Using the two-way coupled magnetohydrodynamics (MHD) withembedded kinetic physics model, we perform a substorm event simulation to study the electron energization phenomena in Bursty Bulk Flow (BBF) events. The simulation results along a Magnetospheric Multiscale (MMS) satellite trajectory show good agreement with observations. Detailed simulation results of a 4-minute interval show the electron velocity distribution functions (VDFs) evolution during BBFs. The electrons exhibit significant energization after the arrival of the BBF. More specifically, when the dipolarization front is near $-15\,R_E$, electrons from the rear end of the BBF to the flux pileup region (FPR) of the BBF demonstrate significant energization. We track the pitch angle distributions (PADs) for electrons at the FPR following the propagation of the BBF. The PADs for electrons show energy dependent features: lower energy electrons exhibit “two-hump” PAD and higher energy electrons demonstrate “pancake” distribution indicating the betatron acceleration mechanism at the FPR.

With the development of small satellites, planar array has become a promising configuration in the very low frequency (VLF: 3–30 kHz) space-borne transmitting system in the near future. In this manuscript, a theory towards a VLF planar array immersed in magnetized plasmas is proposed, which contains both closed-form expressions and numerical techniques. The kernel function for the planar array is derived from the analytical expression of the field radiated by a point current source, and the integral equation is set up based on the boundary condition. By introducing the ten-term form of current distribution and the digital filter of fast Hankel transformation, the matrix of the integral equation is solved with considerable accuracy to determine the current distribution and fed-point impedance under various parameters. With the help of the induced EMF method, the mutual coupling impedance is also determined and discussed. The correctness and the accuracy of the proposed method are shown by comparing the computed result with earlier work and the simulated result by EM simulation software CST Studio Suite.

High-resolution bathymetric and seismic reflection data reveal the presence of diverse sand waves in the offshore wind farm area of the Taiwan Strait. Five consecutive surveys examined the characteristics and temporal changes of sand waves near the Zhuoshui River, the largest river in Taiwan with high sediment yield. The characteristics of sand waves are quantified, and their migration significantly affects seabed levels, with a maximum elevation difference of 6.70 m and a migration distance of 89.40 m observed from April 2016 to July 2018. The seabed evolution shows uneven patterns over various time scales-approximately 27 months, two months, and two weeks-reflecting changes in sand wave migration. The study examines sand wave formation related to currents and large-scaled bedform topography, considering seasonal variations, tidal cycles, and extreme events. A time-to-depth sound velocity function was derived using seismic data for the offshore area. By integrating sequence stratigraphy with high-resolution seismic profiles, it was found that sand waves migrate above a basal surface 5 to 15 m below the seabed. A four-stage model is proposed to explain sand wave evolution and depositional changes since the Last Glacial Maximum, aiding in evaluating geo-risk for offshore wind farm constructions.

Applying a nested watershed framework to concentration-discharge (cQ) relationships offers valuable insights into the spatial and temporal variability of solute transport. We examined nitrate-N cQ relationships at two nested spatial scales in a small agricultural watershed using three years of 30-minute data, analyzing both composite records and individual storm events. Metrics including the flushing index (FI), hysteresis index (HI), cQ slope (b) and the ratio of coefficients of variation for concentration and discharge (CVC/CVQ) were used to compare event-scale and composite cQ patterns, evaluate the influence of metric choice, assess spatial consistency during 97 concurrent storm events, and identify controls on inter-event variability. Composite-scale analyses showed nitrate-N enrichment, while event-scale patterns were dominated by dilution or chemostasis, depending on the metric used. Across scales, nitrate-N enrichment on the falling limb, or post-storm enrichment, emphasized the need for an additional metric to characterize falling limb dynamics. Spatial consistency in cQ behavior varied by metric: CVC/CVQ and FI showed higher consistency during concurrent storms, while cQ slope and HI often revealed contrasting patterns. Controls on event-scale cQ patterns varied across spatial scales. Indicators of seasonality, antecedent moisture, and storm event magnitude influenced the FI and cQ slope only at the subcatchment, while the HI was primarily driven by storm magnitude across scales. These findings highlight the importance of scale, both temporal and spatial, and metric choice in interpreting nitrate-N export dynamics.

