Operational wave prediction of extreme storms in Northern Europe

The disastrous effects of numerous winter storms on the marine environment in the North Sea and the Baltic Sea during the last decade show that wind waves generated by strong winds actually represent natural hazards and require high quality wave forecast systems as warning tools to avoid losses due to the impact of rough seas. Hence, the operational wave forecast system running at the German Weather Service including a regional wave model for the North Sea and the Baltic Sea is checked extensively whether it provides reasonable wave forecasts, especially for periods of extraordinary high sea states during winter storms. For two selected extreme storm events that induced serious damage in the area of interest, comprehensive comparisons between wave measurements and wave model forecast data are accomplished. Spectral data as well as integrated parameters are considered, and the final outcome of the corresponding comparisons and statistical analysis is encouraging. Over and above the capability to provide good short-term forecast results, the regional wave model is able to predict extreme events as severe winter storms connected with extraordinary high waves already about 2 days in advance. Therefore, it represents an appropriate warning tool for offshore activities and coastal environment.     

Semi-diurnal wind variation in the friction layer above the tropical ocean

Conventional theory predicts that in the layer of frictional influence, the semi-diurnal forcing by pressure-gradient oscillations should produce responses in air motion which show reduced amplitude and phase-leading, in comparison with frictionless conditions in the free troposphere. Wind-profile data obtained by anemometers on a floating mast during the ‘1965-Atlantic Meteor Expedition’ at an anchor station in the SE-trade-wind regime near the equator showed that the amplitude of the west component at the 4-m level practically equalled the fr ictionless value, while other measurements gave evidence of frictional effects, such as phase-leading, and vertical shear from 1 to 10 m. The observed wind response is explained by dynamic coupling as a consequence of forcing by the horizontal pressure gradient oscillation and resulting semi-diurnal variation of surface stress and therefore of eddy diffusivity.     

Late Cretaceous extension overprinting a steep belt in the Northern Calcareous Alps (Schesaplana, R?tikon, Switzerland and Austria)

The Triassic to Cretaceous sediment succession of the Lechtal Nappe in the western part of the Northern Calcareous Alps (NCA) has been deformed into large-scale folds and crosscut by thrust and extensional faults during Late Cretaceous (Eoalpine) and Tertiary orogenic processes. The following sequence of deformation is developed from overprinting relations in the field: (D1) NW-vergent folds related to thrusting; (D2) N–S shortening leading to east–west-trending folds and to the formation of a steep belt (Arlberg Steep Zone) along the southern border of the NCA; (D3) E–W to NE–SW extension and vertical shortening, leading to low-angle normal faulting and recumbent “collapse folds” like the Wildberg Syncline. D1 and D2 are Cretaceous in age and predate the Eocene emplacement of the Austroalpine on the Penninic Nappes along the Austroalpine basal thrust; the same is probably true for D3. Finally, the basal thrust was deformed by folds related to out-of-sequence thrusting. These results suggest that the NCA were at least partly in a state of extension during the sedimentation of the Gosau Group in the Late Cretaceous.     

An overview of the city of Gweru,Zimbabwe’s water supply chain capacity: towards a demand-oriented approach in domestic water service delivery

Following complaints about water shortages in some areas of Gweru, the paper assessed the availability of enabling capacities to efficiently and sufficiently deliver water to the residents of Gweru in line with the existing level of demand. The key inspected capacity aspects were infrastructure, human resources, finances and physical availability of raw water at source. Purposively selected informants from Zimbabwe National Water Authority (ZINWA) and Gweru city council (GCC) provided data on the infrastructural, financial and human resources situation of GCC. Dam levels data for Gweru’s three supply dams were obtained from ZINWA records through the assistance of Sanyati Catchment Hydrologist. The raw water availability was assessed with the aid of Mann–Kendall test using a 10 years period data set from 2003 to 2012 for trend analysis. Findings revealed that the water sources were not experiencing major changes in water levels, to be precise, the changes were insignificant. However, given the increase in population and demand, any slightest negative change in the supply chain would further widen the gap between supply and demand. The study also uncovered that GCC had challenges in terms of the infrastructure, mainly due to financial constraints. Notably, GCC was not experiencing high staff turnover, but it was however, seriously under staffed and failing to effectively monitor water use in the city. Therefore, strong financial injection is required to support staff and resuscitate the reticulation system. Given the perpetual water shortages in Gweru and the status quo in the supply chain, water demand management strategies, wastewater use and consumer education are consequently proposed as measures that would ensure continuous water supply for all needs in the city.     

