Dynamical aspects of ozone mini-hole formation     

D. Peters  J. Egger  G. Entzian 《Meteorology and Atmospheric Physics》1995,55(3-4):205-214

Summary A case study and statistical evaluations provide evidence that so-called ozone mini-hole events over Europe, where a rapid drop of total ozone is followed by complete recovery after a few days, are due to the northeascward motion of patches of air with low total ozone content. These patches appear to originate in subtropical latitudes. They correlate well with minima of potential vorticity near the tropopause. Contour dynamics is invoked to explain some basic features of the deformation and northward motion of the mini-holes as well as the related large-scale flow structures.  相似文献   

Pyroxmangite: Stability in H2O-CO2 mixtures at a total pressure of 2000 bars     

Tj. Peters 《Contributions to Mineralogy and Petrology》1971,32(4):267-273

The curve of the reaction: 1 Rhodochrosite + 1 Quartz Pyroxmangite was determined experimentally using gas mixtures with different CO₂H₂O ratios at a total pressure of 2 kb. In pure CO₂, the equilibrium temperature is 508±2° C. By plotting the equilibrium data in terms of InX_CO2 versus reciprocal temperature, a H of reaction of 51.7 kcal was obtained. This plot shows a straight-line relationship, indicating internal consistency of the data, and is in good agreement with previous findings that CO₂ and H₂O mix ideally within the investigated temperature range (400–600° C). When applied to pyroxmangites formed during moderate greenschist facies metamorphism, these data indicate a high acitivity of H₂O.  相似文献   

K-Ar ages of the metamorphic sole of the Semail Ophiolite: implications for ophiolite cooling history     

Edwin Gnos  Tjerk Peters 《Contributions to Mineralogy and Petrology》1993,113(3):325-332

K–Ar ages have been determined on micas and hornblendes in the basal metamorphic sequence and in metamorphic rocks squeezed into the mantle sequence of the Semail Ophiolite. The hornblende ages of 99±0.5 and 102±0.8 Ma and the 90 Ma ages of coexisting micas from the high-grade metamorphic portion of the sequence are interpreted as cooling stages following the peak of metamorphism (T 800–850° C, P 6.5–9 kbar). The new pressure estimates are based on findings of kyanite in garnet-amphibolite and cordierite in quartzitic rocks. These data indicate a cooling rate of 10–30° C/Ma. The oldest mica ages of 95±1 Ma are observed in the lowest-grade greenschists. These also largely represent cooling ages, but might in part also include formation ages. The pattern of the muscovite ages across the metamorphic sole indicates that the cooling front moved from the low-grade metamorphic zone, through the high-grade rocks and into the base of the overlying ophiolite. Radiometric ages of hornblendes (92.3±0.5 and 94.8±0.6 Ma) indicate that the crustal gabbro sequence cooled below 500° C later than the base of the ophiolite sequence. Metamorphism of the sole rocks occurred during subduction of oceanic sediments and volcanic or gabbroic rocks as they progressively came into contact with hotter zones at the base of the overriding plate. The peak of metamorphism must have been contemporaneous with the main magmatism in the Semail Ophiolite. One of the dated muscovites yields an age of 81.3±0.8 Ma, but this is related to discrete deformation zones that were active during late-stage emplacement of the ophiolite.  相似文献   

Nucleation and growth rates of homogeneously condensing water vapor in argon from shock tube experiments     

F. Peters  B. Paikert 《Mineralium Deposita》1993,28(4):521-530

A special shock tube process combining a reflected expansion wave with a weak shock wave is analyzed and calibrated. The process is employed to transfer water vapor carried in argon into a known supersaturated state for a short period of time (0.5 ms). During that period steady state homogeneous nucleation takes place followed by condensational growth. Nucleation and growth rates are measured by a 90° Mie-light scattering technique in the temperature range 200–260 K. The results are compared with existing theoretical models.  相似文献   

Bioaccumulation and histopathological effects of oil on a stony coral     

Esther C. Peters  Philip A. Meyers  Paul P. Yevich  Norman J. Blake 《Marine pollution bulletin》1981,12(10):333-339

