Frequency distributions and correlations of solar X-ray flare parameters   总被引：3，自引：0，他引：3  

Norma B. Crosby  Markus J. Aschwanden  Brian R. Dennis 《Solar physics》1993,143(2):275-299

We have determined frequency distributions of flare parameters from over 12000 solar flares recorded with the Hard X-Ray Burst Spectrometer (HXRBS) on the Solar Maximum Mission (SMM) satellite. These parameters include the flare duration, the peak counting rate, the peak hard X-ray flux, the total energy in electrons, and the peak energy flux in electrons (the latter two computed assuming a thick-target flare model). The energies were computed above a threshold energy between 25 and 50 keV. All of the distributions can be represented by power laws above the HXRBS sensitivity threshold. Correlations among these parameters are determined from linear regression fits as well as from the slopes of the frequency distributions. Variations of the frequency distributions were investigated with respect to the solar activity cycle.Theoretical models for the frequency distribution of flare parameters depend on the probability of flaring and the temporal evolution of the flare energy build-up. Our results are consistent with stochastic flaring and exponential energy build-up, with an average build-up time constant that is 0.5 times the mean time between flares. The measured distributions of flares are also consistent with predicted distributions of flares from computer simulations of avalanche models that are governed by the principle of self-organized criticality.  相似文献   

Branding the design metropole: the case of Montréal, Canada     

Norma M Rantisi  Deborah Leslie 《Area》2006,38(4):364-376

As part of a broader process of inter-urban competition, city governments have increasingly sought to 'position' themselves as centres of creativity. In these branding initiatives, culture is viewed as a tool of urban regeneration and economic development. Our paper examines the case of Commerce Design Montréal, an annual design competition run by the City of Montréal, which aims to brand Montréal as a centre of design. Commerce Design Montréal is an example of a 'fast' policy initiated by the state, but carried out by business owners and citizens. As such, it represents a downloading of the responsibility for economic development to the private or individual scale and adopts only a partial view of the varied actors and uses that are implicated in the design process. The paper considers the opportunities and challenges that this model presents for promoting design as a form of urban regeneration in a neo-liberal context.  相似文献   

An interhemispheric mechanism for glacial abrupt climate change     

Rubén Banderas  Jorge Alvarez-Solas  Alexander Robinson  Marisa Montoya 《Climate Dynamics》2015,44(9-10):2897-2908

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Spatial organization of decadal and bidecadal rainfall fluctuations in southern North America and southern South America     

Omar Abel Lucero  Norma C. Rodriguez 《Atmospheric Research》2001,57(4)

The spatial organization of decadal and bidecadal components (fluctuations) of annual rainfall is identified in this research for two regions: (1) southern South America, and (2) southern North America (conterminous USA, southeastern Canada and northern and central Mexico). Findings indicate that these decadal and bidecadal components have highly coherent wave-like spatial organization. Two types of organization of decadal and bidecadal components of annual rainfall were identified: a train of propagating fluctuations and quasi-standing fluctuations. For decadal components, such patterns alternate in time. A widespread change in the spatial organization of decadal component of annual rainfall took place simultaneously in both continents in 1932. The bidecadal component is organized as standing fluctuations in southern North America and as travelling fluctuations in southern South America, The spatial pattern of decadal fluctuations of annual rainfall has 12- and 13-year cycles, and the spatial pattern of bidecadal fluctuations has predominantly 21- and 22-year cycles.  相似文献   

Paleohydrology of Andean saline lakes from sedimentological and isotopic records, Northwestern Argentina     

Blas Valero-Garcés  Antonio Delgado-Huertas  Norma Ratto  Ana Navas  Larry Edwards 《Journal of Paleolimnology》2000,24(3):343-359

