A long-standing but fundamental question in lightning studies concerns how lightning is initiated inside storms, given the absence of physical conductors. The issue has revolved around the question ...of whether the discharges are initiated solely by conventional dielectric breakdown or involve relativistic runaway electron processes. Here we report observations of a relatively unknown type of discharge, called fast positive breakdown, that is the cause of high-power discharges known as narrow bipolar events. The breakdown is found to have a wide range of strengths and is the initiating event of numerous lightning discharges. It appears to be purely dielectric in nature and to consist of a system of positive streamers in a locally intense electric field region. It initiates negative breakdown at the starting location of the streamers, which leads to the ensuing flash. The observations show that many or possibly all lightning flashes are initiated by fast positive breakdown.
Fast negative breakdown in thunderstorms Tilles, Julia N; Liu, Ningyu; Stanley, Mark A ...
Nature communications,
04/2019, Letnik:
10, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Thunderstorms are natural laboratories for studying electrical discharges in air, where the vast temporal, spatial, and energy scales available can spawn surprising phenomena that reveal deficiencies ...in our understanding of dielectric breakdown. Recent discoveries, such as sprites, jets, terrestrial gamma ray flashes, and fast positive breakdown, highlight the diversity of complex phenomena that thunderstorms can produce, and point to the possibility for electrical breakdown/discharge mechanisms beyond dielectric breakdown theory based mainly on laboratory experiments. Here we present one such confounding discovery, termed fast negative breakdown, that does not fit with our current understanding of dielectric breakdown. Our adaptation of radio astronomy imaging techniques to study extremely transient lightning-associated events confirms that electrical breakdown in thunderstorms can begin with oppositely-directed fast breakdown of negative polarity, similar and in addition to fast positive breakdown expected from conventional dielectric theory and recent observations. The discovery of fast negative breakdown calls for an addendum to the physical description of electrical discharges in air.
There has been much recent interest in the concept of rewilding as a tool for nature conservation, but also confusion over the idea, which has limited its utility. We developed a unifying definition ...and 10 guiding principles for rewilding through a survey of 59 rewilding experts, a summary of key organizations’ rewilding visions, and workshops involving over 100 participants from around the world. The guiding principles convey that rewilding exits on a continuum of scale, connectivity, and level of human influence and aims to restore ecosystem structure and functions to achieve a self‐sustaining autonomous nature. These principles clarify the concept of rewilding and improve its effectiveness as a tool to achieve global conservation targets, including those of the UN Decade on Ecosystem Restoration and post‐2020 Global Biodiversity Framework. Finally, we suggest differences in rewilding perspectives lie largely in the extent to which it is seen as achievable and in specific interventions. An understanding of the context of rewilding projects is the key to success, and careful site‐specific interpretations will help achieve the aims of rewilding.
Resumen
Recientemente ha habido mucho interés por el concepto de retorno a la vida silvestre como herramienta para la conservación de la naturaleza, pero también ha habido confusión por la idea que ha limitado su utilidad. Desarrollamos una definición unificadora y diez principios básicos para el retorno a la vida silvestre por medio de encuestas a 59 expertos en retorno a la vida silvestre, un resumen de las visiones de las organizaciones más importantes para el retorno a la vida silvestre y talleres que involucraron a más de 100 participantes de todo el mundo. Los principios básicos transmiten que el retorno a la vida silvestre existe en un continuo de escala, conectividad y nivel de influencia humana y que su objetivo es restaurar la estructura y las funciones del ecosistema para lograr una naturaleza autónoma autosustentable. Estos principios aclaran el concepto del retorno a la vida silvestre e incrementan su efectividad como herramienta para lograr los objetivos mundiales de conservación, incluyendo aquellos de la Década de la ONU para la Restauración de Ecosistemas y el Marco de Trabajo de la Biodiversidad Global post 2020. Finalmente, sugerimos que las diferencias en las perspectivas del retorno a la vida silvestre yacen principalmente en el grado al que es visto como factible y en intervenciones específicas. Un entendimiento del contexto de los proyectos de retorno a la vida silvestre es importante para el éxito, y las interpretaciones específicas de sitio ayudarán a lograr las metas del retorno a la vida silvestre.
