Starting from the fully-compressible Euler equations, a two-way-coupled system governing the long-wave behaviour of thin layers (with respect to the radius of Earth) representing the ocean and atmosphere, under an isentropic constraint, was derived. This approach incorporates bathymetry and topographic features as well as three-dimensional atmospheric non-uniformities through their depth-average over a spherical shell. Linear analysis of the obtained system yields two pairs of gravito-acoustic waves which are found to be representative of the fast-travelling atmospheric wave (with a propagation speed mainly governed by the atmospheric-layer-averaged speed of sound) and the slower-travelling gravity waves in the ocean (with a propagation speed mainly governed by local water depth). Remarkably, the 'Proudman resonance', observed in the forced shallow-water equation framework and invoked to justify, in part, observed large wave-heights, vanishes in favour of a continuous transition past the critical water depth, occurring when the two wave propagation speeds are closest. Two-dimensional non-linear global simulations were performed, using atmospheric conditions on the day, showcasing the predictive ability of the model. Local maxima of water-height disturbance in the farfield from the volcano, linked to the atmospheric wave deformation over time, are observed, emphasising the importance of the atmospheric-layer modelling and two-way coupling for any daylong predictions. An efficient implementation of the modelling strategy was carried out in the open source computational framework dNami to demonstrate the ability to perform faster-than-real-time simulations despite the additional equations in the governing system. Future work would see the strategy extended to incorporate additional layers and physics e.g. ocean and atmosphere stratification, interaction with the upper atmosphere.

The Kalahari Basin in southern Africa, shaped by subsidence and epeirogeny, features the Okavango Rift Zone (ORZ) as a significant structural element characterized by diffused extensional deformation forming a prominent depocenter. This study elucidates the Pleistocene landscape evolution of the ORZ by examining the chronology of sediment formation and filling this incipient rift and its surroundings. Modeling of cosmogenic nuclide concentrations in surficial eolian sand from distinct structural blocks around the ORZ provides insights into sand’s residence time on the surface. Sand formation occurred from ~2.2 to 1.1 Ma, coinciding with regional tectonic events. Notably, provenance analyses of sand within ORZ’s lowermost block where large alluvial fans are found indicate different source rocks and depositional environments than those of the more elevated eolian sand. This suggests that the major phase of rift subsidence and the following incision of alluvial systems into the rift occurred after eolian dune formation. Luminescence dating reveals that deposition in alluvial fan settings in the incised landscape began not later than ~250 ka, and that a lacustrine environment existed since at least ~140 ka. The established chronological framework constrains the geomorphological effects of the different tectono-climatic forces that shaped this nascent rifting area. It highlights two pronounced stages of landscape development, with the most recent major deformation event in the evolving rift probably occurring during the middle Pleistocene transition (1.2-0.75 Ma). This event is reflected as a striking change in the depositional environments due to the configurational changes accompanying rift progression.

The northeastern part of the North Atlantic subpolar gyre is a key passage for the Atlantic Meridional Overturning Circulation upper cell. To this day, the precise pathway and intensity of bottom currents in this area have not reached a consensus. In this study, we make use of regional high resolution numerical modeling to suggest that the main bottom current flowing south of Iceland originates from both the Faroe-Bank Channel and the Iceland-Faroe Ridge (with about equal contributions) and then flows along the topographic slope centered. When flowing over the rough topography, this bottom current generates a bottom mixed layer reaching 200 m height. We further demonstrate that many submesoscale structures are generated at the southernmost tip of the Icelandic shelf, thus spreading water masses in the open Iceland Basin. These findings have major implication in the better understanding of the transport of dense water masses in the North Atlantic.

A document by Wen-Pin Hsieh. Click on the document to view its contents.

