The Hvar survey for roAp stars: II. Final results (Research Note)

The 60 known rapidly oscillating Ap (roAp) stars are excellent laboratories to test pulsation models in the presence of stellar magnetic fields. Our survey is dedicated to search for new group members in the Northern Hemisphere. We attempt to increase the number of known chemically peculiar stars that are known to be pulsationally unstable. About 40 h of new CCD photometric data of 21 roAp candidates, observed at the 1m Austrian-Croatian Telescope (Hvar Observatory) are presented. We carefully analysed these to search for pulsations in the frequency range of up to 10mHz. No new roAp star was detected among the observed targets. The distribution of the upper limits for roAp-like variations is similar to that of previoius similar efforts using photomultipliers and comparable telescope sizes. In addition to photometric observations, we need to consolidate spectroscopic information to select suitable targets.Comment: 8 pages, 5 figures, accepted by Astronomy & Astrophysic

The institutional foundations of surf break governance in Atlantic Europe

The sport of surfing is best enjoyed with one rider on one wave, but crowding makes that optimal assignment increasingly hard to attain. This study examines the phenomenon of surf localism, whereby competitors are excluded from waves by intimidation and the threat of violence. An alternative way to accommodate crowds is contained in the surfer’s code, which sets informal rules and self-enforced regulations to avoid conflict in the water. Both regimes establish property rights over common pool resources with no state intervention, creating a setting wherein users face the question of cooperation or conflict. The disposition to cooperate and follow norms has been shown to vary substantially across different cultures, though. Employing data from over seven hundred surf spots on the European Atlantic coast, this study reports evidence that certain informal cultural norms significantly reduce the probability of violent exclusion, while formal state institutions mostly are irrelevant. The results also indicate that informal norms become more important with greater resource quality and, possibly, with increasing scarcity

Uncertainties in selected river water quality data

International audienceMonitoring of surface waters is primarily done to detect the status and trends in water quality and to identify whether observed trends arise from natural or anthropogenic causes. Empirical quality of river water quality data is rarely certain and knowledge of their uncertainties is essential to assess the reliability of water quality models and their predictions. The objective of this paper is to assess the uncertainties in selected river water quality data, i.e. suspended sediment, nitrogen fraction, phosphorus fraction, heavy metals and biological compounds. The methodology used to structure the uncertainty is based on the empirical quality of data and the sources of uncertainty in data (van Loon et al., 2005). A literature review was carried out including additional experimental data of the Elbe river. All data of compounds associated with suspended particulate matter have considerable higher sampling uncertainties than soluble concentrations. This is due to high variability within the cross section of a given river. This variability is positively correlated with total suspended particulate matter concentrations. Sampling location has also considerable effect on the representativeness of a water sample. These sampling uncertainties are highly site specific. The estimation of uncertainty in sampling can only be achieved by taking at least a proportion of samples in duplicates. Compared to sampling uncertainties, measurement and analytical uncertainties are much lower. Instrument quality can be stated well suited for field and laboratory situations for all considered constituents. Analytical errors can contribute considerably to the overall uncertainty of river water quality data. Temporal autocorrelation of river water quality data is present but literature on general behaviour of water quality compounds is rare. For meso scale river catchments (500?3000 km2) reasonable yearly dissolved load calculations can be achieved using biweekly sample frequencies. For suspended sediments none of the methods investigated produced very reliable load estimates when weekly concentrations data were used. Uncertainties associated with loads estimates based on infrequent samples will decrease with increasing size of rivers

Uncertainties in selected surface water quality data

International audienceMonitoring of surface waters is primarily done to detect the status and trends in water quality and to identify whether observed trends arise form natural or anthropogenic causes. Empirical quality of surface water quality data is rarely certain and knowledge of their uncertainties is essential to assess the reliability of water quality models and their predictions. The objective of this paper is to assess the uncertainties in selected surface water quality data, i.e. suspended sediment, nitrogen fraction, phosphorus fraction, heavy metals and biological compounds. The methodology used to structure the uncertainty is based on the empirical quality of data and the sources of uncertainty in data (van Loon et al., 2006). A literature review was carried out including additional experimental data of the Elbe river. All data of compounds associated with suspended particulate matter have considerable higher sampling uncertainties than soluble concentrations. This is due to high variability's within the cross section of a given river. This variability is positively correlated with total suspended particulate matter concentrations. Sampling location has also considerable effect on the representativeness of a water sample. These sampling uncertainties are highly site specific. The estimation of uncertainty in sampling can only be achieved by taking at least a proportion of samples in duplicates. Compared to sampling uncertainties measurement and analytical uncertainties are much lower. Instrument quality can be stated well suited for field and laboratory situations for all considered constituents. Analytical errors can contribute considerable to the overall uncertainty of surface water quality data. Temporal autocorrelation of surface water quality data is present but literature on general behaviour of water quality compounds is rare. For meso scale river catchments reasonable yearly dissolved load calculations can be achieved using biweekly sample frequencies. For suspended sediments none of the methods investigated produced very reliable load estimates when weekly concentrations data were used. Uncertainties associated with loads estimates based on infrequent samples will decrease with increasing size of rivers

Investigation of parameter uncertainty and identifiability of the hydrological model WaSiM-ETH

International audienceThe identification of optimum model parameters may be influenced by temporal or event-specific changes of optimum parameter ranges and the length and information content of calibration data. These effects were studied for the hydrological model WaSiM-ETH in a 170 km2 catchment. Based on a Monte-Carlo simulation including seven model parameters, we investigated temporal and state dependent changes of parameter identifiability using the DYNIA algorithm. The effect of data length was studied using a modified DYNIA approach based on a growing window algorithm. The DYNIA analysis revealed temporal changes of identifiability for the snow melt runoff parameter cmelt, which is only identifiable during winter runoff, and for the drainage density parameter drd. The drd parameter was closely related to observed discharge (or catchment moisture), when re-ordering the time series by discharge. Such dependencies probably result from processes not included in model equations. The growing window analysis shows that more than one year of data did not result in improved identification of model parameters cmelt and drd. Using the re-ordered data series, good identifiability of cmelt was bound to high discharges, while identifiability of drd changed with the addition of further values in descending or ascending order. The methodology revealed structural problems with regard to the parameter drd, which are not yet completely understood and require further investigation