Surface radiation budget at Barrow,Alaska   总被引：2，自引：0，他引：2  

G. Wendler  F. Eaton 《Theoretical and Applied Climatology》1990,41(3):107-115

Summary At Barrow, the most northerly point in the U.S., radiation measurements were carried out. It was found that multiple reflection between the ground and stratus clouds, due to high surface albedo in winter, enhances the global radiation. These measurements are in agreement with model results. This, together with cloud amount, makes effective transmittance of the atmosphere highest in spring, resulting in the highest values of irradiation in May. For the same cloud amount, the effective transmittance of the atmosphere is always larger in winter, when there is a highly reflective surface, than in summer.Irradiation on a south slope, inclined to latitude (71°) and south wall was higher in spring and fall, but lower than the horizontal in summer. The annual mean was not substantially different for all three surfaces.The net radiation was positive for only three months (June, July, and August). May, with the largest amount of global radiation, displayed values around zero. The high surface albedo reflects most of the incoming radiation back to space, indicating that the net radiation is more controlled by the albedo than by the incoming global radiation.With 11 Figures  相似文献   

The impact of anoxia on Mn fluxes in the Chesapeake Bay     

A. Eaton 《Geochimica et cosmochimica acta》1979,43(3):429-432

Release of Mn into bottom waters of the Chesapeake Bay occurs in massive quantities during summertime periods of anoxia. The measured flux is much greater than can be accounted for by diffusion from pore waters under normal concentration gradients and is enhanced by dissolution of Mn-oxides under low Eh conditions. Extrapolating flux rates to the area of the Bay which goes anoxic during the summer indicates that this internal cycling accounts for four times as much Mn entering Bay waters as the total annual input (soluble and suspended) from the Susquehanna River.  相似文献   

The influence of Lake Minchumina,Interior Alaska,on its surroundings     

Y. Kodama  Dr. F. Eaton  Prof. Dr. G. Wendler 《Theoretical and Applied Climatology》1983,33(3):199-218

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Petrologic constraints on rift-zone processes     

MO Garcia  RA Ho  JM Rhodes  EW Wolfe 《Bulletin of Volcanology》1989,52(2):81-96

The Puu Oo eruption in the middle of Kilauea volcano's east rift zone provides an excellent opportunity to utilize petrologic constraints to interpret rift-zone processes. Emplacement of a dike began 24 hours before the start of the eruption on 3 January 1983. Seismic and geodetic evidence indicates that the dike collided with a magma body in the rift zone. Most of the lava produced during the initial episode of the Puu Oo eruption is of hybrid composition, with petrographic and geochemical evidence of mixing magmas of highly evllved and more mafic compositions. Some olivine and plagioclase grains in the hybrid lavas show reverse zoning. Whole-rock compositional variations are linear even for normally compatible elements like Ni and Cr. Leastsquares mixing calculations yield good residuals for major and trace element analyses for magma mixing. Crystal fractionation calculations yield unsatisfactory residuals. The highly evolved magma is similar in composition to the lava from the 1977 eruption and, at one point, vents for these two eruptions are only 200 m apart. Possibly both the 1977 lava and the highly evolved component of the episode 1 Puu Oo lava were derived from a common body of rift-zone-stored magma. The more mafic mixing component may be represented by the most mafic lava from the January 1983 eruption; it shows no evidence of magma mixing. The dike that was intruded just prior to the start of the Puu Oo eruption may have acted as a hydraulic plunger causing mixing of the two rift-zone-stored magmas.  相似文献   

Modeling of climate change effects on stream temperatures and fish habitats below dams and near groundwater inputs     