Increasing deployment of dense arrays has facilitated detailed structure imaging for tectonic investigation, hazard assessment and resource exploration. Strong velocity heterogeneity and topographic changes have to be considered during passive source imaging. However, it is quite challenging for ray-based methods, such as Kirchhoff migration or the widely used teleseismic receiver function, to handle these problems. In this study, we propose a 3-D passive source reverse time migration strategy based on the spectral element method. It is realized by decomposing the time reversal full elastic wavefield into amplitude-preserved vector P and S wavefields by solving the corresponding weak-form solutions, followed by a dot-product imaging condition to get images for the subsurface structures. It enables us to use regional 3-D migration velocity models and take topographic variations into account, helping us to locate reflectors at more accurate positions than traditional 1-D model-based methods, like teleseismic receiver functions. Two synthetic tests are used to demonstrate the advantages of the proposed method to handle topographic variations and complex velocity heterogeneities. Furthermore, applications to the Laramie array data using both teleseismic P and S waves enable us to identify several south-dipping structures beneath the Laramie basin in southeast Wyoming, which are interpreted as the Cheyenne Belt suture zone and agree with, and improve upon previous geological interpretations.

The prediction of post-sunset equatorial plasma depletions (EPDs), often called ionospheric plasma bubbles, has remained a challenge for decades. In this study, we introduce the Ionospheric Bubble Probability (IBP), an empirical model predicting the occurrence probability of EPDs derived from 9 years of CHAMP and 8.5 years of Swarm magnetic field measurements. The model predicts the occurrence probability of EPDs for a given longitude, day of year, local time and solar activity, for the altitude range 350-500 km, and low geographic latitudes of ± 45◦. IBP has been found to successfully reconstruct the distribution of EPDs as reported in previous studies from independent data. IBP has been further evaluated using one-year of partly untrained data of the Ionospheric Bubble Index (IBI). IBI is a Level 2 product of the Swarm satellite mission used for EPD identification. The relative operating characteristics (ROC) curve shows positive excursion above the no-skill line with Hanssen and Kuiper’s Discriminant (H&KSS) score of 0.66, 0.73, and 0.65 at threshold model outputs of 0.22, 0.18, and 0.18 for Swarm A, B, and C satellites, respectively. Additionally, the reliability plots show proximity to the diagonal line with a fairly decent Brier Skill Score (BSS) of 0.317, 0.320, and 0.316 for Swarm A, B, and C respectively. These tests indicate that the model performs significantly better than a no-skill forecast. The IBP model offers a compelling glimpse into the future of EPD forecasting, thus demonstrating its potential to reliably predict EPD occurrences. The IBP model is made publicly available.

The violent eruption of the Hunga (Tonga) submarine volcano on 15 January 2022 caused a 58 km-heigh ash plume, catastrophic tsunami, and significant global seismic and infrasound waves. However, the physical mechanism underpinning its multiple-explosive events remains unclear, and its resolvability relies on the seismic waveform source inversion. The studies of two different point-source models, the seismic moment tensor (MT) and the single force (SF), have been performed separately for this eruption, which, interestingly, can explain the seismic data adequately. Here, we use a joint inversion of MT and SF to unravel a composite source of an explosive MT and a significant upward force for the first major explosive event. Regarding the direction and magnitude, we propose that the upward force is likely a rebound force in response to the pressure drop on the seafloor because the water body above the volcano was abruptly uplifted by the shallow underwater explosion.

The sub-plate mantle flow traction has been considered as a major driving force for plate motion; however, the force acting on the overlying plate is difficult to be well constrained. One reason lies in the variable rheological flow laws of mantle rocks, e.g. linear versus power-law rheology, applied in previous studies. Here, systematic numerical models are conducted to evaluate the mantle flow traction under variable rheological, geometrical and kinematic conditions. The results indicate that mantle flow traction with power-law rheology is much lower than that with linear rheology under the same mantle/plate velocity contrast. In addition, the existence of lithospheric root in the overlying plate enhances the mantle flow traction. In a regime with reasonable parameters, the mantle flow traction with power-law rheology is comparable to the ridge push on the order of 1012 N/m, whereas that with linear rheology is comparable to the slab pull of 1013 N/m.

