Article
Mechanics
Thomas Pahtz, Orencio Duran
Summary: We use a numerical model to simulate non-suspended sediment transport across a wide range of particle-fluid density ratios. Based on simulations and experiments, we derive simple scaling laws for aeolian transport and find that the cessation threshold is controlled by only one dimensionless parameter. Only one existing model is somewhat consistent with the data, but it fails to capture the grain size dependence of the transport rate, indicating a lack of understanding in this area.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Geosciences, Multidisciplinary
M. Llena, R. J. Batalla, M. W. Smith, D. Vericat
Summary: The study found that badlands do not always control the export of sediments, with seasonal sediment production sometimes exceeding the amount exported. The channel network plays a key role in controlling pulses of sediment transfer, depending on whether the drainage network acts as a sediment sink or source.
Article
Geosciences, Multidisciplinary
Santiago J. Benavides, Eric Deal, Matthew Rushlow, Jeremy G. Venditti, Qiong Zhang, Ken Kamrin, J. Taylor Perron
Summary: The study discusses how sediment transport near the threshold of grain motion is influenced by rare transport events, making it difficult to calibrate sediment transport laws and define a clear threshold for grain entrainment. The research presents a model to capture this intermittency and utilize noisy statistics of sediment transport to predict the sediment entrainment threshold and fluid stress variations. The findings suggest strategies for improving measurements and predictions of sediment flux and hint at potential changes in the sediment transport law near the threshold of motion.
GEOPHYSICAL RESEARCH LETTERS
(2022)
Article
Physics, Fluids & Plasmas
Sualeh Khurshid, Diego A. Donzis, Katepalli R. Sreenivasan
Summary: Recent work has shown that the power laws in derivative statistics in turbulence can occur at lower microscale Reynolds numbers around 10, and exhibit the same exponents as those at very high Reynolds numbers. In this study, we use well-resolved direct numerical simulations to confirm this finding under different initial conditions and forcing mechanisms. Furthermore, we demonstrate that transverse velocity gradients have larger scaling exponents than longitudinal moments, indicating their higher intermittency.
Article
Geosciences, Multidisciplinary
Sandesh Kamath, Yaping Shao, Eric J. R. Parteli
Summary: The study investigates the transport of wind-blown sand over sparsely sand-covered soils through numerical simulations and establishes a quantitative model for sand transport rate variation with wind shear velocity. The research provides important insights for modeling Aeolian transport under low sand availability conditions.
GEOPHYSICAL RESEARCH LETTERS
(2022)
Article
Mechanics
P. Debue, V. Valori, C. Cuvier, F. Daviaud, J. -M. Foucaut, J. -P. Laval, C. Wiertel, V. Padilla, B. Dubrulle
Summary: By studying the three-dimensional structure of turbulent velocity fields around extreme events of local energy transfer in the dissipative range, it was found that most extreme events of local energy transfer correspond to the vortex stretching topology, with large velocity and vorticity norms, and the structure of the vorticity field around these events agrees with previous observations.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Environmental Sciences
Veronica Carrillo, John Petrie, Luis Timbe, Esteban Pacheco, Washington Astudillo, Carlos Padilla, Felipe Cisneros
Summary: The study introduced an experimental procedure to determine bedload sediment transport rates in channels with high gradients and coarse sediment. Through laboratory experiments, a mathematical bedload transport model was established, showing agreement with some models in existing literature. The closest match was found with models developed for steep slopes considered in the study.
Article
Engineering, Civil
Amirreza Ghesemi, James F. Fox
Summary: This study investigates the scaling and implications of the -1 power region of the turbulence spectrum, which is responsible for energy production. Experiment results show that this region accounts for 42% of the turbulence kinetic energy in open-channel flows. The energy of this production region scales similarly for different gravel bed types and can be predicted using logarithmic and exponential equations. The study also reveals that the low and high wavenumber boundaries of this region have similar functions, suggesting a common control mechanism.
JOURNAL OF HYDRAULIC ENGINEERING
(2023)
Article
Geography, Physical
J. K. Haschenburger
Summary: This study reports fractional transport rates in the lower San Antonio River, Texas, and finds that the range of transported sizes generally expands as flow magnitude increases, while the proportion of bedload grain sizes relative to those in the bed material may approach similarity conditions.
