Wind shear at tilted inversions     

Burghard Brümmer 《Boundary-Layer Meteorology》1991,57(3):295-308

Vertical wind shear at a temperature inversion can be caused by baroclinicity associated with a tilt of the inversion. Four observational cases of tilted inversions are presented. The tilts on horizontal scales of 20–100 km range from 2–10 × 10^-3 and the vertical wind shear is between 1 and 25 m/s per 100 m. In general, there is remarkable agreement between observed and geostrophic wind shear.The observations show that the inversion tilt is particularly strong at the edges of mesoscale cloud fields. The Richardson number can reach subcritical values. Cloud fields may be surrounded by a cyclonically rotating wind field and cloud gaps by an anticyclonically rotating wind field.  相似文献   

Atmospheric effects from post-nuclear fires     

Paul J. Crutzen  Ian E. Galbally  Christoph Brühl 《Climatic change》1984,6(4):323-364

During a large nuclear war, the atmosphere would be loaded with huge quantities of pollutants, which are produced by fires in urban and industrial centers, cultivated lands, forests and grasslands. Especially detrimental are the effects of light absorbing airborne particles. An analysis of the amounts of the various types of fuels which could burn in a nuclear war indicates that more than 10¹⁴ g of black smoke could be produced by fires started by the nuclear explosions. Due to this, the penetration of sunlight to the earth's surface would be reduced greatly over extended areas of the northern hemisphere, maybe even globally. This could temporarily cause extreme darkness in large areas in midlatitudes and reduce crop growth and biospheric productivity.This situation would last for several weeks and cause very anomalous meteorological conditions. Much solar radiation would be absorbed in the atmosphere instead of at the earth's surface. The land areas and lower atmosphere would, therefore, cool and the overlying atmosphere warm, creating strong vertical thermal stability in a highly polluted atmosphere. For extended periods and in large parts of the world, weather conditions would be abnormal. The resulting cold, probably freezing, temperatures at the ground would interfere severely with crop production during the growing season and cause extreme conditions for large sections of the biosphere. The combination of lack of sunlight, frost and other adverse meteorological conditions would add enormously to the already huge problems of the survivors.  相似文献   

Suevite of the ries crater,Germany: Source rocks and implications for cratering mechanics     

Prof. Dr. Wolf von Engelhardt  Günther Graup 《International Journal of Earth Sciences》1984,73(2):447-481

Suevites are impact breccias with a montmorillonitic matrix that contains shocked and unshocked mineral and rock fragments from the crystalline basement, glass inclusions and a small amount of sedimentary clasts. Data are given of the modal composition of fall-out suevites (deposited at isolated points around the crater) and crater suevite (forming a layer below post-impact lake sediments in the crater cavity). Fall-out suevites contain aerodynamically shaped bombs which are absent in crater suevite. Taking into account not only large glass fragments and bombs, but also the finer fractions, the glass content of fall-out and crater suevites amounts to 47 and 29 vol%, respectively. Crystalline clasts in suevites consist of all igneous and metamorphic rock types that constitute the local basement which consists of an upper layer of igneous rocks (mainly granites) and a lower series of gneisses and amphibolite. Based on a collection of 1 200 clasts from 13 suevite occurrences the average crystalline clast population of suevites was determined. Suevites contain on the average 46 % igneous and 54 % metamorphic clasts. In constrast, weakly shocked and unshocked crystalline ejecta of the Ries structure consist of 82 % igneous and 18 % metamorphic rocks. From 138 analyses of crystalline rock samples average compositions of the major rock types were calculated. Comparison of these averages with the average glass composition leads to the conclusion that suevite glasses were formed by shock melting of gneisses in deeper levels of the basement. Suevite matrices consist in most cases of 80 to 90 % montmorillonite, in special cases of celadonite. Chemical analyses are given of some matrices and montmorillonite formulas calculated. It is supposed that montmorillonite was formed by early hydrothermal alteration of rock flour or fine glass particles. In the latter case the original glass content of suevites was higher than at present. Of all ejecta from the Ries crater only crystalline rocks contained in suevites occur in all stages of shock metamorphism up to complete fusion. The overwhelming majority of the ejecta from the sedimentary sequence (about 580 m) show no indications of shock pressures above 10 GPa. The same holds true for crystalline megablocks and breccias around the crater which consist mainly of granites from upper levels of the basement. We assume that the Ries impact can be approximated by a deep-burst model: The projectile penetrated through the sedimentary cover into the basement in such a way that the highest pressures and temperatures developed within the gneiss complex below the upper, predominately granitic layer and that rocks of the sedimentary sequence experienced weak shock compression. Numerical data are given for such a model of the Ries impact on transient crater geometry and volumes of vaporized, melted, shocked and excavated rocks. Fall-out suevites are supposed to have been lifted from the central zone by an expanding plume of vaporized rocks and deposited as fluidized turbulent masses outside the crater whereas the main mass of crater suevite was not removed from the crater cavity.  相似文献   

