Beardsley vs. Faith: physical diversity among H5 chondrites

The microstructure and some physico-mechanical properties of Beardsley and Faith, both H5 chondrites, were compared. Although the bulk sample porosities are respectively 9.1% and 14.5%, suggesting lower consolidation of Faith, the effective porosities are 5.63% and 1.79%—much higher for Beardsley. The material of Faith, characterized by vugs, vesicles and closed channels—abundant but all sized below 0.01 μm—is of higher strength than that of Beardsley, where joints, fissures, open channels and microcracks are sized from 0.1 to 10 μm. The higher elastic properties of Faith are shown by the velocity of the compressional wave of 6.66 km s⁻¹ against that of 5.12 km s⁻¹ for Beardsley. An example of physical diversity among chondrites to the same chemical-petrologic type is therefore demonstrated.     

Deep structure of the Earth's crust in the contact zone of the Palaeozoic and Precambrian Platforms in Poland (Tornquist-Teisseyre zone)

One of the major tectonic problems in Europe concerns the southwest margin of the East European Platform in the region of the so-called Polish-Danish trough. In general, this margin is assumed to be the Tornquist-Teisseyre (T-T) Line, running approximately from northwest to southeast in this part of Europe. Determination of deep crustal structure of the contact zone between the Precambrian Platform and the Palaeozoic Platform was the main aim of the deep seismic sounding (DSS) programme in Poland in 1965–1982.Deep seismic soundings of the Earth's crust have been made in the T-T Line zone along nine profiles with a total length of about 2600 km. The results of deep seismic soundings have shown that the crust in the marginal zone of the East European Platform has highly anomalous properties. The width of this zone ranges from 50 km in northwest Poland to about 90 km in southeast Poland. The crustal thickness of the Palaeozoic Platform in Poland is 30–35 km, and of the Precambrian Platform 42–47 km, while in the T-T tectonic zone it varies from 50 to 55 km. Above the Moho boundary, in the T-T zone, at a depth of 40–45 km, there is a seismic discontinuity with P-wave velocities of 7.5–7.7 km/s. Boundary velocities, mean velocities and stratification of the Earth's crust vary distinctly along the T-T zone. There are also observed high gravimetric and magnetic anomalies in the T-T zone. The T-T tectonic zone determined in this manner is a deep tectonic trough with rift properties.The deep fractures delineating the T-T tectonic zone are of fundamental importance for the localization of the plate edge of the Precambrian Platform of eastern Europe. In the light of DSS results, the northeastern margin of the T-T tectonic zone is a former plate boundary of the East European Platform.     

Seismic model of the lithosphere of the East European Platform beneath the Baltic Sea-Black Sea profile

This paper presents the results of seismic measurements along the Baltic Sea-Black Sea profile. The basic wave groups recorded up to distances of 900 km are characterized. The main elements of a lithospheric model of the southwestern part of the Precambrian East European Platform are given. The thickness of the Earth's crust is about 45 km and the mean velocity of the crust is about 6.3 km/s. At a depth of 65 km, the velocity increases from 8.2 to 8.5 km/s. In the depth interval 110 to 135 km, there is a series of layers with low and high velocities. The lower boundary of the lithosphere is probably defined by the boundary at a depth of 110 km.     

Physics of basic motions in asymmetric continuum

We consider the advantages of a formalism based on concept of the asymmetric continuum and we present some equivalence theorems relating it to the asymmetric elasticity and to micropolar and micromorphic theories as founded by Nowacki, Cosserats and Eringen. We consider the basic processes in an asymmetric continuum which could be reduced to the point basic motions/deformations. The co-action of spin and shear motions is assumed to play the main role in fracturing process, while the constitutive relation between the antisymmetric stresses and rotations replaces the friction constitutive law.     

The distribution of meteoric <Superscript>36</Superscript>Cl/Cl in the United States: a comparison of models

