Particle Acceleration Due to Coronal Non-null Magnetic Reconnection     

James Threlfall  Thomas Neukirch  Clare Elizabeth Parnell 《Solar physics》2017,292(3):45

Various topological features, for example magnetic null points and separators, have been inferred as likely sites of magnetic reconnection and particle acceleration in the solar atmosphere. In fact, magnetic reconnection is not constrained to solely take place at or near such topological features and may also take place in the absence of such features. Studies of particle acceleration using non-topological reconnection experiments embedded in the solar atmosphere are uncommon. We aim to investigate and characterise particle behaviour in a model of magnetic reconnection which causes an arcade of solar coronal magnetic field to twist and form an erupting flux rope, crucially in the absence of any common topological features where reconnection is often thought to occur. We use a numerical scheme that evolves the gyro-averaged orbit equations of single electrons and protons in time and space, and simulate the gyromotion of particles in a fully analytical global field model. We observe and discuss how the magnetic and electric fields of the model and the initial conditions of each orbit may lead to acceleration of protons and electrons up to 2 MeV in energy (depending on model parameters). We describe the morphology of time-dependent acceleration and impact sites for each particle species and compare our findings to those recovered by topologically based studies of three-dimensional (3D) reconnection and particle acceleration. We also broadly compare aspects of our findings to general observational features typically seen during two-ribbon flare events.  相似文献   

Teleconnections between Andean and New Zealand glaciers   总被引：1，自引：1，他引：0  

B. Blair Fitzharris  Gareth R. Clare  Jim Renwick 《Global and Planetary Change》2007,59(1-4):159

Retreat and advance of glaciers in the Southern Alps of New Zealand have occurred over two distinct 20-yr climate periods (1954–1974) and (1974–1994). Changes in tropical and southern Andean glaciers are compared over these same periods. Behaviour of glaciers in the tropical Andes are out of phase with the Southern Alps glaciers, but some glaciers in Patagonia appear to be in phase. Southern Hemisphere atmospheric circulation using 700 hPa geopotential height anomalies and sea surface temperature patterns are examined for these periods. Glacier response on inter-decadal timescales is linked with distinctive shifts in atmospheric circulation patterns around the Southern Hemisphere. Retreat (advance) of glaciers in the Southern Alps and southern Andean glacier and advance (retreat) of glaciers in the tropical Andes are all associated with weaker (stronger) westerlies, blocking events in the South-east Pacific, negative (positive) geopotential height anomalies over Southern Africa and higher latitudes of the Southern Hemisphere. These glacier changes are also linked with the negative (positive) phase of the Inter-decadal Pacific Oscillation, a higher frequency of La Niña (El Niño) events, and warm (cool) sea surface temperatures in the New Zealand region and cool (warm) sea surface temperatures in the equatorial eastern region of the Pacific Ocean off the coast of Peru.  相似文献   

Effects of settling organic matter on the bioaccumulation of cadmium and BDE-99 by Baltic Sea benthic invertebrates     

Thorsson MH  Hedman JE  Bradshaw C  Gunnarsson JS  Gilek M 《Marine environmental research》2008,65(3):264-281

Settling organic matter (OM) is the major food source for heterotrophic benthic fauna. The high sorption affinity of many contaminants for OM implies that OM can influence both the distribution and bioavailability of contaminants. Here, we experimentally examine the role of settling OM of various nutritional qualities on the bioaccumulation of cadmium and the flame retardant BDE-99 by three benthic invertebrates; Macoma balthica, Monoporeia affinis and Marenzelleria sp. Contaminants were associated with three types of OM; a microalgae (Tetraselmis spp.), lignin and sediment. Bioaccumulation of Cd was proportional to OM nutritional quality for all three species, and was species-specific in the order Marenzelleria>M. balthica>M. affinis. BDE-99 bioaccumulation was highest in the treatment with the most nutritious OM (Tetraselmis). Consequently, both benthic species composition and the nutritive value of organic matter settling to the seafloor can have a substantial effect on the bioaccumulation of both metals and organic contaminants.  相似文献   

Wyville Thomson Ridge Overflow Water: Spatial and temporal distribution in the Rockall Trough     

Clare Johnson  Toby Sherwin  Denise Smythe-Wright  Tracy Shimmield  William Turrell 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(10):1153-1162

