Self Attraction and Loading (SAL), which includes the deformation of the solid Earth under the load of the ocean tide and the self-gravitation of the so-deformed Earth as well as of the ocean tides themselves, is an important term to include in numerical models of the ocean tides. Computing SAL is a challenging problem that is usually tackled using spherical harmonics. The spherical harmonic approach has several drawbacks which limit its accuracy. In this work, we propose an alternative technique based on a spherical convolution. We implement the convolution technique in the Modular Ocean Model, version 6, and demonstrate that it allows for more accurate tides when measured against tidal datasets based upon satellite altimetry. The convolution based SAL reduces the error by reducing spurious oscillations associated with the Gibbs phenomenon. These oscillations are large in coastal regions under the traditional spherical harmonic approach.
Abstract Total extraction mining, such as longwall mining, results in subsidence at the surface above the mined area. It was assumed that subsidence occurs within a relatively short time after mining. Based on theoretical considerations and conventional levelling, it was generally assumed that subsidence stops 3–5 years after mining. Since satellite data images became freely available for research at the end of the last century, surface movements above mined areas can be studied over very long periods of time. This results in new insights. The case study focuses on the coal longwall mines in the Belgian Campine coal district. Mining stopped completely in 1992, when the last mine was closed. The analysis is based on successive remote sensing datasets since 1992. The main conclusion is that surface movements are still recorded more than 30 years after the mines were closed, i.e. much longer than the usual 3–5 years that were assumed. The variation in surface movements in the post-mining phase is also more complex. After a period of further subsidence, the direction of surface movements reverses and an uplift of the surface above the mined areas is observed (relative to the end of the subsidence phase). This uplift is still ongoing in 2025. These new findings have practical implications, as these long-term movements further affect the loading of buildings and other infrastructure, leading to possible new damage. It also has a negative impact on the natural environment, e.g., on surface water management. Article highlights In the post-mining phase, additional surface movements still occur above coal longwall panels. The long-term behaviour has consequence for the stability of buildings, the integrity of infrastructure and the natural environment. Remote sensing satellite data are extremely useful to study surface movements over large areas and during long time periods.
Sergey N. Britvin, Oleg S. Vereshchagin, Natalia S. Vlasenko
et al.
The lack of benchmark data on the real minerals, native ammonium carriers in Solar System gives rise to controversial opinions on extraterrestrial ammonium reservoirs. We herein report on discovery of the first mineral carrier of meteoritic ammonium and show its relevance to the compositional and spectral characteristics of cometary and asteroidal bodies. Chemically distant from previously inferred volatile organics or ammoniated phyllosilicates, it is an aqueous metal-ammonium sulfate related to a family of so-called Tutton salts. Nickeloan boussingaultite, (NH4)2(Mg,Ni)(SO4)2 6H2O, occurs in Orgueil, a primitive carbonaceous chondrite closely related to (162173) Ryugu and (101955) Bennu, the C-type asteroids. The available spectroscopic, chemical and mineralogical data signify that natural Tutton salts perfectly fit into the role of ammonium reservoir under conditions of cometary nuclei and carbonaceous asteroids.
This work tackles a significant challenge in dynamo theory: the possibility of long-term amplification and maintenance of an axisymmetric magnetic field. We introduce a novel model that allows for non-trivial axially-symmetric steady-state solutions for the magnetic field, particularly when the dynamo operates primarily within a ``nearly-spherical'' toroidal volume inside a fluid shell surrounding a solid core. In this model, Ohm's law is generalized to include the dissipative force, arising from electron collisions, that tends to align the velocity of the shell with the rotational speed of the inner core and outer mantle. Our findings reveal that, in this context, Cowling's theorem and the neutral point argument are modified, leading to magnetic energy growth for a suitable choice of toroidal flow. The global equilibrium magnetic field that emerges from our model exhibits a dipolar character. The central insight of the model developed here is that if an additional force is incorporated into Ohm's law, symmetric dynamos become possible.