B. A. Sinokrot  H. G. Stefan  J. H. McCormick  J. G. Eaton 《Climatic change》1995,30(2):181-200

A deterministic heat transport model was developed to calculate stream water temperatures downstream of reservoir outlets (tailwaters) and groundwater sources. The model calculates heat exchange between the atmosphere, the water and the sediments and is driven by climate and stream hydrologic parameters. Past and projected climate conditions were used as input to the stream water temperature model. To produce a projected future weather scenario, output from the Columbia University Goddard Institute for Space Studies (GISS) global circulation model (GCM) for a doubling of atmospheric CO₂ were used to adjust past (1955–1979) weather parameters. Stream reach lengths, within which water temperatures are suitable for survival or good growth of 28 fish species, were determined for four selected streams. Several alternative upstream inflow conditions were chosen: Discharges from surface (epilimnion) and bottom (hypolimnion) outlets of reservoirs, and two groundwater inflow scenarios. By applying water temperature criteria for fish survival and good growth (Stefanet al., 1993) to simulated stream temperatures, it was possible to estimate stream lengths with suitable habitat. When simulated suitable habitat was compared to actual fish observations, good agreement was found. For projected climate change, the simulations showed how much of the available stream habitat would be lost. In the examples presented the effect of cold hypolimnetic water release from a reservoir or groundwater discharges is felt as far as 48 km (30 miles) downstream from its source, especially in smaller shaded streams. The impact of climate change on stream temperatures below dams is more pronounced when the water release is from the epilimnion (reservoir surface) rather than the hypolimnion (deep water). Examples used for this study show elimination of coldwater habitat for rainbow trout when the upstream release is from the surface of a reservoir, but only reductions of coldwater habitat when the upstream release is from a reservoir hypolimnion.  相似文献   

From feeding the locals to selling the locale: Adapting local sustainable food projects in Niagara to neocommunitarianism and neoliberalism     

Emily Eaton 《Geoforum》2008,39(2):994-1006

This paper traces attempts to foster local, sustainable food projects in Niagara, Canada as part of community economic development (CED) projects during two distinct periods of provincial governance. In the first period (1990-1995), social democratic government support for local sustainable food projects through CED can be understood as neocommunitarian in nature. During this time there was a concerted attempt to link local people with access to local food and also to support a relationship between local food projects and agri-tourism. I argue that this neocommunitarian policy was an accommodation to a wider and more global neoliberal hegemony and was underlain by a romanticism of petty commodity production and a tenuous link to social and ecological sustainability. In the second period of governance (beginning in 1995) the progressive conservative government led by Mike Harris pursued particularly virulent, revanchist forms of neoliberal governance. With many of their state supports slashed, Niagara NGOs and activists turned, and were pushed, to more market-led, elitist forms of local food projects and agri-tourism. In these latter food projects, the practices of ecological and social sustainability were significantly hollowed out and their local and light green nature was harnessed as accumulation strategies. The paper is based on interviews conducted in the year 2003 with people involved in various urban and rural food projects (including community gardening, community supported agriculture, local/seasonal cuisine, organic/ecological farming and food box programs).  相似文献   

The growth of the CCArray Observational network in western Canada     

Hersh Gilbert  David Eaton 《《地质学报》英文版》2018,92(Z1):146-147

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Growth of volcanic ash aggregates in the presence of liquid water and ice: an experimental approach     

Alexa R. Van Eaton  James D. Muirhead  Colin J. N. Wilson  Corrado Cimarelli 《Bulletin of Volcanology》2012,74(9):1963-1984

Key processes influencing the aggregation of volcanic ash and hydrometeors are examined with an experimental method employing vibratory pan aggregation. Mechanisms of aggregation in the presence of hail and ice pellets, liquid water (≤30?wt%), and mixed water phases are investigated at temperatures of 18 and ?20?°C. The experimentally generated aggregates, examined in hand sample, impregnated thin sections, SEM imagery, and X-ray microtomography, closely match natural examples from phreatomagmatic phases of the 27?ka Oruanui and 2010 Eyjafjallaj?kull eruptions. Laser diffraction particle size analysis of parent ash and aggregates is also used to calculate the first experimentally derived aggregation coefficients that account for changing liquid water contents and subzero temperatures. These indicate that dry conditions (<5–10?wt% liquid) promote strongly size selective collection of sub-63?μm particles into aggregates (given by aggregation coefficients >1). In contrast, liquid-saturated conditions (>15–20?wt% liquid) promote less size selective processes. Crystalline ice was also capable of preferentially selecting volcanic ash <31?μm under liquid-free conditions in a two-stage process of electrostatic attraction followed by ice sintering. However, this did not accumulate more than a monolayer of ash at the ice surface. These quantitative relationships may be used to predict the timescales and characteristics of aggregation, such as aggregate size spectra, densities, and constituent particle size characteristics, when the initial size distribution and water content of a volcanic cloud are known. The presence of an irregularly shaped, millimeter-scale vacuole at the center of natural aggregates was also replicated during interaction of ash and melting ice pellets, followed by sublimation. Fine-grained rims were formed by adding moist aggregates to a dry mixture of sub-31?μm ash, which adhered by electrostatic forces and sparse liquid bridges. From this, we infer that the fine-grained outer layers of natural aggregates reflect recycled exposure of moist aggregates to regions of volcanic clouds that are relatively dry and dominated by <31?μm ash.  相似文献   

