European temperature records of the past five centuries based on documentary/instrumental information compared to climate simulations

Two European temperature reconstructions for the past half-millennium, January-to-April air temperature for Stockholm (Sweden) and seasonal temperature for a Central European region, both derived from the analysis of documentary sources and long instrumental records, are compared with the output of climate simulations with the model ECHO-G. The analysis is complemented by comparisons with the long (early)-instrumental record of Central England Temperature (CET). Both approaches to study past climates (simulations and reconstructions) are burdened with uncertainties. The main objective of this comparative analysis is to identify robust features and weaknesses in each method which may help to improve models and reconstruction methods. The results indicate a general agreement between simulations obtained with temporally changing external forcings and the reconstructed Stockholm and CET records for the multi-centennial temperature trend over the recent centuries, which is not reproduced in a control simulation. This trend is likely due to the long-term change in external forcing. Additionally, the Stockholm reconstruction and the CET record also show a clear multi-decadal warm episode peaking around AD 1730, which is absent in the simulations. Neither the reconstruction uncertainties nor the model internal climate variability can easily explain this difference. Regarding the interannual variability, the Stockholm series displays, in some periods, higher amplitudes than the simulations but these differences are within the statistical uncertainty and further decrease if output from a regional model driven by the global model is used. The long-term trend of the CET series agrees less well with the simulations. The reconstructed temperature displays, for all seasons, a smaller difference between the present climate and past centuries than is seen in the simulations. Possible reasons for these differences may be related to a limitation of the traditional ‘indexing’ technique for converting documentary evidence to temperature values to capture long-term climate changes, because the documents often reflect temperatures relative to the contemporary authors’ own perception of what constituted ‘normal’ conditions. By contrast, the amplitude of the simulated and reconstructed inter-annual variability agrees rather well.     

A hybrid simplex genetic algorithm for estimating geoacousticparameters using matched-field inversion

Matched-fieId inversion (MFI) undertakes to estimate the geometric and geoacoustic parameters in an ocean acoustic scenario by matching acoustic field data recorded at hydrophone array with numerical calculations of the field. The model which provides the best fit to the data is the estimate of the actual experimental scenario. MFI provides a comparatively inexpensive method for estimating ocean bottom parameters over an extensive area. The basic components of the inversion process are a sound propagation model and matching (minimization) algorithm. Since a typical MFI problem requires a large number of computationally intensive sound propagation calculations, both of these components have to be efficient. In this study, a hybrid inversion algorithm which uses a parabolic equation propagation model and combines the downhill simplex algorithm with genetic algorithms is introduced. The algorithm is demonstrated on synthetic range-dependent shallow-water data generated using the parabolic equation propagation model. The performance for estimating the model parameters is compared for realistic signal-to-noise ratios in the synthetic data     

Search for finite dimensional attractors in atmospheric turbulence

The question is investigated whether the dynamics of turbulent wind fields in the atmospheric boundary layer can be satisfactorily described by a low-dimensional deterministic system. Special emphasis is laid on the detection of a possibly existing, underlying strange attractor. Fast response wind measurements of an ultrasonic anemometer with a sampling rate of 21 Hz were carried out over periods of several days in the near surface boundary layer. The correlation dimension of the resulting time series, several million data points long, is estimated by means of the Grassberger-Procaccia algorithm. No sign of a low dimensional attractor can be detected. By comparison with different types of random noise, the existence of an attractor with dimension lower than six can be excluded in the present data sets.     

The Radio-Silent Start of an Intense Solar Gamma-Ray Flare

Radio-silent -ray flares are solar flares that lack any significant emission in the (non-thermal) radio wave band during their impulsive hard X-ray and -ray emission phases. Flares with extremely suppressed long-wavelength spectra have previously been reported by White et al. (1992) and have been discussed in different context by Hudson and Ryan (1995). A striking example of a radio-silent flare was observed by SMM during the onset of the 6 March 1989 energetic -ray flare. We argue that the absence of radio emission at wavelengths longer than microwave wavelengths is an indication of the compactness of the flare rather than that the flare did not exhibit non-thermal properties. Probably the flare site was restricted to altitudes above the photosphere in a newly emerging loop configuration lower than the equivalent altitude corresponding to an emission frequency of 1.4 GHz. This implies the presence of a dense and highly magnetized closed field configuration confining the electron component which causes the impulsive -ray continuum. Reconnection in such a configuration did not lead to open magnetic fields and streamer formation. Acceleration of particles in the and hard X-ray bursts was restricted to closed field lines. Thermal expansion of the loop system may subsequently lead to the generation of radially propagating blast waves in the solar corona which are accompanied by type II solar radio bursts and decimetre emissions. The emission during the onset of the flare was dominated by a continuum originating from electron bremsstrahlung at X-ray and -ray energies with only little evidence for the presence of energetic ions. It is, therefore, concluded that energetic electrons have been primary and not secondary products of the particle acceleration process.     

Buchbesprechungen

Ohne Zusammenfassung     

Carbon isotope geochemistry of the Precambrian Lomagundi carbonate province,Rhodesia

Carbon isotope measurements carried out on 67 dolomite samples from the Middle Precambrian Lomagundi Group (Rhodesia) have yielded a δ¹³C mean of +8.2 ± 2.6%. vs PDB. With the outcrop of these dolomites extending over a distance of almost 300 km, the Lomagundi dolomite faces is likely to represent the largest isotopically anomalous sedimentary carbonate province ever recorded. It is concluded that the anomalous carbonates formed in a closed basin whose δ¹³C level had been substantially increased as a result of a preferential removal (within sedimentary organics) of the light carbon isotope.     

A linearization scheme for hysteretic systems subjected to random excitation

The problem of predicting the response of hysteretic yielding systems under random excitation is considered. The paper presents a linearization scheme which is motivated by extensive simulation studies of the bilinear hysteretic system. The response process is decomposed into a low frequency drift component and a component with a frequency near the linearized natural frequency of the system. Effective stiffness and damping parameters are presented. The accuracy of the various steps of the scheme is examined. The approach gives results which are in close agreement with simulation estimates even for large-system non-linearity.     

Petrographische Untersuchungen am nordwestdeutschen Posidonienschiefer

Zusammenfassung Die vorliegende Arbeit gibt eine Beschreibung der petrographischen Verhältnisse im Posidonienschiefer. An neuen Mineralien wurden anomale zweiachsige Calcite und Whewellit festgestellt. Die Feinschichtung läßt sich nach Zählung von dickeren Lagen als Warvenschichtung erkennen. Kleine Strömungen haben Erosionsrinnen geschaffen. Von besonderem Interesse ist ein Gliederungsversuch der organischen Substanz, die sich in der differentiellen Thermoanalyse als besonders vielfältig erweist. Durch verschiedene Vorgänge bei der Diagenese wird organische durch anorganische Substanz ersetzt. Eine ganze Reihe von solchen diagenetischen Reaktionen werden beschrieben. Der stete Wechsel zwischen Sapropel—Gyttja und sogar sauerstoffreichem Wasser läßt vermuten, daß das Sediment immer wieder ein Stadium durchlief, in dem die Erdölbildung stattfinden konnte. Es kommt also als Erdölmuttergestein voraussichtlich in Frage. Weitere Untersuchungen sind abzuwarten.