Article
Geosciences, Multidisciplinary
Jiyong Lee, Arvind Singh, Michele Guala
Summary: Bedforms appear in various shapes and sizes under strong shear flow, and can be observed in data from submarine canyons, rivers, deserts, and planetary bodies. The two main characteristics of bedforms are the ability to transport particles collectively and to generate form drag, which increases flow resistance. These mechanisms compete with each other and result in slower migration of larger bedforms. In an experiment using a large open channel flow facility, hierarchies of fluvial bedforms were generated and measured under equilibrium conditions. The corresponding migration velocity and mass flux contributions were quantified in terms of wave number and frequency. The experimental results were compared with theoretical models and showed that ripples or dunes reach an equilibrium state when drag partitioning ensures sufficient frictional drag for sediment transport and low enough form drag to allow migration of the largest bedforms. This mechanism is believed to restrict the growth of bedforms when sediment supply is not the limiting factor.
JOURNAL OF GEOPHYSICAL RESEARCH-EARTH SURFACE
(2023)
Article
Geology
Alessio Radice
Summary: The dynamics of river bedforms were studied through a laboratory experiment, revealing oscillation patterns of key properties of sediment transport at the measuring location and demonstrating multi-scale propagation. These results have implications for bedform analysis, live-bed scour processes, and quantifying sediment transport rates using surrogate quantities.
Article
Engineering, Environmental
Yu-Ying Huang, Christina W. Tsai
Summary: Eddies have different impacts on the motion of particles within the turbulence boundary layer depending on their length and velocity scales. Attached eddies, particularly the type-A eddies directly attached to the wall, play a significant role in the turbulent kinetic energy and Reynolds shear stresses in the turbulence boundary layer. This study combines the attached eddies hypothesis with the stochastic diffusion particle tracking model to simulate the transport of suspended sediment particles under the influence of attached eddies.
STOCHASTIC ENVIRONMENTAL RESEARCH AND RISK ASSESSMENT
(2023)
Article
Geosciences, Multidisciplinary
Santiago J. Benavides, Eric Deal, Jeremy G. Venditti, Ryan Bradley, Qiong Zhang, Ken Kamrin, J. Taylor Perron
Summary: Near the threshold of grain motion, sediment transport is intermittent, with rare bursts and long periods of low transport. The origin of intermittency is found in the velocity distributions of rolling grains, rather than the activity of grains. Incorporating this type of intermittency into sediment transport models can lead to improved predictions of sediment flux.
GEOPHYSICAL RESEARCH LETTERS
(2023)
Article
Engineering, Marine
Tarandeep S. Kalra, Steve E. Suttles, Christopher R. Sherwood, John C. Warner, Alfredo L. Aretxabaleta, Gibson R. Leavitt
Summary: This study estimated asymmetric wave shapes using two methods and compared the sediment transport results. The parameterized waveform had 25% higher bedload transport compared to the direct waveform, primarily due to the parameterized waveform not accounting for negative skewness.
JOURNAL OF MARINE SCIENCE AND ENGINEERING
(2022)
Article
Engineering, Marine
Xuguang Chen, Xian Zhang, Xixi Liu, Fengpeng Zhang, Jiahao Yan, Huapeng Wang
Summary: This study investigates the characteristics of pile scour in consolidated silt (CS) and compares it with loose silt. The results show that the scour depth and radius in CS are smaller than those in loose silt, but the slope angle in CS is larger and the scour depth is inversely proportional to the dry density. Existing scour equations cannot predict the scour depth in CS accurately.
Article
Meteorology & Atmospheric Sciences
Clement Guilloteau, Antonios Mamalakis, Lawrence Vulis, Phong V. V. Le, Tryphon T. Georgiou, Efi Foufoula-Georgiou
Summary: Spectral PCA (sPCA) identifies organized spatio-temporal patterns within specific frequency bands and extracts dynamical modes, but faces issues like high sensitivity to noise and overfitting. To address this, a rotated spectral PCA (rsPCA) method is proposed to optimize the spatial regularity of eigenvectors, achieving more reliable results.