Principios Básicos para el Retorno a la Vida Silvestre
The persistence of endangered species may depend on the fate of a very small number of individual animals. In situ conservation alone may sometimes be insufficient. In these instances, the ...International Union for Conservation of Nature provides guidelines for ex situ conservation and the Convention on Biological Diversity (CBD) indicates how ex situ management can support the CBD's objectives by providing insurance policies for species. The circumstances that justify its use are uncertain. To evaluate the current in situ extinction risk and ex situ management of 43 critically endangered species of mammalian megafauna, we used nonmetric multidimensional scaling and geopolitical variables related to governance, economics, and national policy within their extant ranges. We then fitted generalized additive models to assess the contribution of each variable to the ordination. Fifteen (almost one‐third) of the world's terrestrial mammalian megafauna are not the subject of any ex situ management. Seventy‐three percent of these taxa occur in areas characterized by political uncertainty, such as border zones or areas affected by armed conflicts, mainly in Africa and the Middle East. A further 23% of taxa in ex situ programs do not meet sustainability criteria for inbreeding avoidance. Strategic conservation planning, such as the One Plan approach, may improve ex situ management for these taxa. Given the escalating trend in threats afflicting megafauna, ex situ management should be considered more rigorously, particularly in politically unstable regions, to achieve CBD Target 12 (prevent extinction of threatened species).
Manejo Ex Situ como Protección contra la Extinción de la Megafauna de Mamíferos en un Mundo Incierto
Resumen
La persistencia de las especies en peligro puede depender del destino de un número muy pequeño de animales individuales. La conservación in situ por sí sola a veces puede ser insuficiente. Bajo estas instancias, la Unión Internacional para la Conservación de la Naturaleza proporciona directrices para la conservación ex situ y la Convención sobre la Diversidad Biológica (CBD) indica cómo el manejo ex situ puede apoyar a lograr sus objetivos al proporcionar políticas de protección para las especies. Las circunstancias que justifican el uso del manejo ex situ son inciertas. Para evaluar el actual riesgo de extinción in situ y el manejo ex situ de 43 especies de megafauna de mamíferos en peligro crítico de extinción usamos un escalamiento multidimensional no métrico, así como variables geopolíticas relacionadas con el gobierno, la economía y las políticas nacionales dentro de la distribución actual de estas especies. Después ajustamos los modelos sumativos generalizados para evaluar la contribución de cada variable a la ordinación. Quince (casi un tercio) de los mamíferos terrestres pertenecientes a la megafauna no están sujetos a ningún tipo de manejo ex situ. El 73% de estos taxones ocurren en áreas conocidas por su incertidumbre política, como zonas fronterizas o áreas afectadas por conflictos armados, principalmente en África y en el Oriente Medio. Además, un 23% de los taxones que sí se encuentran en programas de conservación ex situ no cumplen con los criterios de sustentabilidad para evitar la endogamia. La planeación de la conservación estratégica, como la estrategia de One Plan, podría mejorar el manejo ex situ para estos taxones. Dada la tendencia creciente en las amenazas que afectan a la megafauna, el manejo ex situ debería considerarse de manera más rigurosa, particularmente en las regiones con inestabilidad política, para alcanzar el Objetivo 12 de la CBD (evitar la extinción de especies amenazadas).
摘要
濒危物种的续存可能取决于该物种极少数个体的命运;因此, 仅仅只有就地保护有时还不足够。在这些情况下, 世界自然保护联盟 (IUCN) 为迁地保护提供了指导方针, 《生物多样性公约 (CBD) 》也指出了迁地管理如何通过为物种提供保险政策来支持 CBD 目标。然而, 应在怎样的情况下合理利用迁地保护仍存在疑问。为了评估43种极度濒危的巨型哺乳动物目前的就地灭绝风险和迁地管理, 我们利用非度量多维标度法和动物现生分布区内与治理、经济和国家政策相关的地理政治变量进行了分析。我们还进一步拟合了广义加性模型以评估各变量对等级排序的贡献。世界陆生巨型哺乳动物中有15种 (近三分之一) 未被纳入任何迁地管理项目之中。这些类群中 73%分布在政治不稳定的地区, 如边境地区或受武装冲突影响的地区, 主要在非洲和中东。迁地保护项目中还有 23%的类群没有满足避免近亲繁殖的可持续性标准。战略保护规划, 如一体计划方案 (One Plan approach), 可以帮助改进这些物种的迁地管理。鉴于巨型动物面临的威胁仍在不断加剧, 为了实现 CBD 目标 12 (防止濒危物种灭绝), 应该更严格地考虑迁地管理, 特别是在政治不稳定的地区。 【翻译:胡怡思;审校:聂永刚】
Article impact statement: One‐third of critically endangered large mammals, most occurring in politically unstable areas, are not supported by ex situ management.
