Koszalka I.,University of Oslo |
LaCasce J.H.,University of Oslo |
Andersson M.,University of Bergen |
Orvik K.A.,University of Bergen |
Mauritzen C.,Meteorological Institute
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2011
We compare two methods for estimating mean velocities and diffusivities from surface drifter observations, using data from the Nordic Seas. The first is the conventional method of grouping data into geographical bins. The second relies on a "clustering" algorithm, and groups velocity observations according to nearest-neighbor distance. Capturing the spatial variability of the mean velocity requires using bins with a length scale of ~50km. However, because many bins have few observations, the statistical significance varies substantially between bins. Clustering yields sets with approximately the same number of observations, so the significance is more uniform. At the densely sampled Svinøy section, clusters can be used to construct the mean flow field with ≤10km resolution. Clustering also excels at the estimation of eddy diffusivities, allowing resolution at the 20. km scale in the densely sampled regions. Taking bathymetry into account in the clustering process further improves mean estimates where the data is sparse.Clustering the available surface drifter data, extended by recent deployments from the POLEWARD project, reveals new features in the surface circulation. These are a large anticyclonic vortex in the center of the Lofoten Basin and two anticyclonic recirculations at the Svinøy section. Clustering also yields maps of the eddy diffusivities at unprecedented resolution. Diffusivities are suppressed at the core of the Norwegian Atlantic Current, while they are elevated in the Lofoten Basin and along the Polar Front. © 2011 Elsevier Ltd.
Nesje A.,University of Bergen |
Nesje A.,University Bjerknes Center |
Pilo L.H.,Oppland fylkeskommune |
Finstad E.,Oppland fylkeskommune |
And 8 more authors.
Holocene | Year: 2012
The main aim of this study is to describe consequences of climate change in the mountain region of southern Norway with respect to recently exposed finds of archaeological remains associated with reindeer hunting and trapping at and around ice patches in central southern Norway. In the early years of the twenty-first century, warm summers caused negative glacier mass balance and significant glacier retreat and melting of ice patches in central southern Norway. As a result, prehistoric remains lost and/or left by past reindeer hunters appeared at ice patches in mountain areas of southern Norway. In the warm summer and autumn of 2006 the number of artefact recoveries at ice patches increased significantly because of melting of snow and ice patches and more than 100 objects were recovered in the Oppland county alone. In 2009, detailed multidisciplinary investigations were carried out at the Juvfonne ice patch in Jotunheimen at an elevation of c. 1850 metres. A well-preserved Iron Age hunting station was discovered and in total c. 600 artefacts have been documented at the Juvfonne site alone. Most of the objects were recovered and brought to the Museum of Cultural History at the University of Oslo for conservation, exhibition and storing. Thirteen so called 'scaring sticks' recovered from the recently exposed foreland of Juvfonne were radiocarbon dated, yielding ages that group in two separate time intervals, ad 246-534 and ad 804-898 (±1 sigma). By putting the temporal distribution of the radiocarbon-dated artefacts into the context of late-Holocene glacier-size variations in the Jotunheimen and Jostedalsbreen regions, we conclude that the most extensive reindeer hunting and trapping associated with snow/ice patches was related to periods with prevailing warm summers when the reindeer herds gathered on high-altitude, contracted glaciers and ice patches to avoid insect plagues. The 'freshness' of the fragile organic finds strongly indicates that at least some of the artefacts were rapidly covered by snow and ice and that they may have been more-or-less continuously covered by snow and ice since they were first buried. © The Author(s) 2011.
Lien V.S.,Norwegian Institute of Marine Research |
Gusdal Y.,Meteorological Institute |
Vikebo F.B.,Norwegian Institute of Marine Research
Ocean Dynamics | Year: 2014
The northward flow of warm and saline Atlantic Water through the eastern Nordic Seas sustains a spring-bloom ecosystem that hosts some of the world's largest commercial fish stocks. Abrupt climatic changes, or changes beyond species-specific thresholds, may have severe effects on species abundance and distribution. Here, we utilize a numerical ocean model hindcast to explore the similarities and differences between large-scale anomalies, such as great salinity anomalies, and along-shelf hydrographic anomalies of regional origin, which represent abrupt changes at subannual time scales. The large-scale anomalies enter the Nordic Seas to the south and propagate northward at a speed one order of magnitude less than the Atlantic Water current speed. On the contrary, wind-generated along-shelf anomalies appear simultaneously along the Norwegian continental shelf and propagate northward at speeds associated with topographically trapped Kelvin waves. This process involves changes in the vertical extent of the Atlantic Water along the continental slope. Such a dynamic oceanic response both affects thermal habitats and has the potential to ventilate shelf waters by modifying the cross-shelf transport of nutrients and key prey items for early stages of fish. © 2014 The Author(s).
