Large-scale motions of the tropics in observations and theory     

Jan Paegle  Julia N. Paegle  Fred P. Lewis 《Pure and Applied Geophysics》1983,121(5-6):947-982

Recent observations of the tropical and subtropical atmosphere are interpreted in terms of scaling arguments and wave propagation theory advanced byCharney (1963, 1969).Charney’s idealizations describe the tropical atmosphere in terms of large regions of quasi-nondivergent flow containing small subdomains of heavy convection and divergence, and place emphasis upon the quasi-rotational regions. FGGE (First GARP Global Experiment) observations suggest that strongly divergent local tropical circulations are forced by latent heating and produce important direct modifications of the total wind field. We describe the extent to which the resulting field consists of divergent and rotational components in different analyses of the FGGE data, and present independent supporting documentation of the results in terms of heating estimates and rainfall observations. Local tropical heating rates on the order of 10°C/day are apparently due to latent heat release associated with precipitation rates as large as 6 cm/day during extended periods. The large contribution of the divergent wind is generally underestimated in models that do not retain such energetic local forcings, and this deficiency may be related to general underestimation of tropical-extratropical connections of many linear models. Such connections are commonly cited in relation to El Niño events, the Southern Hemisphere stationary-wave pattern, and in FGGE studies, but are not well simulated in most linear theories. It is not yet clear whether this is an inherent limitation of linear models, or whether the linear models have not yet explored all the potentially relevant ambient states. We explore the latter possibility by construction of a basic state that allows reasonable latitudinal evolution of the wave field. This basic state has zero absolute vorticity gradient throughout the tropics, and deviations linearized about this state are dynamically analogous to a “local” Hadley cell. To the extent that it is appropriate to regard the results in terms of wave propagation, our analysis suggests a prominent role for gravity-inertia waves in the tropics and for the extratropical connections. The relevance of gravity modes to observations and the theoretical explanation of the flat vorticity field remain to be established.  相似文献   

Pb isotopic heterogeneity in basaltic phenocrysts     

Julia G. Bryce  Donald J. DePaolo 《Geochimica et cosmochimica acta》2004,68(21):4453-4468

The Pb isotopic compositions of phenocrystic phases in young basaltic lavas have been investigated using the Getty-DePaolo method (Getty S. J. and DePaolo D. J. [1995] Quaternary geochronology by the U-Th-Pb method. Geochim. Cosmochim. Acta59, 3267-3272), which allows for the resolution of small isotopic differences. Phenocryst, matrix, and whole rock analyses were made on samples from the 17 Myr-old Imnaha basalts of the Columbia River Group, a zero-age MORB from the Mid-Atlantic Ridge, and a ca. 260 kyr-old tholeiite from Mount Etna. Plagioclase feldspar phenocrysts have low-(U, Th)/Pb, and in each sample the plagioclase has significantly lower ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb values than whole rock, matrix, and magnetite-rich separates. The Pb isotopic contrast between plagioclase and matrix/whole rock is found in three samples with varying grain sizes (0.5-2 cm for the Imnaha basalt and MORB and <1 mm for the Etna sample) from different tectonic settings, suggesting that these results are not unique. The isotopic contrasts are only slightly smaller in magnitude than the variations exhibited by whole rock samples from the region. The Imnaha basalts also have Sr isotopic heterogeneity evident only in plagioclase phenocrysts, but the MORB and Etna lavas do not. The isotopic heterogeneities reflect magma mixing, and indicate that isotopically diverse magmas were mixed together just prior to eruption. The results reinforce indications from melt inclusion studies that magma source region isotopic heterogeneities have large amplitudes at short length scales, and that the isotopic variations imparted to the magmas are not entirely homogenized during segregation and transport processes.  相似文献   

The late thermal history of the Ronda area, southern Spain     

Jos Julin Esteban  Lourdes Snchez-Rodríguez  Diane Seward  Julia Cuevas  Jos María Tubía 《Tectonophysics》2004,389(1-2):81-92

The Betic–Rif belt, in the western Mediterranean, experienced a pre-Alpine history and was later extensively reworked by major Alpine tectonics. There is abundant data showing that the Betic chain suffered very high cooling rates during its Alpine history, constrained mainly by geochronology using various isotopic systems and by palaeontological age determinations. In the westernmost part of the chain the high closure-temperature isotopic systems recorded Miocene high-grade metamorphism in the country rocks. In order to constrain the later stages of cooling, fission-track analysis has been applied to both zircon and apatite. The results point to extremely high rates of cooling (400 °C/Ma) between 21 and 19 Ma. Rates slowed to 100 °C/Ma for the time period 19 to about 12 Ma. The fission-track analysis also confirms the existence of an extensional tectonic stage between 19 and 17 Ma.  相似文献   

Material referred to Megalosaurus (Dinosauria: Theropoda) from the Middle Jurassic of Stonesfield, Oxfordshire, England: one taxon or two?     

