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Atmospheric Specifications for Infrasound Studies: 1. Operational Analyses
No full textInternational audienceOperational analysis products issued by weather services are needed for the Comprehensive Nuclear-Test-Ban Treaty's (CTBT) infrasound monitoring activities. They provide atmospheric specifications as high as 80 km altitude. They are used to feed propagation simulations designed to characterize sources of interest. Acoustic waveguides for long-range infrasound propagation form in the lower and middle atmosphere between approximately 10 and 110 km. Analysis products have biases in the stratosphere and above due to the decreasing amount of operational observations available for data assimilation systems. We investigate differences between two state-of-the-art analysis products, namely that of the Integrated Forecasting System, IFS, from the European Center for Medium-range Weather Forecast and that of the ICOsahedral Nonhydrostatic model, ICON, from the German Weather Service. We compare their differing predictions of acoustic waveguides across the International Monitoring System (IMS) of the CTBT. We demonstrate significant differences in prediction of waveguide strength in the equatorial region, related to different amplitudes of the westerly phase of the Semi-Annual Oscillation. Waveguide occurrence predictions can differ by up to 40% across the IMS, in the meridional and zonal directions. We quantify biases with respect to LiDAR wind and temperature observations at three sites. We demonstrate biases of up to 40% and 60% in terms of waveguide occurrence prediction for ICON and IFS, respectively, using the Institute for Atmospheric Physics's LiDAR simultaneous wind and temperature observations. We stress the added-value for more high-resolution measurements in the tropical region where operational products strongly disagree at altitudes that matter for infrasound propagation.Plain Language Summary Weather forecast products are issued daily and feed different operational activities relying on knowledge of the atmospheric state. Among those, the monitoring of the atmosphere with infrasound technology has been put in place to monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). To localize and characterize acoustic sources of interest, meteorological conditions from the surface to high altitudes (120 km) are needed. Indeed winds and temperatures up to ∼120 km height can affect the way acoustic waves propagate through atmospheric layers across large distances (up to 1,000 s of km) before being detected at infrasound stations of the International Monitoring System (IMS). Two state-of-the-art meteorological products are compared with respect to their prediction of acoustic waveguides. They are respectively issued by the European Center for Medium-range Weather Forecast (ECMWF) and by the German Weather Service (DWD). We find notable difference across the IMS and more specifically in equatorial regions in the upper stratosphere where the Semi-Annual Oscillation's amplitude differs between products. We also compare the products with ground-based LiDAR observations, allow scanning of the vertical atmospheric structure at three sites to identify notable differences. This further supports the importance of using measurements to help improve and validate these high-resolution models.</div
ESO Expanding Horizon White Paper: Revealing the properties of matter at supranuclear densities with gravitational waves
No full textInternational audienceUnderstanding dense matter under extreme conditions is one of the most fundamental puzzles in modern physics. Complex interactions give rise to emergent, collective phenomena. While nuclear experiments and Earth - based colliders provide valuable insights, much of the quantum chromodynamics phase diagram at high density and low temperature remains accessible only through astrophysical observations of neutron stars, neutron star mergers, and stellar collapse. Astronomical observations thus offer a direct window to the physics on subatomic scales with gravitational waves presenting an especially clean channel. Next-generation gravitational - wave observatories, such as the Einstein Telescope, would serve as unparalleled instruments to transform our understanding of neutron star matter. They will enable the detection of up to tens of thousands of binary neutron star and neutron star - black hole mergers per year, a dramatic increase over the few events accessible with current detectors. They will provide an unprecedented precision in probing cold, dense matter during the binary inspiral, exceeding by at least an order of magnitude what current facilities can achieve. Moreover, these observatories will allow us to explore uncharted regimes of dense matter at finite temperatures produced in a subset of neutron star mergers, areas that remain entirely inaccessible to current instruments. Together with multimessenger observations, these measurements will significantly deepen our knowledge of dense nuclear matter