Tidewater glaciers contribute significant amounts of freshwater to the global ocean, with the mass input expected to increase in response to a rapidly warming climate. Mass loss at a tidewater glacier terminus, known as frontal ablation, is the sum of ice loss due to both submarine melting and iceberg calving. Despite the rapid observed changes to these tidewater glaciers, the specifics of the dynamic processes occurring at the submarine ocean-ice boundary are highly unconstrained due to the lack of near-terminus observations. Often, near-glacier water conditions and circulation are approximated with observations from further down-fjord, and even the basic shape of the underwater terminus is assumed. However, the terminus shape and near-glacier conditions do matter, as they control where submarine melting occurs and how that melt affects calving frequency and magnitude. Here, we aim to transform our knowledge of subsurface geometries at tidewater glacier termini since only a handful of systems to date have been studied, and we lack a systematic comparison across different environmental and glacier conditions. We process and analyze 30+ raw multibeam sonar scans of submarine termini of tidewater glaciers in Greenland, largely from NASA’s Oceans Melting Greenland 2015 and 2016 field seasons, in addition to multiple passes over several years from Leconte Glacier in Alaska. With the processed data, we categorize the terminus morphologies according to their spatial features, e.g., the angles of overcutting or undercutting, the degree of heterogeneity across the glacier face, the location of any existing subglacial discharge features, and the length scales of persistent vertical and horizontal features. We then compare the resulting terminus morphologies and ocean conditions, e.g., CTD profiles of fjord hydrography, ice flux, grounding line depth, timing in terms of advance/retreat, and so on. By constraining the physical characteristics of the unseen ocean-ice boundary and driving environmental forces, we hope to improve parameterizations of frontal ablation for tidewater glaciers and test whether the simplified terminus geometries used currently are justified.

Tsunamis pose a threat to the coastal communities. Typically, tsunami hazards are estimated using computationally expensive numerical models, often impractical for rapidly determining the expected impacts and community response. To quickly estimate tsunami hazards, we present a data-driven transfer function method to reconstruct onshore hazard curves from offshore hazard curves with corresponding topographic data. The transfer function is approximated by a type of artificial neural network called a Variational Autoencoder (VAE). The VAE first encodes input data, including offshore hazard curves and topographic data. Once encoded, the data is represented by a normal distribution of latent variables. The VAE then uses a trained decoder to sample the distribution created by the latent variables and reconstruct a continuous hazard function at the onshore location. As a probabilistic distribution represents the encoded values, the resulting hazard curve output has inherent stochasticity. Thus, model variance can be found through many realizations of the transfer function for a single set of inputs. We developed a set of transfer functions to accurately predict the onshore hazard curves for flow depth, Froude number (dimensionless velocity), and dimensionless momentum flux. We construct two flow depth transfer functions, with one version utilizing an ”anchor point” taken from established site-specific numerical modeling data. The VAEs to predict velocity and momentum flux incorporate an approach that leverages condensed topographic information around the point of interest (topographic rings). Overall, the transfer function method efficiently estimates onshore tsunami hazard curves and model uncertainty quantification without requiring computationally expensive numerical simulations.

The interpretation of landform responses to environmental forcing and change is important for improving understanding natural hazards and climate change impacts, yet is dependent on the accuracy of methods and data used for observing and detecting geomorphic processes and geomorphic responses. Despite methodological advances in detection of geospatially statistically significant change, new methods and lack of consistent reporting by authors continue to confound how various sources and levels of uncertainty are handled when identifying and calculating what is real change (i.e., erosion and deposition across space and time in a landscape). This presents challenges for identifying key geomorphic responses, both quantitative (e.g., sediment budget responses) and qualitative (e.g., patterns and locations of change), critical for morphodynamic research, ecosystem restoration, and natural hazards assessments that use sequential digital elevation models (DEMs). This study tests the performance of various popular change detection methods using repeat, high resolution, UAS-derived datasets from 2019-2023 at a dynamic beach-dune setting at the Oceano Dunes, California. This work identifies the ability of existing change detection methods to detect real change or noise in coastal dune landscapes, although the methods and findings can be applied to other environments. We examine application of the raster-based Geomorphic Change Detection (GCD) tool (Wheaton et al., 2010), a GCD Fuzzy Inference System variation, CloudCompare M3C2 (Lague et al., 2013), and a probability map (Wernette et al., 2020) to the same 8 datasets to identify variations amongst multiple methods of change detection. The results identify the importance of method selection and how geomorphic processes and responses are represented by each method. The representation of landscape scale sediment movement is important to aid management decisions when site specific goals are highly dependent on the geomorphic responses observed, such as in resilience assessments or restoration effectiveness. This work addresses the continuing need to detect real change with the transparent reporting of data collection, processing methods, and uncertainty assessments within geomorphic change tools by comparing and replicating existing methods.