In Southeast Asia, emerging subduction zones often appear to begin at the corners of small oceanic basins, which have a triangular-indenter continent–ocean boundary geometry. To investigate the influence of a triangular indenter on subduction initiation, we performed a series of three-dimensional numerical simulations with varying indenter angles and base lengths. The results show that the apex of the indenter constitutes the initial location of subduction, irrespective of the angle or the extent of the indenter. Smaller angle indenters are more likely to facilitate subduction initiation. At the same time, wide acute angle indenters are difficult to form. Our findings suggest that triangular indenter structures may facilitate subduction initiation in smaller basins; however, the role such indenters in subduction initiation is limited in larger basins. Our results emphasize the importance of accounting for the three-dimensional geometry of a subduction zone when examining its subduction dynamics and geological features.

In this study, we measure velocity variations during two cycles of crustal inflation and deflation in 2020 on the Reykjanes peninsula (SW Iceland) by applying coda wave interferometry to ambient noise recorded by distributed dynamic strain sensing (also called DAS). We present a new workflow based on spatial stacking of raw data prior to cross-correlation which substantially improves the spatial coherency and the time resolution of measurements. Using this approach, a strong correlation between velocity changes and ground deformation (in the vertical and horizontal direction) is revealed. Our findings may be related to the infiltration of volcanic fluids at shallow depths, even though the concurrent presence of various processes complicates the reliable attribution of observations to specific geological phenomena. Our work demonstrates how the spatial resolution of DAS can be exploited to enhance existing methodologies and overcome limitations inherent in conventional seismological datasets.

The Gulf of Mexico (GoM) is one of the most extensively studied offshore regions, but its Mesozoic evolution remains uncertain. The presence of a thick sedimentary cover and Jurassic salt poses challenges for geophysical imaging, hindering our understanding of the Mesozoic depositional history and crustal architecture evolution. Current tectonic models with rigid plates fail to capture key aspects of GoM evolution. This study introduces a new deformable plate model with optimised focused deformation designed to dynamically adjust stretching factors (SF) during rift evolution. Our model, which calculates crustal thickness and tectonic subsidence (TS) through time and accounts for stretching and thermal subsidence, can explain the depositional history of the pre-salt section and crustal architecture evolution of the GoM. Our model produces a predicted present-day crustal thickness with a root mean square error of 5.6 km with the GEMMA crustal thickness model. The resultant TS of ~1.5 km before the Yucatán block drifted, provides routes for the deposition of red beds through the paleo drainage systems of the northern GoM as successor basin infilling. The model explains ~40 Myrs of missing sedimentary strata, which we attribute to rapid subsidence in the central GoM, shifting red beds deposition beneath the Jurassic salt formations. Extension rate and SF calculations reveal a transition from a magma-rich to a hyperextended margin, with possible mantle exhumation. Our model can be useful in understanding the extent of other Jurassic deposits in the GoM basin and offers a robust framework for comprehending global passive rift margin evolution.

Joule heating is one of the main energy inputs into the thermosphere-ionosphere system. Precise modeling of this process is essential for any space weather application. Existing ionosphere models tend to underestimate the actual Joule heating rate quite significantly. The Thermosphere-Ionosphere-Electrodynamics General-Circulation-Model applies an empirical scaling factor of 1.5 for compensation. We calculate vertical profiles of Joule heating rates from approximately 2220 h of measurements with the EISCAT incoherent scatter radar and the corresponding model runs. We investigate model runs with the plasma convection driven by both the Heelis and the Weimer model. The required scaling of the Joule heating profiles is determined with respect to the Kp index, the Kan-Lee merging electric field EKL, and the magnetic local time. Though the default scaling factor of 1.5 appears to be adequate on average, we find that the required scaling varies strongly with all three parameters ranging from 0.46 to ∼20 at geomagnetically disturbed and quiet times, respectively. Furthermore, the required scaling is significantly different in runs driven by the Heelis and Weimer model. Adjusting the scaling factor with respect to the Kp index, EKL, the magnetic local time, and the choice of convection model would reduce the difference between measurement and model results.

