On the reconstruction of temperature records from proxy data in mid Europe

Summary The problem of the reconstruction of mean summer temperatures from proxy data on a rigorous statistical basis is addressed: Cross spectral analysis is used for evaluating the suitability of linear transfer models between proxy data and temperature, the linear model is estimated from the data of a calibration period and it is verified using the data of a different period. Strict statistical tests are applied at every step of the analysis. Three examples using the proposed method are given: the reconstruction of mean April–July temperatures at Basel from grape harvest data in NE France (1484–1768), mean April–September temperatures at Basel from late wood density of trees from the Swiss Prealps (1270‐1768), and mean April–September temperatures at Great St. Bernhard from the late wood proxy too (1270–1850). The grape harvest data give a very good reconstruction, the resulting temperatures from 1500–1768 are documented. The late wood data fails to give a good reconstruction.

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Die Rekonstruktion von Temperaturreihen aus Proxydaten in Mitteleuropa

Zusammenfassung Es wird das Problem der Rekonstruktion von mittleren Sommertemperaturen aus sogenannten Proxydaten untersucht. Sehr viel Wert wird auf die statistische Signifikanz der Rekonstruktion gelegt. Kreuzspektralanalyse wird benutzt, um die Verwendungsf?higkeit eines linearen Modells als Transfermodell zwischen Temperatur und Proxydaten zu ermitteln. Die Parameter des linearen Transfermodells werden aus den Daten der sogenannten Eichperiode abgesch?tzt und die damit für eine unabh?ngige Periode rekonstruierten Temperaturen werden mit gemessenen verglichen. In jedem Schritt der Analyse werden strikte statistische Tests durchgeführt, um die Ergebnisse zu untermauern. Die Methode wird an drei Beispielen erprobt: die mittlere April–Juli Temperatur in Basel wird mit Hilfe von Weinlesedaten von NE-Frankreich für die Zeit (1484–1768) rekonstruiert, die mittlere April–September Temperatur in Basel und am Gro?en Bernhard wird mit Sp?tholzdichtewerten der Schweizer Voralpen verglichen. Die Weinlesedaten ergeben eine sehr gute Rekonstruktion und die Temperaturreihe für den Zeitraum 1500–1768 wird dokumentiert. Die Sp?tholzdichten liefern keine gute Temperaturrrekonstruktion.

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With 11 Figures     

Use of N stable isotope and microbial analyses to define wastewater influence in Mobile Bay, AL

We assessed short-term ecological and potential human health effects of wastewater treatment plant (WTP) effluent by measuring δ¹⁵N‰ and microbial concentrations in oysters and suspended particulate matter (SPM). We also tested male-specific bacteriophage (MSB) as an alternative to fecal coliforms, to assess potential influence of wastewater contamination on shellfish. WTP effluent did not affect oyster growth or survival, but SPM and oysters acquired wastewater-specific δ¹⁵N‰. δ¹⁵N values were depleted near the WTP, typical of low-level processed wastewater. Fecal coliform and MSB concentrations were higher in samples taken closest to the WTP, and MSB values were significantly correlated with δ¹⁵N‰ in oyster tissues. Overall, oysters demonstrated relatively rapid integration and accumulation of wastewater-specific δ¹⁵N‰ and indicator microorganisms compared to water samples. These data suggest oysters were superior sentinels compared to water, and MSB was a more reliable indicator of wastewater influence on shellfish than fecal coliforms.     

The influence of local fluid flow and the microstructure on elastic and anelastic rock properties

The frequency dependent mechanism of local fluid flow was found to be the decisive absorption and dispersion mechanism in fluid containing sandstones. In the ultrasonic frequency range local fluid flow and grain surface effects control the behaviour of highly porous and highly permeable rock if a pore fluid is present. Both mechanisms depend less on macroscopic rock parameters like porosity and permeability than essentially on microscopic parameters like crack size, crack density and grain contact properties. To demonstrate directly the important influence of the microstructure on the rock elastic and anelastic properties the microstructure of a sandstone was artificially changed by thermal cracking. The cracked rock exhibits a clearly changed behaviour at low uniaxial as well as at high hydrostatic pressure despite small changes of porosity and permeability. Fluid effects increase due to cracking. The experimental results are explained by means of a rock, model and local fluid flow. These results emphasize that it is the microstructure which controls the elastic and anelastic rock behaviour, even at high hydrostatic pressure.     

Development of the water budget for three extra-tropicalcyclones with intense rainfall over Europe

Summary  Three cyclones developing between 28 August and 6 September 1995 were studied with respect to the temporal evolution of their water budget components. The cyclones were simulated with the regional model REMO. Water budget values were determined from hourly model output for circle areas with 500 km radius around the pressure minimum. The results show a maximum liquid water path of about 0.12 kg m⁻² and a maximum ice water path of 0.16 kg m⁻². In the vertical cloud structure the medium cloud layer disappears at the end of the life cycle for all three cyclones. The release of precipitation onto the Baltic Sea drainage basin is different for each cyclone. It lies between 13 and 22 · 10¹² kg. This is about 50% of the total precipitation in the whole area for the strongest cyclone and 65% for the others. The P — E (precipitation minus evaporation) is 15 · 10¹² kg for two of the cyclones and 10 · 10¹² kg for the third one. Received August 7, 2000 Revised March 19, 2001     