The tropospheric distribution of formaldehyde during TROPOZ II     

D. W. Arlander  D. Brüning  U. Schmidt  D. H. Ehhalt 《Journal of Atmospheric Chemistry》1995,22(3):251-269

A series of 149 measurements of the HCHO mixing ratio were made between 0 and 10 km altitude and 70° N to 60° S latitude during TROPOZ II. The data show a vertical decrease of the HCHO mixing ratio with altitude at all latitudes and a broad latitudinal maximum in the HCHO mixing ratio between 30° N and 30° S at all altitudes. The measured mixing ratios of HCHO are considerably higher than those expected from CH₄ oxidation alone, but agree broadly with the average latitude by altitude distribution of HCHO derived by a 2D model including emissions of C₁–C₇ hydrocarbons. A number of the regional scale deviations of the measured HCHO distribution from the average modelled one can be explained in terms of the local wind field.  相似文献   

Can a pollution event be detected using a single biological effects monitoring method?     

von Westernhagen H  Dethlefsen V  Haarich M 《Marine pollution bulletin》2001,42(4):294-297

The trends of malformation prevalence in embryos of dab, Limanda limanda, in the southern North Sea after the year 1990 mirrored the drop in major pollutants in the rivers draining into the German Bight. Despite this general decline, we detected a pollution event in the southern North Sea in winter 1995/1996 employing the prevalence of malformations in pelagic dab embryos as an indicator. An abrupt rise in malformation prevalence in the embryos of dab, corresponded to a dramatic increase in DDT levels in parent fish from the same area, indicating a hitherto unnoticed introduction of considerable quantities of DDT into the system.  相似文献   

Modelling the variability of midlatitude storm activity on decadal to century time scales   总被引：1，自引：0，他引：1  

Irene Fischer-Bruns  H. von Storch  J. F. González-Rouco  E. Zorita 《Climate Dynamics》2005,25(5):461-476

The output of several multi-century simulations with a coupled ocean–atmosphere general circulation model is examined with respect to the variability of global storm activity in winter on time scales of decades and longer. The frequency of maximum wind speed events within a grid box, using the lower limits on the Beaufort wind speed scale of 8 and 10 Bft as thresholds, is taken as the characteristic parameter. Two historical climate runs with time-dependent forcing of the last five centuries, one control simulation, and three climate change experiments are considered. The storm frequency shows no trend until recently. Global maps for the industrially influenced period hardly differ from pre-industrial maps, even though significant temperature anomalies temporarily emerge in the historical runs. Two indicators describing the frequency and the regional shift of storm activity are determined. In historical times they are decoupled from temperature. Variations in solar and volcanic forcing in the historical simulations as well as in greenhouse gas concentrations for the industrially influenced period are not related to variations in storm activity. Also, anomalous temperature regimes like the Late Maunder Minimum are not associated with systematic storm conditions. In the climate change experiments, a poleward shift of storm activity is found in all three storm track regions. Over the North Atlantic and Southern Ocean, storm activity increases, while it decreases over the Pacific Ocean. In contrast to the historical runs, and with the exception of the North Pacific storm frequency index, the storm indices parallel the development of temperature, exceeding the 2 σ-range of pre-industrial variations in the early twenty-first century.  相似文献   

Improved magnetic anomalies of the Antarctic lithosphere from satellite and near-surface data     

Hyung Rae Kim  Ralph R. B. von Frese  Patrick T. Taylor  Alexander V. Golynsky  Luis R. Gaya-Piqué  Fausto Ferraccioli 《Geophysical Journal International》2007,171(1):119-126

