Doppler sounder observations of trade winds and sea breezes along the African west coast near 34 ° S, 19 ° E     

Mark Jury  Garth Spencer-Smith 《Boundary-Layer Meteorology》1988,44(4):373-405

Summer weather conditions along the west coast of Africa near 34 ° S, 18 ° E are investigated using doppler acoustic sounder profiles. Case studies were selected from a two-year record to form composite analyses over the diurnal cycle. The SE trade wind exhibited a low level jet at the level of the temperature inversion due to a sharp reversal in the thermal wind vector aloft. Mean wind speeds reached 14 m s^–1 just before midnight as the surface and upper inversions strengthened. Seabreezes were categorised by the supporting gradient wind and found to have mean depths of 400 m, speeds of over 6 m s^–1 at the 200 m level, and advance/retreat times of 09 hr and 16–20 hr. During seabreezes and weak on-shore gradient flow conditions, the thermal internal boundary layer (TIBL) was monitored with sounder transects in the first 12 km of the coastal zone. The growth height was observed to be 1:20 in the first 5 km and 1:50 farther inland. The sounder climatology, together with surface network and aerial survey results, illustrate the four-dimensional characteristics of trade winds and seabreezes near Cape Town.  相似文献   

The weathering of a late Tertiary volcanic ash: Importance of organic solutes     

Ronald C. Antweiler  James I. Drever 《Geochimica et cosmochimica acta》1983,47(3):623-629

The weathering of a late Tertiary volcanic ash near Jackson, Wyoming, was studied by sampling water percolating through the ash with suction lysimeters, and by examination of the associated solid phases. Soluble organic compounds derived from vegetation control the release and transport of solutes by complexing Al and Fe, and by causing low pH values. The concentrations of Na, K, Ca, and Mg, as well as those of Al and Fe correlate with the dissolved organic carbon concentrations (DOC) and follow an annual cycle with a maximum in spring. DOC concentrations averaged 5O mg C per liter, and values as high as 260 mg/l were observed. Al and Fe concentrations ranged as high as 5 mg/l. The dissolved organic matter was largely in the form of humic acids, although minor amounts of oxalate, acetate, and formate were also present. The pH of the percolating waters ranged from 4.3 to 6.5 with a mean of 5.2.During laboratory weathering experiments with the same ash in the absence of dissolved organic compounds, pH values ranged from 7.3 to 9.5, dissolved Al and Fe concentrations were below the detection limit, and there was little resemblance between the compositions of the solutions and the compositions observed in the field. Any model attempting to describe weathering in a comparable setting must incorporate biological mechanisms as the dominant controls.  相似文献   

Landlords and Lodgers: Socio-Spatial Organization in an Accra Community by Deborah Pellow     

Garth Myers 《The Professional geographer》2007,59(1):149-151

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Fisheries in upwelling regions — with special reference to peruvian waters     

Garth I. Murphy 《Geoforum》1972,3(3):63-71

The anchovy population that is the basis of the Peru fishery, the world's largest, is a phytoplankton feeding species, supported by an upwelling based ecosystem. The fish is very short-lived and grows rapidly — both criteria for high turnover rate — high yield fisheries. The maximum sustainable yield is around 10 million metric tons. Analysis of the dynamics of the fishery suggests that the fleet is overbuilt, applying too much fishing effort, and slightly overfishing the population. In consequence, the population may be approaching a size and stress level at which it will be unstable.  相似文献   

Gypsum and halite from the Mid-Atlantic Ridge,DSDP Site 395     

James I. Drever  James R. Lawrence  Ronald C. Antweiler 《Earth and Planetary Science Letters》1979,42(1):98-102

