Searching for overturning convection in penumbral filaments: slit spectroscopy at 0.2 arcsec resolution

Recent numerical simulations of sunspots suggest that overturning convection is responsible for the existence of penumbral filaments and the Evershed flow, but there is little observational evidence of this process. Here we carry out a spectroscopic search for small-scale convective motions in the penumbra of a sunspot located 5 deg away from the disk center. The position of the spot is very favorable for the detection of overturning downflows at the edges of penumbral filaments. Our analysis is based on measurements of the Fe I 709.0 nm line taken with the Littrow spectrograph of the Swedish 1 m Solar Telescope under excellent seeing conditions. We compute line bisectors at different intensity levels and derive Doppler velocities from them. The velocities are calibrated using a nearby telluric line, with systematic errors smaller than 150 m/s. Deep in the photosphere, as sampled by the bisectors at the 80%-88% intensity levels, we always observe blueshifts or zero velocities. The maximum blueshifts reach 1.2 km/s and tend to be cospatial with bright penumbral filaments. In the line core we detect blueshifts for the most part, with small velocities not exceeding 300 m/s. Redshifts also occur, but at the level of 100-150 m/s, and only occasionally. The fact that they are visible in high layers casts doubts on their convective origin. Overall, we do not find indications of downflows that could be associated with overturning convection at our detection limit of 150 m/s. Either no downflows exist, or we have been unable to observe them because they occur beneath tau=1 or the spatial resolution/height resolution of the measurements is still insufficient.Comment: Accepted for publication in Ap

Combined effects of life-history traits and human impact on extinction risk of freshwater megafauna.

Megafauna species are intrinsically vulnerable to human impact. Freshwater megafauna (i.e., freshwater animals ≥30 kg, including fishes, mammals, reptiles, and amphibians) are subject to intensive and increasing threats. Thirty‐four species are listed as critically endangered on the International Union for Conservation of Nature (IUCN). Red List of Threatened Species, the assessments for which are an important basis for conservation actions but remain incomplete for 49 (24%) freshwater megafauna species. Consequently, the window of opportunity for protecting these species could be missed. Identifying the factors that predispose freshwater megafauna to extinction can help predict their extinction risk and facilitate more effective and proactive conservation actions. Thus, we collated 8 life‐history traits for 206 freshwater megafauna species. We used generalized linear mixed models to examine the relationships between extinction risk based on the IUCN Red List categories and the combined effect of multiple traits, as well as the effect of human impact on these relationships for 157 classified species. The most parsimonious model included human impact and traits related to species’ recovery potential including life span, age at maturity, and fecundity. Applying the most parsimonious model to 49 unclassified species predicted that 17 of them are threatened. Accounting for model predictions together with IUCN Red List assessments, 50% of all freshwater megafauna species are considered threatened. The Amazon and Yangtze basins emerged as global diversity hotspots of threatened freshwater megafauna, in addition to existing hotspots, including the Ganges‐Brahmaputra and Mekong basins and the Caspian Sea region. Assessment and monitoring of those species predicted to be threatened are needed, especially in the Amazon and Yangtze basins. Investigation of life‐history traits and trends in population and distribution, regulation of overexploitation, maintaining river connectivity, implementing protected areas focusing on freshwater ecosystems, and integrated basin management are required to protect threatened freshwater megafauna in diversity hotspots.This work was carried out within the SMART Joint Doctorate (Science for the MAnagement of Rivers and their Tidal systems), funded with the support of the Erasmus Mundus program of the European Union, and is a contribution to the Leibniz Competition project Freshwater Megafauna Futures. S.D.L was supported by the European Unio

Labyrinth Exploration, Emotional Reactivity, and Conditioned Fear in Young Roman/Verh Inbred Rats

An inbreeding program has been carried out with the Swiss sublines of Roman high- and low-avoidance rats since 1993. The present study reports the first experiments conducted with young animals of those inbred strains (RHA-I/Verh and RLA-I/Verh, respectively) from the sixth and seventh inbreeding generations. The results confirmed expected behavioral profiles. Compared to the RHA-I/Verh strain, RLA-I/Verh rats showed decreased entries into the illuminated central arena of an hexagonal tunnel maze, as well as decreased spontaneous locomotor activity and increased defecations, in two independent experiments. Young RLA-I/Verh females explored less than did their RHA-I/Verh counterparts during session 1 of a conditioned-fear experiment preceding shock administration, and in session 2 (conducted 24 h after the application of three footshocks), they showed greater conditioned behavioral inhibition (i.e., reduced amount of rearing), as well as higher defecation scores, than did RHA-I/Verh female

