A document by Dale Richard Durran. Click on the document to view its contents.

Channel meandering is ubiquitous in tidal marshes, yet it is routinely omitted in morphodynamic models. Here we propose a novel numerical method to simulate channel meandering in tidal marshes on a Cartesian grid. The method calculates a first-order flow by considering the balance between pressure gradient and bed friction. To account for flow momentum shift towards meander outer banks, the flow is empirically modified. Unlike previous simplified methods that relied on the curvature of the bank, this modification is based on the curvature of the flow, making the model suitable for use in dendritic channel networks. The modified flow intrinsically accounts for the topographic steering effect, which tends to deflect the momentum toward the outer bank. As a result, the outer bank becomes steeper and erodes due to soil creep. Additionally, the outer bank experiences erosion proportional to the flow curvature. This erosion mechanism parameterizes the direct erosion caused by flow impacting the bank through a proportionality coefficient, which modulates the rate of lateral channel migration. Deposition on the inner bank is automatically simulated by the model, triggered by reduced bed shear stress in that area. The model accurately reproduces meander sinuosity, migration rates, and associated processes such as cutoffs, channel piracies, and network reorganizations. The model provides an efficient tool for predicting marsh landscape evolution from decades to millennia, which will enable exploring how lateral migration and meandering of tidal channels affect marsh ecomorphodynamics, carbon and nutrient cycling, drainage efficiency, and pond dynamics.

For seismographic stations with short acquisition duration, the signal-to-noise ratios (SNRs) of ambient noise cross-correlation functions (CCFs) are typically low, preventing us from accurately measuring surface wave dispersion curves or waveform characteristics. In addition, with low-quality CCFs, it is difficult to monitor temporal variations of subsurface physical states or extract relatively weak signals such as body waves. In this study, we propose to use local attributes to improve the SNRs of ambient noise CCFs, which allows us to enhance the quality of CCFs for stations with limited acquisition duration. Two local attributes: local cross-correlation and local similarity, are used in this study. The local cross-correlation allows us to extend the dimensionality of daily CCFs with computational costs similar to global cross-correlation. Taking advantage of this extended dimensionality, the local similarity is then used to measure non-stationary similarity between the extended daily CCFs with a reference stacking trace, which enables us to design better stacking weights to enhance coherent features and attenuate incoherent background noises. Ambient noise recorded by several broadband stations from the USArray in North Texas and Oklahoma, the Superior Province Rifting EarthScope Experiment in Minnesota and Wisconsin and a high-frequency nodal array deployed in the San Bernardino basin are used to demonstrate the performance of the proposed approach for improving the SNR of CCFs.

A document by Anne Springer. Click on the document to view its contents.

We show that steric sea-level varies with a period of 18.6 years along the western European coast. We hypothesize that this variation originates from the modulation of semidiurnal tides by the lunar nodal cycle and associated changes in ocean mixing. Accounting for the steric sea level changes in the upper 400 m of the ocean solves the discrepancy between the nodal cycle in mean sea level observed by tide gauges and the theoretical equilibrium nodal tide. Namely, by combining the equilibrium tide with the nodal modulation of steric sea level, we close the gap with the observations. This result supports earlier findings that the observed phase and amplitude of the 18.6-year cycle do not always correspond to the equilibrium nodal tide.

Under a warming climate, it is unclear how environments associated with US tornado outbreaks are changing. This work narrows this gap by using maximum covariance analysis (MCA) to find multivariate relationships between 500-hPa geopotential height anomalies and a severe thunderstorm proxy – WMAXSHEAR (a product of convective available potential energy and 0–6 km vertical wind shear) associated with past (1950-2019) May major tornado outbreaks. Results highlight three main patterns that explain the majority of covariance between tornado outbreaks and the large-scale atmospheric environment. Tornado outbreaks occurring under the dominant pattern (MCA1) initiate at different hours of the day and tend to last for many hours. Tornado outbreaks associated with the second (MCA2) and third (MCA3) patterns are shorter in duration and tend to initiate during the warmest daytime hours. Moreover, an increase in the magnitude and the spatial extent of the patterns conducive to tornado outbreaks was observed after 1980.

This study examines how wind shear affects precipitating marine stratocumulus clouds under different cloud droplet number concentrations (Nd). We performed a series of large eddy simulations (LES) of nocturnal marine stratocumulus clouds using Cloud Model 1 (CM1). The simulations show that Nd is the dominant factor for cloud cellular organization in this cloud regime rather than wind shear. Low Nd characterizes the open cellular structure with a high in-cloud liquid water path (LWP). When wind shear is increased, the cloud fraction tends to decrease along with LWP, suggesting the cloud top region is significantly influenced by the entrainment and mixing of dry air from the free troposphere. We also examine cold pools in open and closed cellular clouds. Open-cell clouds produce larger and deeper cold pools compared to closed-cell clouds. Interestingly, cold pools can exist without surface precipitation and are produced by evaporation of light precipitation (drizzle) below the cloud base with weak downdrafts. The evaporation of raindrops and drizzle play an important role in initiating new convection, particularly where colliding outflows occur downstream of the cloud. This secondary convection contributes to the development and maintenance of the cloud cellular organization and formation. 

