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Abstract

The Mediterranean region is experiencing pronounced aridification and in certain areas higher occurrence of intense precipitation. In this work, we analyze the evolution of the precipitation probability distribution in terms of precipitating days (or “wet-days”) and all-days quantile trends, in Europe and the Mediterranean, using the ERA5 reanalysis. Looking at the form of wet-days quantile trends curves, we identify four regimes. Two are predominant: in most of northern Europe the precipitation quantiles all intensify, while in the Mediterranean the low-medium quantiles are mostly decreasing as extremes intensify or decrease. The wet-days distribution is then modeled by a Weibull law with two parameters, whose changes capture the four regimes. Assessing the significance of the parameters' changes over 1950–2020 shows that a signal on wet-days distribution has already emerged in northern Europe (where the distribution shifts to more intense precipitation), but not yet in the Mediterranean, where the natural variability is stronger. We extend the results by describing the all-days distribution change as the wet-days’ change plus a contribution from the dry-days frequency change, and study their relative contribution. In northern Europe, the wet-days distribution change is the dominant driver, and the contribution of dry-days frequency change can be neglected for wet-days percentiles above about 50%. In the Mediterranean, however, the change of precipitation distribution comes from the significant increase of dry-days frequency instead of an intensity change during wet-days. Therefore, in the Mediterranean the increase of dry-days frequency is crucial for all-days trends, even for heavy precipitation.

A new study out of The University of Texas at Arlington shows that frozen land in Alaska is eroding faster than it can be replaced due to climate change.

Scientists at the University of Southampton have answered one of the most puzzling questions in plate tectonics: how and why "stable" parts of continents gradually rise to form some of the planet's greatest topographic features.

Even though climate change is bringing more frequent and severe heat waves, there is no standard, global way to measure heat-wave severity, and existing indices have different thresholds for defining dangerous heat-stress conditions.

Synthetic aperture radar (SAR) is a type of remote sensing from satellites that uses the reflection of radio waves to relay information about the surface of the earth. This reflection, or backscatter, is responsive to physical properties, such as roughness, vertical structure, and moisture. SAR is widely used for different types of mapping and monitoring, but signal interference in urban environments can cause distortions that make SAR data difficult to interpret.

Abstract

Efforts to detect long-term changes in global mean evaporation minus precipitation over the ocean remain ambiguous. Here we define an ad hoc sea surface salinity index to assess the observed and simulated intensification of the freshwater flux pattern over the global ocean and, thus, of the overall water cycle. A recent salinity reconstruction shows a long-term amplification of the climatological patterns, thereby supporting the popular “fresh gets fresher, salty gets saltier” paradigm. Unlike in a previous study, no systematic underestimation of this amplification is found in the latest generation of global climate models. Yet, the “fresh gets fresher” paradigm is much more robust than its “salty gets saltier” counterpart and the proposed salinity index does not yet provide a strong constraint on the model-dependent projected intensification of the global water cycle intensification along the 21st century.

Dense hydrous magnesium silicates (DHMSs) are generally considered as primary water carriers from the shallow lithosphere to the deep mantle transition region (MTR; 410–660 km in depth). Among DHMSs, Superhydrous phase B (hereafter, SuB) holds the chemical formula, Mg10Si3H3O18.

Abstract

Two outstanding questions for the future of the Greenland Ice Sheet are (a) how enhanced meltwater draining beneath the ice will impact the behavior of large tidewater glaciers, and (b) to what extent tidewater glacier velocity is driven by changes at the terminus versus changes in sliding velocity due to meltwater. We present a two-way coupled framework to simulate the nonlinear feedbacks of evolving subglacial hydrology and ice dynamics using the Subglacial Hydrology And Kinetic, Transient Interactions (SHAKTI) model within the Ice-sheet and Sea-level System Model (ISSM). Through coupled simulations of Helheim Glacier, we find that terminus effects dominate the seasonal velocity pattern up to 15 km from the terminus, while hydrology drives the velocity response upstream. With increased melt, the hydrology influence yields seasonal acceleration of several hundred meters per year in the interior, suggesting that hydrology will play an important role in future mass balance of tidewater glaciers.

Abstract

Despite in-situ observations of perennial firn aquifers (PFAs) at specific locations of the Antarctic ice sheet, a comprehensive continent-wide mapping of PFA distribution is currently lacking. We present an estimate of their distribution across Antarctica in the form of a probability assessment using a Monte Carlo technique. Our approach involves a novel methodology that combines observations from Sentinel-1 and Advanced SCATterometer (ASCAT) with output from a regional climate model. To evaluate our method, we conduct an extensive comparison with Operation Ice Bridge observations from the Greenland Ice Sheet. Application to Antarctica reveals high PFA probabilities in the Antarctic Peninsula (AP), particularly along its northern, northwestern, and western coastlines, as well as on the Wilkins, Müller, and George VI ice shelves. Outside the AP, PFA probability is low, except for some locations with marginally higher probabilities, such as on the Abbot, Totten, and Shackleton ice shelves.

