Mariner 9 ultraviolet spectrometer experiment: Pressure-altitude measurements on Mars     

C.W. Hord  K.E. Simmons  L.K. McLaughlin 《Icarus》1974,21(3):292-302

Ultraviolet spectrometer measurements of the reflectance at 3050 Å are modeled to give pressure-altitudes for Mars assuming a quiescent atmosphere. Ultraviolet light that is Rayleigh-scattered by the Mars molecular atmosphere, with allowance for uniform turbidity, is proportional to surface pressure independent of atmospheric temperature structure. All model constants except the over-all scaling factors are found by requiring ultraviolet spectrometer pressures of 47 locations on the planet to be the same when measured at different geometries. The overall scaling factor is found by intercomparison with Mariner 9 occultation pressures. Comparison with other Mars pressure-altitude measurements show deviations from the assumption of uniform turbidity to occur over the Hesperia plateau for ultraviolet measurements obtained during the 13–26 February 1972 time period.  相似文献   

Physiographic and bathymetric characteristics of the continental slope,northwest Gulf of Mexico     

William R. Bryant  John R. Bryant  Mary H. Feeley  Gregory R. Simmons 《Geo-Marine Letters》1990,10(4):182-199

Bathymetric charts of the continental slope of the northwestern Gulf of Mexico reveal the presence of over 90 intraslope basins with relief in excess of 150 m. The evolution and the general configuration of the basins are a function of halokinesis of allochthonous salt. Intraslope-interlobal and intraslope-superlobal basins occupy the upper and lower continental slope, respectively. Other structures on the slope associated with salt tectonics are the Sigsbee Escarpment, the seaward edge of the Sigsbee salt nappe, and the Alaminos and Keathley canyons. Major erosional features are the Mississippi Canyon and portions of a submarine canyon on the southern extreme of the Sigsbee Escarpment.  相似文献   

Seasonal variability in Atlantic Water off Spitsbergen     

Vladimir V. Ivanov  Igor V. Polyakov  Igor A. Dmitrenko  Edmond Hansen  Irina A. Repina  Sergey A. Kirillov  Cecillie Mauritzen  Harper Simmons  Leonid A. Timokhov 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(1):1-14

A combination of 2-year-long mooring-based measurements and snapshot conductivity–temperature–depth (CTD) observations at the continental slope off Spitsbergen (81°30′N, 31°00′E) is used to demonstrate a significant hydrographic seasonal signal in Atlantic Water (AW) that propagates along the Eurasian continental slope in the Arctic Ocean. At the mooring position this seasonal signal dominates, contributing up to 50% of the total variance. Annual temperature maximum in the upper ocean (above 215 m) is reached in mid-November, when the ocean in the area is normally covered by ice. Distinct division into ‘summer’ (warmer and saltier) and ‘winter’ (colder and fresher) AW types is revealed there. Estimated temperature difference between the ‘summer’ and ‘winter’ waters is 1.2 °C, which implies that the range of seasonal heat content variations is of the same order of magnitude as the mean local AW heat content, suggesting an important role of seasonal changes in the intensity of the upward heat flux from AW. Although the current meter observations are only 1-year long, they hint at a persistent, highly barotropic current with little or no seasonal signal attached.  相似文献   

A necessary voice: Climate change and lived experiences of youth in Rigolet,Nunatsiavut, Canada     

Joanna Petrasek MacDonald  Sherilee L. Harper  Ashlee Cunsolo Willox  Victoria L. Edge 《Global Environmental Change》2013,23(1):360-371

Globally, youth voices and their experiences, observations, and perceptions about climatic and environmental change and variability are relatively absent in the published literature to date. To address this gap, the goal of this research was to explore the observations and perceptions of climate change held by youth (12–25 years old) in the Inuit community of Rigolet, Nunatsiavut, Canada. Twenty in-depth interviews were conducted with youth in Rigolet to gather data about climatic and environmental changes young people have observed, and the subsequent impacts of these changes on their lives, culture, and community. Youth reported observing and experiencing climatic and environmental changes throughout their lives, with reported impacts falling within five main themes: changing travel conditions and access to hunting; challenges to Inuit culture; a concern for Elder and senior well-being; strong climate-related emotional responses; and youth-identified potential adaptation strategies. More broadly, this research demonstrated that young people have valuable knowledge and perspectives to offer. In particular, researchers, community leaders, and policy makers are encouraged to meaningfully engage youth as crucial stakeholders in future climate change work, research, dialogue, and policy.  相似文献   

Groundwater recharge to a sedimentary aquifer in the topographically closed Uley South Basin, South Australia   总被引：1，自引：1，他引：0  

Carlos M. Ordens  Adrian D. Werner  Vincent E. A. Post  John L. Hutson  Craig T. Simmons  Benjamin M. Irvine 《Hydrogeology Journal》2012,20(1):61-72

The chloride mass balance (CMB) and water-table fluctuation (WTF) analysis methods were used to estimate recharge rates in the Uley South Basin, South Australia. Groundwater hydrochemistry and isotope data were used to infer the nature of recharge pathways and evapotranspiration processes. These data indicate that some combination of two plausible processes is occurring: (1) complete evaporation of rainfall occurs, and the precipitated salts are washed down and redissolved when recharge occurs, and (2) transpiration dominates over evaporation. It is surmised that sinkholes predominantly serve to by-pass the shallow soil zone and redistribute infiltration into the deeper unsaturated zone, rather than transferring rainfall directly to the water table. Chlorofluorocarbon measurements were used in approximating recharge origins to account for coastal proximity effects in the CMB method and pumping seasonality was accounted for in the WTF-based recharge estimates. Best estimates of spatially and temporally averaged recharge rates for the basin are 52?C63 and 47?C129?mm/year from the CMB and WTF analyses, respectively. Adaptations of both the CMB and WTF analyses to account for nuances of the system were necessary, demonstrating the need for careful application of these methods.  相似文献   