Boundary layer structure over an inhomogeneous surface: Simulation with a non-hydrostatic mesoscale model

A three-dimensional, non-hydrostatic mesoscale model is used to study boundary-layer structure over an area characterized by the city of Copenhagen, the Øresund strait, and adjacent coastal farmland. Simulations are compared with data obtained on June 5, 1984 during the Øresund experiment.Under moderately strong wind conditions, a stable internal boundary layer (IBL) developed over the Øresund strait during the day. Near-surface winds decelerate over water due to diminished vertical momentum transfer.The turbulent kinetic energy field closely reflects the surface roughness distribution due to the imposed relatively strong wind forcing. TKE budgets over water, farmland and a city area are discussed by inspection of vertical profiles of the individual terms. The buoyancy term is used to indicate IBL heights because it changes sign at the boundary between different stability regimes. Measured and simulated dissipation rates show a decrease in the transition zone as the air travels over water and an abrupt increase when the IBL over a downwind city area is intersected. The top of the stable IBL is characterized by a minimum in the vertical TKE profile.     

Climate Variability-Observations, Reconstructions, and Model Simulations for the Atlantic-European and Alpine Region from 1500-2100 AD

A detailed analysis is undertaken of the Atlantic-European climate using data from 500-year-long proxy-based climate reconstructions, a long climate simulation with perpetual 1990 forcing, as well as two global and one regional climate change scenarios. The observed and simulated interannual variability and teleconnectivity are compared and interpreted in order to improve the understanding of natural climate variability on interannual to decadal time scales for the late Holocene. The focus is set on the Atlantic-European and Alpine regions during the winter and summer seasons, using temperature, precipitation, and 500 hPa geopotential height fields. The climate reconstruction shows pronounced interdecadal variations that appear to “lock” the atmospheric circulation in quasi-steady long-term patterns over multi-decadal periods controlling at least part of the temperature and precipitation variability. Different circulation patterns are persistent over several decades for the period 1500 to 1900. The 500-year-long simulation with perpetual 1990 forcing shows some substantial differences, with a more unsteady teleconnectivity behaviour. Two global scenario simulations indicate a transition towards more stable teleconnectivity for the next 100 years. Time series of reconstructed and simulated temperature and precipitation over the Alpine region show comparatively small changes in interannual variability within the time frame considered, with the exception of the summer season, where a substantial increase in interannual variability is simulated by regional climate models.     

Sensitivity of European glaciers to precipitation and temperature – two case studies

A nonlinear backpropagation network (BPN) has been trained with high-resolution multiproxy reconstructions of temperature and precipitation (input data) and glacier length variations of the Alpine Lower Grindelwald Glacier, Switzerland (output data). The model was then forced with two regional climate scenarios of temperature and precipitation derived from a probabilistic approach: The first scenario (“no change”) assumes no changes in temperature and precipitation for the 2000–2050 period compared to the 1970–2000 mean. In the second scenario (“combined forcing”) linear warming rates of 0.036–0.054°C per year and changing precipitation rates between −17% and +8% compared to the 1970–2000 mean have been used for the 2000–2050 period. In the first case the Lower Grindelwald Glacier shows a continuous retreat until the 2020s when it reaches an equilibrium followed by a minor advance. For the second scenario a strong and continuous retreat of approximately −30 m/year since the 1990s has been modelled. By processing the used climate parameters with a sensitivity analysis based on neural networks we investigate the relative importance of different climate configurations for the Lower Grindelwald Glacier during four well-documented historical advance (1590–1610, 1690–1720, 1760–1780, 1810–1820) and retreat periods (1640–1665, 1780–1810, 1860–1880, 1945–1970). It is shown that different combinations of seasonal temperature and precipitation have led to glacier variations. In a similar manner, we establish the significance of precipitation and temperature for the well-known early eighteenth century advance and the twentieth century retreat of Nigardsbreen, a glacier in western Norway. We show that the maritime Nigardsbreen Glacier is more influenced by winter and/or spring precipitation than the Lower Grindelwald Glacier.     

