Study of sporadic-E clouds by backscatter radar   总被引：1，自引：0，他引：1  

Z. Houminer  C. J. Russell  P. L. Dyson  J. A. Bennett 《Annales Geophysicae》1997,14(10):1060-1065

It is shown that swept-frequency backscatter ionograms covering a range of azimuths can be used to study the dynamics of sporadic-E clouds. A simple technique based on analytic ray tracing can be used to simulate the observed narrow traces associated with E_s patches. This enables the location and extent of the sporadic-E clouds to be determined. The motion of clouds can then be determined from a time sequence of records. In order to demonstrate the method, results are presented from an initial study of 5 days of backscatter ionograms from the Jindalee Stage B data base obtained during March-April 1990. Usually 2–3 clouds were observed each day, mainly during the evening and up to midnight. The clouds lasted from 1–4 h and extended between 30°–80° in azimuth and 150–800 km in range. The clouds were mostly stationary or drifted generally westward with velocities of up to 80 ms^–1. Only one cloud was observed moving eastward.  相似文献   

Corrigendum to “Deformation of polycrystalline iron up to 30 GPa and 1000 K” [Phys. Earth Planet Inter. 145 (2004) 239–251]     

Sbastien Merkel  Hans-Rudolf Wenk  Philippe Gillet  Ho-kwang Mao  Russell J. Hemley 《Physics of the Earth and Planetary Interiors》2005,150(4):351-352

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Geospatial analysis of a coastal sand dune field evolution: Jockey's Ridge, North Carolina     

Helena Mitasova  Margery Overton  Russell S. Harmon 《Geomorphology》2005,72(1-4):204-221

Preservation and effective management of highly dynamic coastal features located in areas under development pressures requires in-depth understanding of their evolution. Modern geospatial technologies such as lidar, real time kinematic GPS, and three-dimensional GIS provide tools for efficient acquisition of high resolution data, geospatial analysis, feature extraction, and quantification of change. These techniques were applied to the Jockey's Ridge, North Carolina, the largest active dune field on the east coast of the United States, with the goal to quantify its deflation and rapid horizontal migration. Digitized contours, photogrammetric, lidar and GPS point data were used to compute a multitemporal elevation model of the dune field capturing its evolution for the period of 1974– 2004. In addition, peak elevation data were available for 1915 and 1953. Analysis revealed possible rapid growth of the dune complex between 1915–1953, followed by a slower rate of deflation that continues today. The main dune peak grew from 20.1 m in 1915 to 41.8 m in 1953 and has since eroded to 21.9 m in 2004. Two of the smaller peaks within the dune complex have recently gained elevation, approaching the current height of the main dune. Steady annual rate of main peak elevation loss since 1953 suggests that increase in the number of visitors after the park was established in 1974 had little effect on the rate of dune deflation. Horizontal dune migration of 3–6 m/yr in southerly direction has carried the sand out of the park boundaries and threatened several houses. As a result, the south dune section was removed and the sand was placed at the northern end of the park to serve as a potential source. Sand fencing has been an effective management strategy for both slowing the dune migration and forcing growth in dune elevation. Understanding the causes of the current movements can point to potential solutions and suggest new perspectives on management of the dune as a tourist attraction and as a recreation site, while preserving its unique geomorphic character and dynamic behavior.  相似文献   

Lateglacial palaeoenvironments and palaeoclimates from Conty and Houdancourt, northern France, reconstructed from Beetle remains     

Philippe Ponel  Russell Coope  Pierre Antoine  Nicole Limondin-Lozouet  Chantal Leroyer  Andr-Valentin Munaut  Jean-Franois Pastre  Frdric Guiter 《Quaternary Science Reviews》2005,24(23-24):2449-2465

