Comparison of the Energy Spectra and Number Fluxes From a simple Flare Model to Observations     

Iain G. Hannah  Lyndsay Fletcher 《Solar physics》2006,236(1):59-74

In this paper, we investigate the energy spectra produced by a simple test particle X-point model of a solar flare for different configurations of the initial electromagnetic field. We find that once the reconnection electric field is larger than 1 Vm^-1 the particle distribution transits from a heated one to a partially accelerated one. As we close the separatrices of the X-point and the angle in the inflow direction widens we find that more particles are accelerated out of the thermal distribution and this power–law component extends to lower energies. When we introduce a guiding magnetic field component we find that more particles are energised, but only up to a maximum energy dictated primarily by the reconnection electric field. Despite being able to accelerate particles to observable energies and demonstrate behaviour in the energy spectra that is consistent with observations, this single X-line model can only deliver the number fluxes required for microflares.  相似文献   

Spectroscopic anatomy of a meteor trail cross section with the European Southern Observatory Very Large Telescope     

Peter Jenniskens  Emmanuel Jehin  Remi A. Cabanac  Christophe O. Laux  Iain D. Boyd 《Meteoritics & planetary science》2004,39(4):609-616

Abstract— A meteor spectrum was recorded serendipitously at the European Southern Obrervatory (ESO) Very Large Telescope (VLT) during a long exposure in long‐slit spectroscopic mode with FORS1. The ?8 magnitude fireball crossed the narrow 1Î × 7î slit during the observation of a high z supernova in normal service mode operation on May 12, 2002. The spectrum covered the range of 637–1050 nm, where the meteor's air plasma emissions from N₂, N, and O dominate. Carbon atom emission was not detected in the relatively unexplored wavelength range above 900 nm, but the observed upper limit was only 3 sigma less than expected from the dissociation of atmospheric CO₂. The meteor trail was resolved along the slit, and the emission had a Gaussian distribution with a dimension of FWHM = 7.0 (±0.4) * sin(α) * H (km)/90 m, where α is the unknown angle between the orientation of the meteor path and slit and H the assumed altitude of the meteor in km. To our knowledge, this is the first observation of a spatially resolved spectrum across a meteor trail. Unlike model predictions, the plasma excitation temperature varied only from about 4,300 to 4,365 K across the trail, based on the ratio of atomic and molecular nitrogen emissions. Unfortunately, we conclude that this was because the meteor at 100 km altitude was out of focus.  相似文献   

The Allen Telescope Array     

David Deboer  Rob Ackermann  Leo Blitz  Douglas Bock  Geoffrey Bower  Michael Davis  John Dreher  Greg Engargiola  Matt Fleming  Girmay Keleta  Gerry Harp  John Lugten  Jill Tarter  Doug Thornton  Niklas Wadefalk  Sander Weinreb  William J. Welch 《Experimental Astronomy》2004,17(1-3):19-34

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Preface     

Thornton  I. W. B. 《GeoJournal》1983,7(6):479-479

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Woodleigh impact structure,Australia: Shock petrography and geochemical studies     

Wolf Uwe REIMOLD  Christian KOEBERL  Robert M. HOUGH  Iain MCDONALD  Alex BEVAN  Kassa AMARE  Bevan M. FRENCH 《Meteoritics & planetary science》2003,38(7):1109-1130