The natural distribution of ³⁶Cl/Cl in groundwater across the continental United States has recently been reported by Davis et al. (2003). In this paper, the large-scale processes and atmospheric sources of ³⁶Cl and chloride responsible for controlling the observed ³⁶Cl/Cl distribution are discussed.The dominant process that affects ³⁶Cl/Cl in meteoric groundwater at the continental scale is the fallout of stable chloride from the atmosphere, which is mainly derived from oceanic sources. Atmospheric circulation transports marine chloride to the continental interior, where distance from the coast, topography, and wind patterns define the chloride distribution. The only major deviation from this pattern is observed in northern Utah and southern Idaho where it is inferred that a continental source of chloride exists in the Bonneville Salt Flats, Utah.In contrast to previous studies, the atmospheric flux of ³⁶Cl to the land surface was found to be approximately constant over the United States, without a strong correlation between local ³⁶Cl fallout and annual precipitation. However, the correlation between these variables was significantly improved (R ²=0.15 to R ²=0.55) when data from the southeastern USA, which presumably have lower than average atmospheric ³⁶Cl concentrations, were excluded. The total mean flux of ³⁶Cl over the continental United States and total global mean flux of ³⁶Cl are calculated to be 30.5±7.0 and 19.6±4.5 atoms m^–2 s^–1, respectively.The ³⁶Cl/Cl distribution calculated by Bentley et al. (1986) underestimates the magnitude and variability observed for the measured ³⁶Cl/Cl distribution across the continental United States. The model proposed by Hainsworth (1994) provides the best overall fit to the observed ³⁶Cl/Cl distribution in this study. A process-oriented model by Phillips (2000) generally overestimates ³⁶Cl/Cl in most parts of the country and has several significant local departures from the empirical data.

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Resumen Davis et al. (2003) han informado de la distribución natural de la proporción ³⁶Cl/Cl en las aguas subterráneas de la parte continental de los Estados Unidos de América [EUA]. En este artículo, se discute cuáles son los procesos a gran escala y las fuentes atmosféricas del ³⁶Cl y del cloruro que dan lugar a la distribución observada de ³⁶Cl/Cl.El proceso dominante que afecta a la relación ³⁶Cl/Cl en las aguas subterráneas de origen meteórico a escala continental es el aporte de cloruro estable desde la atmósfera, que procede principalmente de los océanos. La circulación atmosférica transporta el cloruro marino hacia el interior, donde la distancia a la costa, topografía y corrientes del viento definen la distribución del cloruro. La única desviación principal de este esquema tiene lugar al norte de Utah y en el sur de Idaho, donde se deduce que existe una fuente continental de cloruro en los Rellanos Salados de Bonneville (Salt Flats).En contraste con estudios previos (Knies et al. 1994; Phillips 2000), se ha descubierto que el flujo atmosférico de ³⁶Cl hacia la superficie terrestre es aproximadamente constante en todos los estados, sin deducirse una correlación fuerte entre el aporte de ³⁶Cl y la precipitación anual. Sin embargo, la correlación entre estas variables se ve mejorada de forma significativa, con coeficientes de regresión comprendidos entre 0,15 y 0,55, cuando se excluyen los datos recogidos en el sudeste de los EUA, que tienen concentraciones de ³⁶Cl atmosférico presuntamente inferiores a la media. El flujo medio total de ³⁶Cl calculado en la zona continental de los Estados Unidos vale 30,5±7,0 átomos por metro cuadrado y segundo, mientras que el flujo total global de ³⁶Cl es de 19,6±4,5 átomos por metro cuadrado y segundo.La distribución de ³⁶Cl/Cl calculada por Bentley et al. (1986) infravalora la magnitud y variabilidad observada en los valores medidos a lo largo de los Estados Unidos. El modelo propuesto por Hainsworth (1994) proporciona el mejor ajuste conjunto a la distribución observada de ³⁶Cl/Cl en este estudio. El modelo orientado a procesos de Phillips (2000) sobreestima por lo general la distribución de ³⁶Cl/Cl en la mayoría del país y difiere significativamente de algunos valores locales empíricos.

