The effects of global climate change on the cycling and processes of persistent organic pollutants (POPs) in the North Sea

The fate and cycling of two selected legacy persistent organic pollutants (POPs), PCB 153 and gamma-HCH, in the North Sea in the 21st century have been modelled with combined hydrodynamic and fate and transport ocean models
(HAMSOM and FANTOM, respectively). To investigate the impact of climate variability on POPs in the North Sea in the 21st century, future scenario model runs for three 10-year periods to the year 2100 using plausible levels of both in
situ concentrations and atmospheric, river and open boundary inputs are performed. This slice mode under a moderate scenario (A1B) is sufficient to provide a basis for further analysis. For the HAMSOM and atmospheric forcing, results of the IPCC A1B (SRES) 21st century scenario are utilized, where surface forcing is provided by the REMO downscaling of the ECHAM5 global atmospheric model, and open boundary conditions are provided by the MPIOM global ocean model.
Dry gas deposition and volatilization of gamma-HCH increase in the future relative to the present by up to 20% (in the spring and summer months for deposition and in summer for volatilization). In the water column, total mass of
gamma-HCH and PCB 153 remain fairly steady in all three runs. In sediment,
gamma-HCH increases in the future runs, relative to the present, while PCB 153 in sediment decreases exponentially in all three runs, but even faster in the future, due to the increased number of storms, increased duration of gale wind conditions and increased water and air temperatures, all of which are the result of climate change. Annual net sinks exceed sources at the ends of all periods.
Overall, the model results indicate that the climate change scenarios considered here generally have a negligible influence on the simulated fate and transport of the two POPs in the North Sea, although the increased number and magnitude of storms in the 21st century will result in POP resuspension and ensuing revolatilization events. Trends in emissions from primary and secondary sources will remain the key driver of levels of these contaminants over time.

Wind generation and electricity demand during the severe winter of 2009/10 in Ireland

Throughout the world the share of wind power in the generation mix is increasing. In the All Island Grid, of the Republic of Ireland and Northern Ireland there is now over 1.5 GW of installed wind power. As the penetration of these variable, non-dispatchable generators increases, power systems are becoming more sensitive to weather events on the supply side as well as on the demand side. In the temperate climate of Ireland, sensitivity of supply to weather is mainly due to wind variability while demand sensitivity is driven by space heating or cooling loads. The interplay of these two weather-driven effects is of particular concern if demand spikes driven by low temperatures coincide with periods of low winds. In December 2009 and January 2010 Ireland experienced a prolonged spell of unusually cold conditions. During much of this time, wind generation output was low due to low wind speeds. The impacts of this event are presented as a case study of the effects of weather extremes on power systems with high penetrations of variable renewable generation.

What do high penetrations of wind power mean for gas generation?

Dependency on thermal generation and continued wind power growth in Europe due to renewable energy and greenhouse gas emissions targets has resulted in an interesting set of challenges for power systems. The variability of wind power impacts dispatch and balancing by grid operators, power plant operations by generating companies and market wholesale costs. This paper quantifies the effects of high wind power penetration on power systems with a dependency on gas generation using a realistic unit commitment and economic dispatch model. The test system is analyzed under two scenarios, with and without wind, over one year. The key finding of this preliminary study is that despite increased ramping requirements in the wind scenario, the unit cost of electricity due to sub-optimal operation of gas generators does not show substantial deviation from the no wind scenario.

A techno-economic feasibility study of high altitude wind power in Northern Ireland

Globally the amount of installed terrestrial wind power both onshore and offshore has grown rapidly over the last twenty years. Most large onshore and offshore wind turbines are designed to harvest winds within the atmospheric boundary layer, which can be vary variable due to terrain and weather effects. The height of the neutral atmospheric boundary layer is estimated at above 1300m. A relatively new concept is to harvest more consistent wind conditions above the atmospheric boundary layer using high altitude wind harvesting devices such as tethered kites, air foils and dirigible rotors. This paper presents a techno-economic feasibility study of high altitude wind power in Northern Ireland. First this research involved a state of the art review of the resource and the technologies proposed for high altitude wind power. Next the techno-economic analysis involving four steps is presented. In step one, the potential of high altitude wind power in Northern Ireland using online datasets (e.g. Earth System Research Laboratory) is estimated. In step two a map for easier visualisation of geographical limitations (e.g. airports, areas of scenic beauty, flight paths, military training areas, settlements etc.) that could impact on high altitude wind power is developed. In step three the actual feasible resource available is recalculated using the visualisation map to determine the ‘optimal’ high altitude wind power locations in Northern Ireland. In the last step four the list of equipment, resources and budget needed to build a demonstrator is provided in the form of a concise techno-economic appraisal using the findings of the previous three steps.

