E-voting discourses in the UK and the Netherlands

A qualitative case study of the e-voting discourses in the UK and the Netherlands was performed based on the theory of strategic niche management. In both countries, eight e-voting experts were interviewed on their expectations, risk estimations, cooperation and learning experiences. The results show that differences in these variables can partly explain the variations in the embedding of e-voting in the two countries, from a qualitative point of view

Internal wave band eddy fluxes above a continental slope

Three weeks of velocity and temperature measurements from the bottom 45 m above the continental slope in the Bay of Biscay are used to evaluate the role of the internal wave band in boundary mixing near a sloping bottom. Utilizing acoustic Doppler current profilers and thermistor strings, internal wave band eddy fluxes of momentum and heat are estimated. The instrumentation is specifically designed to resolve internal wave band processes. Due to unresolved Doppler shifting, this wave band may include turbulence as well as internal waves. A very energetic and highly variable near-bottom environment is found. Periods of mixing and restratification alternate at the M2 tidal frequency. Interpreting the observations in an Ekman sense, the three-week mean current is downwelling-favorable, which is consistent with existing boundary layer theories. However, a bi-directional flow associated with sloping boundary mixing is not found in the near-bottom layer, possibly due to observed strong stratification all the way to the bottom. We evaluated boundary layer dynamics and the effect of internal wave-band fluxes from two frequency ranges (σ ≥ 15 cpd and σ ≥ 1.9 cpd, including tides) on the three-week mean flow. The high-frequency range (σ ≥ 15 cpd) of the internal wave band supports significant momentum and buoyancy fluxes while the low-frequency range (σ ≥ 1.9 cpd) only supports significant momentum fluxes. Mean bottom-normal eddy diffusivities associated with anisotropic, nonlinear internal waves, are negative and O (-10-2 m2s-1). Interpreting these negative eddy diffusivities as indication of a restratification process, high mixing efficiencies are expected throughout the mixing layer, which extends typically 20 m above the bottom. Mean eddy viscosities are positive in cross-slope direction and negative in alongslope direction, implying a strong anisotropy in the interaction between internal wave band eddies and the mean flow. Alongslope momentum is transferred from the internal tide to the mean flow. Buoyancy and pressure gradient forces, which we could not determine directly, may generate a buoyancy-driven secondary flow. The buoyancy equation is dominated by advection, possibly balanced by divergence of cross-slope and alongslope internal wave band fluxes

Fast thermistor string observations at the slope of Great Meteor Seamount

International audienceA very fast thermistor string has been built to accommodate the scientific need to accurately monitor fast and vigorous internal wave and overturning processes above sloping bottoms in the ocean. The thermistors and their custom designed electronics can register temperature at an estimated precision of about 1mK with a response time faster than 0.25 s down to depths of 6000 m. The present string holds 128 synoptically measuring sensors at 0.5 m intervals, which are all read-out within 0.5 s. When sampling at 1Hz, the batteries and the memory capacity of the recorder allow for deployments of up to 2 weeks. Detailed examples of the first field observations are presented, which show overturning and very high-frequency (Doppler-shifted) internal waves besides occasionally large turbulent bores moving up the sloping side of Great Meteor Seamount, Canary Basin, North-Atlantic Ocean

High sampling rate thermistor string observations at the slope of Great Meteor Seamount

International audienceA high sampling rate (1 Hz) thermistor string has been built to accommodate the scientific need to accurately monitor high-frequency and vigorous internal wave and overturning processes in the ocean. The thermistors and their custom designed electronics can register temperature at an estimated precision of about 0.001° C with a response time faster than 0.25 s down to depths of 6000 m. With a quick in situ calibration using SBE 911 CTD an absolute accuracy of 0.005° C is obtained. The present string holds 128 sensors at 0.5 m intervals, which are all read-out within 0.5 s. When sampling at 1 Hz, the batteries and the memory capacity of the recorder allow for deployments of up to 2 weeks. In this paper, the instrument is described in some detail. Its performance is illustrated with examples from the first moored observations, which show Kelvin-Helmholtz overturning and very high-frequency (Doppler-shifted) internal waves besides occasionally large turbulent bores moving up the sloping side of Great Meteor Seamount, Canary Basin, North-Atlantic Ocean

Observations on the vertical structure of tidal and inertial currents in the central North Sea

Tidal and inertial current ellipses, measured at several locations and depths in the central North Sea during a number of monthly periods in 1980, 1981 and 1982, are decomposed into counterrotating, circular components to which Ekman dynamics are applied to determine Ekman layer depths and vertical phase differences, from which are inferred overall values of the eddy viscosity and drag coefficient. Stratification effects produce an additional vertical phase shift of the anticyclonic rotary component, indicative of an inverse proportionality of the eddy viscosity to the vertical density gradient. From the time variations of the Ekman layer depths of the semidiurnal tidal components, as well as from the vertical structure of the inertial current component, we infer variations in the relative vorticity of the low-frequency flow

