536 research outputs found
Classification of vegetative lagg types and hydrogeomorphic lagg forms in bogs of coastal British Columbia, Canada
No full textA “lagg” is usually defined as the confined transition zone along the outside margin of a raised bog, characterized by a fen or swamp plant community. It is an important landscape element for biodiversity and helps to maintain a high water table within the peat mass of a bog, but has received little research attention. Greater knowledge of the variability in laggs will improve designation of appropriate conservation sites and restoration of damaged bogs. We therefore examined the hydrological, hydro-chemical, vegetative, and peat characteristics of laggs of bogs in coastal British Columbia, Canada. The 17 studied lagg transects were classified into four vegetative lagg types: Spiraea Thicket, Carex Fen, Peaty Forest, and Direct Transition. These vegetative lagg types fell within two hydrogeomorphic lagg forms: confined or unconfined. The Spiraea Thicket and Carex Fen laggs were topographically confined at the bog margin and characterized by a higher water table and a smaller tree basal area compared to the unconfined Peaty Forest and Direct Transition laggs. Half of the studied laggs were unconfined, highlighting the importance of considering both confined and unconfined laggs in the delineation, conservation, and restoration of raised bog ecosystems
The essential role of the lagg in raised bog function and restoration: a review
No full textThe lagg of a raised bog is a transition zone where runoff collects from the ombrotrophic (rain-fed) bog and adjacent mineral soils. Distinct hydrological and hydrochemical gradients exist across the lagg zone, resulting in specific plant communities. Little research emphasis has been placed on the lagg zone in the past, with studies tending to focus on the more easily-defined bog instead. Recently, peatland researchers have begun to discuss the importance of the lagg to raised bog restoration. This paper reviews current knowledge on lagg zones, the function of this transition zone, some useful indicators to determine its location in the field, and argues that restoration of the lagg should be a key element in raised bog restoration
Coring and assessment of the lagg fen at Cors Caron NNR, Ceredigion, Wales
No full textFive sample cores were taken from two areas of lagg fen surrounding Cors Caron West Bog and described using the Tröels-Smith system of sediment classification. Two cores were selected for further laboratory analyses; one (Lagg2) was located near to the western hill slope margin and the other (Lagg5) on the banks of the Teifi river channel. Plant macrofossil analyses of core Lagg2 showed that peat development began in a marginal woodland, which was overtaken by a relatively dry raised bog community. The bog developed for several thousand years and was eventually invaded by low hummock and lawn Sphagna typical of wet oceanic raised bogs. At the same point the Sphagnum-rich peat shows signs of disturbance in the form of charcoal layers and an increase in soil fungi. These features may represent secondary decomposition after peat cutting. The bog assemblage is abruptly replaced by a wet fen assemblage that may represent in-filling of an abandoned peat cutting. Lagg2 is almost certainly not an intact sequence and the modern lagg vegetation most probably represents the latest stage in a secondary succession towards raised bog. The succession from wet fen to the modern vegetation appears to be an undisturbed record. This part of the sequence may represent a valuable analogue for the development of marginal pools and blocked former-cuttings on the present day peat surface. The depth of the hiatus in the Lagg2 record (110cm) suggests that the presumed peat cutting occurred several hundred years ago. This conclusion is supported by some preliminary observations of SCP concentrations in the upper peat. Most if not all of the industrial period appears to be represented within the upper three zones of Lagg2.Core Lagg5 provides a contrasting history of lagg development. On the banks of the Teifi fen conditions have prevailed throughout the time period represented by the core. Various Carex species, including Carex rostrata and Curta are present throughout the peat sequence. Other constant species include potentilla palsutris, Galium palustre and Eriophorum vaginatum. More detailed pollen and SCP analyses will be required to verify these findings prior to using the site for a high resolution reconstruction of vegetation development.In summary, the lagg fen on the banks of the Teifi may provide a valuable record of continuous lagg fen development, whereas the superficially similar lagg communities on the western margin of the West Bog have been significantly disturbed albeit several hundred years ago. The western lagg does provide a detailed and well preserved record of secondary lagg development after the abandonment of cuttings.<br/