Colonies of the shallow-water Caribbean coral Manicina areolata incorporated petroleum hydrocarbons into their tissues during exposure to water accommodated fractions of No. 2 fuel oil for three months. This contamination was not removed after depuration periods of up to two weeks. Although these corals remained alive, evidence of pathological responses was found which included impaired development of reproductive tissues, degeneration and loss of symbiotic zooxanthellae, and atrophy of mucous secretory cells and muscle bundles.  相似文献   

Manganese pyroxenoids and carbonates: Critical phase relations in metamorphic assemblages from the Alps     

Tj. Peters  V. Trommsdorff  J. Sommerauer 《Contributions to Mineralogy and Petrology》1978,66(4):383-388

The compositions of coexisting pyroxmangites, rhodonites, rhodochrosites and manganese calcites in regional metamorphosed manganese cale-silicate marbles from Val Scerscen and Alagna were analysed by microprobe and permit definition of critical tie lines at metamorphic grades appropriate to temperatures between 400 and 450 °C.Variations in composition of coexisting mineral pairs in one and the same locality are attributed to variations in and not to metamorphic temperatures. From the analysed assemblages isothermal plots (with SiO₂ as excess component) were constructed for the system CaO-MnO-SiO₂-CO₂.  相似文献   

High pressure single-crystal synthesis, structure and compressibility of the garnet Mn2+ 3Mn3+ 2[SiO4]3     

T. Arlt  T. Armbruster  R. Miletich  P. Ulmer  T. Peters 《Physics and Chemistry of Minerals》1998,26(2):100-106

Single crystals of the garnet Mn²⁺ ₃Mn³⁺ ₂[SiO₄]₃ and coesite were synthesised from MnO₂-SiO₂ oxide mixtures at 1000°C and 9 GPa in a multianvil press. The crystal structure of the garnet [space group Ia3¯d, a=11.801(2) Å] was refined at room temperature and 100 K from single-crystal X-ray data to R1=2.36% and R1=2.71%, respectively. In contrast to tetragonal Ca₃Mn³⁺ ₂[GeO₄]₃ (space group I4₁/a), the high-pressure garnet is cubic and does not display an ordered Jahn-Teller distortion of octahedral Mn³⁺. A disordered Jahn-Teller distortion either dynamic or static is evidenced by unusual high anisotropic displacement parameters. The room temperature structure is characterised by following bond lengths: Si-O=1.636(4) Å (tetrahedron), Mn³⁺-O=1.995 (4) Å (octahedron), Mn²⁺-O=2.280(5) and 2.409(4) Å (dodecahedron). The cubic structure was preserved upon cooling to 100 K [a=11.788(2) Å] and upon compressing up to 11.8 GPa in a diamond-anvil cell. Pressure variation of the unit cell parameter expressed by a third-order Birch-Murnaghan equation of state led to a bulk modulus K ₀=151.6(8) GPa and its pressure derivatives K′=6.38(19). The peak positions of the Raman spectrum recorded for Mn²⁺ ₃Mn³⁺ ₂[SiO₄]₃ were assigned based on a calderite Mn²⁺ ₃Fe³⁺ ₂[SiO₄]₃ model extrapolated from andradite and grossular literature data.  相似文献   

Peat extraction, conservation and the rural economy in Northern Ireland     

MM Cruickshank  RW TomlinsonD BondPM DevineCJW Edwards 《Applied geography (Sevenoaks, England)》1995,15(4)

Northern Ireland has a tradition of peat cutting; 78 per cent by area of remaining lowland bogs and 46 per cent of blanket bogs have been cut in the past. Since the early 1980s, machine peat extraction for fuel and horticulture has increased, against a background of changing economic support for agriculture, high rural unemployment and agricultural underemployment. Cutting fuel peat can reduce household fuel costs and some peat fuel is sold to gain income. Horticultural peat is cut mainly for sale. Expansion of machine extraction, with possible environmental impacts, occurred as interest in peatland conservation increased. Potential conflict arises between local economic needs and conservation. Machine cutting for fuel is widespread, but affects only 2.6 per cent of the blanket peat area; horticultural extraction is more localized and is only one-fifth of the extent of fuel extraction. Altitude, distance from roads, land ownership and rights, turbary, religious affiliation, local economic needs and the role of government departments all contribute to explaining the distribution and extent of extraction.  相似文献   