Two Lateglacial insect sequences are described (a) from Conty, in the Selle valley and (b) from Houdancourt in the Oise valley, both in northern France. These investigations are part of a multidisciplinary investigation involving archaeology, sedimentology, geomorphology, geochronology and palaeontology (pollen, macroscopic plant remains, vertebrates, molluscs and insect fossils). The sequences of insect assemblages date from the latter part of the Bølling to the end of the Allerød periods. Environmental analysis of these faunas shows that rivers with riffles and pools meandered across flood plains. The river was extensively fringed with reedy vegetation. The only trees growing close to the river were of Salix and/or Populus. All the insect assemblages indicate that the thermal climates during the Bølling and Allerød periods were similar to one another and during both periods were very nearly as warm as that of the present day. No insect fossils were recovered from the sediments attributed to the Older Dryas interval though other evidence from these sites suggests that this event was decidedly colder than those immediately preceding and succeeding it. Comparisons are made between Lateglacial climatic patterns in northern France with those elsewhere in Europe.  相似文献   

A revised evolutionary history of armadillos (Dasypus) in North America based on ancient mitochondrial DNA          下载免费PDF全文

Beth Shapiro  Russell W. Graham  Brandon Letts 《Boreas: An International Journal of Quaternary Research》2015,44(1):14-23

The large, beautiful armadillo, Dasypus bellus, first appeared in North America about 2.5 million years ago, and was extinct across its southeastern US range by 11 thousand years ago (ka). Within the last 150 years, the much smaller nine‐banded armadillo, D. novemcinctus, has expanded rapidly out of Mexico and colonized much of the former range of the beautiful armadillo. The high degree of morphological similarity between these two species has led to speculation that they might be a single, highly adaptable species with phenotypical responses and geographical range fluctuations resulting from environmental changes. If this is correct, then the biology and tolerance limits for D. novemcinctus could be directly applied to the Pleistocene species, D. bellus. To investigate this, we isolated ancient mitochondrial DNA from late Pleistocene‐age specimens of Dasypus from Missouri and Florida. We identified two genetically distinct mitochondrial lineages, which most likely correspond to D. bellus (Missouri) and D. novemcinctus (Florida). Surprisingly, both lineages were isolated from large specimens that were identified previously as D. bellus. Our results suggest that D. novemcinctus, which is currently classified as an invasive species, was already present in central Florida around 10 ka, significantly earlier than previously believed.  相似文献   

The Satah Mountain and Baldface Mountain volcanic fields: Pleistocene hot spot volcanism in the Anahim Volcanic Belt,west-central British Columbia,Canada     

Christian Kuehn  Bernard Guest  James K. Russell  Jeff A. Benowitz 《Bulletin of Volcanology》2015,77(3):1-27

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The eccentric case of a fast-rotating,gravity-gradient-perturbed satellite attitude solution     

Noble Hatten  Ryan P. Russell 《Celestial Mechanics and Dynamical Astronomy》2018,130(11):71

A closed-form first-order perturbation solution for the attitude evolution of a triaxial space object in an elliptical orbit is presented. The solution, derived using the Lie–Deprit method, takes into account gravity-gradient torque and is facilitated by an assumption of fast rotation of the object. The formulation builds on the earlier implementation of Lara and Ferrer, which assumes a circular orbit. The previously presented work—which assumes spin about an object’s axis of maximum inertia—is further extended by the explicit presentation of the transformations required to apply the solution to an object spinning about its axis of minimum inertia. Additionally, several numerical analyses are presented to more completely assess the utility of the solution. These studies (1) validate the elliptical solution, (2) assess the impact of varying the small parameter of the perturbation procedure, (3) analyze the assumption of fast rotation, and (4) apply the solution to the common and important scenario of a tumbling rocket body.  相似文献   

Early‐middle Holocene land snail shell stable isotope record from Grotta di Latronico 3 (southern Italy)     

André C. Colonese  Giovanni Zanchetta  Elisabeth Dotsika  Russell N. Drysdale  Anthony E. Fallick  Renata Grifoni Cremonesi  Giuseppe Manganelli 《第四纪科学杂志》2010,25(8):1347-1359

