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The flare likelihood and region eruption forecasting (FLARECAST) project: flare forecasting in the big data & machine learning era
Full text linkLOFAR Observations of a Jet-driven Piston Shock in the Low Solar Corona
Full text linkThe Sun produces highly dynamic and eruptive events that can drive shocks through the corona. These shocks can accelerate electrons, which result in plasma emission in the form of a type II radio burst. Despite the large number of type II radio burst observations, the precise origin of coronal shocks is still subject to investigation. Here, we present a well-observed solar eruptive event that occurred on 2015 October 16, focusing on a jet observed in the extreme ultraviolet by the Atmospheric Imaging Assembly (SDO/AIA), a streamer observed in white light by the Large Angle and Spectrometric Coronagraph (SOHO/LASCO), and a metric type II radio burst observed by the LOw Frequency Array (LOFAR). LOFAR interferometrically imaged the fundamental and harmonic sources of a type II radio burst and revealed that the sources did not appear to be cospatial, as would be expected from the plasma emission mechanism. We correct for the separation between the fundamental and harmonic using a model that accounts for scattering of radio waves by electron density fluctuations in a turbulent plasma. This allows us to show the type II radio sources were located ∼0.5R⊙ above the jet and propagated at a speed of ∼1000 km s−1, which was significantly faster than the jet speed of ∼200 km s−1. This suggests that the type II burst was generated by a piston shock driven by the jet in the low corona
Varia Hibernica. 1. The Syntax of at-bail 'dies, perishes'. 2. ettae, 3pl. rel. of ithid 'eats'. 3. desruith, desruithithir. 4. bríath, bríad 'remnant, residue' in Bérla na filed. 5. maoi in Bérla na filed.
Full text linkWINTERC-G: mapping the upper mantle thermochemical heterogeneity from coupled geophysical–petrological inversion of seismic waveforms, heat flow, surface elevation and gravity satellite data
Full text linkBetween Innovation and Tradition: Code-Switching in the Transmission of the Commentary to the Félire Óengusso
Full text linkThis article presents a case study that explores the issue of code-switching in medieval text transmission with initial data mined in a three-year project run at the Dublin Institute for Advanced Studies. The case study is based on a bilingual corpus of glosses and notes in Irish and Latin that accompanies the ninth-century Martyrology of Óengus. This collection of material is referred to as the Commentary to the Félire Óengusso and is found in ten manuscripts. This provides an excellent opportunity to compare different versions of a bilingual text in order to analyse the way in which different scribes dealt with the bilingual material that they copied. In my analysis, a twofold approach to the material will be adopted: first, from the perspective of linguistics, I examine whether the grammatical characteristics of a code-switch influence its transmission. For this, I use Pieter Muysken’s typology of code-mixing (2000) to distinguish between complex and simple code-switches. Secondly, from the perspective of palaeography, I examine whether highly abbreviated words that could be interpreted as either Latin or Irish (visual diamorphs) may cause so-called »triggered« code-switches in transmission. The aim of the comparison is to provide a window on scribal practice in bilingual texts
How deep ocean-land coupling controls the generation of secondary microseism Love waves
Full text linkWind driven ocean wave-wave interactions produce continuous Earth vibrations at the seafloor called secondary microseisms. While the origin of associated Rayleigh waves is well understood, there is currently no quantified explanation for the existence of Love waves in the most energetic region of the microseism spectrum (3–10 s). Here, using terrestrial seismic arrays and 3D synthetic acoustic-elastic simulations combined with ocean wave hindcast data, we demonstrate that, observed from land, our general understanding of Rayleigh and Love wave microseism sources is significantly impacted by 3D propagation path effects. We show that while Rayleigh to Love wave conversions occur along the microseism path, Love waves predominantly originate from steep subsurface geological interfaces and bathymetry, directly below the ocean source that couples to the solid Earth. We conclude that, in contrast to Rayleigh waves, microseism Love waves observed on land do not directly relate to the ocean wave climate but are significantly modulated by continental margin morphologies, with a first order effect from sedimentary basins. Hence, they yield rich spatio-temporal information about ocean-land coupling in deep water
Dynamic earthquake triggering response tracks evolving unrest at Sierra Negra volcano, Galápagos Islands
Full text linkThe propensity for dynamic earthquake triggering is thought to depend on the local stress state and amplitude of
the stress perturbation. However, the nature of this dependency has not been confirmed within a single crustal
volume. Here, we show that at Sierra Negra volcano, Galápagos Islands, the intensity of dynamically triggered
earthquakes increased as inflation of a magma reservoir elevated the stress state. The perturbation of short-term
seismicity within teleseismic surface waves also increased with peak dynamic strain. Following rapid coeruptive
subsidence and reduction in stress and background seismicity rates, equivalent dynamic strains no longer triggered
detectable seismicity. These findings offer direct constraints on the primary controls on dynamic triggering
and suggest that the response to dynamic stresses may help constrain the evolution of volcanic unrest
Quantifying strong seismic propagation effects in the upper volcanic edifice using sensitivity kernels
Full text linkIn volcanic environments, the correct interpretation of the signals recorded by a seismic station is critical for a determination of the internal state of the volcano. Those signals contain information about both the seismic source and the properties of the path travelled by the seismic wave. Therefore, understanding the path effect is necessary for both source inversions and geophysical investigation of the volcanoes' properties at depth. We present an application of the seismic adjoint methodology and sensitivity kernel analysis to investigate seismic wave propagation effects in the upper volcanic edifice. We do this by performing systematic numerical simulations to calculate synthetic seismograms in two-dimensional models of Mount Etna, Italy, considering different wave velocity properties. We investigate the relationship between different portions of a seismogram and different parts of the structural volcano model. In particular, we examine the influence of known near-surface low-velocity volcanic structure on the recorded seismic signals. Results improve our ability to understand path effects highlighting the importance of the shallowest velocity structure in shaping the recorded seismograms and support recent studies that show that, although long-period seismic events are commonly associated with magma movements in resonant conduits, these events can be reproduced without the presence of fluids. We conclude that edifice heterogeneities impart key signatures on volcano seismic traces that must be considered when investigating volcano seismic sources
2D Synthetic dataset of numerical simulations of long-period seismicity in a volcanic edifice and related sensitivity kernels
Full text linkThis work describes the data used in the EPSL research ar- ticle “Quantifying strong seismic propagation effects in the upper volcanic edifice using sensitivity kernels”. The dataset is generated in order to investigate to what extent the seis- mic signals recorded on volcanoes are affected by near sur- face velocity structure. Data were calculated using the com- putational spectral elements scheme SPECFEM2D, where the wave propagation beneath Mount Etna volcano, Italy, was simulated in both homogeneous and heterogeneous models. The heterogeneous model comprises a low-velocity super- ficial structure (top several hundred meters) based on the previously published studies. Several different source mech- anisms and locations were used in the simulations. The seismic wavefield was “recorded”by 15 surface receivers distributed along the surface of the volcano. The associ- ated sensitivity kernels were also computed. These kernels highlight the region of the velocity model that affects the recorded seismogram within a desired time window