Since the 2010 launch of Cryosat-2, a new generation of altimeters, referred to as SAR altimetry, has emerged and partially replaced the previous conventional altimeters known as LRM altimetry. A surface slope correction has been previously developed for LRM altimetry. However, the differences in the way the two altimeters work, and in particular their radar footprint, make LRM altimeter slope correction inapplicable to SAR altimetry. Thus, in this paper, a slope correction model is provided for SAR altimetry, derived from the LRM-based approach. The shape of the SAR footprint induces that height correction depends on each satellite mission. Consequently, a generic method allowing to generate global maps of height correction for distinct missions is provided. The maps are computed for the Sentinel-6A mission and the importance of correcting this effect for SAR altimetry is highlighted by studying the sea surface height anomaly biases between Jason-3 LRM altimetry and Sentinel-6A SAR altimetry during their tandem phase. Finally, it is shown that applying the slope correction to Sentinel-6A SAR mode sea surface height anomaly measurements enhances their correlation with the latest MSS model, reducing the root mean square error between the sea surface height anomaly and the MSS model by up to 1 cm.

Seismic faults are known to exhibit a high level of spatial and temporal complexity, and the causes and consequences of this complexity have been the topic of numerous research works in the past decade. In this paper, we investigate the origins and the structure of this complexity by considering a numerical model of laboratory earthquake experiment, where we introduce a statistically homogeneous fault but allow it to evolve spontaneously to its natural level of complexity. This is achieved by coupling the elastic deformability of the off-fault medium (and therefore allowing for heterogeneous stress fields to develop) and the discrete degradation and gouge formation at the fault plane (and therefore allowing for structural heterogeneity to develop). Numerical results show the development of persistent stress, damage, and gouge thickness heterogeneities, with a much larger variability in space than in time. Strong positive correlations are found between these quantities, which suggest a positive feedback between local normal stress and damage rate, only mildly mitigated by the mobility of the granular gouge in the interface. For a wide range of confining stresses, after a sufficient number of seismic cycles, the fault reaches a state of established disorder with a constant quadratic roughness, a certain amount of periodicity at the millimetric scale, and a self-affine character for smaller spatial scales. Both the typical height-to-wavelength ratio of geometrical asperities and the Hurst exponent of along-slip stress profiles are in good agreement with previous field or lab estimates.

A document by Joseph Nicholas. Click on the document to view its contents.

Understanding the impacts of high-resolution ocean model provides valuable insights for future research. However, the outcomes of sea surface state changes in both the tropics and mid-latitudes remain unclear, and initialized seasonal forecasts have not been studied extensively. This study investigates the impact of ocean model resolution with the first long-term hindcast experiment of an eddy-resolving (0.1°) ocean model used for global seasonal forecasting. We show that using the high-resolution ocean model significantly changes boreal winter jet streams in the atmosphere, based on the comparison of 30-year hindcasts with ocean resolutions ranging from 1° to 0.1° for the Japan Meteorological Agency/Meteorological Research Institute Coupled Prediction System version 3. In boreal winters, the cold sea surface bias in the equatorial Pacific is significantly reduced, leading to an equatorward shift in the intertropical convergence zone and enhanced convective activity in the western equatorial Pacific. The subtropical jet shifts southward due to the intertropical convergence zone shift and the weakening of equatorward propagation of mid-latitude atmospheric eddies. The enhanced convective activity in the tropics has a remote influence in the mid-latitudes, significantly reducing the upward eddy propagation of zonal wavenumber 1. Sea surface warm-up in the mid-latitudes partially cancels the reduction impact by enhancing the zonal wavenumber 2. Overall, the polar night jet accelerates due to the reduced supply of eddy forcing.