Natural and engineered media usually involve combinations of solid, fluid and porous layers, and accurate and stable modelling of wave propagation in such complex multilayered media is fundamental to evaluating their properties with wave-based methods. Here we present a general stiffness matrix method for modelling waves in arbitrary multilayers. The method first formulates stiffness matrices for individual layers based on the governing wave equations for fluids and solids, and the Biot theory for porous materials. Then it utilises the boundary conditions considered at layer interfaces to assemble the layer matrices into a global system of equations, to obtain solutions for reflection and transmission coefficients at any incidence. Its advantage over existing methods is manifested by its unconditional computational stability, and its validity is proved by experimental validations on single solid sheets, porous layers, and porous-solid-porous battery electrodes. This establishes a powerful theoretical platform that allows us to develop advanced wave-based methods to quantitatively characterise properties of the layers, especially for layers of porous materials.
The efficiency of regolith production is key in understanding the properties of airless surfaces. Debris aprons, of fillets, around rocks are an ubiquitous morphology on many surfaces without atmosphere, which origin and evolution are largely unknown. Here we show that fillet originates from the juxtaposed rock under abrasion and that rocks of different cohesion have fillets with distinct morphological evolution. Thus, a fillet around a rock allows to disentangle rock cohesion from its surface exposure age. By combing topographic diffusion modeling with images of blocks of known age on the Moon we find abrasion rates for cm-sized boulders similar to regional rates (0.2 mm/Myr), whereas for 10-m sized blocks the rate is two order of magnitude higher (20 mm/Myr). Rates for instances of rocks of higher strength are reduced by ~50%. Fillets around lunar rocks are consistent with abrasion by isotropic micrometeoroid bombardment.
Oleg I. Berngardt, Sergey V. Voeykov, Natalia P. Perevalova
A comparative statistical analysis of AATR and WTEC indices was conducted based on data from the ISTP SB RAS GNSS receivers network. It is shown that at high levels of ionospheric disturbance (for WTEC > 0.1 TECU), the AATR index is proportional to the WTEC index with a factor of $1.5min^{-1}$. At small levels of ionospheric disturbance (for WTEC < 0.1 TECU), this proportionality is violated. It is shown that the contribution of daily dynamics of the background ionosphere to the AATR index is higher than to the WTEC index. This leads to a higher sensitivity of the WTEC index to disturbances. This also leads to violating the proportionality between WTEC and AATR indices at low levels of ionospheric disturbance. It is shown that at high latitudes the dynamics of the WTEC and AATR indices correlate significantly with the level of geomagnetic disturbance Kp. At mid-latitudes, the contribution of solar radiation variations (F10.7 index) and vertical seismic variations exceeds the influence of Kp variations. The program for calculating WTEC indices, used in the paper is put into open access.
Neutrino geophysics, the study of the Earth's interior by measuring the fluxes of geologically produced neutrino at its surface, is a new interdisciplinary field of science, rapidly developing as a synergy between geology, geophysics and particle physics. Geoneutrinos, antineutrinos from long-lived natural isotopes responsible for the radiogenic heat flux, provide valuable information for the chemical composition models of the Earth. The calculations of the expected geoneutrino signal are discussed, together with experimental aspects of geoneutrino detection, including the description of possible backgrounds and methods for their suppression. At present, only two detectors, Borexino and KamLAND, have reached sensitivity to the geoneutrino. The experiments accumulated a set of $\sim$190 geoneutrino events and continue the data acquisition. The detailed description of the experiments, their results on geoneutrino detection, and impact on geophysics are presented. The start of operation of other detectors sensitive to geoneutrinos is planned for the near future: the SNO+ detector is being filled with liquid scintillator, and the biggest ever 20 kt JUNO detector is under construction. A review of the physics potential of these experiments with respect to the geoneutrino studies, along with other proposals, is presented. New ideas and methods for geoneutrino detection are reviewed.
Mobile gravimetry is important in metrology, navigation, geodesy, and geophysics. Atomic gravimeters could be among the most accurate mobile gravimeters, but are currently constrained by being complex and fragile. Here, we demonstrate a mobile atomic gravimeter, measuring tidal gravity variations in the laboratory as well as surveying gravity in the field. The tidal gravity measurements achieve a sensitivity of 37 $μ$Gal/$\sqrt{\rm Hz}$ and a long-term stability of better than 2 $μ$Gal, revealing ocean tidal loading effects and recording several distant earthquakes. We survey gravity in the Berkeley Hills with an accuracy of around 0.04 mGal and determine the density of the subsurface rocks from the vertical gravity gradient. With simplicity and sensitivity, our instrument paves the way for bringing atomic gravimeters to field applications.