A fundamental assumption in thermochronology is extrapolation of kinetic parameters over geologic timescales, temperatures, and mineral compositions that often differ significantly from the laboratory conditions used to quantify them. In this study, we aim to test and intercalibrate kinetic parametersof multiple thermochronometric systems using a tractable, natural thermal perturbation associated with the emplacement of a small, young basalt intrusion into granite in the Sierra Nevada, the site of the classic study of Calk and Naeser (1973). We collected a suite of samples along a linear transect orthogonal to the contact, from which the minerals apatite, zircon, titanite, epidote, magnetite, biotite, horneblende, K-feldspar, and plagioclase were separated. Our results to date reveal that the (U-Th)/He system in apatite was completely reset within ~7 m of the contact during basalt emplacement ~8 Ma. At distances >16 m from the contact, the apatite He ages are uniformly ~58 Ma, which likely represents the background (i.e., unperturbed) cooling ages of the granite. Apatite 4 He/ 3 He thermochronometry and an observed transition from background-to rest-ages of these samples are quantitatively consistent with a higher degree of thermal perturbation nearer to the contact. As predicted by our current quantification of radiation damage accumulation influence on He diffusion kinetics (Flowers et al, 2009), we observe correlation between the "effective uranium" concentration and He ages of individual apatite crystals, particularly within this transition zone. In contrast, the (U-Th)/He system in zircon is only partially reset ~7 m from the contact, and the background cooling ages at distances >10 m are ~78 Ma, consistent with a 40 Ar/ 39 Ar age-spectrum from a distal K-feldspar that rises from ~70 to ~80 Ma; both observations are consistent with the relative, experimentally determined temperature sensitivities of these minerals. We present ongoing numerical modeling that provides a framework with which to quantitatively compare and assess these results with forthcoming 40 Ar/ 39 Ar and fission track results in various mineral systems. Inversion of data using these multi-material conductive models will be used to assess the sensitivity of results to assumptions about geometry (1D, 2D, 3D), duration of basalt emplacement, and pre-intrusion cooling rate.

Ocean eddies play an important role in the distribution of heat, salt, and other tracers in the global ocean. But while surface eddies have been studied extensively, deeper eddies are less well understood. Here we study deep coherent vortices (DCVs) in the Northeast Atlantic Ocean using a high resolution numerical simulation. We perform a census of the DCVs on the $27.60$ kg/m$^3$ isopycnal, at the depth of $700-1500$ m, where DCVs of Mediterranean water (meddies) propagate. We detect a large number of DCVs, with maxima around continental shelves, and islands, dominated by small and short-lived cyclones. However, the large and long-lived DCVs are mostly anticyclonic. Among the long-lived DCVs, anticyclonic meddies, stand out. They grow in size by merging with other anticyclonic meddies. Cyclonic meddies are also regularly formed, but most of them are destroyed near their formation sites due to the presence of the energetic anticyclonic meddies, which destroy cyclones by straining and wrapping the positive vorticity around their core. During their life cycle, as they propagate to the southwest, anticyclonic meddies can interact with other DCVs, including anticyclones containing Antarctic Intermediate Water generated near the Moroccan coast, Canary anticyclonic DCVs and cyclonic DCVs generated south of $30^\circ$N along the African continental shelf. With these latter, they can form dipoles, and with the former, they co-rotate pro tempore. Thus, a more detailed view of the life cycle of anticyclonic meddies is proposed: they grow by merging, undergo multiple interactions along their path, and they decay at low latitudes.

Geodetic methods can monitor changes in terrestrial water storage (TWS) across large regions in near real-time. Here, we investigate the effect of assumed Earth structure on TWS estimates derived from Global Navigation Satellite System (GNSS) displacement time series. Through a series of synthetic tests, we systematically explore how the spatial wavelength of water load affects the error of TWS estimates. Large loads (e.g., >1000 km) are well recovered regardless of the assumed Earth model. For small loads (e.g., <10 km), however, errors can exceed 75% when an incorrect model for the Earth is chosen. As a case study, we consider the sensitivity of seasonal TWS estimates within mountainous watersheds of the western U.S., finding estimates that differ by over 13% for a collection of common global and regional structural models. Errors in the recovered water load generally scale with the total weight of the load; thus, long-term changes in storage can produce significant uplift (subsidence) enhancing errors. We demonstrate that regions experiencing systematic and large-scale variations in water storage, such as the Greenland ice sheet, exhibit significant differences in predicted displacement (over 20 mm) depending on the choice of Earth model. Since the discrepancies exceed GNSS observational precision, an appropriate Earth model must be adopted when inverting GNSS observations for mass changes in these regions. Furthermore, regions with large-scale mass changes that can be quantified using independent data (e.g., altimetry, gravity) present opportunities to use geodetic observations to refine structural deficiencies of seismologically derived models for the Earth’s interior structure.

