Stenoeciteit van de Nederlandse flora Een nieuwe parameter op grond van ecologische amplitudo's van de Nederlandse plantensoorten en toepassingsmogelijkheden

Er is een dBase gemaakt waarin op basis van expertkennis voor ruim 1750 Nederlandse plantensoorten ieder afzonderlijk op grond van de amplitudo’s van zeven milieuvariabelen (trofie, zuurgraad, zoutgehalte, vocht, bodemtextuur en bodemdynamiek en daglichttoestand) hun stenoeciteit berekend is. De uitkomst is gecheckt door de invoergegevens te vergelijken met actuele meetgegevens. De resultaten zijn gunstig, ook wat betreft de correlatie met plantensociologische data. Voor het eerst is de ecologie van de stadsplanten systematisch bepaald. Het blijkt dat onze floristische zorgenkinderen alle ecologisch zeer kieskeurig zijn. Het risico van uitsterven van soorten valt samen met een stenoeciteit van 26,5 en minder. Het wordt aanbevolen dit begrip ook voor andere groepen organismen toe te passen, waarvoor samenwerking met andere kennisdragers essentieel is. Door de bondigheid van de notie is het mogelijk om correlaties te onderzoeken met tal van data uit andere kennisdomeinen. Stenoeciteit kan ons in geografisch opzicht goed behulpzaam zijn om gebieden met relatief veel of weinig kieskeurige soorten aan te geven. Stenoeciteit past goed als maat én meetlat om bijvoorbeeld zowel nationaal als internationaal over gebiedskwaliteit te communiceren en bij realisatie van te verwachten nieuw EU-beleid voor GLB- of CAPmaatregelen (landbouw)

The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics

An Observational Overview of Solar Flares

We present an overview of solar flares and associated phenomena, drawing upon a wide range of observational data primarily from the RHESSI era. Following an introductory discussion and overview of the status of observational capabilities, the article is split into topical sections which deal with different areas of flare phenomena (footpoints and ribbons, coronal sources, relationship to coronal mass ejections) and their interconnections. We also discuss flare soft X-ray spectroscopy and the energetics of the process. The emphasis is to describe the observations from multiple points of view, while bearing in mind the models that link them to each other and to theory. The present theoretical and observational understanding of solar flares is far from complete, so we conclude with a brief discussion of models, and a list of missing but important observations.Comment: This is an article for a monograph on the physics of solar flares, inspired by RHESSI observations. The individual articles are to appear in Space Science Reviews (2011

Observations of Photospheric Dynamics and Magnetic Fields: From Large-Scale to Small-Scale Flows

International audienceThis paper reviews solar flows and magnetic fields observed at the photospheric level. We first present the context in which these observations are performed. We describe the various temporal and spatial scales involved, and the coupling between them. Then we present small-scale flows, mainly supergranulation and flows around active regions. Flows at the global scale are then reviewed, again with emphasis on the flows, i.e. differential rotation, torsional oscillation and meridional circulation. In both small- and global-scale we discuss the coupling between flow fields and magnetic field and give an overview of observational techniques. Finally, the possible connection between studies of solar activity and stellar activity is briefly discussed