Floating matter: a neglected component of the ecological integrity of rivers

Floating matter (FM) is a pivotal, albeit neglected, element along river corridors contributing to their ecological integrity. FM consists of particulate matter of natural (e.g. wood, branches, leaves, seeds) and anthropogenic (e.g. plastic, human waste) origin as well as of organisms that, due to its properties, is able to float on the water surface. In this paper, we provide a comprehensive overview of the FM cycle and the fundamental environmental functions FM provides along rivers. Indeed, FM serves as an important geomorphological agent, a dispersal vector for animals and plant propagules, a habitat, a resource, and a biogeochemical component. Furthermore, we collected data on the amount of FM accumulating at dams and in reservoirs, and related it to key characteristics of the respective catchments. River fragmentation truncates the natural dynamics of FM through its extraction at damming structures, alteration in the flow regime, and low morphological complexity, which may decrease FM retention. Finally, we identify key knowledge gaps in relation to the role FM plays in supporting river integrity, and briefly discuss FM management strategies. (c) 2019, Springer Nature Switzerland AG.This work has been carried out within the SMART Joint Doctorate Programme ‘Science for the MAnagement of Rivers and their Tidal systems’, funded by the Erasmus Mundus programme of the European Union (http://www.riverscience.it). We also acknowledge financial support through the Excellence Initiative at the University of Tübingen, funded by the German Federal Ministry of Education and Research (BMBF) and the German Research Foundation (DFG). OS is thankful for a partial support from IGB equal opportunity fund for young female scientists and DFG (SU 405/10-1). SDL has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant agreement no. 748625

Is the solar spectrum latitude dependent? An investigation with SST/TRIPPEL

Context: In studies of the solar spectrum relative to spectra of solar twin stars, it has been found that the chemical composition of the Sun seems to depart systematically from those of the twins. One possible explanation is that the effect is due to the special aspect angle of the Sun when observed from Earth, as compared with the aspect angles of the twins. Thus, a latitude dependence of the solar spectrum, even with the heliocentric angle constant, could lead to effects of the type observed. Aim: We explore a possible variation in the strength of certain spectral lines, used in the comparisons between the composition of the Sun and the twins, at loci on the solar disk with different latitudes but at constant heliocentric angle. Methods: We use the TRIPPEL spectrograph at the Swedish 1-m Solar Telescope on La Palma to record spectra in five spectral regions in order to compare different locations on the solar disk at a heliocentric angle of 45 deg. Equivalent widths and other parameters are measured for fifteen different lines representing nine atomic species. Results: The relative variations in equivalent widths at the equator and at solar latitude 45 deg are found to be less than 1.5 % for all spectral lines studied. Translated to elemental abundances as they would be measured from a terrestrial and a hypothetical pole-on observer, the difference is estimated to be within 0.005 dex in all cases. Conclusion: It is very unlikely that latitude effects could cause the reported abundance difference between the Sun and the solar twins. The accuracy obtainable in measurements of small differences in spectral line strengths between different solar disk positions is very high.Comment: 9 pages, 10 figures, accepted by Astronomy & Astrophysic

Theoretical Models of Sunspot Structure and Dynamics

Recent progress in theoretical modeling of a sunspot is reviewed. The observed properties of umbral dots are well reproduced by realistic simulations of magnetoconvection in a vertical, monolithic magnetic field. To understand the penumbra, it is useful to distinguish between the inner penumbra, dominated by bright filaments containing slender dark cores, and the outer penumbra, made up of dark and bright filaments of comparable width with corresponding magnetic fields differing in inclination by some 30 degrees and strong Evershed flows in the dark filaments along nearly horizontal or downward-plunging magnetic fields. The role of magnetic flux pumping in submerging magnetic flux in the outer penumbra is examined through numerical experiments, and different geometric models of the penumbral magnetic field are discussed in the light of high-resolution observations. Recent, realistic numerical MHD simulations of an entire sunspot have succeeded in reproducing the salient features of the convective pattern in the umbra and the inner penumbra. The siphon-flow mechanism still provides the best explanation of the Evershed flow, particularly in the outer penumbra where it often consists of cool, supersonic downflows.Comment: To appear in "Magnetic Coupling between the Interior and the Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200