Accurately determining the seismic structure of the deep crust of continents is crucial for understanding the geological record and continental dynamics. However, traditional surface wave methods often face challenges in solving the trade-offs between elastic parameters and discontinuities. In this work, we present a new approach that combines two established inversion techniques, receiver function H-ᵰ5; stacking and joint inversion of surface wave dispersion and receiver function waveforms, within a Bayesian Monte Carlo (MC) framework to address these challenges. As demonstrated by the synthetic test, the new method greatly reduces trade-offs between critical parameters, such as the deep crustal Vs, Moho depth, and crustal Vp/Vs ratio. This eliminates the need for assumptions regarding crustal Vp/Vs ratios in joint inversion, leading to a more accurate outcome. Furthermore, it improves the precision of the upper mantle velocity structure by reducing its trade-off with Moho depth. Additional notes on the sources of bias in the results are also included. Application of the new approach to USArray stations in the Northwestern US reveals consistency with previous studies and also identifies new features. Notably, we find elevated Vp/Vs ratios in the crystalline crust of regions such as coastal Oregon, suggesting potential mafic composition or fluid presence. Shallower Moho depth in the Basin and Range indicates reduced crustal support to the topography. The uppermost mantle Vs, averaging 5 km below Moho, aligns well with the Pn-derived Moho temperature map, offering the potential of using Vs as an additional constraint to Moho temperature and crustal thermal properties.

We use seismic ambient noise recorded by dense ocean bottom nodes (OBNs) in the Gorgon gas field, Western Australia, to compute time-lapse seafloor models of shear-wave velocity. The extracted hourly cross-correlation (CC) functions in the frequency band 0.1 – 1 Hz contain mainly Scholte waves with very high signal to noise ratio. We observe temporal velocity variations (dv/v) at the order of 0.1% with a peak velocity change of 0.8% averaged from all station pairs, from the conventional time-lapse analysis with the assumption of a spatially homogeneous dv/v. With a high-resolution reference (baseline) model from full waveform inversion of Scholte waves, we present an elastic wave equation based double-difference inversion (EW-DD) method, using arrival time differences between the reference and time-lapsed Scholte waves, for mapping temporally varying dv/v in the heterogeneous subsurface. The time-lapse velocity models reveal increasing/decreasing patterns of shear-wave velocity in agreement with those from the conventional analysis. The velocity variation exhibits a ~24-hour cycling pattern, which appears to be inversely correlated with sea level height, possibly associated with dilatant effects for porous, low-velocity shallow seafloor and rising pore pressure with higher sea level. This study demonstrates the feasibility of using dense passive seismic surveys for quantitative monitoring of subsurface property changes in the horizontal and depth domain.

The Paleocene-Eocene Thermal Maximum (PETM) was a transient global warming event recognised in the geologic record by a prolonged negative carbon isotope excursion (CIE). The onset of the CIE was the result of a rapid influx of 13C-depleted carbon into the ocean-atmosphere system. However, the mechanisms required to sustain the negative CIE remains unclear. Previous studies have identified enhanced mobilisation of petrogenic organic carbon (OCpetro) and argued that this was likely oxidised, increasing atmospheric carbon dioxide (CO2) concentrations after the onset of the CIE. With existing evidence limited to the mid-latitudes and subtropics, we determine whether: (i) enhanced mobilisation and subsequent burial of OCpetro in marine sediments was a global phenomenon; and (ii) whether it occurred throughout the PETM. To achieve this, we utilised a lipid biomarker approach to trace and quantify OCpetro burial in a global compilation of PETM-aged shallow marine sites (n = 7, including five new sites). Our results confirm that OCpetro mass accumulation rates (MARs) increased within the subtropics and mid-latitudes during the PETM, consistent with evidence of higher physical erosion rates and intense episodic rainfall events. The high-latitude sites do not exhibit distinct changes in the organic carbon source during the PETM. This may be due to the more stable hydrological regime and/or additional controls. Crucially, we also demonstrate that OCpetro MARs remained elevated during the recovery phase of the PETM. Although OCpetro oxidation was likely an important positive feedback mechanism throughout the PETM, we show that this feedback was both spatially and temporally variable.

