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Impact of seasonal snow on the recharge of a mountain karst aquifer under climate change: the Dévoluy case study (Southern Alps, France)
No full textPreprint to HESS (Hydrology and Earth System Sciences) - Discussion started: 9 January 2026International audienceSeasonal snow strongly influences groundwater recharge in mountain aquifers, yet its role in mid-altitude karst systems under climate warming remains poorly quantified. We investigated the Dévoluy karst aquifer (Southern French Alps) to assess how snow controls recharge and how spring discharge may respond to rising temperatures. Using the KarstMod platform, we developed a rainfall–snow–discharge model incorporating a degree-day snow routine to partition precipitation between rainfall and snow, and simulate the snowmelt. The model was calibrated and validated over four contrasting years (two low-snow, one high-snow, and one very high-snow year). Results show that accounting for snow processes is essential to reproduce the observed discharge dynamics, highlighting the dominant role of snow accumulation and melt in controlling both flow timing and magnitude. Under +2 °C and +4 °C warming scenarios, simulated winter flows increase while snowmelt peaks occur earlier, resulting in earlier and more severe summer low-flow periods. August discharge decreases by 28 % to 44 %, respectively, compared to present conditions. These findings demonstrate the critical role of seasonal snow in regulating recharge in mid-altitude karst aquifers and highlight that ongoing warming will substantially reduce summer water availability in mountain regions
Evaluating the NASA MPLNET Rain Masking Algorithm at Goddard Space Flight Center and Barcelona sites: Relevance to EarthCARE Cloud Profiling Radar Validation
No full textInternational audienceWe analyze the volcanic plume from the April 2015 Calbuco eruption over a 35‐day period using simulations from Meso‐NH, a non‐hydrostatic mesoscale atmospheric model. A dedicated parameterization of the deep injection of the plume into the stratosphere ensures a realistic representation when compared to Infrared Atmospheric Sounding Interferometer satellite observations. During the first 12 hr of the eruption, on 22 April 2015, SO 2 mixing ratio reached 29 ppmv between 15 and 18 km for the first eruption pulse, and 38 ppmv between 12 and 16 km for the second. Most SO 2 was injected directly into the stratosphere, with a stratospheric load reaching 308 ktS (kilotons of atomic sulfur, i.e. 616 kilotons of SO 2 ) after the eruption. After 1 month, both stratospheric and tropospheric SO 2 loads returned to near‐background levels. During analysis, the chemical conversion of SO 2 into H 2 SO 4 removed a part of SO 2 from the stratosphere. During the long‐range advection, the co‐location between the subtropical jet stream and the Calbuco plume led to three significant stratospheric intrusions on 24, 26 and 28 April 2015. These events transferred stratospheric SO 2 into the troposphere, SO 2 mixing ratios in the upper troposphere reaching 15 ppmv, 26 and 15 ppbv, respectively. SO 2 is gradually oxidized into H 2 SO 4 , with up to 5 ktS of gaseous H 2 SO 4 in the stratosphere on 30 April, but dynamical processes dominate the SO 2 atmospheric budget over chemical transformations. This study demonstrates that stratospheric intrusions can play a critical role in the removal of volcanic material from the stratosphere following a major eruption
Euclid: Improving redshift distribution reconstruction using a deep-to-wide transfer function
No full textInternational audienceThe Euclid mission seeks to understand the Universe expansion history and the nature of dark energy, which requires a very accurate estimate of redshift distribution. Achieving this accuracy relies on reference samples with spectroscopic redshifts, together with a procedure to match them to survey sources for which only photometric redshifts are available. One important source of systematic uncertainty is the mismatch in photometric properties between galaxies in the Euclid survey and the reference objects. We develop a method to degrade the photometry of objects with deep photometry to match the properties of any shallower survey in the multi-band photometric space, preserving all the correlations between the fluxes and their uncertainties. We compare our transfer method with more demanding image-based methods, such as Balrog from the Dark Energy Survey Collaboration. According to metrics, our method outperforms Balrog. We implement it in the redshift distribution reconstruction, based on the self-organising map approach of arXiv:1509.03318, and test it using a realistic sample from the Euclid Flagship Simulation. We find that the key ingredient is to ensure that the reference objects are distributed in the colour space the same way as the wide-survey objects, which can be efficiently achieved with our transfer method. In our best implementation, the mean redshift biases are consistently reduced across the tomographic bins, bringing a significant fraction of them within the Euclid accuracy requirements in all tomographic bins. Equally importantly, the tests allow us to pinpoint which step in the calibration pipeline has the strongest impact on achieving the required accuracy. Our approach also reproduces the overall redshift distributions, which are crucial for applications such as angular clustering