Abstract— The large, complex Woodleigh structure in the Carnarvon basin of Western Australia has recently been added to the terrestrial impact crater record. Many aspects of this structure are, however, still uncertain. This work provides a detailed petrographic assessment of a suite of representative drill core samples from the borehole Woodleigh 1 that penetrated uplifted basement rocks of the central part of this structure. Fundamental rock and mineral deformation data and high‐precision chemical data, including results of PGE and oxygen isotopic analysis, are presented. The sampled interval displays likely impact‐produced macrodeformation in the form of fracturing and breccia veining at the microscopic scale. Contrary to earlier reports that these breccias represent pseudotachylite (friction melt) or even shock/shear‐produced pseudotachylitic melt breccia cannot be confirmed due to pervasive post‐impact alteration. Abundant planar deformation features (PDFs) in quartz, in addition to diaplectic glass and partial isotropization, are the main shock deformation effects observed, confirming that Woodleigh is of impact origin. Over the investigated depth interval, the statistics of quartz grains with a variable number of sets of PDFs does not change significantly, and the patterns of crystallographic orientations of PDFs in randomly selected quartz grains does not indicate a change in absolute shock pressure with depth either. The value of oxygen isotopes for the recognition of meteoritic contamination, as proposed by earlier Woodleigh workers, is critically assessed. Neither INA nor PGE analyses of our samples support the presence of a meteoritic component within this basement section, as had been claimed in earlier work.  相似文献   

Distribution and petrogenetic behaviour of trace elements in granitic pegmatite quartz from South Norway   总被引：1，自引：0，他引：1  

Rune?B.?LarsenEmail author  Iain?Henderson  Peter?M.?Ihlen  Francois?Jacamon 《Contributions to Mineralogy and Petrology》2004,147(5):615-628

The present study documents that the trace-element distribution in granitic quartz is highly sensitive to CAFC processes in granitic melts. Igneous quartz efficiently records both the origin and the evolution of the granitic pegmatites. Aluminium, P, Li, Ti, Ge and Na in that order of abundance, comprises >95% of the trace elements. Most samples feature >1 ppm of any of these elements. The remnant 5% includes K, Fe, Be, B, Ba and Sr whereas the other elements are present at concentrations lower than the detection limit. Potassium, Fe, Be and Ti are relatively compatible hence obtain the highest concentrations in early formed quartz. Phosphorous, Ge, Li and Al are relatively incompatible and generally obtain the highest concentrations in quartz that formed at lower temperatures from more evolved granitic melts. The Ge/Ti, the Ge/Be, the P/Ge and the P/Be ratios of quartz are strongly sensitive to the origin and evolution of the granitic melts and similarly the Rb/Sr and the Rb/K ratios of K-feldspars may be utilised in petrogenetic interpretations. However, the quartz trace element ratios are better at distinguishing similarities and differences in the origin and evolution of granitic melts. After evaluating the different trace element ratios, the Ge/Ti ratio appears to be most robust during subsolidus processes in the igneous systems, hence probably should be the preferred ratio for analysing and understanding petrogenetic processes in granitic igneous rocks.Editorial responsibility: J. Hoefs  相似文献   

Influence of wave and sediment dynamics on cordgrass (<Emphasis Type="Italic">Spartina anglica</Emphasis>) growth and sediment accumulation on an exposed intertidal flat     

Andrew?SwalesEmail author  Iain?T.?MacDonald  Malcolm?O.?Green 《Estuaries and Coasts》2004,27(2):225-243

Isolated patches ofSpartina anglica (cordgrass) at two sites on a wave-exposed mid-intertidal flat of the 340 km² Manukau Harbor (Auckland, New Zealand) have developed very differently since being planted in the mid-1970s. Although the two sites are only 0.5 km apart and at the same intertidal elevation,Spartina patches at the easternmost site (site 1) have as much as an order of magnitude higher biomass and accumulated sediment volume thanSpartina patches at site 2. A field experiment was conducted to characterize waves and associated sediment dynamics at each site, which might explain whySpartina patches at the two sites have developed so differently over the past 25 yr or so. Suspended sediments were measured and wave characteristics were inferred from subsurface pressure data measured for 5 wk at bothSpartina sites and at an intermediate location. Bed-orbital speeds and frictional wave-energy dissipation were consistently lower at the easternmost site with the largerSpartina patches. The west-to-east reduction in wave energy is due to the spatial arrangement of theSpartina sites relative to the predominant wind fetches. The wave-energy gradient is maintained by tidal-cycle variations in fetch and bed friction and results in a west-to-east reduction in sand suspension. Silt, which is largely resuspended under southwest winds, is redeposited in the low wave-energy conditions in and around the larger site 1Spartina patches. Shell accumulation bySpartina patches at site 1 occurs infrequently, during southwest winds >10 m s⁻¹ and water depths >0.7 m, when waves are least attenuated by bed friction. Large between-site differences in the growth of and sediment accumulation by theSpartina patch are consistent with the observed wave-energy gradient. The resulting spatial patterns of silt, sand, and shell resuspension and deposition directly influence the rate of sediment accumulation bySpartina patches and the composition of accumulated sediment on this wave-exposed intertidal flat.  相似文献   