Hydrochemical and microbiological distinction and function of ombrotrophic peatland lagg as ecotone between
No full textThe testate amoeba, ciliate and rotifera communities living in interstitial waters in peatbog in eastern Poland were studied. Sampling was done on a monthly basis from April to November 2007–2008. Microbial communities were examined in a transect including three sites: (1) pine forest (site located 5 m from the lagg/forest contact zone), (2) lagg, (3) open peatbog (the centre of the peatbog). At each of the sites, interstitial water was sampled by means of piezometric wells placed to a depth of 1 m. The species richness and abundance of protozoa and rotifers significantly differed between the studied stations, with the lowest numbers in the pine forest and the highest in the lagg. These differences between macro-habitats may be due to differences in environmental conditions. The distribution of samples in ordination space led to conclude that studied habitats are distributed along the falling gradient of pH and rising gradient of total organic carbon, water table depth and nitrate nitrogen. Assemblages of all three groups showed a strong compositional gradient correlated with water-table depth, conductivity and total phosphorus. However, species composition of ciliates and rotifers was explained by nitrate nitrogen and/or phosphates concentrations. The results suggest that lagg zone of a raised bog can fulfil the function of an ecotone zone, distinguished by a significant increase in biodiversity, abundance and species specificity of micro-organisms. It can also be a place of very efficient matter and energy flow in a peat bog ecosystem
Quiet Sun magnetic fields observed by Hinode: Support for a local dynamo
No full textContext. The Hinode mission has revealed copious amounts of horizontal flux covering the quiet Sun. Local dynamo action has been proposed to explain the presence of this flux. Aims. We sought to test whether the quiet Sun flux detected by Hinode is due to a local or the global dynamo by studying long-term variations in the polarisation signals detectable at the disc centre of the quiet Sun between November 2006 and May 2012, with particular emphasis on weak signals in the internetwork. Methods. The investigation focusses on line-integrated circular polarisation Vtot and linear polarisation LPtot profiles obtained from the Fe I 6302.5 Å absorption line in Hinode SOT/SP. Results. Both circular and linear polarisation signals show no overall variation in the fraction of selected pixels from 2006 until 2012. There is also no variation in the magnetic flux in this interval of time. The probability density functions (PDF) of the line-of-sight magnetic flux can be fitted with a power law from 1.17 × 1017 Mx to 8.53 × 1018 Mx with index α = −1.82 ± 0.02 in 2007. The variation of α’s across all years does not exceed a significance of 1σ. Linearly polarised features are also fitted with a power law, with index α = −2.60 ± 0.06 in 2007. Indices derived from linear polarisation PDFs of other years also show no significant variation. Conclusions. Our results show that the ubiquitous horizontal polarisation on the edges of bright granules seen by Hinode are invariant during the minimum of cycle 23. This supports the notion that the weak circular and linear polarisation is primarily caused by a
Cross-systems multi-level data pipelines optimization for predicting sunspot emergence
No full textThe proliferation of big data pipelines has spurred collaborative efforts across multiple disciplines to explore the intricacies of those domains. One notable collaboration involves the synergy between Computer Science and other natural sciences. Researchers in diverse domains possess valuable insights that can significantly enhance the extraction of novel and impactful findings within their respective fields. However, the optimal utilization of these pipelines often requires harnessing the full potential of High Performance Computing (HPC) systems. A significant challenge arises from the fact that these pipelines are optimized for scientific accuracy, and therefore may fail to exploit the available resources to their maximum capacity. To address this issue, this thesis explores various approaches to separate the scientific development on the pipeline by the domain scientist from the HPC resource optimization by the computer scientist, and to capture the runtime conditions of processes, identify potential imbalances, and elucidate their underlying causes. The concept is exemplified by applying it to a pipeline proposed by Korpi-Lagg et al. [1]. We conduct a statistical analysis of this pipeline, and investigate existing imbalances and areas for optimization within the pipelines. Through these efforts, the thesis aims to contribute to the enhancement of big data pipeline efficiency and effectiveness across diverse domains.
