A document by Ekaterina Bogdanovich. Click on the document to view its contents.

A technique for predicting the secular variation (SV) of the geomagnetic field based on the echo state network (ESN) model is proposed. SV is controlled by the geodynamo process in the Earth’s outer core. However, it is difficult to model the realistic nonlinear behaviors of the geodynamo due mainly to the very small Ekman number of the actual outer core. This study employs the ESN to represent the temporal evolution of the geomagnetic field on the Earth’s surface. The hindcast results of SV demonstrate that the ESN enables us to predict SV for several years with satisfactory accuracy. In particular, the nonlinear behaviors of SV is accurately predicted for the case where accurate geomagnetic data with a 1-year time resolution are available. It is found that an increase in the number of training data does not necessarily improve prediction accuracy. The results suggest that the information on the latest temporal variations is important for the short-term prediciton by the ESN valid for, say 5 years.

The Lost City hydrothermal field (LCHF) is considered an analogue of Archean alkaline hydrothermal vents where life on Earth may have spawned. Although Lost City was discovered more than 20 years ago, it remains unclear to what extent microbes are involved in the precipitation of the various minerals constituting the hydrothermal chimneys. Most chimneys preserve flow textures comprised of mineral walls bounding paleo-channels, which are preserved in inactive vent structures to a varying degree. Brucite lines the internal part of these channels, while aragonite dominates the exterior. Calcite is also present locally, mostly associated with brucite. Based on a combination of microscopic and geochemical analyses, we interpret brucite, calcite, and aragonite as primary minerals that precipitate abiotically from mixing seawater and hydrothermal fluids. We observe local brucite precipitation on microbial filaments and, in some cases, microbial filaments may affect the growth direction of brucite crystals. The link between brucite and organic compounds is further confirmed by fluorescence microscopy: brucite shows a strong fluorescence not observed in calcite and aragonite. Our results point to brucite as an important link to microbial life in alkaline fluids and is potentially a key aspect for future research on the origin of life.

{A numerical scheme is developed to simulate the transport of natural gravel. Starting with computerized tomographic (CT) scans of natural grains, our method approximates the shapes of these grains by “gluing” spheres of different sizes together with overlaps. The conglomerated spheres move using a Discrete Element Method (DEM) which is coupled with a Lattice Boltzmann Method (LBM) fluid solver, forming the first complete workflow from particle shape measurement to high resolution simulations with hundreds of distinct shapes. The simulations are quantitatively benchmarked by flume experiments. The numerical tool is used to further validate a recently proposed modified sediment transport relation, which takes particle shape effects into account, including the competition between hydrodynamic drag and material friction. Unlike a physical experiment, our simulations allow us to vary the hydrodynamic drag coefficient of the natural gravel independently of the material friction. Our studies support the modified sediment transport relation. The simulations also provide insights on the particle-level kinematics, such as particle orientations, in the bedload transport process. Particles below the bed surface prefer to orient with their shortest axes perpendicular to the bed surface, but the tendency goes down as the packing fraction decreases far from the bed surface. The particles rotate freely in the dilute particle flow regime. }

Spontaneous aggregation of deep convection is a common feature of idealized numerical simulations of the tropical atmosphere in Radiative-Convective Equilibrium (RCE). However, at coarse grid resolution where deep convection is not fully resolved, the occurrence of this phenomenon is extremely sensitive to subgrid-scale processes. This study focuses on the role played by mixing and entrainment, either provided by the turbulence model or the implicit numerical dissipation. We have analyzed the results of two different models, WRF and SAM, and we have compared different configurations by varying the turbulence models, the numerical schemes and the horizontal spatial resolution. At coarse grid resolution (3 km), removing turbulent mixing prevents the occurrence of Convective Self-Aggregation (CSA) in low numerical diffusion models, while delaying it in high numerical diffusion models. When the horizontal grid resolution is refined to 1 km (thus reducing the implicit numerical dissipation), CSA is achieved only by increasing the explicit turbulent mixing. In this case, CSA was found to occur even with a small amount of shallow clouds. Therefore, this study suggests that the sensitivity of CSA to horizontal grid resolution is not primarily due to the corresponding decrease in shallow clouds. Instead, it is found that turbulent mixing and dissipation at small scales regulate the amplitude of humidity perturbations introduced by convection in the free troposphere: the greater the dissipation at small scales, the greater the size and the strength of humidity perturbations in the free troposphere that can destabilize the RCE state.