This paper compares stable isotope (δ¹⁸O and δ¹³C) records of early–middle Holocene land snail shells from the archaeological deposits of Grotta di Latronico 3 (LTR3; southern Italy) with modern shell isotopic data. No substantial interspecific variability was observed in shell δ¹⁸O (δ¹⁸Os) of modern specimens (Pomatias elegans, Cornu aspersum, Eobania vermiculata, Helix ligata and Marmorana fuscolabiata). In contrast, interspecific shell δ¹³C (δ¹³Cs) variability was significant, probably due to different feeding behaviour among species. The δ¹⁸Os values of living land snails suggest that species hibernate for a long period during colder months, so that the signal of ¹⁸O‐depleted winter rainfall in their δ¹⁸Os is lost. This suggests that δ¹⁸Os and δ¹³Cs values of Pomatias elegans from this archaeological succession provide valuable clues for seasonal (spring–autumn) climatic conditions during the early–middle Holocene. The δ¹⁸Os values of fossil specimens are significantly lower than in modern shells and in agreement with other palaeoclimatic records, suggesting a substantial increase of precipitation and/or persistent changes in air mass source trajectories over this region between ca. 8.8 cal ka BP and 6.2–6.7 ka ago. The δ¹³Cs trend suggests a transition from a slightly ¹³C‐enriched to a ¹³C‐depleted diet between early and middle Holocene compared to present conditions. We postulate that this δ¹³Cs trend might reflect changes in the C3 vegetation community, potentially combined with other environmental factors such as regional moisture increase and the progressive decrease of atmospheric CO₂ concentration. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Habitat Restoration from an Ecosystem Goods and Services Perspective: Application of a Spatially Explicit Individual-Based Model     

R. S. Fulford  M. Russell  J. E. Rogers 《Estuaries and Coasts》2016,39(6):1801-1815

Estuarine ecosystems provide many services to humans, but these ecosystems are also under pressure from human development, which has led to large investments in habitat protection and restoration. Restoration in estuaries is typically focused on emergent and submerged vegetation with the goal of achieving target areal coverage based on historic conditions. Such restoration targets assume no spatial heterogeneity in habitat value and bypass the functional target of restoring or maintaining delivery of ecosystem goods and services (EGS). We have developed a spatially explicit individual-based behavioral model intended to explore the functional role of habitat restoration on EGS delivery in an index system (Tampa Bay, FL) and for an index EGS (recreational fishing). Model scenarios are based on interaction of inter-annual differences in salinity/temperature patterns (wet, dry, average) with hindcasted “increases” in coverage and distribution of seagrass. Model predictions indicated that the effect of seagrass restoration to historic (1950s) levels on both fish and fishery production is dependent on salinity and temperature. This dependence is based on predicted fish response both to habitat changes and the effective spatial scale of different habitat components. Overall, average salinity/temperature conditions facilitated the highest positive functional response to seagrass restoration with extreme wet/dry years yielding lower or even negative functional responses, but these responses were localized and not homogenous about the estuary. The results of this study provide a methodology for using functional targets in restoration planning and highlight the importance of considering the entire habitat mosaic in valuing restored habitat from an EGS perspective.  相似文献   

Conodont geothermometry in pyroclastic kimberlite: constraints on emplacement temperatures and cooling histories     

Pell  Jennifer  Russell  James K.  Zhang  Shunxin 《Mineralogy and Petrology》2018,112(2):477-490

Kimberlite pipes from Chidliak, Baffin Island, Nunavut, Canada host surface-derived Paleozoic carbonate xenoliths containing conodonts. Conodonts are phosphatic marine microfossils that experience progressive, cumulative and irreversible colour changes upon heating that are experimentally calibrated as a conodont colour alteration index (CAI). CAI values permit us to estimate the temperatures to which conodont-bearing rocks have been heated. Conodonts have been recovered from 118 samples from 89 carbonate xenoliths collected from 12 of the pipes and CAI values within individual carbonate xenoliths show four types of CAI distributions: (1) CAI values that are uniform throughout the xenolith; (2) lower CAIs in core of a xenolith than the rim; (3) CAIs that increase from one side of the xenolith to the other; and, (4) in one xenolith, higher CAIs in the xenolith core than at the rim. We have used thermal models for post-emplacement conductive cooling of kimberlite pipes and synchronous heating of conodont-bearing xenoliths to establish the temperature–time history of individual xenoliths within the kimberlite bodies. Model results suggest that the time-spans for xenoliths to reach the peak temperatures recorded by CAIs varies from hours for the smallest xenoliths to 2 or 3 years for the largest xenoliths. The thermal modelling shows the first three CAI patterns to be consistent with in situ conductive heating of the xenoliths coupled to the cooling host kimberlite. The fourth pattern remains an anomaly.

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