WKB estimates for the onset of ideal MHD instabilities in solar coronal loops     

A. W. Hood  P. De Bruyne  R. A. M. Van Der Linden  M. Goossens 《Solar physics》1994,150(1-2):99-115

A WKB approach, based on the method of Connor, Hastie, and Taylor (1979), is used to obtain simple estimates of the critical conditions for the onset of ideal MHD instabilities in line-tied solar coronal loops. The method is illustrated for the constant twist, Gold-Hoyle (1960) field, and the critical conditions are compared with previous and new numerical results. For the force-free case, the WKB estimate for the critical loop length reduces to . For the sufficiently non-force-free case the critical length can be expressed in the forml ₀ +l ₁/m. The results confirm the findings of De Bruyne and Hood (1992) that for force-free fields them = 1 mode is the first mode to become unstable but for the sufficiently strong non-force-free case this reverses with them → ∞ mode being excited first.  相似文献   

Sunspot nests     

M. J. M Castenmiller  C. Zwaan  E. B. J. Van Der Zalm 《Solar physics》1986,105(2):237-255

For the period August 1959–December 1964 the Greenwich Photoheliographic Results were searched for sunspot nests. Such a nest is a sequence of sunspot groups that appear within a small area on the solar surface and that last for several months. The search procedure is described and data for 41 probable sunspot nests are given. At least three quarters of these nests appear to be real, and not chance clusters.The nests are the same type of activity sequences as the Fleckenherde discovered by Becker (1955) and the complexes of activity pointed out by Gaizauskas et al. (1983). The complexes of activity as defined by Bumba and Howard (1965) are different patterns, however; the relation between complexes and the nests is shown.Some properties of the nests are: (i) many nests appear as double structures; (ii) single nests and components of double nests are quite compact: the effective areas are comparable to those of medium-large sunspot groups; (iii) each nest rotates at its own steady rate about the Sun; (iv) the intrinsic scatter in the rotation rates is much larger than the trend in the differential rotation; (v) displacements in latitude are less than a few meters per second; (vi) many nests live for 6 to 15 Carrington rotation periods, the minimum lifetime is not yet determined; (vii) the fraction of the sunspot groups that are members of nests is large (at least 30%).  相似文献   

The Inclusion of Stakeholder Knowledge and Perspectives in Integrated Assessment of Climate Change   总被引：1，自引：0，他引：1  

Penny Kloprogge  Jeroen P. Van Der Sluijs 《Climatic change》2006,75(3):359-389

Over the past few decades Integrated Assessment (IA) has emerged as an approach to link knowledge and action in a way that is suitable to accommodate uncertainties, complexities and value diversities of global environmental risks. Responding to the complex nature of the climate problem and to the changing role of climate change in the international climate policy process, the scientific community has started to include stakeholder knowledge and perspectives in their assessments. Participatory Integrated Assessment (PIA) is in its early stage of development. Methodology varies strongly across PIA projects. This paper analyzes four recent IA projects of climate change that included knowledge or perspectives from stakeholders in one-way or another. Approaches and methods used turn out to differ in whether stakeholders are involved actively or passively, whether the approach is bottom-up or top-down, and whether the different functions in the IA process are open or closed to stakeholder input. Also, differences can be seen in the degree to which boundaries are pre-set that limit the roles and domains of competencies attributed to each scientific or non-scientific participant (so-called boundary work). The paper discusses pros and cons of the various approaches identified, and outlines heuristics and considerations to assist those who plan, design or fund new IA processes with stakeholder input on what approaches best to choose in view of the objectives for stakeholder involvement, in view of the role that the IA plays in the overall risk management process and in view of considerations regarding boundary work.  相似文献   

The thermal continuum in coronal loops: The influence of finite resistivity on the continuous spectrum     