The Antarctic magnetic anomaly map compiled marine and airborne surveys collected south of 60°S through 1999 and used Magsat data to help fill in the regional gaps between the surveys. Ørsted and CHAMP satellite magnetic observations with greatly improved measurement accuracies and temporal and spatial coverage of the Antarctic, have now supplanted the Magsat data. We combined the new satellite observations with the near-surface survey data for an improved magnetic anomaly map of the Antarctic lithosphere. Specifically, we separated the crustal from the core and external field components in the satellite data using crustal thickness variations estimated from the terrain and the satellite-derived free-air gravity observations. Regional gaps in the near-surface surveys were then filled with predictions from crustal magnetization models that jointly satisfied the near-surface and satellite crustal anomalies. Comparisons in some of the regional gaps that also considered newly acquired aeromagnetic data demonstrated the enhanced anomaly estimation capabilities of the predictions over those from conventional minimum curvature and spherical harmonic geomagnetic field models. We also noted that the growing number of regional and world magnetic survey compilations involve coverage gaps where these procedures can contribute effective near-surface crustal anomaly estimates.  相似文献   

Tellurides from Sunrise Dam gold deposit, Yilgarn Craton, Western Australia: a new occurrence of nagyágite     

Y.-H. Sung  C. L. Ciobanu  A. Pring  J. Brügger  W. Skinner  N. J. Cook  M. Nugus 《Mineralogy and Petrology》2007,90(3-4):249-270

Summary The Cu–Fe–Au–Mo (W) deposits in southeastern Hubei are an important component of the Middle–Lower Yangtze River metallogenic belt. Molybdenite from the Fengshandong Cu- (Mo), Ruanjiawan W–Cu- (Mo), Qianjiawan Cu–Au, Tongshankou Cu–Mo and Tonglüshan Cu- (Fe) deposits yielded Re–Os ages of 144.0 ± 2.1 Ma, 143.6 ± 1.7 Ma, 137.7 ± 1.7 Ma, 142.3 ± 1.8–143.7 ± 1.8 Ma and 137.8 ± 1.7–138.1 ± 1.8 Ma, respectively. Phlogopite from the Tieshan Fe- (Cu) deposit yielded an Ar–Ar age of 140.9 ± 1.2 Ma. These data and other published isotopic ages (Re–Os molybdenite and Ar–Ar mica ages) for the Cu–Fe–Au–Mo (W) deposits in the Middle–Lower Yangtze River metallogenic belt show that Cu–Fe–Au–Mo (W) mineralisation in the Tongling, Anqing, Jiurui and Edong ore districts developed in a narrow time span between 135.5 and 144.9 Ma, reflecting an important regional metallogenic event. An integrated study of available petrological and geochronological data, together with relationships to magmatism and the regional geodynamic framework, indicate that the Cu–Fe–Au–Mo (W) mineralisation in the Middle–Lower Yangtze River belt occurred during a regime of lithospheric extension. This extension is probably related to Late Mesozoic processes of lower crustal delamination and lithospheric thinning in East China.  相似文献   

Trace element zoning in pyroxenes from ODP Hole 735B gabbros: diffusive exchange or synkinematic crystal fractionation?     

Yongjun Gao  Jochen Hoefs  Eric Hellebrand  Anette von der Handt  Jonathan E. Snow 《Contributions to Mineralogy and Petrology》2007,153(4):429-442

Major and trace element profiles of clinopyroxene grains in oceanic gabbros from ODP Hole 735B have been investigated by a combined in situ analytical study with ion probe, and electron microprobe. In contrast to the homogeneous major element compositions, trace elements (REE, Y, Cr, Sr, and Zr) show continuous core to rim zoning profiles. The observed trace element systematics in clinopyroxene cannot be explained by a simple diffusive exchange between melts and gabbros along grain boundaries. A simultaneous modification of the melt composition is required to generate the zoning, although Rayleigh fractional crystallization modelling could mimic the general shape of the profiles. Simultaneous metasomatism between the cumulate crystal and the porous melt during crystal accumulation is the most likely process to explain the zoning. Deformation during solidification of the crystal mush could have caused squeezing out of the incompatible element enriched residual melts (interstitial liquid). Migration of the melt along grain boundaries might carry these melt out of the system. This process named as synkinematic differentiation or differentiation by deformation (Natland and Dick in J Volcanol Geotherm Res 110(3–4):191–233, 2001) may act as an important magma evolution mechanism in the oceanic crust, at least at slow-spreading ridges.  相似文献   

Parameterisation of the vertical transport in a small thermally stratified lake     

Christoph von Rohden  Karl Wunderle  Johann Ilmberger 《Aquatic Sciences - Research Across Boundaries》2007,69(1):129-137

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