Zabori J.,University of Stockholm |
Krejci R.,University of Stockholm |
Krejci R.,University of Helsinki |
Ekman A.M.L.,University of Stockholm |
And 7 more authors.
Atmospheric Chemistry and Physics | Year: 2012
Sea spray aerosols are an important part of the climate system through their direct and indirect effects. Due to the diminishing sea ice, the Arctic Ocean is one of the most rapidly changing sea spray aerosol source areas. However, the influence of these changes on primary particle production is not known. In laboratory experiments we examined the influence of Arctic Ocean water temperature, salinity, and oxygen saturation on primary particle concentration characteristics. Sea water temperature was identified as the most important of these parameters. A strong decrease in sea spray aerosol production with increasing water temperature was observed for water temperatures between -1°C and 9°C. Aerosol number concentrations decreased from at least 1400 -3 to 350 cm-3. In general, the aerosol number size distribution exhibited a robust shape with one mode close to dry diameter Dp 0.2 μm with approximately 45% of particles at smaller sizes. Changes in sea water temperature did not result in pronounced change of the shape of the aerosol size distribution, only in the magnitude of the concentrations. Our experiments indicate that changes in aerosol emissions are most likely linked to changes of the physical properties of sea water at low temperatures. The observed strong dependence of sea spray aerosol concentrations on sea water temperature, with a large fraction of the emitted particles in the typical cloud condensation nuclei size range, provide strong arguments for a more careful consideration of this effect in climate models. © Author(s) 2012. CC Attribution 3.0 License.
News Article | September 12, 2016
Currently, in Belgium, photovoltaic systems coupled with lead-acid batteries do not ensure the electrical self-sufficiency of a residence at a reasonable cost. This is the summary conclusion of the study two ULB researchers: their simulations reveal that the maximum rate of self-sufficiency of solar panels would only be about 40%, while the addition of complementary lead-acid batteries would result in a considerable increase of the energy prices. Today, the use of solar panels and energy storage in homes is a much discussed subject. As countries push for renewables and new technologies such as solar panels or electric cars become ever more accessible, it seems as if the house of the future is set to be self-sufficient, independent from the grid, feeding its inhabitants' needs with green energy from the sun. At the Université libre de Bruxelles, Faculty of Sciences, Aero Thermo Mechanics, researchers led by Guilherme Silva and Patrick Hendrick have been focusing on the problematic of home energy self-sufficiency for a long time and have come up with interesting results, recently published on the Applied Energy journal under the title "Lead-acid batteries coupled with photovoltaics for increased electricity self-sufficiency in households". They started by crunching up-to date Belgian data from the Royal Meteorological Institute, energy suppliers and installers and then ran these numbers through their simulation models. The conclusion is that energy self-sufficiency in homes with solar panels and batteries may come with an expensive price tag and that there may be better solutions out there to go green. The problem starts with the bad timing of solar energy and energy consumption: while the sun shines at its maximum around midday, most homes consume the most in the morning and in the evening. Add to that the fact that in many countries most of the solar energy is available in the summer months and you're set for dark times. No matter how many solar panels are added up, the maximum attainable self-sufficiency will be around 40%. The good news is that 40% self-sufficiency is achievable at prices close to the grid ones, given the recent strong reduction in the cost of solar panels and their long lifetime. To go beyond 40% self-sufficiency, energy storage seems the natural answer. The researchers coupled the solar panels with lead-acid batteries and the results are striking: all of a sudden, the energy consumed becomes really expensive. Trying to reach a self-sufficiency of 60% can easily cost twice as much as using the grid. And the batteries' short lifetime and high price are not the only ones to blame: installation costs and extra required electrical equipment also play an important role. The