Reassessment of DLVO theory at sub-nanometric scale: Application to Na-smectite
No full textInternational audienceThe nearly century-old DLVO (Derjaguin, Landau, Verview, and Overbeek) theory decomposes the interaction forces between solid surfaces separated by a fluid into attractive and repulsive components. In its standard version, it applies beyond solid surface separation distances of around 1 nm. For sub-nanometer distances, additional so-called hydration forces were widely invoked to explain the discrepancy between theory and measurements. Alternatively to this semi-empirical approach, either the validity of the theoretical expression for the electrostatic component of the disjoining pressure, or the adaptation of the Boltzmann distribution usually considered in the application of DLVO theory are questioned. Here, it is suggested that the introduction of a hydration component whose parameters cannot be predetermined but are a matter of calibration is unnecessary. Hydration effects, introduced in the calculation of ionic concentrations, directly influence ions distributions and therefore the repulsion of adjacent electric double layers. This effect is thus part of the electrostatic component of the disjoining pressure. An analytical expression extending DLVO theory to small surface separation distances together with a simplified electrical model, both proposed here, enable reproducing data for Na-smectite. Results are also in good agreement with thermodynamic and molecular dynamics calculations. It is confirmed that the discrepancy between theory and observations is mainly due to the underestimation of counterions concentration at the mid-plane identified using an inappropriate electrical model. For ions with radii around 0.1 nm, commonly found in natural media, the standard DLVO expression can still be used, but with mid-plane concentrations calculated using an appropriate electrical mode
Holocene climatic changes in the Kerguelen archipelago (South Indian Ocean) based on marine and lacustrine palaeoclimatic archives
No full textInternational audienceClimatic variability in the Southern Hemisphere is largely controlled by the latitudinal position of the Southern Hemisphere Westerly Winds (SHW), whose migration influences precipitation, temperature, and Antarctic upwelling. This study presents the results of analyses of two lacustrine sediment cores from Lake Armor, located on the subantarctic Kerguelen Islands (49 • 15′S, 69 • 10′E), within the SHW belt. Lipid biomarkers (Glycerol Dialkyl Glycerol Tetraethers, n-alkanes, and their hydrogen isotopes) were used to reconstruct mean annual air temperature above freezing (MAF) and humidity conditions. These records are compared with a high-resolution diatom-based summer sea surface temperature (SST) reconstruction from marine core MD11-3353, situated 150 km southwest of Lake Armor. In the late glacial and Early Holocene, our results reveal a period of warm air temperature, comparable to current values and very warm sea surface temperature, 5°C above the current values. Around 9000 cal a BP, an abrupt transition occurred, marked by a cooling of 5°C in SST and 1.5°C in MAF, interpreted as a northward migration of the SHW and associated oceanic fronts. The Mid-to-Late Holocene period is characterized by pronounced MAF variability, including a notably warm interval between 3000 and 2000 cal a BP, when n-alkane dD suggests the prevalence of wetter conditions. Since ~250 cal a BP, a southward migration of the SHW has produced a 2.5°C rise in MAF. Our findings are overall consistent with previous studies from the Indian Ocean, but permit us to go a step further as by comparing SSTs and air temperatures. This suggests that SST is not a reliable predictor of air temperature on the Kerguelen Islands, particularly during the Early Holocene. We hence argue that Kerguelen air temperature is predominantly controlled by the position of westerly winds, as an indicator of reorganisations in air mass trajectories
Marine litter, microplastic pollution and organic additives assessments in polar areas through an opportunistic cruise ship-based approach