The widespread High Arctic Large Igneous Province (HALIP) exhibits prolonged melting over more than 50 Myr, an observation that is difficult to reconcile with the classic view of large igneous provinces and associated melting in plume heads. Hence, the suggested plume-related origin and classification of HALIP as a large igneous province have been questioned. Here, we use numerical models that include melting and melt migration to investigate a rising plume interacting with variable lithosphere thickness, i.e. an extended-basin-to-craton setting. Models reveal significant spatial and temporal variations in melt volumes and pulses of melt production, including protracted melting for at least about 30-40 Myr, but only if migrating melt transports heat upwards and enhances local lithospheric thinning. Plume material deflected from underneath the Greenland craton can then re-activate melting zones below the previously plume-influenced Sverdrup Basin, even though the plume is already ~500 km away. Hence, melting zones may not represent the location of the deeper plume stem at a given time. Plume flux pulses associated with mantle processes or magma processes within the crust may alter the timing and volume of secondary pulses and their surface expression. Our models suggest that HALIP magmatism is expected to exhibit plume-related trace element signatures throughout time, but potentially shift from mostly tholeiitic magmas in the first pulse towards more alkalic compositions for secondary pulses, with regional variations in timing of magma types. We propose that the prolonged period of rejuvenated magmatism of HALIP is consistent with plume impingement on a cratonic edge.

Pockmarks are morphological depressions commonly observed in ocean and lake floors. Pockmarks form by fluid (typically gas) seepage thorough a sealing sedimentary layer, deforming and breaching the layer. The seepage-induced sediment deformation mechanisms, and their links to the resulting pockmarks morphology, are not well understood. To bridge this gap, we conduct laboratory experiments in which gas seeps through a granular (sand) reservoir, overlaid by a (clay) seal, both submerged under water. We find that gas rises through the reservoir and accumulates at the seal base. Once sufficient gas over-pressure is achieved, gas deforms the seal, and finally escapes via either: (i) doming of the seal followed by dome breaching via fracturing; (ii) brittle faulting, delineating a plug. The gas lifts the plug and seeps through the bounding faults; or (iii) plastic deformation by bubbles ascending through the seal. The preferred mechanism is found to depend on the seal thickness and stiffness: in stiff seals, a transition from doming and fracturing to brittle faulting occurs as the thickness increases, whereas bubbles rise is preferred in the most compliant, thickest seals. Seepage can also occur by mixed modes, such as bubbles rising in faults. Repeated seepage events suspend the sediment at the surface and create pockmarks. We present a quantitative analysis that explains the tendency for the various modes of deformation observed experimentally. Finally, we connect simple theoretical arguments with field observations, highlighting similarities and differences that bound the applicability of laboratory experiments to natural pockmarks.

ANCHOR is a novel assimilative model developed at the U.S. Naval Research Laboratory. It extracts ionospheric parameters from RO and ionosonde data and assimilates them as point measurements into the maps of the background parameters using Kalman Filter approach. This paper introduces the ANCHOR algorithm, discusses its coordinate system and background, explains the background covariance formation, discusses the extraction of the ionospheric parameters from the data and the assimilation process, and, finally, shows the results of the observing system simulation experiment.