R. C. Ireland  R. A. M. Van Der Linden  A. W. Hood  M. Goossens 《Solar physics》1992,142(2):265-289

The normal mode spectrum for the linearized MHD equations is investigated for a cylindrical equilibrium. This spectrum is examined for zero perpendicular thermal conduction, with both zero and non-zero scalar resistivity. Particular attention is paid to the continuous branches of this spectrum, or continuous spectra. For zero resistivity there are three types of continuous spectra present, namely the Alfvén, slow, and thermal continua. It is shown that when dissipation due to resistivity is included, the slow and Alfvén continua are removed and that the thermal continuum is shifted to a different position (where the shift is independent of the exact value of resistivity). The old location of the thermal continuum is covered by a dense set of nearly singular discrete modes called a quasi-continuum. The quasi-continuum is investigated numerically, and the eigenfunctions are shown to have rapid spatial oscillating behaviour. These oscillations are confined to the most unstable part of the equilibrium based on the Field criterion, and may be the cause of fine structure in prominences.  相似文献   

Chemical weathering in the Upper Huang He (Yellow River) draining the eastern Qinghai-Tibet Plateau   总被引：8，自引：0，他引：8  

Lingling Wu  Jianhua Qin  Suzan van Der Lee 《Geochimica et cosmochimica acta》2005,69(22):5279-5294

We examined the fluvial geochemistry of the Huang He (Yellow River) in its headwaters to determine natural chemical weathering rates on the northeastern Qinghai-Tibet Plateau, where anthropogenic impact is considered small. Qualitative treatment of the major element composition demonstrates the dominance of carbonate and evaporite dissolution. Most samples are supersaturated with respect to calcite, dolomite, and atmospheric CO₂ with moderate (0.710-0.715) ⁸⁷Sr/⁸⁶Sr ratios, while six out of 21 total samples have especially high concentrations of Na, Ca, Mg, Cl, and SO₄ from weathering of evaporites. We used inversion model calculations to apportion the total dissolved cations to rain-, evaporite-, carbonate-, and silicate-origin. The samples are either carbonate- or evaporite-dominated, but the relative contributions of the four sources vary widely among samples. Net CO₂ consumption rates by silicate weathering (6-120 × 10³ mol/km²/yr) are low and have a relative uncertainty of ∼40%. We extended the inversion model calculation to literature data for rivers draining orogenic zones worldwide. The Ganges-Brahmaputra draining the Himalayan front has higher CO₂ consumption rates (110-570 × 10³ mol/km²/yr) and more radiogenic ⁸⁷Sr/⁸⁶Sr (0.715-1.24) than the Upper Huang He, but the rivers at higher latitudes are similar to or lower than the Upper Huang He in CO₂ uptake by silicate weathering. In these orogenic zones, silicate weathering rates are only weakly coupled with temperature and become independent of runoff above ∼800 mm/yr.  相似文献   

Growth histories derived from otolith microstructure of three Norwegian cod stocks co-reared in mesocosms; effect of initial size and prey size changes   总被引：2，自引：1，他引：1  

Suthers  I. M.; Van Der Meeren  T.; Jorstad  K. E. 《ICES Journal of Marine Science》1999,56(5):658-672

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Trade in ‘virtual carbon’: Empirical results and implications for policy     

Giles Atkinson  Kirk HamiltonGiovanni Ruta  Dominique Van Der Mensbrugghe 《Global Environmental Change》2011,21(2):563-574

The fact that developing countries do not have carbon emission caps under the Kyoto Protocol has led to the current interest in high income countries in border taxes on the ‘virtual’ carbon content of imports. We use GTAP data and input-output analysis to estimate the flows of virtual carbon implicit in domestic production technologies and the pattern of international trade. The results present striking evidence on the wide variation in the carbon-intensiveness of trade across countries, with major developing countries being large net exporters of virtual carbon. Our analysis suggests that a tax on virtual carbon could lead to very substantial effective tariff rates on the exports of the most carbon-intensive developing nations. As an illustration, we find that average tariff rates of 10%, 8% and 12% would be faced by imports from China, India and South Africa if carbon is taxed at $50/ton CO₂. Moreover, there is wide variation in intensiveness across sectors within countries with implications for the disparate effective tariff burdens on particulars parts of the economies of these countries. Such empirical findings, we argue, are useful for framing on-going discussions about the principles and practice of border taxes on virtual carbon.  相似文献   