Gypsum and halite crystals, together with saponite and phillipsite, were found in a vein in a basalt sill 625 m below the sea floor at DSDP Site 395A, located 190 km west of the crest of the Mid-Atlantic Ridge. The δ³⁴S value of the gypsum (+19.4‰) indicates a seawater source for the sulfate. The δ¹⁸O values of the saponite (+19.9‰) and phillipsite (+18.1‰) indicate either formation from normal seawater at about 55°C or formation from¹⁸O-depleted seawater at a lower temperature.The gypsum (which could be secondary after anhydrite) was formed by reaction between Ca²⁺ released from basalt and SO₄^2? in circulating seawater. The halite could have formed when water was consumed by hydration of basalt under conditions of extremely restricted circulation. A more probable mechanism is that the gypsum was originally precipitated as anhydrite at temperatures above 60°C. As the temperature dropped the anhydrite converted to gypsum. The conversion would consume water, which could cause halite precipitation, and would cause an increase in the volume of solids, which would plug the vein and prevent subsequent dissolution of the halite.  相似文献   

Controls on the chemistry of springs at Teels Marsh,Mineral County,Nevada     

Cole L. Smith  James I. Drever 《Geochimica et cosmochimica acta》1976,40(9):1081-1093

Evaporative process plays a dominant role in determining the water chemistry of the springs at Teels Marsh, a closed basin in western Nevada. Analysis of the spring waters indicates that calcium, magnesium, sulfate, and silica are removed from solution during dry periods, even though groundwater is undersaturated with respect to gypsum, amorphous silica, and sepiolite. The removal mechanism is precipitation of authigenic phases such as gypsum above the water table, in the vadose zone.In episodes of rain and snowfall in which none of the waters enters the phreatic zone, ions in the rain and snow accumulate near the ground surface. This accumulation of material, together with the sparse rain and snowfall, inhibits chemical weathering of silicate minerals. Only at high elevations in the basin is there sufficient fluxing of water through the alluvium for silicate weathering to make a significant contribution to the sodium content of the springs. When a sufficiently heavy rainfall occurs, salts are partially dissolved and the ions transported to the permanent groundwater. The kinetics of dissolution of secondary phases in the vadose zone exert an important control on the composition of the springs.  相似文献   

METASTABLE GROWTH PATTERNS IN SOME TERRESTRIAL AND LUNAR ROCKS     

Harald I. Drever  Robert Johnston 《Meteoritics & planetary science》1972,7(3):327-340

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Framboidal pyrite associated with lead-zinc mineralisation in mid-Wales     

J. Garth Raybould 《Lithos》1973,6(2):175-181

Framboidal pyrite occurs in the breccia fragments of country rock found in lead-zinc veins, while it is generally absent from unmineralised rocks. It is thought to be cogenetic with the main mineralisation, representing an early stage of deposition.  相似文献   

The unusual and large drawdown response of buried-valley aquifers to pumping     

van der Kamp G  Maathuis H 《Ground water》2012,50(2):207-215

The buried-valley aquifers that are common in the glacial deposits of the northern hemisphere are a typical case of the strip aquifers that occur in many parts of the world. Pumping from a narrow strip aquifer leads to much greater drawdown and much more distant drawdown effects then would occur in a sheet aquifer with a similar transmissivity and storage coefficient. Widely used theories for radial flow to wells, such as the Theis equation, are not appropriate for narrow strip aquifers. Previously published theory for flow to wells in semiconfined strip aquifers is reviewed and a practical format of the type curves for pumping-test analysis is described. The drawdown response of strip aquifers to pumping tests is distinctive, especially for observation wells near the pumped well. A case study is presented, based on extensive pumping test experience for the Estevan Valley Aquifer in southern Saskatchewan, Canada. Evaluation of groundwater resources in such buried-valley aquifers needs to take into account the unusually large drawdowns in response to pumping.  相似文献   

Ashley Dene: Lincoln University Farm: the first 100 years edited by Dick Lucas , Neil Gow and Alistair Nicol (eds), Lincoln University,Canterbury, 2012. 146 pp. ISBN 978‐0‐86476‐250‐4.     

Garth Cant 《New Zealand geographer》2013,69(1):81-82

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