Black carbon (BC) has several direct, indirect, semi-direct, and microphysical effects on the Earth’s climate system. Analyses of the decade-long measurement of BC aerosols at Varanasi (from 2009 to 2021) was done to understand its impact on radiative balance. General studies suggest that the daily BC mass concentration (mean of 9.18±6.53 µg m–3) ranges from 0.07 to 46.23 µg m–3 and show a strong interannual and intra-annual variation over the 13-year study period. Trend analyses suggest that the interannual variability of BC shows significant decreasing trend (-0.47 µg m–3 yr-1) over the station. The decreasing trend is maximum during the post-monsoon (-1.86 µg m–3 yr-1) and minimum during the pre-monsoon season (-0.31 µg m–3 yr-1). The radiative forcing caused specifically by BC (BC-ARF) at the top of the atmosphere (TOA), surface (SUR), and within the atmosphere (ATM) is found to be 10.3 ± 6.4, -30.1 ± 18.9, and 40.5 ± 25.2 Wm−2, respectively. BC-ARF shows strong interannual variability with a decreasing trend at the TOA (–0.47 Wm–2 yr-1) and ATM ((–1.94 Wm–2 yr-1) forcing, while it showed an increasing trend at the SUR (1.33 Wm–2 yr-1). To identify the potential source sectors and the transport pathways of BC aerosols, concentrated weighted trajectories (CWT) and potential source contribution function (PSCF) analyses have been conducted over the station. These analyses revealed that the primary source of pollution at Varanasi originate from the upper IGP, lower IGP, and central India.

The Chinese Loess Plateau (CLP) in northern China serves one of the most prominent loess records in the world. The CLP is an extensive record of changes in past aeolian dust activity in East Asia; however, the interpretation of the loess records is hampered by ambiguity regarding the origin of loess-forming dust and an incomplete understanding of the circulation forcing dust accumulation. In this study, we used a novel modeling approach combining a dust emission model FLEXDUST with simulated back trajectories from FLEXPART to trace the dust back to where it was emitted. Over 21 years (1999-2019), we modeled back trajectories for fine (~ 2mu) and super-coarse (~ 20mu) dust particles at six CLP sites during the peak dust storm season from March to May. The source receptor relationship from FLEXPART is combined with the dust emission inventory from FLEXDUST to create site-dependent high-resolution maps of the source contribution of deposited dust. The nearby dust-emission areas dominate the source contribution at all sites. Wet deposition is important for dust deposition at all sites, regardless of dust size. Non-negligible amounts of dust from distant emission regions could be wet deposited on the CLP following high-level tropospheric transport, with the super-coarse dust preferentially from emission areas upwind of sloping topography. On an interannual scale, the phase of the Arctic Oscillation (AO) in winter was found to have a strong impact on the deposition rate on the CLP, while the strength of the East Asian Winter Monsoon was less influential.

A document by Peter Chu. Click on the document to view its contents.

The paper presents a new method for the decomposition of the horizontal wind divergence among the linear wave solutions on the sphere: inertia-gravity (IG), mixed Rossby-gravity (MRG), Kelvin and Rossby waves. The work is motivated by the need to quantify the vertical velocity and momentum fluxes in the tropics where the distinction between the Rossby and gravity regime, present in the extratropics, becomes obliterated. The new method decomposes divergence and its power spectra as a function of latitude and pressure level. Its application on ERA5 data in August 2018 reveals that the Kelvin and MRG waves made about 6% of the total divergence power in the upper troposphere within 10S-10N, that is about 25% of divergence. Their contribution at individual zonal wavenumbers k can be much larger; for example, Kelvin waves made up to 24% of divergence power at synoptic k in August 2018. The relatively small roles of the Kelvin and MRG waves in tropical divergence power are explained by decomposing their kinetic energies into rotational and divergent parts. The Rossby wave divergence power is 0.3-0.4% at most, implying up to 6% of global divergence due to the beta effect. The remaining divergence is about equipartitioned between the eastward- and westward-propagating IG modes in the upper troposphere, whereas the stratospheric partitioning depends on the background zonal flow. This work is a step towards a unified decomposition of the momentum fluxes that supports the coexistence of different wave species in the tropics in the same frequency and wavenumber bands. 