Abstract

If, as previously hypothesized, the effective elastic response of the lithosphere is sensitive to the imposed stress regime, then it may vary in time and produce distinctive geomorphic responses. Such effects will be at their most crucial in landscapes of low relief. Motivated by the existence of numerous small endorheic (internally-drained) basins in central Australia, we examine the influence of changing elastic response in the presence of large embedded loads in the lithosphere underlying stable continental interiors. Focusing on the western Lake Eyre Basin and adjoining Lake Lewis basin—an area with a close correlation between drainage pattern and extreme Bouguer gravity anomalies—we devise a set of numerical simulations that incorporate the flexural response to time-transient horizontal stresses. The simulations demonstrate that transient changes in the effective elastic thickness can drive topographic changes in low-relief landscapes, including drainage capture and the development of endorheic basins, consistent with field observations.

Abstract

Aircraft observations of the four chloromethanes: carbon tetrachloride (CCl4), methyl chloride (CH3Cl), dichloromethane (CH2Cl2), and chloroform (CHCl3), collected over North America between 2000 and 2022, were used to evaluate their vertical distributions and temporal trends in the atmosphere. We examine the vertical profiles, from the surface to the lower stratosphere (LS), of these increasingly important contributors to ozone-depleting chlorine in both altitude and potential temperature space. Airborne chloromethane trends were compared with those measured at long-term, ground-based monitoring stations. Below 20 km altitude, CCl4 trends were decreasing at all levels studied in the North American atmosphere (−1.1 ppt yr−1). CHCl3 and CH2Cl2 airborne observations were comparable to ground network measurements: CHCl3 increased between 2000 and 2018 and then decreased leading to a negligible trend over the 22 years studied and CH2Cl2 has been increasing at all levels in the troposphere (+2.41 ppt yr−1, 2000–2022, <20 km).

Abstract

Magnetosonic (MS) waves with frequencies above the proton gyrofrequency can be locally generated by ring-beam protons in the Martian heavy ion-rich ionosphere. In this study, we conduct a parametric analysis to investigate the effects of heavy ion concentrations, energy (Erb ), and angle (αrb ) of ring-beam protons, and wave normal angle on the excitation features of Martian ionospheric MS waves. We find the growth rates and frequency range of MS waves decrease by including O+ and O2 + ions but are insensitive to their relative concentrations. With increasing Erb or αrb , the growth rates of MS waves show a general dropping tendency. Meanwhile, their frequency and wavenumber range are almost unaffected by increasing Erb but shrink to a narrower range mainly distributed in high frequencies by increasing αrb . Unstable MS waves expand to a wider wavenumber range but shrink to a narrower frequency range as they become more oblique.

Abstract

The Quasi-Biennial Oscillation and the Semiannual Oscillation have been identified to be the leading modes of variability in the tropical middle atmosphere. With reanalysis data and independent rocket soundings from a low latitude site, we report the existence of yet another variability in the tropical lower mesosphere which is primarily evident as easterly bursts in zonal winds during the months of May-July. It occurs with a variable interval of 2–5 yrs in the late 20th century and 7–9 yrs in the early 21st century. These Quasi-Periodic Easterly Bursts are found to have remote influences on the Antarctic polar vortex as well as residual circulation in the lower mesosphere. We identify a potential causative mechanism for the easterly bursts that involve enhanced cross equatorial advection of momentum as well as gravity wave drag. A close association with Quasi Biennial Oscillation winds is observed, however, cause of the observed periodicity remains elusive.

Abstract

Carbon dioxide (CO2) emissions affect local temperature; quantifying that local response is important for learning about the earth system, the impacts of mitigation, and adaptation needs. We assume the climate system can be represented as a time-dependent linear system, diagnosing Green's Functions for the spatial temperature response to CO2 emissions based on CMIP6 earth system models. This allows us to emulate the linear component of the temperature response to CO2. This approach is sufficient to capture the spatial temperature response of CMIP6 experiments within one standard deviation of the multimodel spread across most regions, though accuracy is lower in the Southern Ocean and the Arctic. Our approach reveals where nonlinear feedbacks are important in current CMIP6 models, and where the local system response is well represented by a time-dependent linear differential operator. It incorporates emissions path dependency and may be useful for evaluating large ensembles of emission scenarios.

Abstract

The energy budget and the interplay between stable friction evolution and dynamic stick-slips are tested here under continuous slip along rough faults. We conducted 34 direct-shear experiments coupled with precise roughness measurements on diabase and limestone fault samples. The faults broad roughness ranges from highly rough and interlocked fractured interfaces to smooth polished surfaces. The analysis focuses on two slip phases: (a) the evolution of the shear strength of rough sample under stable, cumulative displacement; and (b) the dynamic of unstable stick-slip sliding. We found that the breakdown work during frictional strength evolution increases with roughness increase across multiple scales. The diabase samples are more sensitive to roughness increase than limestone samples in terms of the breakdown work implied by frictional evolution. We attribute this increased diabase sensitivity with fault roughness to its higher bulk elasticity and not to the fault shear stiffness. The diabase faults displayed multiple periodic system-size stick-slips, and the measured stored energy during the preparatory stage were surprisingly independent of the fault roughness. This finding suggests that during the preparatory stage a balance between the intracycle fault stiffness and stress drop govern the stored energy magnitude. Further, this energy balance suggests that some interface conditioning occurs before the spontaneous slip overcomes a sticking barrier.