Slot width augmentation in a slotted-wall transonic linear cascade wind tunnel

Transonic tests in linear cascade wind tunnels can suffer
from significant test section boundary interference effects in pitch. A slotted tailboard has been designed and optimised with an in-house Euler numerical method to reduce such ef- fects. Wind tunnel measurements on an overspeed Mach 1.27 discharge from a Rolls-Royce T2 cascade, featuring strong end-wall shock-induced interference, showed a 77% reduction in the flow pitchwise periodicity error with the optimised tail- board, with respect to the baseline open-jet cascade flow. Two-dimensional Euler predictions were also cross-validated against a three-dimensional Reynolds averaged computation, to explore the three-dimensionality of the discharge

Long-term changes in oxygen depletion in a small temperate lake: effects of climate change and eutrophication

1. We analysed 41 years of data (1968–2008) from Blelham Tarn, U.K., to determine the consequences of eutrophication and climate warming on hypolimnetic dissolved oxygen (DO).
2. The establishment of thermal stratification was strongly related to the onset of DO depletion in the lower hypolimnion. As a result of a progressively earlier onset of stratification and later overturn, the duration of stratification increased by 38 ± 8 days over the 41 years.
3. The observed rate of volumetric hypolimnetic oxygen depletion (VHODobs) ranged from 0.131 to 0.252 g O2 m−3 per day and decreased significantly over the study period, despite the increase in the mean chlorophyll a (Chl a) concentration in the growing season. The vertical transport of DO represented from 0 to 30% of VHODobs, while adjustments for interannual differences in hypolimnetic temperature were less important, ranging from −11 to 9% of VHODobs.
4. The mean wind speed during May made the strongest significant contribution to the variation in VHODobs. VHODobs adjusted for the vertical transport of DO and hypolimnetic temperature differences, VHODadj, was significantly related to the upper mixed layer Chl a concentration during spring.
5. Hypolimnetic anoxia (HA) ranged from 27 to 168 days per year and increased significantly over time, which undoubtedly had negative ecological consequences for the lake.
6. In similar small temperate lakes, the negative effects of eutrophication on hypolimnetic DO are likely to be exacerbated by changes in lake thermal structure brought about by a warming climate, which may undermine management efforts to alleviate the effects of anthropogenic eutrophication.

Effects of environmental conditions on planktonic abundances, benthic recruitment and growth rates of the bivalve mollusc Ruditapes decussatus in a Portuguese coastal lagoon

Controlling environmental parameters for the early stages of marine invertebrates have received little attention, particularly in field studies. This study involves measurement of abundances and growth rates of the bivalve Ruditapes decussatus Linnaeus 1758 during its planktonic larval and early benthic life stages in a coastal lagoon: Ria Formosa, Portugal. Measured abundances were compared with tidal amplitude, water temperature, salinity, wind velocity and direction, and a food availability indicator 2chlorophyll a). Data were obtained on abundance and prodissoconch length of the larvae, measured two tothreetimes perweek,and ofpost-larval stagesindividuals thathadsettled inartificial collectors over10months.Larval and juvenile cohorts were identified using size-frequency distributions and larval ages estimated by larval shell growth lines.

Dispachability improvement of wind generation by the virtual power producers

Nowadays, there is a growing environmental concern about were the energy that we use comes from, bringing the att ention on renewable energies. However, the use and trade of renewable e nergies in the market seem to be complicated because of the lack of guara ntees of generation, mainly in the wind farms. The lack of guarantees is usually addressed by using a reserve generation. The aggregation of DG p lants gives place to a new concept: the Virtual Power Producer (VPP). VPPs can reinforce the importance of wind generation technologies, making them valuable in electricity markets. This paper presents some resul ts obtained with a simulation tool (ViProd) developed to support VPPs in the analysis of their operation and management methods and of their strat egies effects.