Highlights • Synthetic Rating Curve (SRC) adjustment factors for the NHDPlus river network across the United States are predicted using explainable Machine Learning models. • The predicted flood inundation maps for Hurricane Matthew show a mean improvement of 18-20% after SRC adjustment. • A 14% mean improvement is found in the percentage of buildings hit by the predicted flood inundation maps after the SRC adjustment.

Using three-dimensional MHD simulations, we explore the stability of magnetotail configurations that include a local enhancement of $B_z$ (a “$B_z$ hump”). We focus on configurations that were previously found to be unstable in 2-D, neglecting cross-tail ($y$) variations as well as a cross-tail magnetic field component $B_y$.\, but approached final 2-D stable states. Not surprisingly, the 2-D unstable configurations were also found unstable in 3-D, developing 3-D structure after an initial rise as in 2-D. This is consistent with the fact that the selected $B_z$ hump configurations are characterized also by a local tailward decrease of field line entropy, which has been found to govern ballooning/interchange (B/I) instability \cite{schi04}. The evolution of the maximum electric field of the unstable 3-D modes showed an early exponential growth, which was only modestly faster than the 2-D mode. This might suggest that the unstable ballooning regime extends from $k_y \to \infty$ (proper ballooning modes) over finite $k_y$ even to $k_y \to 0$, at least for some equilibria. When the 3-D modes had evolved they grew significantly faster than the 2-D modes. This was associated with an evolution into several narrow beams. The 3-D modes did not approach stable final configurations. The final 2-D stable configurations approached from the unstable ones were found to be unstable in 3-D. These findings are again consistent with the fact that the 2-D evolution, governed by ideal MHD, did not alter the characteristics of the entropy function.

Biharmonic (or higher order) mixing of potential vorticity (PV) combines biharmonic mixing of momentum and isopycnal thickness. It is applied in a realistic eddy-permitting model of the North Atlantic Ocean by a simple modification of the standard scheme for harmonic isopycnal thickness mixing or bolus velocity. The effect of biharmonic PV mixing is compared to the one of biharmonic mixing of momentum only. Results are similar except for more realistic mixed layer depths using PV mixing. It is also shown how harmonic isopycnal thickness mixing with negative definite dissipation representing an energy source, in short negative bolus velocity, can be implemented in existing ocean models by another simple modification of the standard scheme. While negative bolus velocity injects available potential energy to the model, previous backscatter formulations using negative definite harmonic momentum mixing inject kinetic energy by sharpening velocity gradients. Both backscatter formulations, combined with the more scale selective dissipation by biharmonic PV mixing and a subgrid-energy budget to control the energetics, reproduce previously reported positive effects by backscatter, such as a more realistic north-west corner of the North Atlantic Current and Gulf Stream path, but negative bolus velocity works better in our configuration. Furthermore, eddy production rates by baroclinic instability are enhanced by negative bolus velocity, but reduced to zero by backscatter using negative definite harmonic momentum mixing.

We present a statistical study of large magnetic field vector residuals between Swarm observations and the 13th generation International Geomagnetic Reference Field (IGRF-13) model under quiet to weakly disturbed geomagnetic conditions. Since the vast majority of data are taken during relatively quiet geomagnetic conditions, statistics of these large residuals are important for estimating potential errors for satellite operation when using IGRF-13 as reference, as well as for magnetosphere-ionosphere-thermosphere (MIT) studies. Residuals with magnitude of vector differences between Swarm observations and IGRF-13 estimations larger than 300 nT under Dst >-50 nT are studied from 2014 to 2020. All large residuals appear in the high-latitude auroral zone region peaking around 70° (-70°) magnetic latitude (MLAT) in the northern hemisphere (southern hemisphere) but there is also a secondary occurrence peak just below 80° (-80°) MLAT. However, the two hemispheres show clear asymmetries in the magnetic longitude (MLON) distribution where both hemispheres show high concentration of large residuals around the geographic poles. Since the two geographic poles are located at different geomagnetic locations and polar satellite’s orbits give rise to highly biased number of observations around the geographic poles, it results in high occurrence of large residuals around the geographic poles but a decrease in occurrence rate with respect to the total number of measurements. Identifying the interhemispheric asymmetries resulting from the asymmetry of the geographic poles with respect to the magnetic poles under relatively quiet geomagnetic conditions is helpful for a better understanding of interhemispheric asymmetry for the MIT system.