Julia J. Day 《Proceedings of the Geologists' Association. Geologists' Association》2004,115(4):359-366

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The implications for paleodietary and paleoclimatic reconstructions of intrapopulation variability in the oxygen and carbon isotopes of teeth from modern feral horses     

Kathryn A. Hoppe  Sue Stuska 《Quaternary Research》2005,64(2):138-146

We analyzed the isotopic patterns found in the tooth enamel of modern feral horses from Shackleford Banks, North Carolina (USA), which has a temperate climate and supports primarily C₄ grasslands. Enamel δ¹³C values averaged −4.1‰ with a standard deviation (1σ) of 1.7‰, which corresponds to an average diet of 66 ± 12% C₄ plants. Our results differ from dietary reconstructions from 1978 to 1981, which found that horses consumed 91% C₄ plants. This suggests that horses have increased their consumption of C₃ forbs, likely as a result of the removal of cattle, sheep, and goats from the island. Shackleford surface waters had δ¹⁸O values that averaged −3.3 ± 0.5‰ and −1.3 ± 1.8‰ on the western and eastern ends of the island, respectively. Tooth enamel samples averaged 27.3 ± 1.5‰ and displayed the same range of δ¹⁸O values as surface waters. The variability of both δ¹⁸O and the δ¹³C values among individuals within this population demonstrates that horses from relatively homogenous temperate environments can display a wide range of isotopic values. Given the observed range of isotopic values for modern horses, we suggest that researchers use the mean values of multiple (≥9) equids when attempting to reconstruct average paleodiets and/or paleoenvironmental conditions.  相似文献   

Trace Element Determination by ICP-AES and ICP-MS: Developments and Applications Reported During 2004 and 2005     

Kathryn L. Linge 《Geostandards and Geoanalytical Research》2006,30(3):157-174

This review describes significant developments in trace element determination using inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS) that were reported in 2004 and 2005. It focuses on the application of ICP techniques to geological and environmental samples; fundamental studies in ICP-MS and ICP-AES instrumentation are not included. The literature reviewed indicated that the majority of new publications concerned advances in ICP-MS analysis rather than ICP-AES. However, ICP-AES developments are still being published, particularly in the areas of sample preconcentration and sample introduction. The trend in increasing publication of developments in hyphenated speciation techniques looks set to persist as knowledge of elemental speciation becomes critical for many environmental studies. Collision or reactions cells were the most reported technique for spectral interference removal in ICP-MS, probably reflecting the growing adoption of cell instruments in laboratories during the last few years.  相似文献   

Quantifying PCE and TCE in DNAPL Source Zones: Effects of Sampling Methods Used for Intact Cores at Varied Contaminant Levels and Media Temperatures   总被引：1，自引：0，他引：1  

Robert L. Siegrist  Kathryn S. Lowe  Michelle L. Crimi  Michael A. Urynowicz 《Ground Water Monitoring & Remediation》2006,26(2):114-124

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Observations of Solitary Waves in the Stable Atmospheric Boundary Layer     

Julia M. Rees  Philip S. Anderson  John C. King 《Boundary-Layer Meteorology》1998,86(1):47-61

Large amplitude, isolated, wave-like phenomena have been observed in the lowest 40 m of the strongly stably stratified atmospheric boundary layer overlying a coastal Antarctic ice shelf. The waves only occur when prevailing wind speeds are low. They always propagate from over the land, with phase speeds exceeding the local mean wind speed. They have wavelengths of the order of 200 m. Several examples are described and a summary of the statistical properties of these waves events is presented.  相似文献   

Observation of converted Moho reflections in the north-west of the Iberian Peninsula     

Julia Téllez  Diego Córdoba 《Geophysical Journal International》1996,124(1):7-17

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Heat flow and regional uplift at the north-eastern border of the Ebro basin, NE Spain     

Julia Cabal  Manel Fernàndez 《Geophysical Journal International》1995,121(2):393-403

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