The effect of Doppler correction on measures of storm track intensity

In climate research, the intensity of a storm track is often measured by the band pass filtered eddy kinetic energy, geopotential variance or related variables. The interpretation of such fields disregards the influence the advection speed might have on these measures. In this paper the need for a Doppler corrected storm track measure is discussed. A Doppler corrected measure is defined and applied to 10 years of ECMWF reanalysis data, correcting the storm track measure for spatial and temporal variability of the advection speed. The storm track intensity is also calculated correcting only for the temporal variability of the advection speed. It is also related to fluctuations of the NAO teleconnection pattern. The Doppler correction suggests that (1) maximum and minimum baroclinic activity is found somewhat downstream of the locations indicated by non-corrected measures, (2) the storm track activity estimated by conventional measures is much too low in the areas of the eastern ends of the storm tracks, (3) the monthly mean time series of the strength of a storm track, as estimated by conventional measures, is strongly influenced by the variability of the advection speed at times, (4) the strength of the storm track seems to be less strongly connected with teleconnection patterns such as NAO or with the background mean flow speed than usually thought on the basis of conventional Eulerian statistics.     

Impact of primary ice nucleation parameterizations on the formation and maintenance of cirrus

Different ice nucleation algorithms are implemented in a cloud microphysical scheme and numerical simulations of clouds are performed using a three-dimensional mesoscale model. The predicted ice crystal fields are found to be sensitive to the different modes of calculation of the number of deposition/ condensation freezing nuclei and contact freezing nuclei. Also a time and supercooling dependence of this sensitivity is established.The general features of the cirrus clouds observed by the research aircraft Falcon during the 1989 (International Cirrus Experiment) mission ICE212 are compared to those of the cirrus clouds generated by the model. The cloud top height, the cloud ice content and the ice number concentrations seem to be reproduced well.     

Scale Dependence of Hydraulic and Structural Parameters in the Crystalline Rock of the KTB

— Knowledge of rock properties controlling the fluid movement is a basic prerequisite to understand the dynamical processes and the temperature and stress regime of the upper crust. Fracture networks were investigated on different scales to obtain quantitative results of fracture geometry like fracture length, orientation and fracture frequencies. Due to the scale effect, these parameters differ in several orders of magnitude in dependence of the scale of investigation. On the microscopic scale, fluorescent thin sections from cores were analysed and permeability was estimated for 2-D hydraulic networks. On the macroscopic scale, fracture parameters were determined from images of structural borehole measurements. The vicinity of the drill site represents the megascopic scale, where seismic reflectors were assumed as active hydraulic structures for construction of a fracture network. Compiling the fracture densities from all investigated scales and taking into consideration only the networks above the percolation threshold, the fracture length distribution follows a power law with an exponent of ?1.9 ± 0.05. Besides the scale differences of the geometric parameters like fracture density and length and the hydraulic parameters like permeability, the connectivity of the networks seems to be a confining characteristic. This is quantitatively described by the percolation parameter and the mean number of intersections per fracture. When assuming a macroscopic hydraulic system at the percolation threshold for the KTB site, the macroscopic mean fracture length can be estimated to approximately 30 m. This stands in agreement with the hydraulic experiments on site.     

Electromagnetic and geoelectric investigation of the Gurinai Structure, Inner Mongolia, NW China

In three field campaigns between the years 2000 and 2004 geophysical measurements were conducted in the Ejina Basin, NW China. Research work in the year 2004, which is described in this paper, was concentrated on the Gurinai Structure (101°25′E, 41°N) situated in the southeastern part of the Ejina Basin in transition to the dune fields of the Badain Jaran Shamo. On satellite images the Gurinai Structure can be identified by two almost 100 km long, subparallel, N–S-striking lineaments, which may indicate tectonic deformations of late Quaternary sediments. To get a coherent picture of the structure a geophysical survey employing three electromagnetic methods – magnetotellurics (MT), transient electromagnetics (TEM), and geoelectrics (DC) – has been conducted to map the subsurface resistivity at different depth scales.The geophysical data interpretation for shallow and intermediate depth down to a few hundred meters links the subsurface distribution of electric resistivity to geomorphological units known from field work in reference with satellite images. The westerly lineament of the Gurinai Structure coincides with a subvertical change in electric resistivity. Together with geomorphological indications from fieldwork and the analysis of elevation data (SRTM), a tectonic deformation of unconsolidated sediments along a fault with an extensional component is interpreted. In the central and eastern part of the Gurinai Structure a shallow resistive subsurface layer can be traced into the first dunes of the Badain Jaran Shamo. This resistive subsurface layer is linked to the presence of fresh water, indicating infiltration from the dune field. Also, in the eastern part of the Gurinai Structure a resistive, approximately ENE-striking feature can be seen at intermediate depth, which is interpreted as a crystalline basement ridge. Towards the southern margin of the Gurinai Structure a trough-shaped unit with low resistivities and a thickness of about 1 km is identified and can be explained by a sediment package saturated with fluids of high salinity or substantial amounts of clay. The strike direction of the structure can be connected to the regional pattern of tectonic faults and seismicity.The interpretation of electromagnetic data at various depth scales contributes to the general understanding of the Ejina Basin's buildup and tectonic setting in the vicinity of the Gurinai Structure.     