The Tibetan Plateau was formed by intense Cenozoic shortening (up to 1100 km) of a composite “proto-Tibet”, itself the product of a long Paleozoic and Mesozoic history of accretion of Gondwana-derived continental fragments and volcanic arcs against the Asian continental margin. The difficult access and the scarcity of outcrops have long limited the possibilities of studying these Mesozoic suture zones in the heart of the Plateau. In this work, we present new U-Pb and 40Ar/39Ar ages from the highly deformed units of the Yushu mélange, along the Jinsha Suture in the northeastern Qiangtang terrane. Early Triassic (c. 253 Ma) to Middle Jurassic ages (c. 165 Ma) complement the existing dataset and help to refine the chronology of the Paleo-Tethyan oceanic subductions which have structured the northeastern part of the Qiangtang terrane. The Yushu mélange records at least three successive tectono-magmatic events. The opening of a back-arc basin during the northward Paleo-Tethyan subduction along the Longmu Co-Shuanghu Suture during Early to Middle Triassic; then its closure during the southward subduction of the Songpan-Ganze Ocean along the Jinsha Suture in Late Triassic. Finally, a shortening phase related to the continental collision of the Songpan-Ganze and Qiangtang blocks from Late Triassic to Early-Middle Jurassic. No evidence for any high- or mid-temperature Cenozoic reactivation of the Jinsha suture in our study area is recorded.

We have analyzed TROPOMI data over the Copperbelt mining region (Democratic Republic of Congo and Zambia). Despite high background values, we find that annual 2019-2022 means of TROPOMI NO2 show local enhancements consistent with six point sources (mines and cities) where high-emission industrial activities take place. We have quantified annual NO2 emissions for the six sources, identified temporal trends in these emissions, and found strong correlations with mine/refinery production data. CAMS-GLOB-ANT v5 inventory emissions are lower than TROPOMI-derived emissions by 61-96 % and lack the temporal trends observed in TROPOMI and mine/oil refinery production. Lack of TROPOMI SO2 enhancements over the point sources analyzed indicates SO2 capture and transformation into sulfuric acid, a profitable byproduct. These results demonstrate the potential for satellite monitoring of mining/oil refining activity which impacts the air quality of local communities. This is particularly important for Africa, where mining is increasing aggressively.

The accuracy of initial conditions is an important driver of the forecast skill of numerical weather prediction models. Increases in the quantity of available measurements, in particular high-resolution remote sensing observational data products from satellites, are valuable inputs for improving those initial condition estimates. However, the data assimilation methods used for integrating observations into forecast models are computationally expensive. This makes incorporating dense observations into operational forecast systems challenging, and it is often prohibitively time-consuming. As a result, large quantities of data are discarded and not used for state initialization. We demonstrate, using the Lorenz-96 system for testing, that a simple machine learning method can be trained to assimilate high-resolution data. Using it to do so improves both initial conditions and forecast accuracy. Compared to using the Ensemble Kalman Filter with high-resolution observations ignored, our augmented method has an average root-mean-squared error reduced by 15%. Ensemble forecasts using initial conditions generated by the augmented method are more accurate and reliable at up to 10 days of forecast lead time.

A document by Jonathan Wolf. Click on the document to view its contents.

A document by Michael Lockwood. Click on the document to view its contents.