Understanding the dynamics of sulfur dioxide (SO2) degassing is of primary importance to track temporal variations of volcanic activity. We develop here an algorithm to automatically estimate daily SO2 masses flux from space-borne hyperspectral images (such as those provided by Sentinel-5P/TROPOMI) without requiring prior knowledge of plume direction or speed. The method computes a linear regression, as a function of distance, of SO2 mass integrated in a series of nested circular domains centered on the volcano. An additional term proportional to the square of the distance, depending solely on a cutoff on the minimum reliable pixel column amount, allows for estimating pixel noise and posterior uncertainty. A statistical test is introduced to automatically detect occurrences of volcanic degassing, by comparing estimated flux and its associated uncertainty. After inversion, a single multiplication by plume speed suffices to deduce the SO2 mass flux, without requiring to re-run the inversion. This way, a range of plume speed scenarios can be easily explored. The method is suited for weakly degassing sources or high-latitude volcanoes. It is applied to two case-studies, where temporal correlation between degassing and seismic energy is highlighted: (a) a one-year-long period of intense degassing at Etna, Italy (2021), and (b) a two-years-long period including three eruptions at Piton de la Fournaise, La Réunion (2021–2023). The method is open-source, and is implemented as an interactive tool within the VolcPlume web portal, facilitating near-real-time exploitation of the TROPOMI archive for both volcano monitoring and assessment of volcanogenic atmospheric hazards.

Understanding the formation of the solar system can provide a simplified look at the universe at large. This is because we have a lot of evidence about the formation of our solar system, and because the universe is homogeneous on a large scale. In this paper, we propose a new way for investigating the formation of the Earth and other Solar System objects. Our approach offers insights into details of the formation of the multiple layers within Earth, the existence of water and oil, the variation in mass distribution within Earth, and the origin of mountains, erratic boulders, and moons. According to our proposed approach, Roche Radius can explain the origin of moons, rings and mountains on planets. We have listed and use critical conditions that are required to form celestial objects.

We develop a method to estimate relative seismic moments M0 and corner frequencies fc of acoustic emission events recorded in laboratory experiments from amplitude spectra of signal’s coda composed of reverberated and scattered waves. This approach has several advantages with respect to estimations from direct waves that are often clipped and also are difficult to separate in experiments performed on small samples. Also, inversion of the coda spectra does not require information about the source locations ans mechanisms. We use the developed method to analyze the data of two experiments: (1) on granite from the Voronezh crystal massif and (2) on Berea sandstone. The range of absolute corner frequencies estimated in both experiments is around 70-700 kHz. The range of relative seismic moments covers 103.5. The relation between fc and M0 observed on the first stages of both experiments, consisted of increasing isotropic confining pressure, approximately follow M0 ~ fc-3 scaling and the b-value of the Gutenberg-Richter distribution was found close to 1. This can be interpreted as rupturing of preexisting material defects with a nearly constant stress-drop and has a similarity with observations of ‘natural’ earthquakes. Deviations from this ‘earthquake-like’ behavior observed after applying axial loading and initiation of sample damaging can be interpreted as changes in stress-drop. Lower stress-drops prevail for sandstone and higher for granite sample respectively that can be related to the strength of corresponding material.

A document by Claudia Finger. Click on the document to view its contents.

Volcanic eruptions generate continuous or episodic tremor, which can provide unique information about activity changes during eruption. However, the wealth of information in episodic tremor patterns is often not harvested and transitions between patterns remain obscure. The 2021 Geldingadalir eruption of the Fagradalsfjall Fires, Iceland, is an exceptional case, where the lava effusion caused continuous tremor, and 8696 tremor episodes spanning two orders of magnitude in duration and repose. Based on seismometer and video camera data, we associate several-minute-long, symmetrical episodes with an open vent system, where lava remains in the crater bowl during repose, connected to a shallow magma compartment. Ramp-shaped episodes, lasting several hours, are associated with a temporary closure of the vent system, where no lava remains in the crater bowl during repose and more time is required to resume effusion. The transition from continuous to episodic effusion is related to the cumulative time spent in effusion and repose, and to external factors like crater wall collapses.