A document by Benjamin Rabe. Click on the document to view its contents.

Mesoscale-to-microscale coupling is an important tool to conduct turbulence-resolving multiscale simulations of realistic atmospheric flows, which are crucial for applications ranging from wind energy to wildfire spread studies. Different techniques are used to facilitate the development of realistic turbulence in the large-eddy simulation (LES) domain while minimizing computational cost. Here, we explore the impact of a simple and computationally efficient Stochastic Cell Perturbation method using momentum perturbation (SCPM-M) to accelerate turbulence generation in boundary-coupled LES simulations using the Weather Research and Forecasting (WRF) model. We simulate a convective boundary layer (CBL) to characterize the production and dissipation of turbulent kinetic energy (TKE) and the variation of TKE budget terms. Furthermore, we evaluate the impact of applying momentum perturbations of three magnitudes below, up to, and above the CBL on the TKE budget terms. Momentum perturbations greatly reduce the fetch associated with turbulence generation. When applied to half the vertical extent of the boundary layer, momentum 1 perturbations produce an adequate amount of turbulence. However, when applied above the CBL, additional structures are generated at the top of the CBL, near the inversion layer. The magnitudes of the TKE budgets produced by SCPM-M when applied at varying heights and with different perturbation amplitudes are always higher near the surface and inversion layer than those produced by No-SCPM, as are their contributions to the TKE. This study provides a better understanding of how SCPM-M reduces computational costs and how different budget terms contribute to TKE in a boundary-coupled LES simulation.

A document by Nolan Roth. Click on the document to view its contents.

• A physics-informed neural network trained without ground truths can provide accurate initial fields for numerical prediction. • The system's kinetic features are embedded into the model through our four-dimensional variational form loss function. • We show on Lorenz96 that the proposed method can be used directly for accurate data assimilation at a low computational cost.

A document by Bo Yang. Click on the document to view its contents.

A document by Antoine Lucas. Click on the document to view its contents.

A document by Martijn van den Ende. Click on the document to view its contents.

It is widely recognized that fluid injection can trigger fault slip. However, the processes by which the fluid-rock interactions facilitate or inhibit slip are poorly understood and some are neglected or oversimplified in most models of injection-induced slip. In this study, we perform a 2D antiplane shear investigation of aseismic slip that occurs in response to fluid injection into a permeable fault governed by rate-and-state friction. We account for pore dilatancy and permeability changes that accompany slip, and quantify how these processes affect pore pressure diffusion, which couples to aseismic slip. The fault response to injection has two phases. In the first phase, slip is negligible and pore pressure closely follows the standard linear diffusion model. Pressurization of the fault eventually triggers aseismic slip in the immediate vicinity of the injection site. In the second phase, the aseismic slip front expands outward and dilatancy causes pore pressure to depart from the linear diffusion model. Aseismic slip front overtakes pore pressure contours, with both subsequently advancing at constant rate along fault. We quantify how prestress, initial state variable, injection rate, and frictional properties affect the migration rate of the aseismic slip front, finding values ranging from less than 50 to 1000 m/day for typical parameters. Additionally, we compare to the case when porosity and permeability evolution are neglected. In this case, the aseismic slip front migration rate and total slip are much higher. Our modeling demonstrates that porosity and permeability evolution, especially dilatancy, fundamentally alters how faults respond to fluid injection.

Quantifying the volume of water that is stored in the subsurface is critical to studies of water availability to ecosystems, slope stability, and water-rock interactions. In a variety of settings, water is stored in fractured and weathered bedrock as rock moisture. However, few techniques are available to measure rock moisture in unsaturated rock, making direct estimates of water storage dynamics difficult to obtain. Here, we use borehole nuclear magnetic resonance (NMR) at two sites in seasonally dry California to quantify dynamic rock moisture storage. We show strong agreement between NMR estimates of dynamic storage and estimates derived from neutron logging and mass balance techniques. The depths of dynamic storage are up to 9 m and likely reflect the depth extent of root water uptake. To our knowledge, these data are the first to quantify the volume and depths of dynamic water storage in the bedrock vadose zone via NMR.

The Terrestrial Gamma-ray Flashes (TGF) to lightning ratio, computed over the 3 tropical chimneys, presents a paradox: African thunderstorms produce the most lightning but yield the lowest fraction of TGF when compared to American and Southeast Asian thunderclouds. To understand the physical insights into this asymmetry, TRMM Precipitation Radar measurements are used to depict the vertical precipitation structure of the observed thunderstorms in the 3 regions and the thunderstorms during TGF occurrences detected by AGILE, Fermi-GBM and RHESSI sensors. African thunderstorms are taller, smaller and have higher concentration of dense ice particles above the freezing level. TGF thunderstorms are taller and less intense (0.5-2dBZ), besides presenting similar radar reflectivity decay with height independent of the region. In addition, these storms show thicker electrical charge layers separated by 4.7-5.2 km and also a positive charge fraction reduction between -20 o C and -40 o C and enhancement above -50 o C when compared to the overall thunderstorms.

