AbstractThis review paper provides a critical examination of underground hydrogen storage (UHS) as a viable solution for large-scale energy storage, surpassing 10 GWh capacities, and contrasts it with aboveground methods. It exploes into the challenges posed by hydrogen injection, such as the potential for hydrogen loss and alterations in the petrophysical and petrographic characteristics of rock structures, which could compromise the efficiency of UHS systems. Central to our analysis is a detailed overview of hydrogen solubility across various solvents, an extensive database of potential mineralogical reactions within underground storage environments, and their implications for hydrogen retention. We particularly focus on the effects of these reactions on the porosity of reservoir and cap rocks, the role of diffusion in hydrogen loss, and the consequences of multiphase flow induced by hydrogen injection. Our findings highlight the critical mineralogical reactions—specifically, goethite reduction and calcite dissolution—and their pronounced impact on increasing cap rock porosity. We underscore a notable discovery: hydrogen's solubility in non-aqueous phases is significantly higher than in aqueous phases, nearly an order of magnitude greater. The paper not only presents quantitative insights into the mechanisms of hydrogen loss but also pinpoints areas in need of further research to deepen our understanding of UHS dynamics. By identifying these research gaps, we aim to guide future studies towards enhancing the operational efficiency and safety of UHS facilities, thereby supporting the transition towards sustainable energy systems. This work is pivotal for industry stakeholders seeking to optimize UHS practices, ensuring both the effective utilization of hydrogen as a clean energy carrier and the advancement of global sustainable energy goals.
The phase lag between an applied forcing and a response to that forcing is a fundamen tal parameter in geophysical signal processing. For solid deforming materials, the phase lag between an oscillatory applied stress and the resulting strain response encapsulates information about the dynamical behavior of materials and attenuation. The phase lag is not directly measured and must be extracted through multiple steps by carefully comparing two time-series signals. The extracted value of the phase lag is highly sensitive to the analysis method, and often there are no comparable values to increase confidence in the calculated results. In this study, we propose a method for extracting the phase lag between two signals when either one or both include an underlying nonlinear trend, which is very common when measuring attenuation in creeping materials. We demonstrate the robustness of the method by analyzing artificial signals with known phases and quantifying their absolute and relative errors. We apply the method to two experimental datasets and compare our results with those of previous studies
Full 3D modelling of time-domain electromagnetic data requires tremendous computational resources. Consequently, simplified physics models prevail in geophysics, using a much faster but approximate (1D) forward model. We propose to join the accuracy of a 1D simplified physics model with the flexibility of coarse grids to reduce the modelling errors, thereby avoiding the full 3D accurate simulations. We exemplify our approach on airborne time-domain electromagnetic data, comparing the modelling error with the standard 3% measurement noise. We find that the modelling error depends on the specific subsurface model (electrical conductivity values, angle representing the deviation of the 1D assumption) and the specific (temporal) discretization. In our example, the computation time is decreased by a factor of 27. Our approach can offer an alternative for surrogate models, statistical relations derived from large 3D datasets, to replace the full 3D simulations.
The Disturbance storm time (Dst) index has been widely used as a proxy for the ring current intensity, and therefore as a measure of geomagnetic activity. It is derived by measurements from four ground magnetometers in the geomagnetic equatorial regions. We present a new model for predicting $Dst$ with a lead time between 1 and 6 hours. The model is first developed using a Gated Recurrent Unit (GRU) network that is trained using solar wind parameters. The uncertainty of the $Dst$ model is then estimated by using the ACCRUE method [Camporeale et al. 2021]. Finally, a multi-fidelity boosting method is developed in order to enhance the accuracy of the model and reduce its associated uncertainty. It is shown that the developed model can predict $Dst$ 6 hours ahead with a root-mean-square-error (RMSE) of 13.54 $\mathrm{nT}$. This is significantly better than the persistence model and a simple GRU model.
Anthropogenic emissions of CO2 must soon approach net-zero to stabilize the global mean temperature. Although several international agreements have advocated for coordinated climate actions, their implementation has remained below expectations. One of the main challenges of international cooperation is the different degrees of socio-political acceptance of decarbonization. Here we interrogate a minimalistic model of the coupled natural-human system representing the impact of such socio-political acceptance on clean energy investments and the path to net-zero emissions. We show that incentives and carbon pricing are essential tools to achieve net-zero before critical CO2 concentrations are reached, and deep international coordination is necessary for a rapid and effective transition. Although a perfect coordination scenario remains unlikely, as investments in clean energy are ultimately limited by myopic economic strategies and a policy system that promotes free-riding, more realistic decentralized cooperation with partial efforts from each actor could still lead to significant emissions cuts.