Neoichnology and implications for stratigraphy of reworked Upper Oligocene oysters,Antigua, West Indies     

Stephen K. Donovan  David A.T. Harper  Roger W. Portell  Willem Renema 《Proceedings of the Geologists' Association. Geologists' Association》2014

The Late Oligocene oyster Hyotissa antiguensis (Brown) is locally common in the Antigua Formation of Hughes Point, eastern Antigua, Lesser Antilles; it was not commonly bored at that time. Its valves and shells are robust, and reworked into the shallow water near-shore environment in Antigua; it could potentially be incorporated into younger rocks. Its neoichnology includes clues that would facilitate identification of these oysters as reworked fossils. The suite of modern borings found in these specimens includes common Caulostrepsis taeniola Clarke, Gastrochaenolites isp. cf. G. turbinatus Kelly and Bromley and Entobia isp., and rare Oichnus simplex Bromley and Rogerella? isp. The latter three taxa are limited to oyster shell substrates. Of the common ichnotaxa, Caulostrepsis and Gastrochaenolites are particularly prominent in limestone clasts and limestone cemented to oyster shells, which would be an indicator of reworking if found in a post-Oligocene lithified deposit. Caulostrepsis and Gastrochaenolites are relatively less common in oyster shells and valves, and in many specimens are seen to terminate against the shell. Entobia is the only common boring limited to the shell substrate. The fidelity of preservation of modern borings is also superior in limestone clasts. This suite of borings is comparable with those found in the Neogene of the Antillean region.  相似文献   

Stepwise inversion of a groundwater flow model with multi-scale observation data   总被引：1，自引：0，他引：1  

Zhenxue Dai  Elizabeth Keating  Carl Gable  Daniel Levitt  Jeff Heikoop  Ardyth Simmons 《Hydrogeology Journal》2010,18(3):607-624

Based on the regional hydrogeology and the stratigraphy beneath the Los Alamos National Laboratory (LANL) site, New Mexico (USA), a site-scale groundwater model has been built with more than 20 stratified hydrofacies. A stepwise inverse method was developed to estimate permeabilities for these hydrofacies by coupling observation data from different sources and at various spatial scales including single-well test, multiple-well pumping test and regional aquifer monitoring data. Statistical analyses of outcrop permeability measurements and single-well test results were used to define the prior distributions of the parameters. These distributions were used to define the parameter initial values and the lower and upper bounds for inverse modeling. A number of inverse modeling steps were performed including the use of drawdown data from the pump tests at two wells (PM-2 and PM-4) separately, and a joint inversion coupling PM-2 and PM-4 pump test data and head data from regional aquifer monitoring. Parameter sensitivity coefficients for different data sets were computed to analyze if the model parameters can be estimated accurately with the data provided at different steps. The joint inversion offers a reasonable fit to all data sets. The uncertainty of estimated parameters for the hydrofacies is addressed with the parameter confidence intervals.  相似文献   

Modeling the dynamics of spring-driven oscillating-foil propulsion     

Harper  K.A. Berkemeier  M.D. Grace  S. 《Oceanic Engineering, IEEE Journal of》1998,23(3):285-296

In this paper we present a model for oscillating-foil propulsion in which springs are used to transmit forces from the actuators to the foil. The expressions for hydrodynamic force and moment on the foil come from classical, linear, unsteady aerodynamics, and these are coupled to linearized rigid-body mechanics to obtain the complete model for swimming. The model is presented as a low-order set of ordinary differential equations, which makes it suitable for the application of techniques from systems and control theory. The springs serve to reduce energy costs, and we derive explicit expressions for spring constants which are optimal in this sense. However, the use of springs can potentially lead to unstable dynamics. Therefore, we also derive a set of necessary and sufficient conditions for stability. A detailed example is presented in which energy costs for one actuator are reduced by 33%  相似文献   

The role of in situ stress in determining hydraulic connectivity in a fractured rock aquifer (Australia)     

Luke Mortimer  Adnan Aydin  Craig T. Simmons  Graham Heinson  Andrew J. Love 《Hydrogeology Journal》2011,19(7):1293-1312

Fracture network connectivity is a spatially variable property that is difficult to quantify from standard hydrogeological datasets. This critical property is related to the distributions of fracture density, orientation, dimensions, intersections, apertures and roughness. These features that determine the inherent connectivity of a fracture network can be modified by secondary processes including weathering, uplift and unloading and other mechanisms that lead to fracture deformation in response to in situ stress. This study focussed on a fractured rock aquifer in the Clare Valley, South Australia, and found that fracture network connectivity could be discriminated from several geological, geophysical and hydrogeological field datasets at various scales including single well and local- to regional-scale data. Representative hydromechanical models of the field site were not only consistent with field observations but also highlighted the strong influence of in situ stress in determining the distribution of fracture hydraulic apertures and the formation of hydraulic chokes that impede fluid flow. The results of this multi-disciplinary investigation support the notion that the hydraulic conductivity of a fracture network is limited to the least hydraulically conductive interconnected fractures, which imposes a physical limit on the bulk hydraulic conductivity of a fractured rock aquifer.  相似文献   

Column theme: Groundwater research and training     

Grabert VK  Kaback DS  Simmons CT 《Ground water》2011,49(6):783-793

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