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Résumé La distribution naturelle du rapport ³⁶Cl/Cl dans les eaux souterraines des États-Unis a été récemment présentée par Davis et al. (2003). Dans ce travail, les processus à grande échelle et les sources atmosphériques de ³⁶Cl et de chlorure responsables du contrôle de la distribution observée du rapport ³⁶Cl/Cl sont discutés. Le processus dominant qui affecte le rapport ³⁶Cl/Cl dans les eaux souterraines dorigine météorique à léchelle continentale est lapport atmosphérique de chlorure stable, qui provient pour lessentiel de sources océaniques. La circulation atmosphérique transporte des chlorures marins vers lintérieur des continents, où la distribution de chlorure est définie par la distance à la côte, la topographie et les régimes des vents. La seule exception majeure à ce schéma est observée dans le nord de lUtah et le sud de lIdaho où lon suppose quil existe une source continentale de chlorure dans les bas-fonds salés de Bonneville. Au contraire de précédentes études (Knies et al. 1994; Phillips 2000), on trouve que le flux atmosphérique de ³⁶Cl vers le sol est approximativement constant sur lensemble des États-Unis, sans forte corrélation entre la retombée locale de ³⁶Cl et les précipitations annuelles. Cependant, la corrélation entre ces variables devient significative (R ²=0.15 à 0.55) lorsquon supprime les données du sud-est des États-Unis, dont on pense quelles présentent des concentrations en ³⁶Cl atmosphérique inférieures à la moyenne. Le flux total moyen de ³⁶Cl sur les États-Unis continentaux et le flux moyen global de ³⁶Cl sont respectivement évalués à 30.5 ± 7.0 et 19.6 ± 4.5 atomes.m^–2.s^–1. La distribution du rapport ³⁶Cl/Cl calculée par Bentley et al. (1986) sous-estime lordre de grandeur et la variabilité observés pour la distribution mesurée du rapport ³⁶Cl/Cl sur les États-Unis continentaux. Le modèle proposé par Hainsworth (1994) fournit le meilleur ajustement densemble à la distribution du rapport ³⁶Cl/Cl observée dans cette étude. Un modèle orienté vers les processus proposé par Phillips (2000) surestime dans lensemble le rapport ³⁶Cl/Cl dans la plupart des régions du pays et présente plusieurs désaccords locaux avec les données empiriques.

     

Newly identified historical tornadoes in the Czech Republic from 16th to the 20th centuries

Tornadoes have occurred in the territory of the Czech Republic throughout history. Although their frequency and intensity are not as high as in the USA, they can cause severe damage as well. That is why a systematic effort to document individual occurrences of this dangerous meteorological phenomenon as far as possible back into the past began in the 1990s. The aim of this investigation is to extend the first European catalogue of tornadoes originally published by Wegener [Wegener A., 1917. Wind-und Wasserhosen in Europe], by the addition of these cases from the Czech Republic.This paper adds further to Setvák, Šálek and Munzar [Setvák M., Šálek M., Munzar J., 2003. Tornadoes within the Czech Republic—from medieval chronicles to the internet society. Atmos. Res. 67–68, 589–605], who reported the earliest documented tornado in the land of the Czech Republic which occurred in AD 1119 in Prague. In so doing, it presents recently discovered tornado cases from the 16th to the early 20th centuries, found in a variety of historical sources since the last ECSS conference held in Prague in 2002. In particular we will focus on the case from Jablonec nad Nisou (northern Bohemia) in 1925, which was probably the first case in the Czech Republic with accompanying photographic documentation of damage caused by a tornado.     

Diagnostic analyses of convective events — The effect of propagating gust fronts

This paper is devoted to the testing experiment of a postprocessing tool aimed at the objective analysis of propagating gust fronts in a given convective environment. The tool is being developed to be applicable in the operational mode by utilizing NWP model outputs. The experiment was carried out on two summer convective cases which occurred in the Czech Republic. The cases were numerically simulated by the limited area NWP model LM COSMO with the horizontal resolution of 2.8 km. They represent different types of convective systems, both accompanied by objectively identifiable gust fronts and causing heavy precipitation. The event from July 2000 was characterised by the development of isolated thunderstorms. The other event from July 1998 was a long-lasting and organised convective system — a squall line. The hypothesis was that the developed postprocessing tool is capable to evaluate the role which downdraft outflows played in the decay and initiation of convective cells by interaction with convective environment and thus in prolongation of convection lifetime.The procedures of the Objective Analysis of Gust Fronts (OAGF) were applied to the thermodynamic outputs of the LM COSMO. The aim was to determine the position of gust fronts within the domain and to assess their speed of movement and the potential to initiate convection according to the properties of ambient vertical shear and stability as well as humidity conditions ahead of the respective downdraft outflows. In addition, the Radar Simulation Model (RSM) was employed to monitor the simulated convective systems in arbitrary PPI and RHI scans and to verify qualitatively the LM COSMO precipitation forecasts.The case studies has confirmed the applicability of the LM COSMO–OAGF chain and RSM, which may represent the potential for improving the operational nowcasting of hazardous convection phenomena. In both simulations, the objective gust fronts moved on into the vertical shear-favourable environment for triggering new convection. In addition to the dynamical organisation, there were also favourable stability and humidity conditions in the area of forced upward motions in the simulation of the event from July 2000.