The Leech River fault (LRF) zone located on southern Vancouver Island is a major regional seismic source. We investigate potential interactions between earthquake ruptures on the LRF and the neighboring Southern Whidbey Island fault (SWIF), which can be interpreted as a step-over fault system. Using a linear slip-weakening frictional law, we perform 3D finite element simulations to study rupture jumping scenarios from the LRF (source fault) to the SWIF (receiver fault), focusing on the influences of the offset distance, fault initial stress level, and fault burial depth. We find a smaller offset distance, a higher initial stress level on either fault or a shallower fault burial depth will promote rupture jumping. Jumping scenarios can be interpreted as the response of the receiver fault to stress perturbations radiated from the source fault rupture. We demonstrate that the final rupture jumping scenario depends on various parameters, which can be collectively quantified by two keystone variables, the time-averaged Over Stressed Zone (where shear stress exceeds static frictional strength on the receiver fault) size $\overline{R_e}$ and the receiver fault initial stress level. Specifically, a smaller offset distance, a higher initial shear stress level, or a shallower burial depth will lead to a larger $\overline{R_e}$. The seismic moment on the receiver fault increases with increasing $\overline{R_e}$. When $\overline{R_e}$ reaches the threshold dependent on the receiver fault initial stress level, the rupture becomes break-away.

We present a 700 km airborne electromagnetic survey of late-spring fast ice and sub-ice platelet layer (SIPL) thickness distributions, from McMurdo Sound to Cape Adare, providing a first-time inventory of thickness close to its annual maximum. The overall modal consolidated ice (including snow) thickness was 1.9 m, less than its mean of 2.6±1.0 m. Our survey was partitioned into level and rough ice, and SIPL thickness was estimated under level ice. Although results show a prevalence of level ice, with a mode of 2.0 m and mean of 2.0±0.6 m, rough ice covered 41% of the transect by length, 50% by volume, with a mode of 3.3 m and mean of 3.2±1.2 m. The thickest 10% of rough ice was almost 6 m on average, and a 2 km segment in Moubray Bay had a thickness greater than 8 m, demonstrating the overwhelming influence of deformation against coastal features. The fast ice was thus significantly thicker than adjacent pack ice. The presence of a significant SIPL was observed in Silverfish Bay, offshore Hells Gate Ice Shelf, New Harbour, and Granite Harbour where the SIPL transect volume was a significant fraction (0.30) of the consolidated ice volume. The thickest 10% of SIPLs had an average thickness of nearly 3 m, and near Hells Gate Ice Shelf the SIPL was almost 10 m thick, implying vigorous heat loss to the ocean (~ 90Wm-2). We conclude that polynya-induced deformation and interaction with continental ice influence fast ice thickness in the western Ross Sea.

Simulating magma propagation pathways requires both a well-calibrated model for the stress state of the volcano and models for dike advance within such a stress field. With the purpose of establishing a framework for calculating computationally efficient and flexible shallow magma propagation scenarios, we develop three-dimensional models for the stress state of volcanoes with complex topographies and edifice histories as well as a new simplified three-dimensional model of dike propagation using the stress state of the volcano as input. Next, we combine all these models to calculate shallow dike propagation scenarios for complex caldera settings. The resulting synthetic magma pathways and eruptive vent locations broadly reproduce the variability observed in natural calderas.

The ice stream geometry and large ice surface velocities at the onset region of the Northeast Greenland Ice Stream (NEGIS) are not yet well reproduced by ice sheet models. The quantification of basal sliding and a parametrisation of basal conditions remains a major gap. In this study, we assess the basal conditions of the onset region of the NEGIS in a systematic analysis of airborne ultra-wideband radar data. We evaluate basal roughness and basal return echoes in the context of the current ice stream geometry and ice surface velocity. We observe a change from a smooth to a rougher bed where the ice stream widens, and a distinct roughness anisotropy, indicating a preferred orientation of subglacial structures. In the upstream region, the excess ice mass flux through the shear margins is evacuated by ice flow acceleration and along-flow stretching of the ice. At the downstream part, the generally rougher bed topography correlates with a decrease in flow acceleration and lateral variations in ice surface velocity. Together with basal water routing pathways, this hints to two different zones in this part of the NEGIS: the upstream region collecting water, with a reduced basal traction and downstream, where the ice stream is slowing down and is widening on a rougher bed, with a distribution of basal water towards the shear margins. Our findings support the hypothesis that the NEGIS is strongly interconnected to the subglacial water system in its onset region, but also to the subglacial substrate and morphology.

The tsunami-generated magnetic field is a magnetic field that show up with the moving of tsunami. In the previous studies, researchers claimed that the tsunami-generated magnetic field arrives earlier than the tsunami sea level change based on analytical solutions and numerical simulations. In this paper, we used the world's first simultaneous data of sea level change and magnetic field in the 2009 Samoa and 2010 Chile tsunamis to study the relation between these two physical quantities. We found that the vertical component of tsunami magnetic field arrives earlier than the sea level change. Moreover, the horizontal component of tsunami magnetic field arrives even earlier than the vertical component. The tsunami magnetic field was also revealed that it can be used to estimate the tsunami wave height very accurately. We investigated the observed tsunami magnetic field by our 3-D time-domain simulation. However, the currently existing tsunami source models were unable to reproduce the observation in our research area. We confirmed that a better source model can improve the simulation. It follows that our high precision tsunami wave height data converted from the magnetic field should be used to construct a better tsunami source model.