The paleohydrological evolution of several high altitude, saline lakes located in the southernmost Altiplano (El Peinado and San Francisco basins, Catamarca province, NW Argentina) was reconstructed applying sedimentological, geochemical and isotopic techniques. Several playa lakes from the San Francisco basin (26° 56 S; 68° 08 W, 3800-3900 m a.s.l.) show evidence of a recent raise in the watertable that led to modern deposition of carbonate and diatomaceous muds. A 2 m - long core from El Peinado Lake (26° 29 59 S, 68°05 32 W, 3820 m a.s.l.) consists of calcitic crusts (unit 3), overlaid by an alternation of macrophyte-rich and travertine clast- rich, laminated muds (unit 2), and topped by travertine facies (unit 1). This sedimentary sequence illustrates a paleohydrological evolution from a subaerial exposure (unit 3) to a high lake stand (unit 2), and a subsequent smaller decrease in lake level (unit 1). The ¹³C_{organic matter}record also reflects the lake transgression between units 3 and 2. Although there is a general positive correlation between ¹⁸O_carbonate and salinity proxies (Na, Li and B content), the large data dispersion indicates that other factors besides evaporation effects control chemical and isotopic composition of lakewater. Consequently, the oxygen isotopic composition cannot be interpreted exclusively as an indicator of salinity or evaporation ratio. The degassing of CO₂ during groundwater discharge can explain the enriched ¹³C values for primary carbonates precipitated. The carbon budget in these high altitude, saline lakes seems to be controlled by physical rather than biological processes.The Altiplano saline lakes contain records of environmental and climatic change, although accurate ¹⁴C dating of these lacustrine sediments is hindered by the scarcity of terrestrial organic material, and the large reservoir effects. Sedimentologic evidence, a ²¹⁰Pb-based chronology, and a preliminary U/Th chronology indicate a very large reservoir effect in El Peinado, likely as a result of old groundwaters and large contributions of volcanic and geothermal ¹⁴C-free CO₂ to the lake system. Alternative chronologies are needed to place these paleorecords in a reliable chronological framework. A period of increased water balance in the San Francisco basin ended at about 1660 ± 82 yr B.P. (calendar yr U/Th age), and would correlates with the humid phase between 3000 and 1800 yr B.P detected in other sites of the southern Altiplano. Both, ²¹⁰Pb and preliminary U/Th dating favor a younger age for the paleohydrological changes in El Peinado. The arid period reflected by subaerial exposure and low lake levels in unit 3 would have ended with a large increase in effective moisture during the late 17th century. The increased lake level during deposition of unit 2 would represent the period between AD1650 - 1900, synchronous to the Little Ice Age. This chronological framework is coherent with other regional records that show an abrupt transition from more arid to more humid conditions in the early 17th century, and a change to modern conditions in the late 19th century. Although there are local differences, the Little Ice Age stands as a significant climatic event in the Andean Altiplano.  相似文献   

A method for studying iron silicate liquids under reducing conditions with negligible iron loss     

Dean C. Presnall  Norma L. Brenner 《Geochimica et cosmochimica acta》1974,38(12):1785-1788

In studies of iron silicate liquids under reducing conditions at 1 atm pressure, iron losses from the melt can be minimized by suspending the liquid as a drop from a short segment of fine Pt wire. For a basaltic composition at 1275°C and oxygen fugacities appropriate to terrestrial magmas, iron losses from the melt are less than 0.5 wt.% of the amount present for run times less than about 20 hr.  相似文献   

Quaternary palaeoecology and nature conservation: a general review with examples from the neotropics     

T. Vegas-Vilarrúbia  V. Rull  E. Montoya  E. Safont 《Quaternary Science Reviews》2011,30(19-20):2361-2388

Palaeoecology, as an ecological discipline, is able to provide relevant inputs for conservation science and ecosystem management, especially for issues involving long-term processes, such as ecological succession, migration, adaptation, microevolution, and extinction. This use of palaeoecology has been noted for several decades, and it has become widely accepted, especially in the frame of ongoing and near-future global warming and its potential biotic consequences. Selected palaeoecological insights of interest for conservation include the following: 1) species respond in an individualistic manner to environmental changes that lead to changes in community composition, suggesting that future ecosystems would have no modern analogues; 2) in the short-term, acclimation is more likely a response of species that are expected to persist in the face of global warming, but the possibility of evolutionary change linked to the existence of pre-adapted genomes cannot be dismissed; 3) species unable to acclimate or adapt to new conditions should migrate or become extinct, which has been observed in past records; 4) current extinction estimates for the near-future should be revised in light of palaeoecological information, which shows that spatial reorganisations and persistence in suitable microrefugia have been more common than extinction during the Quaternary; 5) biotic responses to environmental changes do not necessarily follow the rules of equilibrium dynamics but depend on complex and non-linear processes that lead to unexpected “surprises”, which are favoured by the occurrence of thresholds and amplifying positive feedbacks; 6) threshold responses can cause the movement of ecosystems among several potentially stable states depending on their resilience, or the persistence of transient states; 7) species and their communities have responded to environmental changes in a heterogeneous fashion according to the local and regional features, which is crucial for present and future management policies; 8) the global warming that occurred at the end of the Younger Drays cold reversal (ca 13.0 to 11.5 cal kyr BP) took place at similar rates and magnitudes compared to the global warming projected for the 21st century, thus becoming a powerful past analogue for prediction modelling; 9) environmental changes have acted upon ecosystems in an indirect way by modifying human behaviour and activities that, in turn, have had the potential of changing the environment and enhancing the disturbance effects by synergistic processes involving positive feedbacks; 10) the collapse of past civilisations under climate stress has been chiefly the result of inadequate management procedures and weaknesses in social organisation, which would be a warning for the present uncontrolled growth of human population, the consequent overexploitation of natural resources, and the continuous increase of greenhouse gas emissions; 11) the impact of fire as a decisive ecological agent has increased since the rise of humans, especially during the last millennia, but anthropic fires were not dominant over natural fires until the 19th century; 12) fire has been an essential element in the development and ecological dynamics of many ecosystems, and it has significantly affected the worldwide biome distribution; 13) climate–fire–human synergies that amplify the effects of climate, or fire alone, have been important in the shaping of modern landscapes. These general paleoecological observations and others that have emerged from case studies of particular problems can improve the preservation of biodiversity and ecosystem functions. Nature conservation requires the full consideration of palaeoecological knowledge in an ecological context, along with the synergistic cooperation of palaeoecologists with neoecologists, anthropologists, and conservation scientists.  相似文献   