We investigate the drift wave -- zonal flow dynamics in a shearless slab geometry with the new flux-balanced Hasegawa-Wakatani model. As in previous Hasegawa-Wakatani models, we observe a sharp transition from a turbulence dominated regime to a zonal jet dominated regime as we decrease the plasma resistivity. However, unlike previous models, zonal structures are always present in the flux-balanced model, even for high resistivity, and strongly reduce the level of particle and vorticity flux. The more robust zonal jets also have a higher variability than in previous models, which is further enhanced when the computational domain is chosen to be elongated in the radial direction. In these cases, we observe complex multi-scale dynamics, with multiple jets interacting with one another, and intermittent bursts. We present a detailed statistical analysis which highlights how the changes in the aspect ratio of the computational domain affect the third-order statistical moments, and thus modify the turbulent dynamics.
Trent M. Hare, Angelo P. Rossi, Alessandro Frigeri
et al.
For more than a decade there has been a push in the planetary science community to support interoperable methods for accessing and working with geospatial data. Common geospatial data products for planetary research include image mosaics, digital elevation or terrain models, geologic maps, geographic location databases (e.g., craters, volcanoes) or any data that can be tied to the surface of a planetary body (including moons, comets or asteroids). Several U.S. and international cartographic research institutions have converged on mapping standards that embrace standardized geospatial image formats, geologic mapping conventions, U.S. Federal Geographic Data Committee (FGDC) cartographic and metadata standards, and notably on-line mapping services as defined by the Open Geospatial Consortium (OGC).
Shravan M. Hanasoge, Martin Woodard, H. M. Antia
et al.
In this article, we derive and compute the sensitivity of measurements of coupling between normal modes of oscillation in the Sun to underlying flows. The theory is based on first-Born perturbation theory, and the analysis is carried out using the formalism described by \citet{lavely92}. Albeit tedious, we detail the derivation and compute the sensitivity of specific pairs of coupled normal modes to anomalies in the interior. Indeed, these kernels are critical for the accurate inference of convective flow amplitudes and large-scale circulations in the solar interior. We resolve some inconsistencies in the derivation of \citet{lavely92} and reformulate the fluid-continuity condition. We also derive and compute sound-speed kernels, paving the way for inverting for thermal anomalies alongside flows.
The Earth's magnetic field is generated by dynamo action driven by convection in the outer core. For numerical reasons, inertial and viscous forces play an important role in geodynamo models; however, the primary dynamical balance in the Earth's core is believed to be between buoyancy, Coriolis and magnetic forces. The hope has been that by setting the Ekman number to be as small as computationally feasible, an asymptotic regime would be reached in which the correct force balance is achieved. However, recent analyses of geodynamo models suggest that the desired balance has still not yet been attained. Here we adopt a complementary approach consisting of a model of rapidly rotating convection in which inertial forces are neglected from the outset. Within this framework we are able to construct a new branch of solutions in which the dynamo generates a strong magnetic field that satisfies the expected force balance. The resulting strongly magnetized convection is dramatically different to the corresponding solutions in which the field is weak.
Pluto has been observed by the New Horizons space probe to have some relatively fresh ice on the old ices covering most of the surface. Pluto was thought to consist of only a rocky core below the ice. Here I show that Pluto can have an iron core, as can also its companion Charon, which has recently been modelled to have one. The presence of an iron core means the giant impact origin calculations should be redone to include iron and thus higher temperatures. An iron core leads to the possibility of a different geology. An originally molten core becomes solid later, with contraction and a release of latent heat. The space vacated allows the upper rock layers to flow downwards at some locations at the surface of the core, and some of the ice above the rock to descend, filling the spaces left by the rock motion downwards. These phenomena can lead to the forces recently deforming the icy surface of Pluto, and in a lesser way, of Charon.