lack of a long term energy policy keeps homeowners and installers cautious, afraid to invest and bear all the risks, a problem that recently granted Belgium a public reprimand from the International Energy Agency. The researchers also took a look at the impact on the power grid of solar panels and home energy storage and the results seem grim. Homes equipped with such systems place a greater strain on the power grid. Also, power plants will need to be able to answer to quicker variations in demand. All this will impact power grid prices, a field where research is still lacking. Fortunately, all is not lost. The paper points out that a hybrid approach must be taken for a sustainable energy use. Using several energy sources helps to balance out each one's disadvantages. Consumption can also be adapted through intelligent appliances that can adjust to the conditions available, as can the energy storage system work in a more intelligent way. Recent energy storage technologies, such as li-ion batteries, continue to enjoy strong price reductions while the share of electric vehicles continues to increase. The field is evolving fast and research continues but, in the meanwhile, there is no magic bullet, the best option is to keep some solar panels and continue to play along with the grid. Explore further: Some suggest it's time to rethink which direction we point our solar panels More information: Guilherme de Oliveira e Silva, Patrick Hendrick. Lead-acid batteries coupled with photovoltaics for increased electricity self-sufficiency in households. Applied Energy 178: 856-867 (2016)
Antuna J.C.,Meteorological Institute |
Kalnay E.,University of Maryland University College |
Mesquita M.D.S.,University Climate
Eos | Year: 2014
The Future of Climate Extremes in the Caribbean Extreme Cuban Climate (XCUBE) project, which is funded by the Norwegian Directorate for Civil Protection as part of an assignment for the Norwegian Ministry of Foreign Affairs to support scientific cooperation between Norway and Cuba, carried out a training workshop on seasonal forecasting, reanalysis data, and weather research and forecasting (WRF). The workshop was a follow-up to the XCUBE workshop conducted in Havana in 2013 and provided Cuban scientists with access to expertise on seasonal forecasting, the WRF model developed by the National Center for Atmospheric Research (NCAR) and the community, data assimilation, and reanalysis. ©2014. American Geophysical Union. All Rights Reserved.
Schubert S.,MPI International |
Schubert S.,Meteorological Institute |
Lucarini V.,Meteorological Institute |
Lucarini V.,University of Reading
Quarterly Journal of the Royal Meteorological Society | Year: 2015
The classical approach for studying atmospheric variability is based on defining a background state and studying the linear stability of the small fluctuations around such a state. Weakly nonlinear theories can be constructed using higher order expansion terms. While these methods undoubtedly have great value for elucidating the relevant physical processes, they are unable to follow the dynamics of a turbulent atmosphere. We provide a first example of the extension of classical stability analysis to a nonlinearly evolving quasi-geostrophic flow. The so-called covariant Lyapunov vectors (CLVs) provide a covariant basis describing the directions of exponential expansion and decay of perturbations to the nonlinear trajectory of the flow. We use such a formalism to re-examine the basic barotropic and baroclinic processes of the atmosphere with a quasi-geostrophic beta-plane two-layer model in a periodic channel driven by a forced meridional temperature gradient ΔT. We explore three settings of ΔT, representative of relatively weak turbulence, well-developed turbulence and intermediate conditions. We construct the Lorenz energy cycle for each CLV describing the energy exchanges with the background state. A positive baroclinic conversion rate is a necessary but not sufficient condition for instability. Barotropic instability is present only for a few very unstable CLVs for large values of ΔT. Slowly growing and decaying hydrodynamic Lyapunov modes closely mirror the properties of the background flow. Following the classical necessary conditions for barotropic/baroclinic instability, we find a clear relationship between the properties of the eddy fluxes of a CLV and its instability. CLVs with positive baroclinic conversion seem to form a set of modes for constructing a reduced model of the atmospheric dynamics. © 2015 Royal Meteorological Society.