Assessing the potential impact of climate change on the UK’s electricity network   总被引：1，自引：1，他引：0  

Lynsey McColl  Erika J. Palin  Hazel E. Thornton  David M. H. Sexton  Richard Betts  Ken Mylne 《Climatic change》2012,115(3-4):821-835

We investigate how weather affects the UK’s electricity network, by examining past data of weather-related faults on the transmission and distribution networks. By formalising the current relationship between weather-related faults and weather, we use climate projections from a regional climate model (RCM) to quantitatively assess how the frequency of these faults may change in the future. This study found that the incidences of both lightning and solar heat faults are projected to increase in the future. There is evidence that the conditions that cause flooding faults may increase in the future, but a reduction cannot be ruled out. Due to the uncertainty associated with future wind projections, there is no clear signal associated with the future frequency of wind and gale faults, however snow, sleet and blizzard faults are projected to decrease due to a reduction in the number of snow days.  相似文献   

The influence of hurricane risk on tourist destination choice in the Caribbean     

Johanna Forster  Peter W. Schuhmann  Iain R. Lake  Andrew R. Watkinson  Jennifer A. Gill 《Climatic change》2012,114(3-4):745-768

Climate change could have major implications for the global tourism industry if changing environmental conditions alter the attractiveness of holiday destinations. Countries with economies dependent on tourism and with tourism industries reliant on vulnerable natural resources are likely to be particularly at risk. We investigate the implications that climate-induced variations in Atlantic hurricane activity may have for the tourism-dependent Caribbean island of Anguilla. Three hundred tourists completed standardised questionnaires and participated in a choice experiment to determine the influence hurricane risk has on their risk perceptions and decisions regarding holiday preferences. The hurricane season had been considered by 40?% of respondents when making their holiday choice, and the beaches, climate and tranquility of the island were more important than coral reef-based recreational activities in determining holiday destination choice. Choice models demonstrated that respondents were significantly less likely to choose holiday options where hurricane risk is perceived to increase, and significantly more likely to choose options that offered financial compensation for increased risk. However, these choices and decisions varied among demographic groups, with older visitors, Americans, and people who prioritize beach-based activities tending to be most concerned about hurricanes. These groups comprise a significant component of the island’s current clientele, suggesting that perceived increases in hurricane risk may have important implications for the tourism economy of Anguilla and similar destinations. Improved protection of key environmental features (e.g. beaches) may be necessary to enhance resilience to potential future climate impacts.  相似文献   

Synergies and trade-offs between adaptation,mitigation and development     

Thomas F. Thornton  Claudia Comberti 《Climatic change》2017,140(1):5-18

To succeed in meeting carbon emissions reduction targets to limit projected climate change impacts, it is imperative that improved synergies be developed between mitigation and adaptation strategies. This is especially important in development policy among remote indigenous communities, where demands for development have often not been accompanied by commensurate efforts to respond to future climate change impacts. Here we explore how mitigation and adaptation pathways can be combined to transform rural indigenous communities toward sustainability. Case studies from communities in Alaska and Nepal are introduced to illustrate current and potential synergies and trade-offs and how these might be harnessed to maximize beneficial outcomes. The adaptation pathways approach and a framework for transformational adaptation are proposed to unpack these issues and develop understanding of how positive transformational change can be supported.  相似文献