Igneous dike intrusion is a primary crust-forming process at the Earth’s plate boundaries. Understanding its mechanism is thus crucially important in lithospheric studies. Our present article combines experimental and field observations to investigate the problem of dike emplacement from a mechanical perspective. We performed scaled laboratory experiments by injecting immiscible liquids into visco-elastic and visco-elasto-plastic host materials at varying volumetric flow rates (VFR = 0.100 ml/sec to 1.670 ml/sec). Another set of experiments used different injecting liquid–host combinations to set their viscosity ratios (η*) at low (105), moderate (106), and (iii) high (109) values. These two lines of experiments allow us to recognize three principal mechanisms of liquid pathways: 1) tensile fracturing of the host, 2) wave instability at the liquid-host interface and coupled fracturing-wave instability process. The three mechanisms give rise to a wide variation in intrusion geometry, ranging from planar structures with elliptical outlines to typical bulbous geometry, with intermediate patterns characterized by in-plane and off-plane wavy interfaces with the host. We use the experimental data to constrain the VFR conditions that determine the fracturing versus wave instability-controlled mechanisms. It is also shown from the experiments that η* can significantly influence the evolution of three-dimensional intrusive geometry. The Chotonagpur Granite Gneiss Complex in eastern India is chosen as our study area to validate our laboratory findings using a 2D shape analysis of the intrusive boundaries in terms of their fractal dimensions (D) and skewness-kurtosis estimates.

Wave energy propagating into the Antarctic marginal ice zone affects the quality and extent of the sea ice, and wave propagation is therefore an important factor for understanding and predicting changes in sea ice cover. Sea ice is notoriously hard to model and in-situ observations of wave activity in the Antarctic marginal ice zone are scarce, due to the extreme conditions of the region. Here, we provide new in-situ data from two drifting Surface Wave Instrument Float with Tracking (SWIFT) buoys deployed in the Weddell Sea in the austral winter and spring in 2019. The buoy location ranges from open water to more than 200 km into the sea ice. We estimate the attenuation of swell with wave periods 8-18 s, and find an attenuation coefficient  α = 4 · 10-6 to 7 · 10-5 m-1 in spring, and approximately five-fold larger in winter. The attenuation coefficients show a power law frequency dependence, with power coefficient 3.3 in spring and 4 in winter. The in-situ data also shows a change in wave direction, where wave direction tends to be more perpendicular to the ice edge farther into the sea ice. A possible explanation for this might be a change in the dispersion relation caused by changing sea ice composition. These observations can help shed further light on the influence of sea ice on waves propagating into the Marginal Ice Zone, aiding development of coupled wave-sea ice models.

The Makran subduction zone is unique in its wide onshore thick accretionary wedge, and a volcanic arc not parallel to the E-W trend of the Makran accretionary prism. To investigate the internal structure of the onshore accretionary wedge, the trend of the buried trench, and the crustal nature of fore-arc Jaz Murian Depression, we have calculated a 3D shear-wave velocity model for a region around the border between eastern and western Makran using ambient noise adjoint tomography and data from IASBS/CAM Makran temporary seismic network. Our 3D shear-wave velocity model clearly shows that the onshore accretionary prism consists of two southern low and northern high velocity zones with an average sedimentary cover of 22 and 30 km, respectively. The young age of the surface rocks of the high velocity part of the prism suggests the presence of a significant volume of igneous rocks scraped from the subducting oceanic slab. The 3D model indicates a continental crust of ~40 km with a thick sedimentary cover of ~20 km for the eastern part of Jaz Murian Depression. The presence of a NE-SE trending low velocity region at a depth interval of 40-60 km subparallel with the trend of the volcanic arc, intermediate-depth earthquakes, and geometry of the overriding plate might be related to the trend of the buried trench. This implies that the observed NE-SE trending volcanic arc might be related to the geometry of the buried trench and not the eastward reduction of the subduction angle.

We examine the source parameters of four Mw≥7.0 intraslab earthquakes that occurred near the Tohoku coast over the past two decades: 2003, 2011, 2021, and 2022. By analyzing the finite fault slip histories constrained by inland strong motion observations, we found that these earthquakes occurred within the upper plane of the subducted Pacific Plate due to downdip compression caused by plate unbending. These earthquakes have a more compact fault area and higher stress drop compared to shallow crustal earthquakes. Additionally, intraslab earthquakes have much slower relative rupture velocity than shallow crustal earthquakes. Good spatial correlations between the static stress drop and slip rate are found, which may suggest the compatibility between dynamic stress drop and static stress drop. The rupture area, average slip, asperity area, average static stress drop over the entire fault, and asperities are consistent with the reported scaling relationship for global intraslab earthquakes within a similar depth range. Using plate unbending, we found the recurrence intervals of these intraslab earthquakes are around 600 years, which is comparable with that of the 2011 Tohoku earthquake. A visual spatial-correlation between the locations of these earthquakes and seismicity in the lower plane is reported. These findings provide insights into the tectonic background and source parameters of intraslab earthquakes in the Tohoku region and contribute to better seismic hazard assessment.