Winter climate anomalies in Europe and their associated circulation at 500 hPa

Regional anomalies of the surface climate over Europe are defined by a simultanous EOF-analysis of the normalized monthly mean sea level pressure, temperature and precipitation fields of 100 winters (December–February, 1887–1986) at 40 stations. The monthly amplitudes of the first EOF (about 25% of the total variance) are used as an index for the monthly winter climate anomaly. They characterize a high (low) pressure cell over central Europe associated with a positive (negative) temperature and precipitation anomaly over northern (central-southern) Europe as indicated by a northward (southward) shift of the tail end of the cross-Atlantic cyclone track. These patterns resemble the phenomenological anticyclonic (cyclonic) Grosswetter classification and the European blocking (enhanced zonal flow) regime. The second EOF is of similar magnitude and gives latitudinal corrections to these two basic flow regimes. The joint probability distribution of both amplitudes shows a weak bimodality mainly associated with the first EOF. Further insight into the underlying physical processes of the climate anomaly patterns in Europe is obtained from the extended Eliassen-Palm flux diagnostics of the barotropic transient eddy-mean flow interaction (Hoskins et al. 1983) and the stationary wave propagation (Plumb 1985). The diagnostics confined to the barotropic components and applied to the regression and the composite anomaly fields of the transient and stationary eddy flows of the 500 hPa geopotential (1946–87, north of 20°N) leads to the following results: (1) The bandpass filtered transient eddy variances of the 500 hPa geopotential show a shift of the cross-Atlantic storm track: In high (low) pressure situations over Europe the cross-Atlantic storm track intensity is enhanced (reduced) and its tail end is shifted northward (remains zonal); the North Pacific storm track extends further (less) eastward and thus closer to the west coast of North America. (2) The extreme high pressure system over Europe tends to be supported by an anomalous transient eddy forcing of the mean flow stream-function: it enhances the zonal wind to its north and generates anticyclonic vorticity about 10° upstream from its center. In the low pressure composite the anomalous cyclonic vorticity is generated reducing the zonal flow to its north. (3) The occurrence (lack) of a strong eastward stationary wave activity flux over the Atlantic is associated with the high (low) pressure situations over Europe. Finally, a positive feedback is conjectured between the stationary wavetrain modifying the tail end of the cross-Atlantic storm track and the transient eddies intensifying this anomaly.     

On the validation of the atmospheric model REMO with ISCCP data and precipitation measurements using simple statistics

Summary The regional atmospheric model REMO is used to study the energy and water exchange between surface and atmosphere over the Baltic Sea and its catchment area. As a prerequisite for such studies, the model has to be validated. A major part of such a validation is the comparison of simulation results with observational data. In this study the DX product of the International Cloud Climatology Project (ISCCP) and precipitation measurements from 7775 rain gauge stations within the model domain are used for comparisons with the simulated cloud cover and precipitation fields, respectively. The observations are available in this high spatiotemporal resolution for June 1993. To quantify the comparisons of means, variability, and patterns of the data fields simple statistics are used and the significance of the results is determined with resampling methods (Pool Permutation Procedure and Bootstrap-t). The conclusion is that simulated and observed means of the fields are not different at the 5% significance level. The determined variability of the fields is also in good agreement except the space variability in cloud cover. Time mean and anomaly patterns are in good coincidence in case of the comparisons of cloud cover fields, but in reduced coincidence in case of precipitation.With 9 Figures     

Hf-W mineral isochron for Ca,Al-rich inclusions: Age of the solar system and the timing of core formation in planetesimals

