Returns from a speculation     

Ron Johnston  Derek Gregory  Geraldine Pratt  Michael Watts  Sarah Whatmore 《Geoforum》2008,39(3):1105-1107

A reply to a recent paper by Setten.  相似文献   

Fine-Scale Measurements Of Turbulence In The Lower Troposphere: An Intercomparison Between A Kite- And Balloon-Borne, And A Helicopter-Borne Measurement System     

Andreas Muschinski  Ror Frehich  Mike Jensen  Ron Hugo  Axel Hoff  Frank Eaton  Ben Balsley 《Boundary-Layer Meteorology》2001,98(2):219-250

Two state-of-the-art, high-resolution, in situ turbulence measurement systems, which can be deployed at altitudes well above the atmospheric surface layer, are compared: the Tethered Lifting System (TLS) of the Cooperative Institute for Research in Environmental Sciences (CIRES)at the University of Colorado, Boulder, Colorado, and the helicopter-borneturbulence measurement system HELIPOD of the Technical UniversityBraunschweig, Germany, and the University of Hanover, Germany. Whilethe CIRES TLS is a fixed-point platform, HELIPOD is a moving platform.On the basis of data taken with the two systems in separate field campaigns,the system capabilities are quantified and discussed. Criteria for instrumentalrequirements are presented. It is shown that both the CIRES TLS and HELIPODare well suited for measuring fine-scale turbulence that is characterized by very small temperature structure parameters 10⁶ K² m^–2/3 and smaller) and very small energy dissipation rates (10^-7 m² s^-3 and smaller). The authors are not aware of any other turbulence measurement systems that have similar capabilities and can be deployed at altitudes of up to several kilometres. The HELIPOD is ideal for high-resolution horizontal measurements while the TLS is ideal for high-resolution vertical measurements using multiple sensors attached to a suspended line.  相似文献   

Wetland-water column exchanges of carbon, nitrogen, and phosphorus in a southern Everglades dwarf mangrove     

Stephen E. Davis  Daniel L. Childers  John W. Day  David T. Rudnick  Fred H. Sklar 《Estuaries and Coasts》2001,24(4):610-622

We used enclosures to quantify wetland-water column nutrient exchanges in a dwarf red mangrove, (Rhizophora mangle L.) system near Taylor River, an important hydraulic linkage between the southern Everglades and eastern Florida Bay, Florida, USA. Circular enclosures were constructed around small (2.5–4 m diam) mangrove islands (n=3) and sampled quarterly from August 1996 to May 1998 to quantify net exchanges of carbon, nitrogen, and phosphorus. The dwarf mangrove wetland was a net nitrifying environment with consistent uptake of ammonium (6.6–31.4 μmol m⁻² h⁻¹) and release of nitrite +nitrate (7.1–139.5 μmol m⁻² h⁻¹) to the water column. Significant flux of soluble reactive phosphorus was rarely detected in this nutrient-poor, P-limited environment. We did observe recurrent uptake of total phosphorus and nitrogen (2.1–8.3 and 98–502 μmol m⁻² h⁻¹, respectively), as well as dissolved organic carbon (1.8–6.9 μmol m⁻² h⁻¹) from the water column. Total organic carbon flux shifted unexplainably from uptake, during Year 1, to export, during Year 2. The use of unvegetated (control) enclosures during the second year allowed us to distinguish the influence of mangrove vegetation from soil-water column processes on these fluxes. Nutrient fluxes in control chambers typically paralleled the direction (uptake or release) of mangrove enclosure fluxes, but not the magnitude. In several instances, nutrient fluxes were more than twofold greater in the absence of mangroves, suggesting an influence of the vegetation on wetland-water column processes. Our findings characterize wetland nutrient exchanges, in a mangrove forest type that has received such little attention in the past, and serve as baseline data for a system undergoing hydrologic restoration.  相似文献   

Migration velocity analysis using a genetic algorithm     

Paul Docherty  Ron Silva  Satish Singh  Zhong-Min Song  Margaret Wood 《Geophysical Prospecting》1997,45(5):865-878

Migration velocity analysis, a method for determining long wavelength velocity structure, is a critical step in prestack imaging. Solution of this inverse problem is made difficult by a multimodal objective function; a parameter space often vast in extent; and an evaluation procedure for candidate solutions, involving the calculation of depth-migrated image gathers, that can be prohibitively expensive. Recognizing the global nature of the problem, we employ a genetic algorithm (GA) in the search for the optimum velocity model. In order to describe a model efficiently, regions of smooth variation are identified and sparsely parametrized. Region boundaries are obtained via map migration of events picked on the zero-offset time section. Within a region, which may contain several reflectors, separate components describe long and short wavelength variations, eliminating from the parameter space, models with large velocity fluctuations. Vital to the success of the method is rapid model evaluation, achieved by generating image gathers only in the neighbourhood of specific reflectors. Probability of a model, which we seek to maximize, is derived from the flatness of imaged events. Except for an initial interpretation of the zero-offset time section, our method is automatic in that it requires no picking of residual moveout on migrated gathers. Using an example data set from the North Sea, we show that it is feasible to solve for all velocity parameters in the model simultaneously: the method is global in this respect also.  相似文献   

An instrument system for high-speed mapping of chlorophyll a and physico-chemical variables in surface waters     