Techniques for Enhancing Wind Energy Generation - A CFD Based Multibody Dynamics Approach in Horizontal Axis Wind Turbines

Wind energy has emerged as a major sustainable source of energy.The efficiency of wind power generation by wind mills has improved a lot during the last three decades.There is still further scope for maximising the conversion of wind energy into mechanical energy.In this context,the wind turbine rotor dynamics has great significance.The present work aims at a comprehensive study of the Horizontal Axis Wind Turbine (HAWT) aerodynamics by numerically solving the fluid dynamic equations with the help of a finite-volume Navier-Stokes CFD solver.As a more general goal,the study aims at providing the capabilities of modern numerical techniques for the complex fluid dynamic problems of HAWT.The main purpose is hence to maximize the physics of power extraction by wind turbines.This research demonstrates the potential of an incompressible Navier-Stokes CFD method for the aerodynamic power performance analysis of horizontal axis wind turbine.The National Renewable Energy Laboratory USA-NREL (Technical Report NREL/Cp-500-28589) had carried out an experimental work aimed at the real time performance prediction of horizontal axis wind turbine.In addition to a comparison between the results reported by NREL made and CFD simulations,comparisons are made for the local flow angle at several stations ahead of the wind turbine blades.The comparison has shown that fairly good predictions can be made for pressure distribution and torque.Subsequently, the wind-field effects on the blade aerodynamics,as well as the blade/tower interaction,were investigated.The selected case corresponded to a 12.5 m/s up-wind HAWT at zero degree of yaw angle and a rotational speed of 25 rpm.The results obtained suggest that the present can cope well with the flows encountered around wind turbines.The areodynamic performance of the turbine and the flow details near and off the turbine blades and tower can be analysed using theses results.The aerodynamic performance of airfoils differs from one another.The performance mainly depends on co-efficient of performnace,co-efficient of lift,co-efficient of drag, velocity of fluid and angle of attack.This study shows that the velocity is not constant for all angles of attack of different airfoils.The performance parameters are calculated analytically and are compared with the standardized performance tests.For different angles of ,the velocity stall is determined for the better performance of a system with respect to velocity.The research addresses the effect of surface roughness factor on the blade surface at various sections.The numerical results were found to be in agreement with the experimental data.A relative advantage of the theoretical aerofoil design method is that it allows many different concepts to be explored economically.Such efforts are generally impractical in wind tunnels because of time and money constraints.Thus, the need for a theoretical aerofoil design method is threefold:first for the design of aerofoil that fall outside the range of applicability of existing calalogs:second,for the design of aerofoil that more exactly match the requirements of the intended application:and third,for the economic exploration of many aerofoil concepts.From the results obtained for the different aerofoils,the velocity is not constant for all angles of attack.The results obtained for the aerofoil mainly depend on angle of attack and velocity.The vortex generator technique was meticulously studies with the formulation of the specification for the right angle shaped vortex generators-VG.The results were validated in accordance with the primary analysis phase.The results were found to be in good agreement with the power curve.The introduction of correct size VGs at appropriate locations over the blades of the selected HAWT was found to increase the power generation by about 4%

Excess open solar magnetic flux from satellite data: 2. A survey of kinematic effects

We investigate the “flux excess” effect, whereby open solar flux estimates from spacecraft increase with increasing heliocentric distance. We analyze the kinematic effect on these open solar flux estimates of large-scale longitudinal structure in the solar wind flow, with particular emphasis on correcting estimates made using data from near-Earth satellites. We show that scatter, but no net bias, is introduced by the kinematic “bunching effect” on sampling and that this is true for both compression and rarefaction regions. The observed flux excesses, as a function of heliocentric distance, are shown to be consistent with open solar flux estimates from solar magnetograms made using the potential field source surface method and are well explained by the kinematic effect of solar wind speed variations on the frozen-in heliospheric field. Applying this kinematic correction to the Omni-2 interplanetary data set shows that the open solar flux at solar minimum fell from an annual mean of 3.82 × 1016 Wb in 1987 to close to half that value (1.98 × 1016 Wb) in 2007, making the fall in the minimum value over the last two solar cycles considerably faster than the rise inferred from geomagnetic activity observations over four solar cycles in the first half of the 20th century.

Ambient solar wind's effect on ICME transit times

Most empirical and numerical models of Interplanetary Coronal Mass Ejection (ICME) propagation use the initial CME velocity as their primary, if not only, observational input. These models generally predict a wide spread of 1 AU transit times for ICMEs with the same initial velocity. We use a 3D coupled MHD model of the corona and heliosphere to determine the ambient solar wind's effect on the propagation of ICMEs from 30 solar radii to 1 AU. We quantitatively characterize this deceleration by the velocity of the upstream ambient solar wind. The effects of varying solar wind parameters on the ICME transit time are quantified and can explain the observed spread in transit times for ICMEs of the same initial velocity. We develop an adjustment formula that can be used in conjunction with other models to reduce the spread in predicted transit times of Earth-directed ICMEs.