Application of ¹⁸²Hf-¹⁸²W chronometry to constrain the duration of early solar system processes requires the precise knowledge of the initial Hf and W isotope compositions of the solar system. To determine these values, we investigated the Hf-W isotopic systematics of bulk samples and mineral separates from several Ca,Al-rich inclusions (CAIs) from the CV3 chondrites Allende and NWA 2364. Most of the investigated CAIs have relative proportions of ¹⁸³W, ¹⁸⁴W, and ¹⁸⁶W that are indistinguishable from those of bulk chondrites and the terrestrial standard. In contrast, one of the investigated Allende CAIs has a lower ¹⁸⁴W/¹⁸³W ratio, most likely reflecting an overabundance of r-process relative to s-process isotopes of W. All other bulk CAIs have similar ¹⁸⁰Hf/¹⁸⁴W and ¹⁸²W/¹⁸⁴W ratios that are elevated relative to average carbonaceous chondrites, probably reflecting Hf-W fractionation in the solar nebula within the first ∼3 Myr. The limited spread in ¹⁸⁰Hf/¹⁸⁴W ratios among the bulk CAIs precludes determination of a CAI whole-rock isochron but the fassaites have high ¹⁸⁰Hf/¹⁸⁴W and radiogenic ¹⁸²W/¹⁸⁴W ratios up to ∼14 ε units higher than the bulk rock. This makes it possible to obtain precise internal Hf-W isochrons for CAIs. There is evidence of disturbed Hf-W systematics in one of the CAIs but all other investigated CAIs show no detectable effects of parent body processes such as alteration and thermal metamorphism. Except for two fractions from one Allende CAI, all fractions from the investigated CAIs plot on a single well-defined isochron, which defines the initial ε¹⁸²W = −3.28 ± 0.12 and ¹⁸²Hf/¹⁸⁰Hf = (9.72 ± 0.44) × 10⁻⁵ at the time of CAI formation. The initial ¹⁸²Hf/¹⁸⁰Hf and ²⁶Al/²⁷Al ratios of the angrites D’Orbigny and Sahara 99555 are consistent with the decay from initial abundances of ¹⁸²Hf and ²⁶Al as measured in CAIs, suggesting that these two nuclides were homogeneously distributed throughout the solar system. However, the uncertainties on the initial ¹⁸²Hf/¹⁸⁰Hf and ²⁶Al/²⁷Al ratios are too large to exclude that some ²⁶Al in CAIs was produced locally by particle irradiation close to an early active Sun. The initial ¹⁸²Hf/¹⁸⁰Hf of CAIs corresponds to an absolute age of 4568.3 ± 0.7 Ma, which may be defined as the age of the solar system. This age is 0.5-2 Myr older than the most precise ²⁰⁷Pb-²⁰⁶Pb age of Efremovka CAI 60, which does not seem to date CAI formation. Tungsten model ages for magmatic iron meteorites, calculated relative to the newly and more precisely defined initial ε¹⁸²W of CAIs, indicate that core formation in their parent bodies occurred in less than ∼1 Myr after CAI formation. This confirms earlier conclusions that the accretion of the parent bodies of magmatic iron meteorites predated chondrule formation and that their differentiation was triggered by heating from decay of abundant ²⁶Al. A more precise dating of core formation in iron meteorite parent bodies requires precise quantification of cosmic-ray effects on W isotopes but this has not been established yet.     

Physical properties of rocks from the upper part of the Yaxcopoil‐1 drill hole,Chicxulub crater

Abstract— Physical properties were determined in a first step on post‐impact tertiary limestones from the depth interval of 404–666 m of the Yaxcopoil‐1 (Yax‐1) scientific well, drilled in the Chicxulub impact crater (Mexico). Thermal conductivity, thermal diffusivity, density, and porosity were measured on 120 dry and water‐saturated rocks with a core sampling interval of 2–2.5 m. Nondestructive, non‐contact optical scanning technology was used for thermal property measurements including thermal anisotropy and inhomogeneity. Supplementary petrophysical properties (acoustic velocities, formation resisitivity factor, internal surface, and hydraulic permeability) were determined on a selected subgroup of representative samples to derive correlations with the densely measured parameters, establishing estimated depth logs to provide calibration values for the interpretation of geophysical data. Significant short‐ and long‐scale variations of porosity (1–37%) turned out to be the dominant factor influencing thermal, acoustic, and hydraulic properties of this post impact limestone formation. Correspondingly, large variations of thermal conductivity, thermal diffusivity, acoustic velocities, and hydraulic permeability were found. These variations of physical properties allow us to subdivide the formation into several zones. A combination of experimental data on thermal conductivity for dry and water‐saturated rocks and a theoretical model of effective thermal conductivity for heterogeneous media have been used to calculate thermal conductivity of mineral skeleton and pore aspect ratio for every core under study. The results on thermal parameters are the necessary basis for the determination of heat flow density, demonstrating the necessity of dense sampling in the case of inhomogeneous rock formations.     

Comparison of petrophysical properties of impactites for four meteoritic impact structures

We reanalyzed and compared unique data sets, which we obtained in the frame of combined petrophysical and geothermal investigations within scientific drilling projects on four impact structures: the Puchezh–Katunki impact structure (Vorotilovo borehole, Russia), the Ries impact structure (Noerdlingen‐73 borehole, Germany), the Chicxulub impact structure (ICDP Yaxcopoil‐1 borehole, Mexico), and the Chesapeake impact structure (ICDP‐USGS‐Eyreville borehole, USA). For a joined interpretation, we used the following previously published data: thermal properties, using the optical scanning technique, and porosities, both measured on densely sampled halfcores of the boreholes. For the two ICDP boreholes, we also used our previously published P‐wave velocities measured on a subset of cores. We show that thermal conductivity, thermal anisotropy, porosity, and velocity can be correlated with shock metamorphism (target rocks of the Puchezh–Katunki and Ries impact structures), and confirm the absence of shock metamorphism in the samples taken from megablocks (Chicxulub and Chesapeake impact structure). The physical properties of the lithic impact breccias and suevites are influenced mainly by their impact‐related porosity. Physical properties of lower porosity lithic impact breccias and suevites are also influenced by their chemical composition. These data allow for a distinction between different types of breccias due to differences concerning the texture and chemistry and the different amounts of melt and rock clasts.