Patchiness in internal tidal beams

Results are presented from measurements on internal tides and near-inertial motions, obtained using deep-towed acoustic Doppler current profilers along a single transect over the continental slope in the Bay of Biscay and, in another experiment, over a flank of Great Meteor Seamount in the Canary Basin. Each measurement lasted two days and involved repeated passage of the same track, making it possible to extract by harmonic analysis the semidiurnal (and, over Great Meteor Seamount, also the combined diurnal/near-inertial) signal. In the Bay of Biscay, the transect covered by the towing was sufficiently long to follow the internal semidiurnal tidal beam for large-scale stratification well beyond its detachment from the continental slope. Here, large-scale stratification is computed from CTD-observations over vertical scales O(100 m). Remarkably, the beam is much more distinct in its phase field, which is coherent throughout, than in its amplitude, which shows a lot of patchiness and small-scale near-horizontal layering. The hypothesis is put forward that this may be associated with the interaction between internal waves and variations in space and time of stratification. In part, it may be attributable to aliased, weaker, near-inertial beams that are more horizontal for large-scale stratification. The diurnal/inertial and, to a lesser extent, semidiurnal signals over Great Meteor Seamount show the same phenomenon, but here co-phase and coamplitude bands are more distinctly nearly horizontal, indicative of near-horizontal energy propagation at all frequencies investigated

Assessment of uncertainties in simulated European precipitation

The research presented in this thesis is aimed to understanding the changes and the simulation of precipitation in Europe. A correct representation of simulated (trends in) European precipitation is important to have confidence in projections of future changes therein. These projections are relevant for different hydrological applications. Among others, simulated changes of summer drying are often accompanied by an enhanced increase in air temperatures [Zampieri et al., 2009]. This can be expected to have large impacts on society and ecosystems, affecting, for example, water resources, agriculture and fire risk [Rowell, 2009]. Projections of changes in extreme precipitation are critical for estimates of future discharge extremes of large river basins, and changes in frequency of major flooding events [e.g. Kew et al., 2010]. The subjects that are studied in this thesis are divided in three parts: (1) evaluation of 20th century European precipitation trends; (2) effect of general circulation model (GCM) spatial resolution on simulated western European winter precipitation in the current climate; and (3) effect of GCM spatial resolution on simulated future summer drying in central and southern Europe. In the first part of the thesis (chapters 2 and 3) an investigation of (extreme) precipitation trends in multi-model ensembles including both global and regional climate models is performed. The results show that these models fail to reproduce the observed trends over (parts of) the past century. In many regions the model spread does not cover the trend in the observations: the models significantly underestimate the observed trend. A misrepresentation of large scale atmospheric circulation changes in climate models is found to be responsible for the underestimation of winter precipitation trends in Europe over the past century. Additionally, the underestimation of trends in winter precipitation extremes in the Rhine basin is directly related to this as well. In summer a misrepresentation of sea surface temperature (SST) trends is responsible for the underestimation of summer precipitation trends along the coastal regions of western Europe. The second part (chapter 4) investigates the effect of GCM spatial resolution on modeled precipitation over Europe using an atmosphere-only GCM at two resolutions (EC-Earth, ~25 km and ~112 km horizontal resolution). The results show that the high resolution model gives a more accurate representation of northern and central European winter precipitation. The medium resolution model has a larger positive bias in precipitation in most of the northern half of Europe. Storm tracks are better simulated in the high resolution model, providing for a more accurate horizontal moisture transport and precipitation. A decomposition of the precipitation difference between the medium- and high resolution model in a part related and a part unrelated to a difference in the distribution of vertical atmospheric velocity confirms that the reduced precipitation in the high resolution model is likely the result of a reduced moisture transport at this resolution: the precipitation difference in this area in unrelated to a difference in the distribution of vertical atmospheric velocity. In areas with orography the change in vertical velocity distribution is more important. Using the same atmosphere-only model, the third part (chapter 5) of this thesis investigates the influence of GCM spatial resolution on the simulated future summer drying of central Europe. High resolution models have a more realistic representation of circulation in the current climate and could provide more confidence on future projections of circulation forced drying. The results show that the high resolution model is characterized by a stronger drying in spring and summer, mainly forced by circulation changes. The initial spring drying intensifies the summer drying by a positive soil moisture feedback. The results are confirmed by finding analogs of the difference between the high and medium-resolution model circulation in the natural variability in another ensemble of climate model simulations. In current climate, these show the same precipitation difference pattern resulting from the summer circulation difference. In future climate the spring circulation plays a key role as well. It is concluded that the reduction of circulation biases due to increased resolution gives higher confidence in the strong drying trend projected for central Europe by the high-resolution version of the model. </p