Braneworld Baryogenesis and QCD-Era Magnetogenesis: A Predictive Link
No full textInternational audienceWe demonstrate that primordial magnetic fields (PMF) play a decisive role in the braneworld baryogenesis scenario of [Phys. Rev. D , 023520 (2024)], where C/CP violation arises from the coupling of visible and hidden matter-antimatter sectors through a pseudo-scalar field. Although this mechanism generates baryon number efficiently only after the quark-hadron transition, by incorporating a realistic stochastic PMF within a semi-analytical framework, we find that matching the observed baryon-antibaryon asymmetry robustly requires PMF strengths of order T right after the transition, in agreement with causal QCD-era magnetogenesis. We further reveal that magnetic fluctuations drive the baryon-density spectrum to white noise on large scales, yielding an isocurvature component compatible with Cosmic Microwave Background (CMB) bounds. This establishes a predictive link between the braneworld baryogenesis model and realistic early-Universe magnetic fields
2D or not 2D? Exploring 3D relativistic magnetic reconnection dynamics with highly accurate numerical simulations
No full textInternational audienceFast reconnection in magnetically dominated plasmas is widely invoked in models of dissipation in pulsar winds, gamma-ray flares in the Crab nebula, and to explain the radio nanoshots of pulsars. When current sheets evolve reaching a critical inverse aspect ratio, scaling as with the plasma Lundquist number, the so-called \textit{ideal} tearing instability sets in, with modes growing, independently of , extremely rapidly on timescales of only a few light-crossing times of the sheet length. We present the first set of fully 3D simulations of current-sheet disruption triggered by the ideal tearing instability within the resistive relativistic MHD approximation, as appropriate in situations where the Alfvén velocity approaches the speed of light. We compare 3D setups with different initial conditions with their 2D counterparts, and we assess the impact of dimensionality and of the magnetic field topology on the onset, evolution, and efficiency of reconnection. In force-free configurations, 3D runs develop ideal tearing, secondary instabilities, and a thick, turbulent current layer, sustaining dissipation of magnetic energy longer than in 2D. In pressure-balanced current sheets with a null guide field, 2D reference runs show the familiar reconnection dynamics, whereas in 3D tearing dynamics is quenched after the linear phase, as pressure-driven modes growing on forming plasmoids outcompete plasmoid coalescence and suppress fast dissipation of magnetic energy. Taken together, these results suggest that the evolution and efficiency of reconnection depend sensitively on the local plasma conditions and current-sheet configuration, and can be properly captured only in fully 3D simulations
Refining the chrono-stratigraphy of the Middle Stone Age at Contrebandiers cave (Témara region)
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UV photocatalysis of ZnO nanowires: the issues of polarity and doping
No full textInternational audienceAs a sustainable wide bandgap compound semiconductor absorbing UV light while exhibiting high photocatalytic activity, ZnO in the form of nanowires has been considered as a promising candidate. Here, its polarity and its intentional doping with Al, Ga, Cu, Sb, Cl, Al-Ga, and Al-Cl are investigated to thoroughly assess their effects on the photocatalytic activity and processes. The photocatalytic processes in ZnO nanowires are found to be governed by the action of •OH hydroxyl radicals, as the main reactive species degrading methyl orange, and hence by free hVB+ acting as the primary active charge carriers on the surfaces of ZnO nanowires, regardless of the nature and concentration of dopants. The photocatalytic activity is further shown to be higher for acceptors than for shallow donors, and to preferentially act on the polar +c-plane top of ZnO nanowires. Eventually, a photo-corrosion phenomenon is concomitant with the photocatalytic processes, raising concerns about the chemical stability of ZnO nanowires. These findings revisit the effects of polarity and intentional doping of ZnO nanowires for photocatalysis and open perspectives to address chemical and technological challenges
Connection between Nonaxisymmetric Structures and Neutral Gas Distribution in Disk Galaxies