Thermal marking of rainbow trout (Oncorhynchus mykiss) otoliths     

Bryan Van Der Walt  Robert A. Faragher 《新西兰海洋与淡水研究杂志》2013,47(4):883-888

A small‐scale experiment was done to test the feasibility of thermally marking hatchery‐reared rainbow trout (Oncorhynchus mykiss Walbaum) fry that are released into rivers and impoundments in New South Wales (NSW), Australia. Fry of rainbow trout were exposed to two different 48‐h thermal cycles each of a cold and warm water period. One thermal regime consisted of a cold water period during which the temperature was reduced from 14 to 8°C for 18 h followed by a return to 14°C for 30 h. For the second thermal treatment, water temperature was reduced to 4°C for 10 h followed by a period of 38 h at 14°C. Thermal cycles were repeated 4 and 8 times for each thermal regime, respectively. Following a growth period after treatment, obvious marks were visible on all treated otoliths as distinct from control otoliths. The 10°C differential treatment created the most visible patterns and growth of these fish was not significantly different from control fish. This marking method could be applied to normal hatchery practices to evaluate the effectiveness of large‐scale rainbow trout stockings in NSW.  相似文献   

Effects of Laboratory Consolidation on Petrophysical Properties of Fine-Grained Marine Sediments: Electron Microscopic Observations     

Jin-Wook Kim  Yir Der E. Le  Thomas T. Tieh  William R. Bryant 《Marine Georesources & Geotechnology》2013,31(4):347-360

Abstract

Pliocene-Recent marine sediments, recovered at site 1125 by ODP Leg 181 on the eastern New Zealand margin, were subjected to laboratory consolidation tests and analyzed by scanning electron microscopy (SEM) before and after consolidation test. The primary objective of this study is to document the effects of consolidation on microfabric and petrophysical properties. X-ray diffraction and grain-size distribution data indicate that the samples are mineralogically and texturally similar and thus are ideal for the present study on the role of consolidation solely on petrophysical properties. Porosity was measured before and after each consolidation test, and permeability was estimated indirectly based on the theoretical method. SEM photomicrographs show details of changes of pore geometry and distribution after the consolidation test that account for the porosity loss.  相似文献   

塔里木盆地中南部麻扎塔格逆冲—褶皱带变形特征及其意义   总被引：1，自引：0，他引：1       下载免费PDF全文

潘家伟  李海兵  孙知明  裴军令  司家亮  Laurie Barrier  邱祝礼  吴富峣  张丽军 《地质科学》2010,45(4):1038-1056

麻扎塔格地区地层、地貌及构造变形特征的研究,对于认识塔里木盆地新生代构造演化过程、塔里木—西昆仑的盆山耦合关系、新构造运动对塔里木油气资源分布的影响以及塔克拉玛干沙漠的气候、环境变化都具有重要意义。本文通过卫星照片解译、野外变形观察、剖面实测、地球物理资料解释等手段,对该地区晚新生代的构造特征进行了研究,确定了麻扎塔格构造带为典型的逆冲—褶皱带,并探讨了麻扎塔格逆冲—褶皱带的构造指向、活动时限、隆升速率及缩短速率、东西方向的延伸等问题,取得如下认识:1)麻扎塔格逆冲—褶皱带为西昆仑山前陆褶皱冲断带的前缘部位,和田河气田就是处在逆冲前锋背斜顶部,晚新生代变形作用已明显地改造了塔里木盆地南部及中部的古生代和中生代构造,并促成了和田河气田的形成;2)麻扎塔格山在中新世末(约7 Ma)和中更新世(约780 ka B.P.)经历了两次构造隆升,后一次形成了麻扎塔格逆冲—褶皱带和麻扎塔格山现今的地貌特征;3)估算出麻扎塔格逆冲—褶皱带中更新世以来的隆升速率约为0.26～0.4 mm/a,缩短速率约为0.9 mm/a;4)认为麻扎塔格逆冲—褶皱带向西应与同属西昆仑山前褶皱—冲断带前缘的喀什背斜相连,东端的突然消失可能是由于东段和田河附近存在北东—南西向的走滑断层造成。  相似文献