Long-period (T > 10 s) shear-wave reverberations between the surface and reflecting boundaries below seismic stations are useful for studying the mantle transition zone (MTZ) but finite-frequency effects may complicate the interpretation of waveform stacks. Using waveform data from the USArray and spectral-element method synthetics for 3-D seismic models, we illustrate that a common-reflection point (CRP) modeling of layering in the upper mantle must be based on 3-D reference structures and accurate calculations of reverberation traveltimes. Our CRP mapping of recorded waveforms places the 410-km and 660-km phase boundaries about 15 km deeper beneath the western US than beneath the central-eastern US if it is based on the 1-D PREM model. The apparent east-to-west deepening of the MTZ disappears in the CRP image if we account for shear-wave velocity variations in the mantle. We also find that ray theory overpredicts the traveltime delays of the reverberations if 3-D velocity variations in the mantle are prescribed by global models S40RTS, SEMUCB-WM1, and TX2015. Undulations of the 410-km and 660-km are underestimated in the analysis when their wavelengths are smaller than the Fresnel zones of the wave reverberations in the MTZ.

Clinopyroxene and orthopyroxene are the two major repositories of rare earth elements (REE) in spinel peridotites. Most geochemical studies of REE in mantle samples focus on clinopyroxene. Recent advances in in situ trace element analysis has made it possible to measure REE abundance in orthopyroxene. The purpose of this study is to determine what additional information one can learn about mantle processes from REE abundances in orthopyroxene coexisting with clinopyroxene in residual spinel peridotites. To address this question, we select a group of spinel peridotite xenoliths (9 samples) and a group of abyssal peridotites (12 samples) that are considered residues of mantle melting and that have major element and REE compositions in the two pyroxenes reported in the literature. We use a disequilibrium double-porosity melting model and the Markov chain Monte Carlo method to invert melting parameters from REE abundance in the bulk sample. We then use a subsolidus reequilibration model to calculate REE redistribution between cpx and opx at the extent of melting inferred from the bulk REE data and at the closure temperature of REE in the two pyroxenes. We compare the calculated results with those observed in clinopyroxene and orthopyroxene in the selected peridotitic samples. Results from our two-step melting followed by subsolidus reequilibration modeling show that it is more reliable to deduce melting parameters from REE abundance in the bulk peridotite than in clinopyroxene. We do not recommend the use of REE in clinopyroxene alone to infer the degree of melting experienced by the mantle xenolith, as HREE in clinopyroxene in the xenolith are reset by subsolidus reequilibration. In general, LREE in orthopyroxene and HREE in clinopyroxene are more susceptible to subsolidus redistribution. The extent of redistribution depends on the modes of clinopyroxene and orthopyroxene in the sample and thermal history experienced by the peridotite. By modeling subsolidus redistribution of REE between orthopyroxene and clinopyroxene after melting, we show that it is possible to discriminate mineral mode of the starting mantle and cooling rate experienced by the peridotitic sample. We conclude that endmembers of the depleted MORB mantle and the primitive mantle are not homogeneous in mineral mode. A modally heterogeneous peridotitic starting mantle provides a simple explanation for the large variations of mineral mode observed in mantle xenoliths and abyssal peridotites. Finally, by using different starting mantle compositions in our simulations, we show that composition of the primitive mantle is more suitable for modeling REE depletion in cratonic mantle xenoliths than the composition of the depleted MORB mantle.

Seismic interferometry is a powerful tool to monitor the seismic velocity change associated with volcanic eruptions. For the monitoring, changes in seismic velocity with environmental origins (such as precipitation) are problematic. In order to model the environmental effects, we propose a new technique based on a state-space model. An extended Kalman filter estimates seismic velocity changes as state variables, with a first-order approximation of the stretching method. We apply this technique to three-component seismic records in order to detect the seismic velocity change associated with the Shinmoe-dake eruptions in 2011 and 2018. First, ambient noise cross-correlations were calculated from May 2010 to April 2018. We also modeled seismic velocity changes resulting from precipitation and the 2016 Kumamoto earthquake, with exponential type responses. Most of the results show no significant changes associated with the eruptions, although gradual inflation of the magma reservoir preceded the 2011 eruption by one year. The observed low sensitivity to static stress changes suggests that the fraction of geofluid and crack density at about 1 km depth is small, and the crack shapes could be circular. Only one station pair west of the crater shows the significant drop associated with the eruption in 2011. The gradual drop of seismic velocity up to 0.05% preceded the eruption by one month. When the gradual drop began, volcanic tremors were activated at about 2 km depth. These observations suggest that the drop could be caused by damage accumulation due to vertical magma migration beneath the summit.