Comparison of model predicted cloud parameters and surface radiative fluxes with observations on the 100 km scale

Summary Cloud parameters and surface radiative fluxes predicted by regional atmospheric models are directly compared with observations for a 10-day period in late summer 1995 characterized by predominantly large-scale synoptic conditions. Observations of total cloud cover and vertical cloud structure are inferred from measurements with a ground-based network of Lidar ceilometers and IR-radiometers and from satellite observations on a 100 kilometer scale. Ground-based observations show that at altitudes below 3 km, implying liquid water clouds, there is a considerable portion of optically non-opaque clouds. Vertical distributions of cloud temperatures simultaneously inferred from the ground-based infrared radiometer network and from satellite can only be reconciled if the occurrence of optically thin cloud structures at mid- and high tropospheric levels is assumed to be frequent. Results of three regional atmospheric models, i.e. the GKSS-REMO, SMHI-HIRLAM, and KNMI-RACMO, are quantitatively compared with the observations. The main finding is that all models predict too much cloud amount at low altitude below 900 hPa, which is then compensated by an underestimation of cloud amount around 800 hPa. This is likely to be related with the finding that all models tend to underestimate the planetary boundary layer height. All models overpredict the high-level cloud amount albeit it is difficult to quantify to what extent due to the frequent presence of optically thin clouds. Whereas reasonably alike in cloud parameters, the models differ considerably in radiative fluxes. One model links a well matching incoming solar radiation to a radiatively transparent atmosphere over a too cool surface, another model underpredicts incoming solar radiation at the surface due to a too strong cloud feedback to radiation, the last model represents all surface radiative fluxes quite well on average, but underestimates the sensitivity of atmospheric transmissivity to cloud amount. Received August 31, 2000 Revised March 15, 2001     

Validation of the small-scale performance of a climate model

A canonical correlation analysis is used to study the simulation of the relationship between small-scale precipitation patterns near the Alps and large-scale flow patterns by the ECHAM (ECMWF model, HAMburg version) climate model. The analysis is performed on a monthly mean time scale for the winter months of ECHAM1/T21, ECHAM3/T21 (improved model physics) and ECHAM3/T42 (increased resolution) simulations. The obtained patterns are compared with an identical analysis of observational data. The coarse structures of the observed relationships seem to be reasonably well simulated by the ECHAM3/T42 model version despite the simple shape of the model Alps (hereafter the model Alps), while the results for the ECHAM1/T21 and ECHAM3/T21 are not as good. This appears to be not only due to the increased resolution but also to the improved model physics, since some indication of the relationship can be found in the simulation of the ECHAM3/T21, but not in the simulation of the ECHAM1/T21 model version.Paper presented in session OA19/ST15, Simulation of climates using comprehensive global models at the XIX General Assembly of the EGS, Grenoble, 25–29 April 1994     

The Baltic Sea Experiment BALTEX: A brief overview and some selected results of the authors

The mechanisms responsible for the transfer of energy and water within the climate system are under worldwide investigation within the framework of the Global Energy and Water Cycle Experiment (GEWEX) to improve the predictability of natural and man-made climate changes at short and long ranges and their impact on water resources. Five continental-scale experiments have been established within GEWEX to enable a more complete coupling between atmospheric and hydrological models. One of them is the Baltic Sea Experiment (BALTEX).In this paper, the goals and structure of BALTEX are outlined. A short overview of measuring and modelling strategies is given. Atmospheric and hydrological model results of the authors only are presented. These include also the validation of precipitation using station measurements as well as validation of modelled cloud cover with cloud estimates from satellite data. Furthermore, results of a large-scale grid based hydrological model to be coupled to atmospheric models are presented.This research has never been possible without the contribution of research groups and operational institutions from all 10 member countries. We concentrate here on results obtained at the GKSS research center.     

Effects of an anisotropic overburden on azimuthal amplitude analysis in horizontal transverse isotropic media

Azimuthal amplitude variation in fractured media, commonly used to characterize fracture systems, is a function not only of reflection at the target but also of transmission through the overburden. This study investigates the sensitivity of amplitudes to various anisotropic overburden effects in horizontal transverse isotropic (HTI) media. Issues considered here are geometric spreading, transmission coefficients and attenuation due to fluid flow. Their influence on the azimuthal amplitude variation is evaluated quantitatively over a wide model space.
Only the variation of transmission coefficients with azimuth proves to be negligible. Geometric spreading alters the amplitude signature significantly over a relatively narrow range of models, and its influence increases with layer thickness. The most severe effect of an anisotropic fractured overburden is attenuation due to fluid flow between the cracks or the cracks and pores in the surrounding matrix. The relative changes in amplitudes between the symmetry directions due to anisotropic absorption are of the same order of magnitude as the changes in the reflection coefficient. The effect is significant over a very wide range of petrophysical parameters. Thus it leads to considerable problems in the amplitude analysis for almost any case of an overburden that contains cracks and pores. A correct amplitude analysis at the target will not be possible unless the effect of attenuation is removed.