Freshwater megafauna diversity: Patterns, status and threats

Aim: Freshwater megafauna remain underrepresented in research and conservation, despite a disproportionately high risk of extinction due to multiple human threats. Therefore, our aims are threefold; (i) identify global patterns of freshwater megafauna richness and endemism, (ii) assess the conservation status of freshwater megafauna and (iii) demonstrate spatial and temporal patterns of human pressure throughout their distribution ranges. Location: Global. Methods: We identified 207 extant freshwater megafauna species, based on a 30 kg weight threshold, and mapped their distributions using HydroBASINS subcatchments (level 8). Information on conservation status and population trends for each species was extracted from the IUCN Red List website. We investigated human impacts on freshwater megafauna in space and time by examining spatial congruence between their distributions and human pressures, described by the Incident Biodiversity Threat Index and Temporal Human Pressure Index. Results: Freshwater megafauna occur in 76% of the world s main river basins (level 3 HydroBASINS), with species richness peaking in the Amazon, Congo, Orinoco, Mekong and Ganges-Brahmaputra basins. Freshwater megafauna are more threatened than their smaller counterparts within the specific taxonomic groups (i.e., fishes, mammals, reptiles and amphibians). Out of the 93 freshwater megafauna species with known population trends, 71% are in decline. Meanwhile, IUCN Red List assessments reported insufficient or outdated data for 43% of all freshwater megafauna species. Since the early 1990s, human pressure has increased throughout 63% of their distribution ranges, with particularly intense impacts occurring in the Mekong and Ganges-Brahmaputra basins. Main conclusions: Freshwater megafauna species are threatened globally, with intense and increasing human pressures occurring in many of their biodiversity hotspots. We call for research and conservation actions for freshwater megafauna, as they are highly sensitive to present and future pressures including a massive boom in hydropower dam construction in their biodiversity hotspots. © 2018 John Wiley & Sons LtdBundesministerium für Bildung und Forschung, Grant/Award Number: “GLANCE” project (01 LN1320A); European Union’s Horizon 2020 Programme for Research, Technological ?evelopment and demonstration, Grant/Award Number: AQUACROSS (642317); Villum Fonden, Grant/Award Number: VKR023371; Education, Audiovisual and Culture Executive Agency (Erasmus Mundus Joint ?octorate programme “SMART”); EU Marie Sklodowska-Curie programme, Grant/Award Number: H2020-MSCA-IF-2015-706784, H2020-MSCA-IF-2016-748625; Ministerium für Wissenschaft, Forschung und Kunst Baden-Württemberg (Junior Professorship Program

Convective motions and net circular polarization in sunspot penumbrae

We have employed a penumbral model, that includes the Evershed flow and convective motions inside penumbral filaments, to reproduce the azimuthal variation of the net circular polarization (NCP) in sunspot penumbrae at different heliocentric angles for two different spectral lines. The theoretical net circular polarization fits the observations as satisfactorily as penumbral models based on flux-tubes. The reason for this is that the effect of convective motions on the NCP is very small compared to the effect of the Evershed flow. In addition, the NCP generated by convective upflows cancels out the NCP generated by the downflows. We have also found that, in order to fit the observed NCP, the strength of the magnetic field inside penumbral filaments must be very close to 1000 G. In particular, field-free or weak-field filaments fail to reproduce both the correct sign of the net circular polarization, as well as its dependence on the azimuthal and heliocentric angles.Comment: Accepted for publication in the Astrophysical Journal. 10 pages, 7 figures (3 in color). Uses emulatedap

On the origin of reverse polarity patches found by Hinode in sunspot penumbrae

The satellite Hinode has recently revealed penumbral structures with a magnetic polarity opposite to the main sunspot polarity. They may be a direct confirmation of magnetic field lines and mass flows returning to the solar interior throughout the penumbra, a configuration previously inferred from interpretation of observed Stokes profile asymmetries. The paper points out the relationship between the reverse polarity features found by Hinode, and the model Micro-Structured Magnetic Atmospheres (MISMAs) proposed for sunspots. We show how the existing model MISMAs produce strongly redshifted reverse polarity structures as found by Hinode. Ad hoc model MISMAs also explain the asymmetric Stokes profiles observed by Hinode. The same modeling may be consistent with magnetograms of dark cored penumbral filaments if the dark cores are associated with the reverse polarity. Such hypothetical relationship will show up only in the far red wings of the spectral lines.Comment: To appear in A&A. 8 pages and 7 figure

Brightness, distribution, and evolution of sunspot umbral dots

We present a 106-minute TiO (705.7nm) time series of high spatial and temporal resolution that contains thousands of umbral dots (UDs) in a mature sunspot in the active region NOAA 10667 at $\mu$=0.95. The data were acquired with the 1-m Swedish Solar Telescope on La Palma. With the help of a multilevel tracking (MLT) algorithm the sizes, brightnesses, and trajectories of 12836 umbral dots were found and analyzed. The MLT allows UDs with very low contrast to be reliably identified. Inside the umbra we determine a UD filling factor of 11%. The histogram of UD lifetimes is monotonic, i.e. a UD does not have a typical lifetime. Three quarters of the UDs lived for less than 150s and showed no or little motion. The histogram of the UD diameters exhibits a maximum at 225km, i.e. most of the UDs are spatially resolved. UDs display a typical horizontal velocity of 420m/s and a typical peak intensity of 51% of the mean intensity of the quiet photosphere, making them on average 20% brighter than the local umbral background. Almost all mobile UDs (large birth-death distance) were born close to the umbra-penumbra boundary, move towards the umbral center, and are brighter than average. Notably bright and mobile UDs were also observed along a prominent UD chain, both ends of which are located at the umbra-penumbra boundary. Their motion started primarily at either of the ends of the chain, continued along the chain, and ended near the chain's center. We observed the splitting and merging of UDs and the temporal succession of both. For the first time the evolution of brightness, size, and horizontal speed of a typical UD could be determined in a statistically significant way. Considerable differences between the evolution of central and peripheral UDs are found, which point to a difference in origin