UAS‐based remote sensing of fluvial change following an extreme flood event          下载免费PDF全文

Aaron D. Tamminga  Brett C. Eaton  Chris H. Hugenholtz 《地球表面变化过程与地形》2015,40(11):1464-1476

The effects of large floods on river morphology are variable and poorly understood. In this study, we apply multi‐temporal datasets collected with small unmanned aircraft systems (UASs) to analyze three‐dimensional morphodynamic changes associated with an extreme flood event that occurred from 19 to 23 June 2013 on the Elbow River, Alberta. We documented reach‐scale spatial patterns of erosion and deposition using high‐resolution (4–5 cm/pixel) orthoimagery and digital elevation models (DEMs) produced from photogrammetry. Significant bank erosion and channel widening occurred, with an average elevation change of ?0.24 m. The channel pattern was reorganized and overall elevation variation increased as the channel adjusted to full mobilization of most of the bed surface sediments. To test the extent to which geomorphic changes can be predicted from initial conditions, we compared shear stresses from a two‐dimensional hydrodynamic model of peak discharge to critical shear stresses for bed surface sediment sizes. We found no relation between modeled normalized shear stresses and patterns of scour and fill, confirming the complex nature of sediment mobilization and flux in high‐magnitude events. However, comparing modeled peak flows through the pre‐ and post‐flood topography showed that the flood resulted in an adjustment that contributes to overall stability, with lower percentages of bed area below thresholds for full mobility in the post‐flood geomorphic configuration. Overall, this work highlights the potential of UAS‐based remote sensing for measuring three‐dimensional changes in fluvial settings and provides a detailed analysis of potential relationships between flood forces and geomorphic change. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Assessing the effect of vegetation‐related bank strength on channel morphology and stability in gravel‐bed streams using numerical models     

Brett C. Eaton  Tim R. Giles 《地球表面变化过程与地形》2009,34(5):712-724

Bank strength due to vegetation dominates the geometry of small stream channels, but has virtually no effect on the geometry of larger ones. The dependence of bank strength on channel scale affects the form of downstream hydraulic geometry relations and the meandering‐braiding threshold. It is also associated with a lateral migration threshold discharge, below which channels do not migrate appreciably across their floodplains. A rational regime model is used to explore these scale effects: it parameterizes vegetation‐related bank strength using a dimensionless effective cohesion, C_r*. The scale effects are explored primarily using an alluvial state space defined by the dimensionless formative discharge, Q*, and channel slope, S, which is analogous to the Q–S diagrams originally used to explore meandering‐braiding thresholds. The analyses show that the effect of vegetation on both downstream hydraulic geometry and the meandering‐braiding threshold is strongest for the smallest streams in a watershed, but that the effect disappears for Q* > 10⁶. The analysis of the migration threshold suggests that the critical discharge ranges from about 5 m³/s to 50 m³/s, depending on the characteristic rooting depth for the vegetation. The analysis also suggests that, where fires frequently affect riparian forests, channels may alternate between laterally stable gravel plane‐bed channels and laterally active riffle‐pool channels. These channels likely do not exhibit the classic dynamic equilibrium associated with alluvial streams, but instead exhibit a cyclical morphologic evolution, oscillating between laterally stable and laterally unstable end‐members with a frequency determined by the forest fire recurrence interval. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献