Deep-sea sediments in the eastern equatorial Atlantic off the African coast and meteorological flow patterns over the Sahel     

Gerd Tetzlaff  Manno Peters 《International Journal of Earth Sciences》1986,75(1):71-79

Deep-sea mineral dust deposits are a powerful tool allowing to deduct atmospheric flow patterns. Here deep-sea sediments from the eastern tropical Atlantic were used to derive climatic conditions over the African continent where in summer the dust is lifted in the transition zone of the Sahara and the Sahel. The meteorological process causing this aeolian dust injection are the squall lines, the rain bearing disturbances of the Sahel. They produce a high surface wind velocity area in their northern vicinity. The deep-sea deposits of sediments and their spatial patterns allowed to conclude that the dust raising mechanism connected with the squall lines were similar for present day conditions and for the time of the last glacial maximum. The Saharan trades and the African monsoon had about the same extension in either time slice coupled with an identical travel belt of the squall lines. However, the intensity and the frequency of the squall lines were lower in glacial times.

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Zusammenfassung Tiefseesedimente liefern interessante und wertvolle Aufschlüsse über atmosphärische Strömungsbedingungen. Hier werden die Sedimente aus dem Gebiet des östlichen tropischen Nordatlantiks verwendet, um klimatische Angaben über die Strömungsverhältnisse über dem afrikanischen Kontinent zu gewinnen, da die Quelle des Staubes auf dem Kontinent im Übergangsbereich zwischen der Sahara und dem Sahel zu suchen ist. Die meteorologische Ursache des systematischen Staubeintrages in die Atmosphäre sind die regenbringenden sommerlichen Störungen des Sahel («>squall lines»<), die in ihrem nördlichen Randbereich ein Gebiet hoher Windgeschwindigkeit am Boden aufweisen, so daß es hier regelmäßig zu Staubaufwirbelungen kommt. Mit Hilfe der räumlichen und zeitlichen Verteilung der Tiefseesedimente konnte schon früher gezeigt werden, daß während der Periode des letzten Hochglazials die Lage der Grenzzone zwischen Passat und afrikanischem Monsun sich im Vergleich zur Gegenwart nicht verändert hat. Hier wird nun zusätzlich deutlich, daß sowohl die Intensität als auch die Frequenz der «>squall lines»< zum Höhepunkt der Vereisung geringer was als heute.

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Résumé Les sédiments amenés par le vent dans les mers profondes fournissent de précieuses indications sur la distribution des courants atmosphériques. Dans cette note, les sédiments de la partie orientale de l'Atlantique tropical sont examinés en vue de déduire les conditions climatiques régnant sur le continent africain, où la source de la poussière est située entre le Sahara et le Sahel. En effet, l'origine météorologique des apports éoliens sont les pertubations pluvieuses (lignes de grains) qui sont accompagnées sur leur bordure nord de vents de grande vitesse au sol. La distribution des sédiments sur le fond océanique a déjà permis de conclure que le mécanisme de transport était, lors de la dernière glaciation (18.000 ans), semblable à ce qu'il est aujourd'hui. Toutefois, l'intensité et la frequence des perturbations étaient plus faibles qu'aujourd'hui.

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. , , , . ("squall lines"), , , . , . , , squall lines .

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The atmospheric transport potential for water vapour and dust in the Sahel region     

Prof. Dr. Gerd Tetzlaff  Manno Peters 《GeoJournal》1986,12(4):387-398

The transport of water vapour and dust in the Sahel can be assigned to identical atmospheric flow systems, the African Easterly Jet, the Easterly Waves and the Squall Lines. The yield of the rainy season in the Sahel depends on the conditions in the preceding rains of the season and is closely coupled to the surface heat budget both in the monsoonal air in the S and the trades in the N. The heat budget, in particular the evaporation after the passage of a Squall Line, is influenced not only by the total amount of preceding rains but also by the plant cover pumping the water to the surface and smoothing the magnitude of the evaporation in time. This feed-back mechanism may be made responsible for the persistence of the Sahel drought as experienced in recent years. The dust export from the African continent towards the Atlantic can only be so effective, because the Squall Lines and the African Easterly Jet are meshed in a way that produces large amounts of suspended material and lifts it to great heights where the transport velocity is very fast.  相似文献