The preference for the axial dipole in planetary dynamos is investigated through the analysis of wave motions in spherical dynamo models. Our study focuses on the role of slow magnetostrophic waves, which are generated from localized balances between the Lorentz, Coriolis and buoyancy (MAC) forces. Since the slow waves are known to intensify with increasing field strength, simulations in which the field grows from a small seed towards saturation are useful in understanding the role of these waves in dynamo action. Axial group velocity measurements in the energy-containing scales show that fast inertial waves slightly modified by the magnetic field and buoyancy are dominant under weak fields. However, the dominance of the slow waves is evident for strong fields satisfying $|ω_M/ω_C| \sim $ 0.1, where $ω_M$ and $ω_C$ are the frequencies of the Alfvén and inertial waves respectively. A MAC wave window of azimuthal wavenumbers is identified wherein helicity generation by the slow waves strongly correlates with dipole generation. Analysis of the magnetic induction equation suggests a poloidal--poloidal field conversion in the formation of the dipole. Finally, the attenuation of slow waves may result in polarity reversals in a strongly driven Earth's core.
An accurate pressure scale is a fundamental requirement to understand planetary interiors. Here, we establish a primary pressure scale extending to the multi-megabar pressures of the Earth's core, by combined measurement of the acoustic velocities and the density from a rhenium sample in a diamond anvil cell using inelastic x-ray scattering and x-ray diffraction. Our scale agrees well with previous primary scales and shock Hugoniots in each experimental pressure range, and reveals that previous scales have overestimated laboratory pressures by at least 20% at 230 gigapascals. It suggests that the light element content in the Earth's inner core (the density deficit relative to iron) is likely to be double what was previously estimated, or the Earth's inner core temperature is much higher than expected, or some combination thereof.
Caroline Eakin, ANU The Earth's biggest earthquakes and most explosive volcanoes occur at subduction zones" where a tectonic plate (the seafloor itself) sinks bank into the Earth's interior. We've been able to compile 100 million years of existing evidence for Subduction Zone Initiation (SZI). One of the biggest things this showed was that subduction breeds subduction.
Soil has been recognized as an indirect driver of global warming by regulating atmospheric greenhouse gases. However, in view of the higher heat capacity and CO2 concentration in soil than those in atmosphere, the direct contributions of soil to greenhouse effect may be non-ignorable. Through field manipulation of CO2 concentration both in soil and atmosphere, we demonstrated that the soil-retained heat and its slow transmission process within soil may cause slower heat leaking from the earth. Furthermore, soil air temperature was non-linearly affected by soil CO2 concentration with the highest value under 7500 ppm CO2. This study indicates that the soil and soil CO2, together with atmospheric CO2, play indispensable roles in fueling the greenhouse effect. We proposed that anthropogenic changes in soils should be focused in understanding drivers of the globe warming.
Lysosomes labeled by uptake of extracellular horseradish peroxidase display remarkable changes in shape and cellular distribution when cytoplasmic pH is experimentally altered. Normally, lysosomes in macrophages and fibroblasts cluster around the cell center. However, when the cytoplasmic pH is lowered to approximately pH 6.5 by applying acetate or by various other means, lysosomes promptly move outward and accumulate in tight clusters at the very edge of the cell, particularly in regions that are actively ruffling before acidification but become quiescent. This movement follows the distribution of microtubules in these cells, and does not occur if microtubules are depolymerized with nocodazole before acidification. Subsequent removal of acetate or the other stimuli to acidification results in prompt resumption of ruffling activity and return of lysosomes into a tight cluster at the cell center. This is correlated with a rebound alkalinization of the cytoplasm. Correspondingly, direct application of weak bases also causes hyperruffling and unusually complete withdrawal of lysosomes to the cell center. Thus, lysosomes appear to be acted upon by microtubule- based motors of both the anterograde (kinesin) type as well as the retrograde (dynein) type, or else they possess bidirectional motors that are reversed by changes in cytoplasmic pH. During the outward movements induced by acidification, lysosomes also appear to be smaller and more predominantly vesicular than normal, while during inward movements they appear to be more confluent and elongated than normal, often becoming even more tubular than in phorbol-treated macrophages (Phaire-Washington, L., S. C. Silverstein, and E. Wang. 1980. J. Cell Biol. 86:641-655). These size and shape changes suggest that cytoplasmic pH also affects the fusion/fission properties of lysosomes. Combined with pH effects on their movement, the net result during recovery from acidification is a stretching of lysosomes into tubular forms along microtubules.
Enceladus's gravity and shape have been explained in terms of a thick isostatic ice shell floating on a global ocean, in contradiction of the thin shell implied by librations. Here we propose a new isostatic model minimizing crustal deviatoric stress, and demonstrate that gravity and shape data predict a $\rm{38\pm4\,km}$-thick ocean beneath a $\rm{23\pm4\,km}$-thick shell agreeing with -- but independent of -- libration data. Isostatic and tidal stresses are comparable in magnitude. South polar crust is only $7\pm4\rm\,km$ thick, facilitating the opening of water conduits and enhancing tidal dissipation through stress concentration. Enceladus's resonant companion, Dione, is in a similar state of minimum stress isostasy. Its gravity and shape can be explained in terms of a $\rm{99\pm23\,km}$-thick isostatic shell overlying a $\rm{65\pm30\,km}$-thick global ocean, thus providing the first clear evidence for a present-day ocean within Dione.