No full textInternational audienceNonaxisymmetric structures, such as bars and spiral arms, are known to concentrate molecular gas and star formation in galaxy centers, actively building up the pseudobulges. However, the direct link between the neutral (i.e., molecular and atomic) gas distribution and the exerted torque forces over a broader radial range of galactic disks still remains to be explored. In the present work, we investigate this link by carefully evaluating the torque force field using the 3.6 μm images for 17 The H I Nearby Galaxy Survey galaxies, and measuring neutral gas distribution on resolved atomic and molecular line maps. We find that galaxies with stronger torque forces show a more concentrated neutral gas distribution over the disk scale, defined as half the isophotal radius at -25.5 mag arcsec 2 . The correlation holds regardless of whether the neutral gas fraction or the effective stellar mass surface density is controlled for. In addition, kiloparsec-scale neutral gas overdensities tend to be located close to the local maxima of torque forces. Most of these correlations involving the torque forces are comparatively stronger than those using the traditional Fourier amplitudes to quantify the nonaxisymmetric structures. These results are consistent with the scenario that nonaxisymmetric structures exert torque forces and trigger dissipative processes to transport gas inward, not only to build the pseudobulges but also to fuel the inner disk growth. In this regard, nonaxisymmetric structures inducing stronger torque forces appear to be more efficient in these processes
A comprehensive broadband analysis of the high-redshift GRB 240218A
No full textInternational audienceContext: The detection and follow-up observations of high-redshift (z > 6) gamma-ray bursts (GRBs) provide a unique opportunity to explore the properties of the distant Universe. Unfortunately, they are rather rare, with only a dozen of them identified so far.Aims: We present here the discovery of the GRB with the second highest spectroscopic redshift measured to date, GRB 240218A at z = 6.782, and the broadband analysis of its afterglow. Following the detection by high-energy satellites, we obtained multi-epoch and multi-wavelength photometric follow-up observations, from 68 s to ∼48 d after the detection. These data allow us to perform a comprehensive study of the emission and physical properties of this event. We also compare these properties with GRBs observed at high and low redshift. Methods: We built the X-ray, near-infrared, and radio light curves and studied their temporal evolution. Moreover, we investigated the spectral energy distribution (SED) at different times to trace possible spectral evolution. We also compared the prompt phase properties, X-ray luminosity, and optical extinction of GRB 240218A with those of the long-duration GRB (LGRB) population.Results: The SED analysis reveals a typical afterglow-like behaviour at late times. The origin of the early-time emission is uncertain, with the probable presence of an additional contribution on top of the afterglow emission. From the broadband physical modelling of the afterglow, we identify a narrow Gaussian jet seen slightly off-axis, θ v = 2.52 +0.57 -0.29 deg, and pinpoint the presence of a possible jet break ∼0.86 d after the trigger.Conclusions: The results of the analysis and the comparison with other high-z GRBs reveal that we can consider GRB 240218A as a 'standard' high-redshift LGRB: the prompt phase properties, the X-ray luminosity, and the optical extinction are consistent with the values derived for the LGRB population. The jet opening angle is narrower but compatible with those of high-z bursts, possibly pointing to more collimated jets at high redshift
Simulation-Based Inference Benchmark for LSST Weak Lensing Cosmology
No full textInternational audienceStandard cosmological analysis, which relies on two-point statistics, fails to extract the full information of the data. This limits our ability to constrain with precision cosmological parameters. Thus, recent years have seen a paradigm shift from analytical likelihood-based to simulation-based inference. However, such methods require a large number of costly simulations. We focus on full-field inference, considered the optimal form of inference. Our objective is to benchmark several ways of conducting full-field inference to gain insight into the number of simulations required for each method. We make a distinction between explicit and implicit full-field inference. Moreover, as it is crucial for explicit full-field inference to use a differentiable forward model, we aim to discuss the advantages of having this property for the implicit approach. We use the sbi_lens package which provides a fast and differentiable log-normal forward model. This forward model enables us to compare explicit and implicit full-field inference with and without gradient. The former is achieved by sampling the forward model through the No U-Turns sampler. The latter starts by compressing the data into sufficient statistics and uses the Neural Likelihood Estimation algorithm and the one augmented with gradient. We perform a full-field analysis on LSST Y10 like weak lensing simulated mass maps. We show that explicit and implicit full-field inference yield consistent constraints. Explicit inference requires 630 000 simulations with our particular sampler corresponding to 400 independent samples. Implicit inference requires a maximum of 101 000 simulations split into 100 000 simulations to build sufficient statistics (this number is not fine tuned) and 1 000 simulations to perform inference. Additionally, we show that our way of exploiting the gradients does not significantly help implicit inference