Wyville Thomson Ridge Overflow Water (WTOW), which is the only part of the outflow from the Norwegian Sea not to directly enter the Iceland Basin, is shown to be a significant water mass in the northern Rockall Trough. It is found primarily at intermediate depths (600–1200 m) beneath the northward flowing warm Atlantic waters, and above recirculating Mediterranean influenced waters and Labrador Sea Water (LSW). The bottom of the WTOW layer can be identified by a mid-depth inflexion point in potential temperature–salinity plots. An analysis of historical data reveals that WTOW has been present in all but eight of the last 31 years at 57.5°N in the Rockall Trough. A denser component of WTOW below 1500 m has also been present, although it appears to be less persistent (12 out of the 31 years) and limited to the west of the section. The signature of intermediate WTOW was absent in two periods, the mid-1980s and early 1990s, both of which coincided with a freshening, and probable increase in volume, of LSW in the trough. Potential temperature–salinity diagrams from historical observations indicate that WTOW persists at least as far south as 55°N (and as far west as 20°W in the Iceland Basin) although its signature is quickly lost on leaving the Rockall Trough. We suggest that a transport of WTOW down the western side of the trough exists, with WTOW at intermediate depths entering the eastern trough either via a cyclonic recirculation, or as a result of eddy activity. Further, WTOW is seen on the Rockall–Hatton Plateau and in the deep channels connecting with the Iceland Basin, suggesting additional possible WTOW transport pathways. These suggested transport routes remain to be confirmed by further observational or modelling studies.  相似文献   

The partitioning of organic carbon fluxes and sedimentary organic matter decomposition rates in the ocean     

Clare E Reimers  Erwin Suess 《Marine Chemistry》1983,13(2):141-168

The partitioning of annual organic carbon fluxes from five stations located in the vicinity of the Pacific-Antarctic Ridge and the Peru continental margin suggests that 35–85% of the total near-bottom organic carbon flux is utilized at or near the sediment-water interface. These estimates have large uncertainties, but illustrate that assessments of organic carbon utilization can be made by several stepwise approaches which are generally applicable to a wide spectrum of marine environments.In one approach, the mineralization of organic carbon from the sediments was predicted from both sedimentary organic carbon and pore water nutrient profiles with comparable results. Neglecting sediment mixing, the rate constants of the anoxic sediments off Peru range from 0.1 × 10^?3 to 4 × 10^?3 y^?1, and rate constants derived for oxic SW Pacific sediments range from 3 × 10^?4 to 7 × 10^?4 y^?1. As with other values reported for sulfate reducing sediments by Toth and Lerman (1977) and for oxic central Pacific sediments by Müller and Mangini (1980), log-log plots of rate constants vs. sedimentation rate define two parallel linear relationships for oxic and anoxic sediments, respectively. The apparently enhanced rates for oxic environments may result from large benthic organisms which redistribute a portion of the available detritus and in doing so convert it into more easily accessible and metabolizable organic matter. In low-oxygen environments, bottom feeders and infauna are less abundant and more likely to irrigate rapidly accumulating sediments.  相似文献   

Scaling Caribbean (in)dependence     

Clare Newstead 《Geoforum》2005,36(1):45-58

Recently there has been much ado about the territorial implications of globalization. Geographers have made a significant contribution to these debates, pointing to the tension between forces of deterritorialization and those of re-territorialization. In particular, there is a growing body of work in political and economic geography that draws attention to processes of re-scaling where, at the same time as scales such as the nation-state appear threatened, new scales of economic, political and social regulation emerge. Much of this literature, however, focuses on the ability of already powerful states to re-scale their activities and manage the border crossing abilities of global capital. In this paper I examine the process of supra-national regional integration in the Caribbean as an example of re-scaling and re-territorialization in a post-colonial context. I draw attention to the historic permeability of Caribbean states and argue regionalism in the Caribbean needs to be viewed as part of a longer process of defining economic, political and cultural independence in what, for post-colonial states, has always been an interdependent world economy. This analysis suggests that while new scales can be understood as spatialized attempts to manage changing global economics, they are also ambivalent productions, and as such, sites of resistance as well as domination and regulation.  相似文献   

Fluvial Geochemistry through a Short-Duration, Tropical-Cyclone Induced Discharge event in the Burdekin River and Hann Creek, North Queensland, Australia     

Jan Alexander  Chris R. Fielding  Simon J. Wakefield  Mark T. George  Clare F. Cottnam 《Aquatic Geochemistry》2001,7(4):275-293

The chemical composition of river water integrates a number of factors such as weathering, land use, climate, vegetation cover and human activity that individually affect its chemistry. Short term variations may also be significant. The Burdekin River, NE Australia, is an example of a class of tropical streams which experiences two to four orders of magnitude variation in discharge in response to seasonal but erratic monsoonal and cyclonic rainfall. In these systems individual discharge events last for days to weeks. Given the inherent difficulty sampling these events published data on water chemistry (and thus calculated fluxes and global budgets) may tend to be biased to low flow conditions. One such discharge event in February 1996 has been investigated for its impact on the chemistry of the water. Major cations (Na, Mg, K, Ca) all decreased in concentration as the water level rose, as did the minor elements Sr, Ba and U. Some other trace elements, notably Rb, Cr, Pb and REE were enriched in the peak flow waters. The flux of all measured elements increased substantially during the seven days of the discharge event. Such short term but significant events will have a major impact on the annual fluxes of elements delivered to the oceans from the land and global discharge budgets may need to take them into account when refining databases in the future.  相似文献   