Abstract

Groundwater level tidal analysis is a powerful technique to monitor aquifer's permeability and hence its change over time. Earthquakes are known to affect aquifer's properties, in their vicinity through static stress changes but also further away through dynamic stresses. Most often changes are in the form of permeability increases, but sometimes decreases; the changes can be either permanent or transient. These observations are relatively well documented but the physical processes behind these changes are not well understood. By combining solid-earth and barometric tidal groundwater level responses in a borehole in a coherent poroelastic theoretical framework, and a bi-layer hydrogeological model, we recover a 15 years-long time series evolution of aquifer transmissivity and shear modulus. This study showcases the full potential of the tidal analysis method, coupling pore pressure diffusion and rock deformation, at the frontier of hydrogeology and rock physics. This unprecedented measurement of permeability and shear modulus evolution by tidal analysis reveals, during interseismic period, high sensitivity of this shallow aquifer to effective stress, and thus to pore pressure. Thanks to additional finite element simulation of seismic wave propagation, we explore the different mechanisms affecting permeability and shear modulus in the studied fractured andesite aquifer. This study confirms the predominant role of seismic dynamic stresses, and more precisely of dynamic shear stresses, in the change of permeability following an earthquake.

Climate models compute vast amounts of information about Earth's climate system—from small water droplets to large-scale weather patterns—to re-create past climate or predict future climate. Accurately re-creating how Earth's energy (measured in watts) is balanced between the atmosphere, land surface, oceans, and sea ice helps scientists understand what factors are causing changes in climate and allows us to better prepare for the future.

Abstract

The Southwestern United States experiences active deformation, seismicity, and magmatism, remarkable in an intraplate setting. The Basin and Range and Colorado Plateau (CP) are inferred to differ in lithospheric thickness, but modeling geophysical properties of the lithosphere, in particular the depth of the Lithosphere-Asthenosphere Boundary (LAB), across the entirety of the region, has proved challenging. Here, we introduce a new model of 1-D depth profiles in shear wavespeed, determined through a probabilistic joint inversion of information from Sp receiver functions and Rayleigh wave phase velocity. From these profiles we quantify the locations and Vs contrast of wavespeed gradients that represent boundaries such as the Moho, the LAB, and intralithospheric discontinuities. We infer a lithosphere that is thinner and lower in Vs in the Basin and Range. In the CP and farther north, the LAB is more gradual, deeper, and intermittently observed. We also observe Mid-Lithospheric Discontinuities (MLDs) near the boundaries between the CP, Wyoming Craton, and Northern Basin and Range, as well as within the Craton. When both an MLD and LAB are observed, the Vs gradient associated with the LAB is narrower than expected. Finally, we image Positive Velocity Gradients beneath areas of thinner lithosphere, which are consistent with recent global observations that have been attributed to the base of a partially molten zone below the lithosphere. Overall, the picture of the lithosphere-asthenosphere system that emerges is one of considerable structural complexity with a strong dependency on tectonic regime and geological history.

Abstract

Some rock and soil samples exhibit significant loss of magnetic susceptibility (χ) with increasing applied field amplitude even at relatively low (10–100s of A/m) fields, a behavior which remains unexplained. Exceptionally strong negative field-dependence of susceptibility (χ HD) is present in sandstones and altered intermediate-felsic igneous rocks in several cores from the northeastern Oklahoma subsurface. These same rocks also show elevated frequency-dependence of susceptibility (χ FD), with reasonable correlation of χ HD to χ FD, and frequency-dependent χ HD. Results from multiple characterization methods indicate that strongly negative χ HD in these rocks is linked to a yet-unidentified phase which begins the approach to magnetic saturation in low fields (<1 mT/800 A/m), shows elevated χ FD to low temperatures, is unstable at high temperatures, possesses significant anisotropy of magnetic susceptibility, and becomes paramagnetic above ∼83°C. Clear associations with fluid alteration features indicate that this material may be highly relevant to rock alteration, diagenetic, and environmental studies.

Author(s): Leheng Chen, Chuang Zhang, and Jin Zhao

Many macroscopic non-Fourier heat conduction models have been developed in the past decades based on Chapman-Enskog, Hermite, or other small perturbation expansion methods. These macroscopic models have achieved great success in capturing non-Fourier thermal behaviors in solid materials, but most of…

[Phys. Rev. E 110, 025303] Published Wed Aug 07, 2024