Initiation of cmes by magnetic flux emergence

The initiation of solar Coronal Mass Ejections (CMEs) is studied in the framework of numerical magnetohydrodynamics (MHD). The initial CME model includes a magnetic flux rope in spherical, axi-symmetric geometry. The initial configuration consists of a magnetic flux rope embedded in a gravitationally stratified solar atmosphere with a background dipole magnetic field. The flux rope is in equilibrium due to an image current below the photosphere. An emerging flux triggering mechanism is used to make this equilibrium system unstable. When the magnetic flux emerges within the filament below the flux rope, this results in a catastrophic behavior similar to previous models. As a result, the flux rope rises and a current sheet forms below it. It is shown that the magnetic reconnection in the current sheet below the flux rope in combination with the outward curvature forces results in a fast ejection of the flux rope as observed for solar CMEs. We have done a parametric study of the emerging flux rate.     

Long-term Regional Dynamic Sea Level Changes from CMIP6 Projections

Anthropogenic climate forcing will cause the global mean sea level to rise over the 21st century.However,regional sea level is expected to vary across ocean basins,superimposed by the influence of natural internal climate variability.Here,we address the detection of dynamic sea level(DSL)changes by combining the perspectives of a single and a multimodel ensemble approach(the 50-member CanESM5 and a 27-model ensemble,respectively,all retrieved from the CMIP6 archive),under three CMIP6 projected scenarios:SSP1-2.6,SSP3-7.0 and SSP5-8.5.The ensemble analysis takes into account four key metrics:signal(S),noise(N),S/N ratio,and time of emergence(ToE).The results from both sets of ensembles agree in the fact that regions with higher S/N(associated with smaller uncertainties)also reflect earlier ToEs.The DSL signal is projected to emerge in the Southern Ocean,Southeast Pacific,Northwest Atlantic,and the Arctic.Results common for both sets of ensemble simulations show that while S progressively increases with increased projected emissions,N,in turn,does not vary substantially among the SSPs,suggesting that uncertainty arising from internal climate variability has little dependence on changes in the magnitude of external forcing.Projected changes are greater and quite similar for the scenarios SSP3-7.0 and SSP5-8.5 and considerably smaller for the SSP1-2.6,highlighting the importance of public policies towards lower emission scenarios and of keeping emissions below a certain threshold.     

微生物结皮对两种一年生植物种子萌发和出苗的影响

在温室中对两种一年生植物的种子在微生物结皮和流沙对照上的萌发和出苗状况进行了实验.结果表明:在湿润和干燥状况下,苔藓结皮和藻结皮对种子萌发和出苗状况的影响,完整的和破坏的苔藓结皮和藻结皮对种子萌发和出苗状况的影响,总的来说雾冰藜(Bassia dasyphlla)在完整的苔藓结皮和破坏的两种结皮中出苗率均较高.完整致密的藻结皮能阻止雾冰藜的根接触土壤从而对其出苗设置了物理屏障.小种子植物小画眉草(Eragrostics poaeoides)因其种子较大,种子植物有相对大的土壤接触面积和具有特殊的结构须根,从而较容易克服结皮造成的物理屏障,穿透完整致密的结皮层而到达土壤.在破坏的微生物结皮中小画眉的出苗率略有降低.水分处理仅对雾冰藜的出苗有显著影响.在湿润处理下雾冰藜的出苗率要高于在干燥处理下的.因此,自然状况下年降雨量和分配状况的差异可能会影响这两种植物每年幼苗出苗率的差异,进而会影响到这两个种群在人工固沙区分布格局的差异.     

Structural patterns in river network organization at both infra‐ and supra‐basin levels: the case of a granitic relief

Within a landform, the channelized water path from any point to the corresponding outlet is split into successive components within the Strahler ordering scheme. The probability density functions (pdf) of the length L of the whole channelized path and of the lengths of the components are studied as multi‐level structural functions. We have considered a granitic area and studied both its main basin and the set of its 48 constituent basins. With respect to the main basin, the pdf of the component lengths exhibit a strong scaling property, except for the highest orders, due to a hierarchical constraint; hence, the pdf of sum L has no particular shape. We have nevertheless identified an underlying structural pattern at particular infra‐ and supra‐basin levels, where the hierarchical constraint is weaker. This identification process entails noting structurally emerging patterns based on multi‐level variables and distributions, which satisfy the general self‐similarity of networks. The fairly good fit of an analytical gamma law with most of these emerging patterns can prove to be a positive step towards both a general modelling approach to the geomorphometric functions and a stronger geomorphological basement of hydrological transfer functions. Copyright © 2005 John Wiley & Sons, Ltd.     

Effect of sand burial depth on seed germination and seedling emergence of Calligonum L. species

A greenhouse study was conducted to determine the effects of sand burial on seed germination and seedling emergence of ten Calligonum L. species. The results suggested that the deeper the seeds in sand, the lower and slower their germination and seedling emergence. Seedling emergence occurred from a maximum depth of 12 cm with most seedlings emerging from 2 and 4 cm depths. The percent seedling emergence, number of days of first emergence, percent seed germination and percent of dormant seeds were significantly affected by different species and burial depth. There was a significant positive correlation between the number of days to first emergence and burial depth. Both mean percent germination and percent seedling emergence were negatively correlated with depth significantly for each species.     