Tracking deepwater oxygen recovery using sedimentary chironomid assemblages: Peninsula Lake revisited     

Jeziorski  Adam  Nelligan  Clare  Corrigan  Dara  Meyer-Jacob  Carsten  Paterson  Andrew M.  Smol  John P. 《Journal of Paleolimnology》2021,66(4):371-387

Journal of Paleolimnology - Peninsula Lake, Ontario, Canada, is a Precambrian Shield lake that has experienced many environmental stressors since European settlement of the watershed in the...  相似文献   

Temporal and spatial variability of biogenic particles fluxes during the JGOFS northeast Atlantic process studies at 47°N, 20°W     

Philip P. Newton  Richard S. Lampitt  Timothy D. Jickells  Penny King  Clare Boutle   《Deep Sea Research Part I: Oceanographic Research Papers》1994,41(11-12)

Particle fluxes to 3100 m depth at 45°50′N, 19°30′W were measured using time-series sediment traps during a 17 month period encompassing 1989 and 1990 JGOFS spring bloom process studies in the northeast Atlantic. There was a marked intra-annual variability in fluxes of mass, particulate inorganic carbon (PIC), particulate organic carbon (POC) and opal, appearing as two major flux events in each year. In 1989, the first flux event represented the settlement of spring bloom-type material, whereas the second, in autumn, was heavily enriched in mucopolysaccharides. In 1990, in contrast, the two flux events comprised spring bloom-type material and arrived at depth at different times relative to the 1989 events. The intra- and interannual variability evident for all three biogenic components was most notable for POC: (i) the autumn 1989 event supplied twice as much POC to 3100 m as the earlier spring bloom settlement—a quite unexpected observation—and (ii) the annual average POC flux in 1989 was 3–4 times more than in 1990. A synthesis of process study datasets with sediment trap data enables an evaluation of the coupling of deep fluxes with surface-water events. Spatial variability of the 1989 deep flux events is assessed by comparing the sediment trap data reported here with those from a second site 100 km away (Honjo and Manganini,Deep-Sea Research II,40, 587–607, 1993). The timing and magnitude of the 1989 spring bloom settlement was indistinguishable in the two datasets, indicating no spatial variability in flux between these sites. In contrast, the autumn 1989 flux event was barely recorded at the second site. Given the biogeochemical importance of this latter event to deep waters, most notable in terms of its contribution to POC flux, this observation of deep-water mesoscale flux variability indicates a significant problem in determining regional carbon budgets. Construction of basin-scale budgets is a central goal of JGOFS and for this to be achieved further studies of mesoscale variability of particle flux are essential.  相似文献   

Experimental determination of the partitioning of gallium between solid iron metal and synthetic basaltic melt: Electron and ion microprobe study     

Michael J. Drake  Horton E. Newsom  Stephen J.B. Reed  M.Clare Enright 《Geochimica et cosmochimica acta》1984,48(8):1609-1615

The distribution of Ga between solid Fe metal and synthetic basaltic melt has been investigated experimentally at two temperatures over a limited range of oxygen fugacities. Reversal experiments were conducted, indicating a close approach to equilibrium. Analysis of run products was performed using an electron and an ion microprobe. At 1 bar total pressure, the solid metal/silicate melt partition coefficient. D(Ga), is given by: 1190°C: logD(Ga) = ?0.92 logfO₂ ? 11.91330°C: logD(Ga) = ?0.77 logfO₂ ? 8.8. For the common assumption of a valence state for Ga of 3 in silicates and assuming ideal solution of Ga in both phases, a slope of ?0.75 is predicted. The slope obtained at 1300°C (?0.77) is indistinguishable from this value, while the slope at 1190°C (?0.92) is somewhat higher. Henry's law is obeyed over the concentration range 0.007 wt.% to 0.15 wt.% Ga in metal, a factor of 20 in concentration. These partition coefficients may be utilized to evaluate metal/silicate fractionation processes in the Earth, Moon and Eucrite Parent Body. The lunar mantle appears to be depleted in Ga by a factor of 20–40 relative to CI abundances. This depletion is consistent with extraction of Ga into a geophysically plausible lunar core if Ga was initially present at a subchondritic concentration. A similar explanation probably accounts for the depletion of Ga in the Eucrite Parent Body. The upper mantle of the Earth appears to be depleted in Ga by a factor of 4– 7 relative to CI abundances. This depletion is far smaller than would be expected as a result of core formation, but is consistent with two quite different hypotheses: (i) a small amount of solid metal and sulfur-bearing metallic liquid was retained in the mantle after core formation; or (ii) addition of a late-stage chondritic component involving 5% to 10% of the upper mantle following core formation.  相似文献