Carbonate-brucite chimneys are a characteristic of low- to moderate-temperature, ultramafic-hosted alkaline hydrothermal systems, such as the Lost City hydrothermal field located on the Atlantis Massif at 30°N near the Mid-Atlantic Ridge. These chimneys form as a result of mixing between warm, serpentinization-derived vent fluids and cold seawater. Previous work has documented the evolution in mineralogy and geochemistry associated with the aging of the chimneys as hydrothermal activity wanes. However, little is known about spatial heterogeneities within and among actively venting chimneys. New mineralogical and geochemical data (87Sr/86Sr and stable C, O, and clumped isotope) indicate that brucite and calcite precipitate at elevated temperatures in vent fluid-dominated domains in the interior of chimneys. Exterior zones dominated by seawater are brucite-poor and aragonite is the main carbonate mineral. Carbonates form mostly out of oxygen and clumped isotope equilibrium due to rapid precipitation upon vent fluid-seawater mixing. In contrast, the carbonates precipitate close to carbon isotope equilibrium, with dissolved inorganic carbon in seawater as the dominant carbon source, and have δ13C values within the range of marine carbonates. Our data suggest that calcite is a primary mineral in the active hydrothermal chimneys and does not exclusively form as a replacement of aragonite during later alteration with seawater. Elevated formation temperatures and lower 87Sr/86Sr relative to aragonite in the same sample suggest that calcite may be the first carbonate mineral to precipitate.

The parameterization IDEMIX for vertical mixing by breaking internal gravity waves is evaluated in three different non-eddy resolving ocean models. Three different products of wave forcing by tidal flow over topography, representing the current uncertainty, are applied and compared to reference simulations without IDEMIX, allowing the model-independent effects of the new closure to be assessed. Common to all models is larger interior mixing work with stronger horizontal structure due to the inhomogeneous forcing functions in all simulations using IDEMIX, in better agreement to observations. Coherent model responses to the stronger mixing work are changes in the thermocline depth including IDEMIX related to stronger shallow overturning cells in the Indo-Pacific Ocean. Furthermore, deeper mixed layer depths in the subpolar North Atlantic are related to an increase of the Atlantic overturning circulation which brings the model closer to observations, coming along with an increase in northward heat transport. In the Southern Ocean, excessive energy input by one of the forcing products leads to unrealistic deep convection in the Weddell Sea in one of the models. The deep Indo-Pacific overturning circulation and the bottom cell of the Atlantic feature an incoherent model response, which may point towards the importance of excessive numerical mixing in the models.

The total energy transfer from the solar wind to the magnetosphere is governed by the reconnection rate at the magnetosphere edges as the IMF $B_z$ turns southward. The delayed response of the ring current to solar wind driving can account for the anomalous growth of the SYM-H under northward IMF $B_z$. The geomagnetic storm on 21-22 January 2005 is considered to be anomalous as the SYM-H index that signifies the strength of ring current, grows and has a sustained peak value lasting more than 6 hrs under northward IMF $B_z$ conditions. In this work, first the standard WINDMI model is utilized to estimate the growth and decay of various magnetospheric currents by using several solar wind-magnetopsehre coupling functions. However, it is found that the WINDMI model driven by any of these coupling functions is not fully able to explain the enhancement of SYM-H under northward IMF $B_z$. The SYM-H variations during the entire duration of the storm were only reproduced when the effects of the dense plasma sheet were included in the WINDMI model. The limitations of directly-driven models relying purely on the solar wind parameters and not accounting for the state of the magnetosphere are highlighted by this work.

A document by Ryan Andrew Green. Click on the document to view its contents.