Emergent geomorphic–vegetation interactions on a subalpine alluvial fan

Following perturbation, an ecosystem (flora, fauna, soil) should evolve as a function of time at a rate conditioned by external variables (relief, climate, geology). More recently, biogeomorphologists have focused upon the notion of co‐development of geomorphic processes with ecosystems over very short through to very long (evolutionary) timescales. Alpine environments have been a particular focus of this co‐development. However, work in this field has tended to adopt a simplified view of the relationship between perturbation and succession, including: how the landform and ecosystem itself conditions the impact of a perturbation to create a complex spatial response impact; and how perturbations are not simply ecosystem destroyers but can be a significant source of ecosystem resources. What this means is that at the within landform scale, there may well be a complex and dynamic topographic and sedimentological template that co‐develops with soil, flora and fauna. Here, we present and test a conceptual model of this template for a subalpine alluvial fan. We combine detailed floristic inventory with soil inventory, determination of edaphic variables and analysis of historical aerial imagery. Spatial variation in the probability of perturbation of sites on the fan surface was associated with down fan variability in the across‐fan distribution of fan ages, fan surface channel characteristics and fan surface sedimentology. Floristic survey confirmed that these edaphic factors distinguished site floristic richness and plant communities up until the point that the soil–vegetation system was sufficiently developed to sustain plant communities regardless of edaphic conditions. Thus, the primary explanatory variable was the estimated age of each site, which could be tied back into perturbation history and its spatial expression due to the geometry of the fan: distinct plant communities were emergent both across fan and down fan, a distribution maintained by the way in which the fan dissipates potentially perturbing events. Copyright © 2015 John Wiley & Sons, Ltd.     

基于复杂性科学的绿洲城镇化演进理论探讨

基于复杂性科学,引入涌现、协同、“吸引盆”等概念和模型,从涌现生成、协同维生、临界相变三个维度构建绿洲城镇化演进的理论框架。对绿洲城镇化的生成、演化和转型的过程与机理进行系统剖析,并据此对诺瑟姆曲线进行新的解读。研究表明：① 绿洲城镇是以人为核心的绿洲地域系统在多时空维度上的结构和功能的整体涌现现象,涌现形成的条件包括生成主体、自组织与受限生成机制、环境策略;② 竞争与协同机制维持了绿洲城镇化系统的生命活力与进化稳定,是系统演化的根本动力,系统不同层级具有不同的协同维生机制,根据协同学和耗散结构理论构建的绿洲城镇化演进的协同度和有序度可以识别系统演化方向;③ 绿洲城镇化过程实质上也是系统的自组织临界相变,该过程是一个渐变与突变、有序与混沌、稳态与非稳态的辩证统一;④ 时空间的正负反馈机制使绿洲城镇化复杂性与有序性不断提高,且不断向自组织临界态靠近,城镇化系统外在表现为活力与多样性增强。     

The job of the river

Earth scientists have traditionally conceptualized rivers and streams as geomorphic machines, whose role is to transfer sediment and to sculpt the landscape. Steady‐state relationships between sediment supply and transport capacity have traditionally been considered normative in fluvial systems. Rivers are hydrological entities, however, whose function is to redistribute excess moisture on land. The geomorphic work of the river – erosion, transport, deposition, etc. – is a byproduct of the hydrological job of the river. There is therefore no reason to expect any particular relationship between sediment supply and transport capacity to develop as a normative condition in fluvial systems. The apparent steady‐state equilibrium slope adjustments of rivers are a byproduct of four basic phenomena: (1) hydraulic selection, which favors channels and branching networks over other flux patterns; (2) water flows along the available path of least resistance; (3) energy dissipation; and (4) finite relaxation times. Recognizing converging trends of stream power or slope and sediment supply as common (but far from inevitable) side effects rather than self‐regulation has important implications for interpreting and predicting fluvial systems, and for river management and restoration. Such trends are variable, transient, contingent, and far from universal. Where they occur, they are an emergent byproduct of fundamental physical mechanisms, not a goal function or attractor state. Copyright © 2009 John Wiley & Sons, Ltd.     

Paleolimnology of three Jackman Sound Lakes,Southern Baffin Island,based on down-core diatom analyses

Three lakes, informally named Lakes Inqua, Instaar and Mercer, from the Jackman Sound area in Southern Baffin Island were cored. The elevation of the three lakes are 36 m above high tide (aht), 10 m aht and 1 m aht. The cores from Lakes Inqua and Mercer penetrated the marine/lacustrine boundary; the core from Lake Instaar is estimated to have come within ca. 5 cm of this boundary. In addition, grab samples and water samples were retrieved from the lakes. The cores have been ¹⁴C dated (AMS). Emergence of the three lake basins from the sea occurred approximately 8650 BP (Lake Inqua), 8630 BP (Lake Instaar) and 7900 BP (Lake Mercer, averaged date). This suggests a very rapid rate (>5 m/100 yrs) of glacio-isostatic rebound for this area. Down-core analyses of diatom assemblages indicate that the paleolimnology in the three lakes was similar. The diatom analyses suggest a change in climate between approximately 8000 and 6000 BP, which is also reflected in the marine record from the same area, and the onset of the neoglacial period around 4500 to 3800 BP. A decrease in diatom-inferred pH is evident in the lakes' development and can probably be related to the general change of the watershed vegetation with time.