Christopher J. Madden  John W. Day 《Estuaries and Coasts》1992,15(3):421-427

A device incorporating microprocessor control and flow-through sampling permits high-speed measurements of chlorophyll a, and physical and chemical variables in aquatic systems. Continuous sampling of chlorophyll a, conductivity, temperature, salinity, incident photosynthetically active radiation (PAR), underwater PAR, and pH facilitates multiple correlations and mapping of variables at both small and large spatial scales. The instrument is portable and can be installed in a small boat for “rapid response” sampling of large areas. The low-voltage DC power requirement and shallow draft make the device especially suitable for work in shallow coastal areas, tidal creeks, bayous, and physically complex aquatic landscapes where larger vessels cannot be operated. Examples of applications of the instrument are discussed. In Fourleague Bay, Louisiana, a shallow estuary on the Gulf of Mexico, we were able to detect horizontal chlorophyll a structure and transient fronts map spatial variations on the scale of a few meters to several kilometers, and follow movements of chlorophyll features through the estuary. These patterns were often not apparent when sampled at discrete stations.  相似文献   

Europe and the environment — into the next century : ‘Global environmental change’, presidential session of the annual conference of the institute of British geographers, Swansea, Wales, 8 January 1992     

Ron Cooke 《Global Environmental Change》1992,2(4)

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Petrology of the Rainy Lake area,Minnesota, USA-implications for petrotectonic setting of the archean southern Wabigoon subprovince of the Canadian Shield     

Warren C. Day 《Contributions to Mineralogy and Petrology》1990,105(3):303-321

The Rainy Lake area in northern Minnesota and southwestern, Ontario is a Late Archean (2.7 Ga) granite-greenstone belt within the Wabigoon subprovince of the Canadian Shield. In Minnesota the rocks include mafic and felsic volcanic rocks, volcaniclastic, chemical sedimentary rocks, and graywacke that are intrucded by coeval gabbro, tonalite, and granodiorite. New data presented here focus on the geochemistry and petrology of the Minnesota part of the Rainy Lake area. Igneous rocks in the area are bimodal. The mafic rocks are made up of three distinct suites: (1) low-TiO₂ tholeiite and gabbro that have slightly evolved Mg-numbers (63–49) and relatively flat rare-earth element (REE) patterns that range from 20–8 x chondrites (Ce/Yb_N=0.8–1.5); (2) high-TiO₂ tholeiite with evolved Mg-numbers (46–29) and high total REE abundances that range from 70–40 x chondrites (Ce/Yb_N=1.8–3.3), and (3) calc-alkaline basaltic andesite and geochemically similar monzodiorite and lamprophyre with primitive Mg-numbers (79–63), enriched light rare-earth elements (LREE) and depleted heavy rare-earth elements (HREE). These three suites are not related by partial melting of a similar source or by fractional crystallization of a common parental magma; they resulted from melting of heterogeneous Archean mantle. The felsic rocks are made up of two distinct suites: (1)low-Al₂O₃ tholeiitic rhyolite, and (2) high-Al₂O₃ calc-alkaline dacite and rhyolite and consanguineous tonalite. The tholeiitic felsic rocks are high in Y, Zr, Nb, and total REE that are unfractionated and have pronounced negative Eu anomalies. The calcalkaline felsic rocks are depleted in Y, Zr, and Nb, and the REE that are highly fractionated with high LREE and depleted HREE, and display moderate negative Eu anomalies. Both suites of felsic rocks were generated by partial melting of crustal material. The most reasonable modern analog for the paleotectonic setting is an immature island arc. The bimodal volcanic rocks are intercalated with sedimentary rocks and have been intruded by pre- and syntectonic granitoid rocks. However, the geochemistry of the mafic rocks does not correlate fully with that of mafic rocks in modern are evvironments. The low-TiO₂ tholeiite is similar to both N-type mid-ocean-ridge basalt (MORB) and low-K tholeiite from immature marginal basins. The calc-alkaline basaltic andesite is like that of low-K calc-alkaline mafic volcanic rocks from oceanic volcanic arcs; however, the high-TiO₂ tholeiite is most similar to modern E-type MORB, which occurs in oceanic rifts. The conundrum may be explained by: (1) rifting of a pre-existing immature arc system to produce the bimodal volcanic rocks and high-TiO₂ tholeiite; (2) variable enrichment of a previously depleted Archean mantle, to produce both the low- and high-TiO₂ tholeiite and the calc-alkaline basaltic andesite, and/or (3) enrichment of the parental rocks of the high-TiO₂ tholeiite by crustal contamination.  相似文献   

Reconstruction of 1852 Banda Arc megathrust earthquake and tsunami     

TszMan L. Fisher  Ron A. Harris 《Natural Hazards》2016,83(1):667-689

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Zip-Code Areas As Statistical Regions     

Ron Abler 《The Professional geographer》1970,22(5):270-274

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Population distribution problems and policies in Asia     

Day FA  Demko GJ 《Population geography : a journal of the Association of Population Geographers of India》1981,3(1-2):16-40

"The main purposes of this paper are (1) to identify the primary population distribution problems in Asia, and (2) to identify the range of explicit population policy instruments or packages designed to alleviate or solve existing maldistribution. As a corollary to these main goals, attempts are made to classify types of spatial population problems and policies and to compare them across nations. Additionally, a qualitative analysis is made to assess the effectiveness of population distribution policies in those cases where there are reasonable data available."  相似文献