Specification and forecast ionospheric parameters, such as ionospheric electron density (Ne), have been an important topic in space weather and ionosphere research. Neural networks (NNs) emerge as a powerful modeling tool for Ne prediction. However, heavy manual attention costs time to determine the optimal NN structures. In this work, we propose to use neural architecture search (NAS), an automatic machine learning method, to address this problem of NN models. NAS aims to find the optimal network structure through the alternated optimization of the hyperparameters and the corresponding network parameters. A total of 16-year data from Millstone Hill incoherent scatter radar (ISR) are used for NN models. One single-layer NN (SLNN) model and one deep NN (DNN) model are trained with NAS, namely SLNN-NAS and DNN-NAS, for Ne prediction and compared with their counterparts without NAS from previous studies, denoted as SLNN and DNN. Our results show that SLNN-NAS and DNN-NAS outperformed SLNN and DNN, respectively. NN models can reveal more finer details than the empirical ionospheric model developed using traditional data fitting approaches. DNN-NAS yields the best prediction accuracy measured by quantitative metrics and rankings of daily pattern prediction. The limited improvement of NAS is likely due to the network complexity and the limitation of fully connected NN without a memory mechanism.

The International Reference Ionosphere (IRI) model is widely used in the ionospheric community and considered the gold standard for empirical ionospheric models. The development of this model was initiated in the late 1960s using the FORTRAN language; for its programming approach, the model outputs were calculated separately for each given geographic location and time stamp. The Consultative Committee on International Radio (CCIR) and International Union of Radio Science (URSI) coefficients provide the skeleton of the IRI model, as they define the global distribution of the maximum usable ionospheric frequency foF2 and the propagation factor M(3000)F2. At the U.S. Naval Research Laboratory (NRL), a novel Python tool was developed that enables global runs of the IRI model with significantly lower computational overhead. This was made possible through the Python rebuild of the core IRI component (which calculates ionospheric critical frequency using the CCIR or URSI coefficients), taking advantage of NumPy matrix multiplication instead of using cyclic addition. This paper explains in detail this new approach and introduces all components of the PyIRI package.

A document by William Edmund Ward. Click on the document to view its contents.

The major objective of this study is to decode the “Wow!” signal - converting it into textual content. A novel feature of the present work consists in a unique approach. When considering the recorded Wow! signal not only the 6 signals received on channel #2 are taken into account, but also total content of the 12 signals received on six different channels as a result of which we got an infographic image. In this study, an algorithmic method was used. The interpretation of the infographic image includes the content similar to the brief characteristic of the solar system. Hence, our cosmic address in this infinite universe is fixed. The distance from the Sun to one of the celestial objects is also recorded (19.9 light-years). The researchers from the Big Ear radio telescope report that at the moment of picking up the signal, the scanning of the sky took place towards the constellation Sagittarius. The binary pair – J. Herschel 5173 AB – is located at approximately the same distance in the indicated direction. According to the calculations of astronomers, the mentioned binary pair of stars and the Sun are approaching each other. The infographic representation of the radio signal displays the same information.Therefore, a rare phenomenon - the stellar convergence can be considered as the motivation for beginning written communication. Thus, we arrived to the conclusion that the aforementioned binary pair may be viewed as a potential star the alien Wow! signal had come from.

The heavily faulted Martian terrains of Ceraunius Fossae and Tractus Fossae, south of the Alba Mons volcano, have previously only been considered as parts of larger tectonic studies of Alba Mons, and the complexity of the faulting remains consequently unclear. As these terrains are in midst of the large Tharsis’ volcanoes, the study of their surface deformation has the potential to help unravel the volcano-tectonic deformation history associated with the growth of Tharsis, as well as decipher details of the responsible magma-tectonic processes. In this study, we distinguish between faults and collapse structures based on image and topographic evidence of pit-crater chains. We mapped ~12,000 faults, which we grouped into 3 distinct fault groups based on orientation, morphology, and relative ages. These show a temporal evolution in the mapped fault orientations from NE to NS to NW, with associated perpendicular stress orientations. Collapse features were also mapped and categorized into 4 different groups: pit-crater chains, catenae, u-shaped troughs and chasma. Examining the 4 collapse structures reveals that they are likely 4 different steps in the erosional evolution of pit-crater chains. Together this revealed a structural history heavily influenced by both local (radial to Alba Mons, Pavonis Mons and Ascraeus Mons) and regional (Tharsis radial) lateral diking, and vertical diking from a proposed Ceraunius Fossae centred magma source. This, along with an updated crater size-frequency distribution analysis of the unit ages, reveals a highly active tectonic and magmatic environment south of Alba Mons, in the Late Amazonian.