The earth system model of intermediate complexity CLIMBER-3α. Part I: description and performance for present-day conditions     

Marisa Montoya  Alexa Griesel  Anders Levermann  Juliette Mignot  Matthias Hofmann  Andrey Ganopolski  Stefan Rahmstorf 《Climate Dynamics》2006,26(2-3):327-328

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Metabolic conversion of cyclohexane by Pacific salmon microsomal preparations     

John M. Kennish  Colleen Montoya  Jane Whitsett  John S. French 《Marine environmental research》1985,17(2-4)

Hydrocarbons are being introduced into the marine environment from a variety of sources including combustion processes, crude oil spills, fuel oil spills, and controlled disposal such as processed ballast water. Even in the relatively clean waters of Alaska hydrocarbons are being released at an alarming rate. The purpose of this study was to determine the optimum conditions for the metabolism of a representative hydrocarbon by Coho Salmon Oncorhynchus kisutch liver microsomes. The product of cyclohexane metabolism in the salmon microsomal system was identified by gas chromatography-mass spectrometry as cyclohexanol. Conditions of the microsome incubation were varied systematically to determine the optimum temperature, pH, and ionic strength for cyclohexanol production. Cyclohexanol was quantified by capillary column gas chromatography. Maximum cyclohexanol formation was achieved at 20°C, a pH of 8·0–8·5 and an ionic strength of 0·026. A linear rate of cyclohexanol formation is seen from 0–60 min of incubation and there is an apparent decrease in the rate from 60–90 min. Poor stability of the microsomal preparation from the species studied was also identified and several stability studies have been undertaken using cyclohexane metabolism as a monitor.  相似文献   

The impact of different cooling strategies on urban air temperatures: the cases of Campinas,Brazil and Mendoza,Argentina     

Noelia?Liliana?AlchaparEmail author  Claudia?Cotrim?Pezzuto  Erica?Norma?Correa  Lucila?Chebel Labaki 《Theoretical and Applied Climatology》2017,130(1-2):35-50

This paper describes different ways of reducing urban air temperature and their results in two cities: Campinas, Brazil—a warm temperate climate with a dry winter and hot summer (Cwa), and Mendoza, Argentina—a desert climate with cold steppe (BWk). A high-resolution microclimate modeling system—ENVI-met 3.1—was used to evaluate the thermal performance of an urban canyon in each city. A total of 18 scenarios were simulated including changes in the surface albedo, vegetation percentage, and the H/W aspect ratio of the urban canyons. These results revealed the same trend in behavior for each of the combinations of strategies evaluated in both cities. Nevertheless, these strategies produce a greater temperature reduction in the warm temperate climate (Cwa). Increasing the vegetation percentage reduces air temperatures and mean radiant temperatures in all scenarios. In addition, there is a greater decrease of urban temperature with the vegetation increase when the H/W aspect ratio is lower. Also, applying low albedo on vertical surfaces and high albedo on horizontal surfaces is successful in reducing air temperatures without raising the mean radiant temperature. The best combination of strategies—60 % of vegetation, low albedos on walls and high albedos on pavements and roofs, and 1.5 H/W—could reduce air temperatures up to 6.4 °C in Campinas and 3.5 °C in Mendoza.  相似文献