Five hundred years of gridded high-resolution precipitation reconstructions over Europe and the connection to large-scale circulation

We present seasonal precipitation reconstructions for European land areas (30°W to 40°E/30–71°N; given on a 0.5°×0.5° resolved grid) covering the period 1500–1900 together with gridded reanalysis from 1901 to 2000 (Mitchell and Jones 2005). Principal component regression techniques were applied to develop this dataset. A large variety of long instrumental precipitation series, precipitation indices based on documentary evidence and natural proxies (tree-ring chronologies, ice cores, corals and a speleothem) that are sensitive to precipitation signals were used as predictors. Transfer functions were derived over the 1901–1983 calibration period and applied to 1500–1900 in order to reconstruct the large-scale precipitation fields over Europe. The performance (quality estimation based on unresolved variance within the calibration period) of the reconstructions varies over centuries, seasons and space. Highest reconstructive skill was found for winter over central Europe and the Iberian Peninsula. Precipitation variability over the last half millennium reveals both large interannual and decadal fluctuations. Applying running correlations, we found major non-stationarities in the relation between large-scale circulation and regional precipitation. For several periods during the last 500 years, we identified key atmospheric modes for southern Spain/northern Morocco and central Europe as representations of two precipitation regimes. Using scaled composite analysis, we show that precipitation extremes over central Europe and southern Spain are linked to distinct pressure patterns. Due to its high spatial and temporal resolution, this dataset allows detailed studies of regional precipitation variability for all seasons, impact studies on different time and space scales, comparisons with high-resolution climate models as well as analysis of connections with regional temperature reconstructions. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Variations of ‘wavelengths’ and ‘bisector indices’ of 70 solar spectral lines between 3300 and 3960 Å in Kitt Peak FTS spectra

Wavelengths and bisector indices (a special measure for the asymmetry of a line near its bottom) are determined for 70 lines in each of 47 high-dispersion spectra. The spectra were obtained with the Fourier Transform Spectrograph connected to the McMath Telescope at Kitt Peak National Observatory; they all cover the same spectral range from 3200 to 4000 Å and concern either the full disk (19 disk spectra), or the disk center (9 center spectra), or two areas at sin = 0.85 on the west- and east-side of the disk (19 limb spectra). The main observing seasons were June 1986, June 1987, April and June/July 1988. The - relative - position of an individual line in one spectrum can be established with a precision of about 4 m s^-1, the precision of one bisector index is 1–2 m s^-1.Wavelengths and bisector indices show of course the typical characteristics which result from the familiar effects known as blueshift, limb effect and line asymmetry. However, concerning their variations in time, unexpected results are obtained:(1) Even in disk spectra the time-scales of the wavelength variations are often in the order of one hour or less. (2) For all 3 types of spectra (disk, center, limb) the variations depend not only on the known parameters such as line depth and - occasionally - excitation potential, but also - often even primarily - on wavelength. (3) In center spectra, the wavelength differences between strong and faint lines can vary by as much as 500 m s^-1, in disk spectra short-time variations of wavelength differences can amount to more than 50 m s^-1. (4) For most spectra there is not only a very pronounced and narrow correlation between line shift and line temperature (a special measure for the line depth), but also a significant correlation between line shift and variation of the bisector index.Clearly, the observed effects must be attributed to variations of the velocity fields in the upper photosphere/lower chromosphere (super-granulation cells, overshooting, oscillations), which either influence the line wavelengths directly via the Doppler-effect, or indirectly by changing the contrast between the blue-shifted granules and the red-shifted intergranular lanes. Because of the snapshot character of the observations, no reliable conclusions can be drawn on the actual time-dependency.     

Zur Qualität des Peilminimums beim Funkpeilen

Zusammenfassung Es wird gezeigt, wie neben dem für die Praxis wichtigen subjektiven Peilbefund durch vergleichende Messungen ein objektiver Befund mit quantitativem Gewicht erhalten werden kann. Die sich daraus ergebenden Folgerungen werden diskutiert.

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On the quality of the minimum intensity in radio-goniometry

Summary In the following paper it is pointed out how it is possible to obtain, in addition to the usual subjective results which are important in practice, objective results of quantitative weight by means of comparative measurements. The consequences resulting therefrom are discussed.

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Quelques remarques sur la qualité du minimum d'intensité en radiogoniométrie

Résumé On montre dans ce traité comment il est possible d'obtenir, outre les résultats usuels subjectifs qui sont d'importance dans la pratique, des résultats objectifs à poids quantitatif par des mesures comparatives, Les conséquences en résultant sont discutées.