[1] M. J. Korpi-Lagg, A. Korpi-Lagg, N. Olspert, and H. L. Truong, “Solarcycle variation of quiet-Sun magnetism and surface gravity oscillation mode,”
Astronomy & Astrophysics, vol. 665, p. A141, Sep. 2022
Evershed and Counter-Evershed Flows in Sunspot MHD Simulations
No full textThere have been a few reports in the literature of counter-Evershed flows observed in well-developed sunspot penumbrae, i.e., flows directed toward the umbra along penumbral filaments. Here, we investigate the driving forces of such counter-Evershed flows in a radiative magnetohydrodynamic simulation of a sunspot, and compare them to the forces acting on the normal Evershed flow. The simulation covers a timespan of 100 solar hours and generates an Evershed outflow exceeding 8 km s−1 in the penumbra along radially aligned filaments where the magnetic field is almost horizontal. Additionally, the simulation produces a fast counter-Evershed flow (i.e., an inflow near ) in some regions within the penumbra, reaching peak flow speeds of ~12 km s−1. The counter-Evershed flows are transient and typically last a few hours before they turn into outflows again. By using the kinetic energy equation and evaluating its various terms in the simulation box, we found that the Evershed flow occurs due to overturning convection in a strongly inclined magnetic field, while the counter-Evershed flows can be well-described as siphon flows
Using the infrared iron lines to probe solar subsurface convection
No full textStudying the properties of the solar convection using high-resolution spectropolarimetry began in the early 90's with the focus on observations in the visible wavelength regions. Its extension to the infrared (IR) remains largely unexplored. The IR iron lines around 15600\,, most commonly known for their high magnetic sensitivity, also have a non-zero response to line-of-sight velocity below . In this paper we aim to tap this potential to explore the possibility of using them to measure sub-surface convective velocities. By assuming a snapshot of a three-dimensional magnetohydrodynamic simulation to represent the quiet Sun, we investigate how well the iron IR lines can reproduce the LOS velocity in the cube and up to what depth. We use the recently developed spectropolarimetric inversion code SNAPI and discuss the optimal node placements for the retrieval of reliable results from these spectral lines. We find that the IR iron lines can measure the convective velocities down to , below the photosphere, not only at original resolution of the cube but also when degraded with a reasonable spectral and spatial PSF and stray light. Meanwhile, the commonly used Fe~{\sc i} 6300\,\AA{} line pair performs significantly worse. Our investigation reveals that the IR iron lines can probe the subsurface convection in the solar photosphere. This paper is a first step towards exploiting this diagnostic potential
A novel technique for magnetic flux emergence diagnostics on the Sun
No full text| openaire: EC/HE/101101005/EU//SYCOSPeer reviewe
Computational approaches to modeling dynamos in galaxies
No full textAbstract Galaxies are observed to host magnetic fields with a typical total strength of around 15 \upmu μ G. A coherent large-scale field constitutes up to a few microgauss of the total, while the rest is built from strong magnetic fluctuations over a wide range of spatial scales. This represents sufficient magnetic energy for it to be dynamically significant. Several questions immediately arise: What is the physical mechanism that gives rise to such magnetic fields? How do these magnetic fields affect the formation and evolution of galaxies? In which physical processes do magnetic fields play a role, and how can that role be characterized? Numerical modelling of magnetized flows in galaxies is playing an ever-increasing role in finding those answers. We review major techniques used for these models. Current results strongly support the conclusion that field growth occurs during the formation of the first galaxies on timescales shorter than their accretion timescales due to small-scale turbulent dynamos. The saturated small-scale dynamo maintains field strengths at only a few percent of equipartition with turbulence. This is in contradiction with the observed magnitude of turbulent fields, but may be reconciled by the further contribution to the turbulent field of the large-scale dynamo. The subsequent action of large-scale dynamos in differentially rotating discs produces field strengths observed in low redshift galaxies, where it reaches equipartition with the turbulence and has substantial power at large scales. The field structure resulting appears consistent with observations including Faraday rotation and polarisation from synchrotron and dust thermal emission. Major remaining challenges include scaling numerical models toward realistic scale separations and Prandtl and Reynolds numbers.European Research Council http://dx.doi.org/10.13039/501100000781National Science Foundation http://dx.doi.org/10.13039/10000000
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