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81.
Jim Best John Woodward Phil Ashworth Greg Sambrook Smith Chris Simpson 《Sedimentary Geology》2006,190(1-4):241-255
Discrete hollows in the bar tops of the South Saskatchewan River are described that form a newly-recognized morphological element of sandy braided rivers. These bar-top hollows, which are up to 1.7 m deep and may extend for 10–30 m down and across flow, have a circular to ovoid planform and are shown, through use of ground penetrating radar, to be filled by a series of distinct, often angle-of-repose, foresets. The hollows form by both erosion and bar-top deposition and may be generated by bar-tail accretion, cross-bar channel cutoff and subsequent fill or lateral accretion at the bar-head. Bar-top hollows occur in the upper part of the bar depositional sequence and may thus prove useful indicators for braid bar reconstruction in ancient sediments, and should not be confused with channel scour. 相似文献
82.
This letter proposes a novel extremely low frequency (ELF) radar for major oil deposits. Using our recently developed whole-Earth electromagnetic wave propagation model based upon the finite-difference time-domain method, we have determined that detection of the radial (vertical) component of the scattered H-field provides a sensitive means to detect oil fields that are located within several kilometers of the Earth's surface. As an example, we provide numerical simulations of ELF radar returns from a hypothetical Alaskan oil field excited by a 20-Hz pulse emitted from the former U.S. Navy site in Wisconsin. The proposed method would potentially provide means to rapidly and inexpensively conduct aerial surveys of thousands of square kilometers for significant oil deposits. 相似文献
83.
I. J. Simpson G. W. Thurtell H. H. Neumann G. Den Hartog G. C. Edwards 《Boundary-Layer Meteorology》1998,87(1):69-99
Flux-gradient relationships based upon similarity theory have been reported to severely underestimate scalar fluxes in the roughness sublayer above forests, as compared to independent flux estimates (for example, eddy covariance or energy balance measurements). This paper presents the results of a unique three-month investigation into the validity of similarity theory in the roughness sublayer above forests. Eddy covariance and flux-gradient measurements of carbon dioxide (CO2) exchange were compared above a mixed deciduous forest at Camp Borden, Ontario, both before and after leaf senescence. The eddy covariance measurements used a Li-Cor infrared gas analyzer, and the flux-gradient (similarity theory) measurements featured a tunable diode laser Trace Gas Analysis System (TGAS). The TGAS resolved the CO2 concentration difference to 300 parts per trillion by volume (ppt) based upon a half-hour sampling period. The measured enhancement factor (the ratio of independent flux estimates, in this case eddy covariance, to similarity theory fluxes) was smaller and occurred closer to the canopy than in most previous investigations of similarity theory. Very good agreement between the eddy covariance and similarity theory fluxes was found between 1.9 and 2.2 canopy heights (hc), and the mean enhancement factors measured before and after leaf senescence were 1.10 plusmn; 0.06 and 1.24 ± 0.07, respectively. Larger discrepancies were measured closer to the canopy (1.2 to 1.4 hc), and mean enhancement factors of 1.60 ± 0.10 and 1.82 ± 0.11 were measured before and after leaf senescence, respectively. Overall, the Borden results suggest that similarity theory can be used within the roughness sublayer with a greater confidence than previously has been believed. 相似文献
84.
Asgeir Sorteberg Øystein Hov Sverre Solberg Kjetil Tørseth Hans Areskoug Martin Ferm Kit Granby Heikki Lättilä Karin Persson David Simpson 《Journal of Atmospheric Chemistry》1998,30(2):241-271
Observations of the concentration of several nitrogen containing compounds at five rural Scandinavian sites during March–June 1993 are reported. Total nitrate (NO
3
-
+ HNO3) and total ammonium (NH
4
+
+ NH3) were measured by denuder and filter pack. In general the methods agree well. At all sites the particulate fraction dominated, with the largest fraction of NO
3
-
and the lowest of NH
4
+
at the sites which were closest to the emission sources. The fraction of NO
3
-
of total nitrate increased with increasing NO2 concentrations, indicating that the nighttime conversion of NO2 to NO
3
-
is an important route of formation for NO
3
-
. A positive correlation was found between HNO3 and O3 in June at all sites, while no correlation was found early in the spring. Model calculations were made with a lagrangian boundary layer photooxidant model for the whole period, and compared to the measured concentrations. The calculated ratio between mean observed and modelled daily maximum concentrations of ozone over the measurement period were within +/–10% at all sites. The models ability to describe the daily ozone maximum concentration was satisfactory with an average deviation of 19–22% from the observed concentrations. HNO3 was underestimated by over 50% at all sites except the one closest to the emission sources. The correlation between modelled and observed concentrations was generally best for the sites with shortest transport distance from the sources of emission. 相似文献
85.
86.