No full textInternational audienceThis study presents findings from the opportunistic cruise, which performed microplastic and chemicalcontaminant sampling in surface waters, sediments, and ice in a sector of the western Arctic and the southwesternpart of the Antarctic Peninsula. Microplastics were detected in 100 % of the samples. Floating microplasticdensities (100–5000 μm) reached up to 314,251 items/km2 in Antarctica and 63,593 items/km2 in theArctic. The smallest particles (100–300 μm) dominated in southwestern Antarctic Peninsula (97 %) where thefibers (80 %) and fragments (19 %) were the main components. In the eastern Arctic, the two size classes(100–300 μm and 300–1000 μm) were more evenly distributed (58 % and 40 % respectively) and polymer diversity.Sediment microplastic concentrations were higher in the Arctic (up to 470 items/kg) compared tosouthwestern Antarctic Peninsula (maximum 399 items/kg). OrganoPhosphate Esters and PhthAlate Esters werealso measured for the first time in southwestern Antarctic Peninsula seawater (35.18 ±18.31 ng/L and 72.68 ±39.71 ng/L, respectively) and ice (50.44 ±24.79 ng/L and 16.72 ±11.46 ng/L, respectively). This studydemonstrates the utility of cruise ship-based sampling for monitoring remote regions and it contributes criticalbaseline data for global microplastic assessments.Cette étude présente les résultats d’une campagne opportuniste menée à bord d’un navire, au cours de laquelle des échantillonnages de microplastiques et de contaminants chimiques ont été réalisés dans les eaux de surface, les sédiments et la glace, dans un secteur de l’Arctique occidental et dans la partie sud-ouest de la péninsule Antarctique. Des microplastiques ont été détectés dans 100 % des échantillons. Les densités de microplastiques flottants (100–5000 µm) ont atteint jusqu’à 314 251 particules/km² en Antarctique et 63 593 particules/km² dans l’Arctique. Les plus petites particules (100–300 µm) dominaient dans la région sud-ouest de la péninsule Antarctique (97 %), où les fibres (80 %) et les fragments (19 %) constituaient les principaux types de particules. Dans l’Arctique oriental, les deux classes de taille (100–300 µm et 300–1000 µm) étaient plus équitablement réparties (58 % et 40 % respectivement), avec une plus grande diversité de polymères. Les concentrations de microplastiques dans les sédiments étaient plus élevées dans l’Arctique (jusqu’à 470 particules/kg) que dans la région sud-ouest de la péninsule Antarctique (maximum de 399 particules/kg). Des esters organophosphorés et des esters de phtalates ont également été mesurés pour la première fois dans l’eau de mer de la région sud-ouest de la péninsule Antarctique (35,18 ± 18,31 ng/L et 72,68 ± 39,71 ng/L, respectivement) ainsi que dans la glace (50,44 ± 24,79 ng/L et 16,72 ± 11,46 ng/L, respectivement). Cette étude démontre l’intérêt des prélèvements réalisés à partir de navires de croisière pour le suivi des régions éloignées et apporte des données de référence essentielles pour les évaluations globales des microplastiques
Shifts in Fossil Benthic Foraminiferal Community Trajectories During the Last Deglaciation Along the European Margin
No full textInternational audienceConstraining how faunal communities vary over time and space in response to environmental change has long been a major goal of paleoecologists. Among fossilized organisms, few yield a better and greater detailed record than foraminifera to understand past marine conditions. The analytical frameworks used to build palaeoenvironmental reconstructions have progressed over the years, providing new perspectives within the field. One of these proposed frameworks, Ecological Trajectory Analysis (ETA), offers the possibility to compare geometric properties of trajectories to understand temporal changes within communities. We provide here an application of ETA to the fossil record by comparing benthic foraminiferal data sets from three previously studied cores from the French Atlantic margin. The three cores are each separated by approximately 350 km and cover the last deglaciation, thus allowing a comparison of community dynamics at spatial and temporal scales. A major perturbation in fossil benthic communities was identified in ETA metrics at the onset of Heinrich Stadial 1, with a twofold departing and recovering trend of communities. The three sites along the French Atlantic margin also show spatial differences during the deglaciation, testimony to a contrasting response of benthic foraminifera to ice sheet dynamics and fluctuating fluvial discharges. In this instance, the application of ETA allows to compare multiple fossil foraminiferal records. At a broader scale, the use of trajectory metrics within one unique multivariate space of community resemblance stands out as a powerful tool to compare many other fossil records within the field of paleoecology
Revisiting FRB 20121102A: milliarcsecond localisation and a decreasing dispersion measure
No full textInternational audienceFRB 20121102A is the original repeating fast radio burst (FRB) source and also the first to be localised to milliarcsecond precision using very-long-baseline interferometry (VLBI). It has been active for over 13 years and resides in an extreme magneto-ionic environment in a dwarf host galaxy at a distance of ~1 Gpc. In this work, we use the European VLBI Network (EVN) to (re-)localise FRB 20121102A and its associated persistent radio source (PRS). We confirm that the two are co-located -- improving on previous results by a factor of ~4 and constraining the FRB and PRS co-location to ~12 pc transverse offset. Over a decade, the PRS luminosity on milliarcsecond scales remains consistent with measurements on larger angular scales, showing that the PRS is still compact. We also present the detection of 18 bursts with the Nancay Radio Telescope (NRT) as part of our ÉCLAT monitoring program. These bursts, together with previously published results, show that the observed dispersion measure (DM) of FRB 20121102A has dropped by ~25 pc/cc in the past five years, highlighting a fractional decrease in the local DM contribution of >15%. We discuss potential physical scenarios and highlight possible future observations that will help reveal the nature of FRB 20121102A, which is one of only a few known FRBs with a luminous PRS