Based on the very-high-frequency (VHF) pulse signal detected by interferometer (INTF) antennas as the reference unit, a lightning location method based on pulse matching and peak extraction is ...proposed in this article. The first key step of this method is to optimize the raw VHF data of the INTF by using the ensemble empirical mode decomposition (EEMD) method to control the quality of the original signal by bandpass filtering to preserve only the relatively high-frequency components of 40-80 MHz. Then, through a combination of main and auxiliary windows, the matching of waveforms from different antennas is realized by means of generalized cross correlation. In a microscale window (11 ns), the pulse signals are further accurately matched, and the arrival time difference is calculated under threshold and similarity constraints. Finally, the 2-D coordinates of the matched pulsed radiation sources are obtained using the nonlinear least-squares method. Compared with the results of the traditional "centroid" approach, the number of radiation sources obtained with the proposed method is greatly increased. For lightning cases with different discharge intensities, the number of located radiation sources can be increased by a factor of 10-20, and for specific short-duration and rapidly changing discharge processes (such as dart leaders and K events), the number of located radiation sources can be increased by a factor of nearly 100. For INTF operation at 20-88 MHz with a sampling rate of 180 MHz, the analytical resolution of the lightning discharge process can be improved to 10 ns. When the radiation sources are fully located, the widths of the lightning channels can be successfully reconstructed from the density of no-size points representing the located radiation sources in space.
Interferometric measurements of very-high-frequency (VHF) radio frequency signals produced by lightning are one of the most effective techniques for studying lightning breakdown processes, so ...uncertainty and error analyses of interferometric location results have become important topics. Based on the plane wave approximation of lightning RF signal transmission for interferometric location, a geometric model for the systematic error in the interferometric location due to the wavefront being spherical is developed and evaluated for short baseline interferometers, beginning with orthogonal and equilateral triangle baseline layouts. The symmetry of the baseline layout is shown to be helpful for reducing the systematic error caused by the plane wave approximation in interferometric location using a geometric relationship. Furthermore, a baseline layout scheme with the center of an equilateral triangle as the coordinate origin optimizes the systematic error caused by the plane wave approximation.
1. In dryland ecosystems, mobility is essential for both wildlife and people to access unpredictable and spatially heterogeneous resources, particularly in the face of climate change. Fences can ...prevent connectivity vital for this mobility. 2. There are recent calls for large-scale barrier fencing interventions to address human-wildlife conflict and illegal resource extraction. Fencing has costs and benefits to people and wildlife. However, the evidence available for facilitating sound decision-making for fencing initiatives is limited, particularly for drylands. 3. We identify six research areas that are key to informing evaluations of fencing initiatives: economics, edge permeability, reserve design, connectivity, ecosystem services and communities. 4. Policy implications. Implementing this research agenda to evaluate fencing interventions in dryland ecosystems will enable better management and policy decisions. The United Nations Conventions on Migratory Species (CMS) and to Combat Desertification (UNCCD) are appropriate international agreements for moving this agenda forward and leading the development of policies and guidelines on fencing in drylands.
Based on the ensemble empirical mode decomposition (EEMD) method, a DAF method for signal construction is proposed that repeatedly decomposes (D) the signal, amplifies (A) the local signal ...characteristics, and then filters (F) the signal. This method is used to decompose and reconstruct the electric field waveform (called a sferic) of an energetic in-cloud pulse (EIP) with a 247-kA peak current detected by a fast antenna (FA). Based on synchronous sub-microsecond very high-frequency (VHF, 14-88 MHz) radio interferometer (INTF) observations and observed downward fast positive and upward fast negative breakdowns, which occurred simultaneously with the EIP, the EIP sferic is decomposed by the DAF method in 11 steps into two independent sferics: a smoother filtered EIP sferic and an embedded narrow bipolar-like event (NBE). It is verified that strong VHF radiation is generated by the NBE-like event, rather than being associated with the smooth EIP sferic. The analysis, decomposition, and reconstruction of the correlated signals by the EEMD-based DAF method proposed in this article support the idea that the large-amplitude EIP sferic was generated by relativistic discharge responsible for an accompanying terrestrial gamma-ray flash (TGF) rather than by streamer or leader activity.
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