Fabric development in brittle-to-ductile shear zones 总被引:3,自引:0,他引:3
Carol Simpson 《Pure and Applied Geophysics》1986,124(1-2):269-288
Brittle-to-ductile shear zones from two separate geological settings are shown to have nucleated on zones of predominantly brittle deformation. The shear zones are not simply foliated cataclasites, since they contain abundant evidence of dynamic recrystallization of constituent minerals. A small quartz diorite lens in the Borrego Springs shear zone, southern California, contains centimeter-scale cataclasite zones that exhibit a gradual transition into foliated rock. Alteration of magnesiohornblende to actinolite, feldspar to white mica plus quartz, and biotite to chlorite, produced elongate minerals that define the foliation. During the later stages of deformation, intracrystalline slip and dynamic recrystallization of quartz and feldspar were important deformation mechanisms.The widespread occurrence of mineralized dilatant cracks predated the development of meter-to-decimeter-scale ductile shear zones in the Striped Rock granite, southern Virginia. Again, important deformation mechanisms in the final stages of deformation were intracrystalline slip and dynamic recrystallization of quartz.In both field areas the role of fluids has been important from the onset of brittle deformation. Fluids may have enhanced early fracturing in addition to causing the alteration and hydrolytic weakening of host rock minerals and the introduction of new mineral species. Each of these processes is thought to have contributed to the later localization of crystal plastic deformation in the rocks. 相似文献
87.
The mineralogy of a fault-related uranium occurrence, in clastic rocks overlying granite, is described from borehole material. Coffinite is the only important uranium mineral. Other notable minerals are sulphides, fluorite, calcite and hydrocarbon. Coffinite is epigenetic and paragenetically late, rimming sulphides and hycrocarbon. It occurs partly in spatial association with a TiO2 mineral (probably anatase). This U-Ti association is attributed to adsorption of U by altered Ti-minerals prior to growth of the U mineral. Thus is has similarities with many diagenetic occurrences, though their mineralogy is usually different (the U-Ti association being represented by uranotitanates). The latter are attributed to local supersaturation of TiO2, which did not occur at Ousdale because Ti was relatively mobile in the fluids. Coffinite + TiO2 + quartz is interpreted as a stable low-temperature assemblage. The mineralogy thus indicates a hydrothermal uranium mineralization of an unusual type (without prominent uraninte), formed from relatively low-temperature fluids containing complexing agents which mobilized Ti. 相似文献
88.
As part of a plant survivability and ground water study in Owens Valley, California, semipermanent installations are used to measure continuous range-land evapotranspiration in the valley's phreatophyte community. A proposed mobile installation also has been designed. The semipermanent micrometeoro-logical station collects continuous data for solution of the Bowen ratio/energy budget equation and the Penman combination equation. Three sites were chosen for this type of installation to provide a representative sampling of Owens Valley. The proposed mobile aerodynamic installation should be capable of calculating evapotranspiration by the eddy correlation method. This instrumentation will be used throughout the valley for short periods of time (up to five days). Many problems with equipment operation, calibration and design have been identified and resolved by means of improved calibration techniques, systematic error-removal techniques, reduced cycle times, modified equipment design and proper observer training. The collected evapotranspiration data will be instrumental in developing a one-dimensional evapotranspiration flux algorithm for a model of valleywide ground water flow. 相似文献
89.
Cumulus mergers in the maritime continent region 总被引:1,自引:0,他引:1
J. Simpson Th. D. Keenan B. Ferrier R. H. Simpson G. J. Holland 《Meteorology and Atmospheric Physics》1993,51(1-2):73-99
Summary We examine a family of tall (up to 20 km) cumulonimbus complexes that develop almost daily over an adjacent pair of flat islands in the Maritime Continent region north of Darwin, Australia, and that are known locally as Hectors. Nine cases observed by a rawinsonde network, surface observations (including radiation and soil measurements), the TRMM/TOGA radar, and one day of aircraft photography are used to analyse the development, rainfall, surface energy budgets, and vertical structure of these convective systems.The systems undergo convective merging which is similar to that observed in previous Florida studies and is multiplicative in terms of rainfall. About 90% of the total rainfall comes from the merged systems, which comprise less than 10% of convective systems, and this has implications for the manner in which tropical rainfall is parameterised in largerscale numerical models. By comparison to the West Indies, GATE, and Florida, the Hector environment contains a weaker basic flow, with less vertical shear. The main thermodynamic difference is that the Darwin area has an unstable upper troposphere and very high tropopause. Numerical modelling results support earlier observations of updraughts in excess of 30 ms–1 in this region, but show that only modest convective drafts are experienced below the freezing level (5 km).The surface fluxes over the islands are estimated from a Monash University study to be mainly in latent form from evapotranspiration, with a Bowen ratio only slightly larger than that commonly observed over oceans. These surface fluxes are crucial to the development of a suitable mixed layer to support deep convection. The flux estimates agree with the observed changes below the cloud base and provide sufficient information for calculations of the bounds on precipitation efficiency. Of particular interest are the observations of Hector development on a day when the islands were under a dense cirrus overcast. We find that the islands still provide sufficient net sensible and latent heat fluxes to initiate convection.With 10 Figures 相似文献
90.