News Article | April 13, 2016
Emerging from a winter that has had staggeringly warm Arctic temperatures, scientists monitoring the vast Greenland ice sheet announced Tuesday that it is experiencing a record-breaking level of melt for so early in the season. The Danish Meteorological Institute reported that although it’s only April, nearly 12 percent of the ice sheet’s surface is covered with a layer of meltwater of a depth of […]
Berman A.,Hebrew University |
Horovitz T.,Meteorological Institute
Journal of Dairy Science | Year: 2012
Reducing thermal radiation on shaded animals reduces heat stress independently of other means of stress relief. Radiant heat exchange was estimated as a function of climate, shade structure, and animal density. Body surface portion exposed to radiant sources in shaded environments was determined by geometrical relations to determine angles of view of radiation sources (roof underside, sky, sun-exposed ground, shaded ground) on the animal's surface. The relative representation of environment radiation sources on the body surface was determined. Animal thermal radiation balance was derived from radiant heat gained from radiation sources (including surrounding animals) and that lost from the animal surface. The animal environment was assumed to have different shade dimensions and temperatures. These were summed to the radiant heat balance of the cow. The data formed served to estimate the effect of changes in intensity of radiation sources, roof and shaded surface dimensions, and animal density on radiant heat balance (Rbal) of cattle. Roof height effect was expressed by effect of roof temperature on Rbal. Roof underside temperature (35 to 75°C) effect on Rbal was reduced by roof height. If roof height were 4m, an increase in its underside temperature from 35 to 75°C would increase mean Rbal from -63 to -2 W·m-2, whereas if roof height were 10m, Rbal would only increase from -99 to -88 W·m-2. A hot ground temperature increase from 35 to 65°C reduced mean Rbal heat loss from -45 to 3 W·m-2. Increasing the surface of the shaded area had only a minor effect on Rbal and on the effect of hot ground on Rbal. Increasing shade roof height reduced the effect of roof temperature on Rbal to minor levels when height was >8m. Increasing the roof height from 4 to 10m decreased Rbal from -32 to -94 W·m-2. Increasing indirect radiation from 100 to 500 W·m-2 was associated with an increase in Rbal from -135 to +23 W·m-2. Their combined effects were lower Rbal with increasing roof height and a reduction in rate of decrease with increasing level of indirect radiation. Roof height as an Rbal attenuator declined with increasing indirect radiation level. The latter factor might be reduced by lowering roof surface radiation absorption and through roof heat transfer, as well as by use of shade structure elements to reduce indirect radiation in the shaded area. Radiant heat from the cow body surface may be reduced by lower cow density. Radiant heat attenuation may thus further elevate animal productivity in warm climates, with no associated operation costs. © 2012 American Dairy Science Association.
Du C.,Meteorological Institute |
Liu S.,The Interdisciplinary Center |
Yu X.,Meteorological Institute |
Li X.,Meteorological Institute |
And 5 more authors.
Aerosol and Air Quality Research | Year: 2013
The characteristics of the planetary boundary layer height (PBLH) and the relationship between PBLH and particular matter (PM) mass concentration in Xi'an, central China, are analyzed in this study. Three PBLH calculation methods are used in this study, namely the Holzworth, Liu, and Nozaki approaches. The daily minimum and maximum PBLHs are determined by the Holzworth method, the hourly PBLHs are calculated by the Nozaki method, and the results of the Nozaki method are evaluated by the Liu method. The PBLH characteristics of annual, seasonal, daily, and diurnal variations are based on hourly values obtained from the Nozaki method. The results show that the Nozaki method can depict typical PBLH diurnal variations, although it substantially overestimates the related values. The daily maximum PBLH occurs from 11:00 to 16:00 Beijing time, and the seasonal maximum PBLH is during spring, due to the annual maximum wind speed at this time. PM2.5, PM1.0 and PM10 mass concentrations are negatively correlated with PBLH on the inter-annual, annual, and seasonal time scales. The anti-phase diurnal variations of PM mass concentrations and PBLH further indicate that PBLH is one of the important factors affecting air quality. The PM2.5 in PM10, PM1.0 in PM2.5, and PM1.0 in PM10 contents show notable monthly variations, indicating that the air quality in Xi'an city is affected upwind windy and dusty weather, along with local pollution sources. © Taiwan Association for Aerosol Research.