During the 21-22 January 2005 magnetic storm, the FAST satellite observed warm (< few keV) ions in discrete energy bands on the dayside at ~3000 km altitude for more than 6.5 hours. We suggest that the ionospheric energy-banded ions represent the low-altitude edge of the warm plasma cloak observed simultaneously by magnetospheric satellites. This is a clear example of the multi-species ion energy bands (10 eV to several keV) observed during strong magnetic storms by the FAST satellite, stretching from the diffuse auroral region to the plasmapause with lifetimes up to 12 hours. The close association of these energy-banded ions with magnetic storms, their broad latitudinal extent, and the presence of multiple ion species in the same energy band, rather than at the same velocity, indicate that this is a distinct phenomenon from other types of energy-banded ions. During the 21-22 January 2005 magnetic storm, the dayside ion energy band structures, centered at 10 eV (H+), 40 eV (H+ and He+), and 160 eV (H+, He+, and O+), were consistent with a “time-of-flight and velocity filter” formation process acting on a near-cusp, impulsive outflow of a < 200 eV multi-species ion-source population, poleward and in the same hemisphere as FAST. Understanding the sources and dynamics of warm energy-banded ions and their linkage to the warm plasma cloak is important because during superstorms these ions are transported deep into the plasmasphere to L values as low as L~1.2 in the dawn sector, significantly altering the energetics of the mid-latitude ionosphere

Occupying the region between the ocean surface and seafloor, the pelagic ecosystem contains the largest portion of the ocean’s biomass. The lack of observations in this region has resulted in limited understanding of ecosystem variability and dynamics. In July 2022, NOAA Ocean Exploration utilized the remotely operated vehicles (ROVs) Deep Discoverer and Seirios to conduct two water column dives over the Mid-Atlantic Ridge North of the Azores (MARNA) marine protected area and the Azores Plateau (AP), the first water column explorations for this region and some of the few dives that explore the benthic boundary layer. During these dives, horizontal transects were conducted at relatively consistent depths throughout the water column (~300-1800 m) and ROV video was annotated. Utilizing the annotations of the visible pelagic fauna to the lowest taxonomy level at first appearance for each transect, Shannon-Wiener biodiversity indices, species abundance, and species evenness were derived, providing critical insight on pelagic fauna inventory and behavior. These analyses showed no significant change in abundance between equivalent taxa at different transect depths; however, there was a significant difference in abundance between the two dive sites. Results suggested no significant difference between species richness of the two dive sites and biodiversity was not significantly different within the deep scattering layer. These insights allow for initial inferences about the variability of pelagic fauna in the vertical dimension from the mesopelagic to bathypelagic zone along with variability between the dive sites that can be compared with the results of future water column observations.

The filling process of large hydropower reservoirs is an often-overlooked process that can attract most of the attention and criticisms of a dam’s lifetime. Understanding what drove past filling efforts and exploring trade-off solutions is therefore critical for regions where hydropower development is flourishing. Here, we focus on the filling strategies of the Upper Mekong hydropower system, one of the largest mega-dam cascades (capacity ≥ 1,000 Mm3) built in the 21st century. Our ex-post analysis for the period 2008-2016 reveals that the historical filling strategies have largely prioritized electricity production at the expense of downstream hydrological alterations—peak discharge decreased by more than 20% during the filling of the largest dams. On the flipside, there are tangible opportunities for designing better trade-off solutions that would be appealing to all riparian countries. Key to this step is the coordination of the filling process of the largest storage facilities.