-- Hardware-agnostic Particle-in-Cell Code for Plasma Astrophysics. II: General Relativistic Module
No full textInternational audienceBlack hole environments often host plasmas that are fully collisionless or contain intrinsically collisionless regions, including relativistic jets and coronae where particle energization is ubiquitous. Capturing the physics of these systems requires numerical methods capable of modeling relativistic, magnetized, collisionless plasmas in strong gravitational fields. In this work, we introduce the general-relativistic module for the Entity -- the first open-source, coordinate-agnostic performance-portable particle-in-cell code. The code enables fast axisymmetric simulations of collisionless plasmas around black holes on any modern high-performance computing architecture (both GPUs and CPUs)
Radiation-mediated shocks in gamma-ray bursts: spectral evolution
No full textInternational audienceRadiation-mediated shocks (RMS) occurring below the photosphere in a gamma-ray burst (GRB) jet could play a crucial role in shaping the prompt emission. In this paper, we study the time-resolved signal expected from such early shocks. An internal collision is modeled using a 1D special relativistic hydrodynamical simulation and the photon distributions in the resulting forward and reverse shocks, as well as in the common downstream region, are followed to well above the photosphere using a designated RMS simulation code. The light curve and time resolved spectrum of the resulting single pulse is computed taking into account the emission at different optical depths and angles to the line-of-sight. For the specific case considered, we find a light curve consisting of a short pulse lasting s for an assumed redshift of . The efficiency is large, with % of the total burst energy being radiated. The spectrum has a complex shape at very early times, after which it settles into a more generic shape with a smooth curvature below the peak energy, , and a clear high-energy power law that cuts off at MeV in the observer frame. The spectrum becomes narrower and softer at late times with steadily decreasing during the pulse decay from keV to keV. The low-energy index, , decreases during the bright part of the pulse from to , although the low-energy part is better fit with a broken power law when the signal-to-noise ratio is high. The high-energy power law is generated by the reverse shock at low optical depths () and has an index that decreases from to . These results provide support for RMSs as potential candidates for the prompt emission in GRBs
Neutrino signal from the hadron-quark phase transition in the conversion of Neutron Stars into Quark Stars
No full textInternational audienceWe calculate in a 1D General Relativistic (GR) hydrodynamic simulation the neutrino luminosity in an astrophysical scenario where a neutron star (NS) displays a hadron-quark phase transition (HQPT) into a Quark Star (QS). Deconfinement is triggered once the central density exceeds a critical threshold above being , saturation density. We use descriptions based on DD2 and the MIT Bag model equations of state (EOSs). We account for neutrinos using a microphysics forward emission model including annihilation, plasmon decay, nucleon (N) modified (or direct) Urca processes, and bremsstrahlung, and, for the post transition, the quark direct Urca and an opacity-based leakage scheme with GR redshift. We find that the neutrino light curve generically develops a short 10-50 ms, spectrally harder feature near deconfinement, appearing as either a prompt shoulder or a distinct secondary peak. Heavy lepton neutrinos result in a delayed peak with respect to the previous. We identify three diagnostics that are only mildly degenerate with hadronic uncertainties: (i) an enhanced peak-to-plateau ratio sourced by latent-heat release, (ii) a characteristic lag between the collapse rise and the HQPT feature that tracks the central density trajectory, and (iii) a flavor hardening driven by quark-matter phase space. After MSW flavor conversion, these signatures remain detectable with current experiments. For a Galactic event ( kpc), IceCube and Hyper-K should resolve the HQPT feature and distinguish it from both no transition NS collapse and canonical core-collapse supernova (CCSN) templates