Metrics for solar wind prediction models: Comparison of empirical, hybrid, and physics-based schemes with 8 years of L1 observations

Space weather effects on technological systems originate with energy carried from the Sun to the terrestrial environment by the solar wind. In this study, we present results of modeling of solar corona-heliosphere processes to predict solar wind conditions at the L1 Lagrangian point upstream of Earth. In particular we calculate performance metrics for (1) empirical, (2) hybrid empirical/physics-based, and (3) full physics-based coupled corona-heliosphere models over an 8-year period (1995–2002). L1 measurements of the radial solar wind speed are the primary basis for validation of the coronal and heliosphere models studied, though other solar wind parameters are also considered. The models are from the Center for Integrated Space-Weather Modeling (CISM) which has developed a coupled model of the whole Sun-to-Earth system, from the solar photosphere to the terrestrial thermosphere. Simple point-by-point analysis techniques, such as mean-square-error and correlation coefficients, indicate that the empirical coronal-heliosphere model currently gives the best forecast of solar wind speed at 1 AU. A more detailed analysis shows that errors in the physics-based models are predominately the result of small timing offsets to solar wind structures and that the large-scale features of the solar wind are actually well modeled. We suggest that additional “tuning” of the coupling between the coronal and heliosphere models could lead to a significant improvement of their accuracy. Furthermore, we note that the physics-based models accurately capture dynamic effects at solar wind stream interaction regions, such as magnetic field compression, flow deflection, and density buildup, which the empirical scheme cannot.

Natural ventilation effects on temperatures within Stevenson screens

Thermometer screen properties are poorly characterised at low wind speeds. Temperatures from a large thermometer screen have been compared with those from an automatically shaded open-air fine-wire resistance thermometer. For the majority of 5-minute average measurements obtained between July 2008 and 2009, the screen and fine-wire temperatures agreed closely, with a median difference <0.05◦C. At low wind speeds however, larger temperature differences occurred. When calm (wind speed at 2 metres, u2, ≤ 0.1 m s−1), the difference between screen and open-air temperatures varied from −0.25◦C to +0.87◦C. At night with u2 < 0.5 m s−1, this difference was −0.14◦C to 0.39◦C, and, rarely, up to −0.68◦C to 1.38◦C. At the minimum in the daily temperature cycle, the semi-urban site at Reading had u2 < 1 m s−1 for 52% of the observations 1997–2008, u2 < 0.5 m s−1 for 34% and calm conditions for 20%. Consequently uncertainties in the minimum temperature measurements may arise from poor ventilation, which can propagate through calculations to daily average temperatures. In comparison with the daily minimum temperature, the 0900 UTC synoptic temperature measurement has a much lower abundance (5%) of calm conditions.

Magnetic discontinuities in the near-earth solar wind: evidence of in-transit turbulence or remnants of coronal structure?

Fluctuations in the solar wind plasma and magnetic field are well described by the sum of two power law distributions. It has been postulated that these distributions are the result of two independent processes: turbulence, which contributes mainly to the smaller fluctuations, and crossing the boundaries of flux tubes of coronal origin, which dominates the larger variations. In this study we explore the correspondence between changes in the magnetic field with changes in other solar wind properties. Changes in density and temperature may result from either turbulence or coronal structures, whereas changes in composition, such as the alpha-to-proton ratio are unlikely to arise from in-transit effects. Observations spanning the entire ACE dataset are compared with a null hypothesis of no correlation between magnetic field discontinuities and changes in other solar wind parameters. Evidence for coronal structuring is weaker than for in-transit turbulence, with only ∼ 25% of large magnetic field discontinuities associated with a significant change in the alpha-to-proton ratio, compared to ∼ 40% for significant density and temperature changes. However, note that a lack of detectable alpha-to-proton signature is not sufficient to discount a structure as having a solar origin.

Lag-time effects on a naturally ventilated large thermometer screen

Systematic natural ventilation effects on measured temperatures within a standard large wooden thermometer screen are investigated under summer conditions, using well-calibrated platinum resistance thermometers. Under low ventilation (2mwind speed u2 < 1.1 m s−1), the screen slightly underestimates daytime air temperature but overestimates air temperature nocturnally by 0.2◦C. The screen’s lag time L lengthens with decreasing wind speed, following an inverse power law relationship between L and u2. For u2 > 2 m s−1, L ∼ 2.5 min, increasing, when calm, to at least 15 min. Spectral response properties of the screen to air temperature fluctuations vary with wind speed because of the lag changes. Ventilation effects are particularly apparent at the higher (>25◦C) temperatures, both through the lag effect and from solar heating. For sites where wind speed decreases with increasing daytime temperature, thermometer screen temperatures may consequently show larger uncertainties at the higher temperatures. Under strong direct beam solar radiation (>850W m−2) the radiation effect is likely to be <0.4◦C. Copyright c 2011 RoyalMeteorological Society