipitation observations. Firstly, snow accumulation on two large ice caps in SE-Iceland and on two large glaciers in central Iceland. Secondly, model output is used as input to the WaSiM-ETH hydrological model to calculate and compare the runoff with observed runoff from six watersheds in Iceland for the water years 1987-2002. Model precipitation compares favourably with both types of validation data. The seasonal and inter-annual variability of precipitation is investigated at low as well as high altitudes. The simulations reveal a negative trend in the winter precipitation in W-Iceland, but a positive trend in the ratio of lowland precipitation to mountain precipitation in E-Iceland. There is in general a substantial inter-annual variability in the ratio of lowland precipitation to precipitation in the mountains, especially in E-Iceland, emphasizing the limitation of precipitation observations in the lowlands as a proxy for precipitation in the mountains. In order to assess the impact of orography on the precipitation climate of Iceland, precipitation is simulated with flat Iceland and compared to a simulation with true orography. It is found that the mountains contribute to a total increase of precipitation in Iceland of the order of 40 %.
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| 6. |
- Rousta, Iman, et al.
(författare)
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The 2000–2017 drought risk assessment of the western and southwestern basins in Iran
- 2020
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Ingår i: Modeling Earth Systems and Environment. - : Springer Science and Business Media LLC. - 2363-6203 .- 2363-6211. ; 6:2, s. 1201-1221
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Tidskriftsartikel (refereegranskat)abstract
- The study investigates the relationship between drought and vegetation variations in three main basins of western and southwestern of Iran, using the comprehensive approach of time-series analysis, Standardized Precipitation Index (SPI), and anomaly calculation. A total of 30 ground stations’ daily meteorological data and the MODIS 16-day composite NDVI products (2000–2017) were used in this case. The results showed that in the Great Karoun River (GKRW) and Karkheh River (KRW) sub-regions, the NDVI decreased slightly over the study period. Simultaneously, in the West Marginal (WMW) sub-region the NDVI slightly increased somewhat. Overall, the NDVI in the whole study area presented an insignificant decrease. Also the results found that there is a significant relationship (p < 0.02) between the NDVI (0.3–0.7) with spring drought and between NDVI (0.2–0.3) with fall drought (p < 0.01). There is a marginally significant relationship (R = 0.43, p = 0.07) between NDVI (0.3–0.4) with fall drought and a relatively high, but insignificant relationship between NDVI (0.7–0.8) with spring drought (R = 0.41, p = 0.09). Low temperature can play an important role in determining the relationship between SPI and NDVI, which evidenced that it can trade-off the effect of a very wet year. As well as a year with very wet condition can affect the NDVI of the coming years. Since summer is hot season in the study area and most of the vegetation consists of shrubs and grasslands, of which the NDVI ranges between 0.2 and 0.4, the vegetation cover can be significantly affected by a wet summer with abundant precipitation.
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