JOURNAL OF CLIMATE
(2021)
Article
Meteorology & Atmospheric Sciences
Abby Stevens, Rebecca Willett, Antonios Mamalakis, Efi Foufoula-Georgiou, Alejandro Tejedor, James T. Randerson, Padhraic Smyth, Stephen Wright
Summary: This study presents a predictive model based on a graph-guided regularizer, which reduces the effective dimensionality of the problem and identifies the most predictive features without specifying them a priori. By using large ensemble simulations from a climate model to construct the regularizer, the structural uncertainty in the estimation is reduced.
JOURNAL OF CLIMATE
(2021)
Article
Meteorology & Atmospheric Sciences
Clement Guilloteau, Efi Foufoula-Georgiou, Pierre Kirstetter, Jackson Tan, George J. Huffman
Summary: This study evaluates five high-resolution multisatellite precipitation products using space-time Fourier spectral analysis, revealing that all products show deficiencies in capturing the spatial organization and dynamics of precipitation systems, appearing excessively "smooth." IMERG-Final product demonstrates superior ability in resolving the space-time dynamics of precipitation at scales down to 200 km and 4 hours.
JOURNAL OF HYDROMETEOROLOGY
(2021)
Article
Multidisciplinary Sciences
Amy T. Hansen, Todd Campbell, Se Jong Cho, Jonathan A. Czuba, Brent J. Dalzell, Christine L. Dolph, Peter L. Hawthorne, Sergey Rabotyagov, Zhengxin Lang, Karthik Kumarasamy, Patrick Belmont, Jacques C. Finlay, Efi Foufoula-Georgiou, Karen B. Gran, Catherine L. Kling, Peter Wilcock
Summary: Despite decades of efforts to reduce nutrient and sediment export from agricultural fields, water quality in intensively managed agricultural landscapes remains highly degraded. Recent analysis shows that current conservation efforts are not enough to reverse water degradation, and a more integrated approach to water quality management is needed. Fluvial wetlands are found to be the most cost-effective management action to reduce nitrate and sediment loads, but interagency cooperation and watershed scale planning are necessary for substantial improvements in water quality.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
(2021)
Article
Environmental Sciences
Zeinab Takbiri, Lisa Milani, Clement Guilloteau, Efi Foufoula-Georgiou
Summary: This research found that under shallow snow cover and low cloud liquid water content conditions, light snowfall can only be detected at 166 GHz frequency, while signals can also be detected at 89 GHz for higher snowfall rates. When snow cover depth exceeds 200 kg m(-2) and cloud liquid water content is higher, the emission from increased liquid water content in snowing clouds becomes the only stronger surrogate microwave signal of snowfall than at the 166 GHz frequency. In high latitude areas above 60 degrees N, snowfall microwave signals could not be detected without considering prior data on snow cover depth and cloud liquid water content.
Article
Geosciences, Multidisciplinary
Lawrence Vulis, Alejandro Tejedor, Ilya Zaliapin, Joel C. Rowland, Efi Foufoula-Georgiou
Summary: Understanding the response of thermokarst lakes on arctic river deltas to rapid warming is crucial for predicting changes in carbon storage and fluxes in vulnerable environments. Research found distinct size distributions and climate trends for perennial lakes and ephemeral wetlands on 12 arctic deltas, with lakes showing a decreasing trend in size with warmer temperatures attributed to thicker permafrost preserving larger lakes.
GEOPHYSICAL RESEARCH LETTERS
(2021)
Article
Environmental Sciences
Simon Michael Papalexiou, Chandra Rupa Rajulapati, Konstantinos M. Andreadis, Efi Foufoula-Georgiou, Martyn P. Clark, Kevin E. Trenberth
Summary: The study evaluated the performance of multiple climate models in reproducing drought characteristics, finding that many simulations have low errors, but no single model consistently outperformed others globally. The research emphasizes the need to probabilistically evaluate climate model simulations to pinpoint model weaknesses and identify the best-performing models for impact assessments.
Article
Geochemistry & Geophysics
Yevgeniy Kovchegov, Ilya Zaliapin, Efi Foufoula-Georgiou
Summary: This paper reviews the appearance and parameterization of scaling laws in complex systems, particularly focusing on hierarchical systems conceptualized by tree graphs. The recently formulated theory of random self-similar trees provides a suite of results on scaling laws between different attributes, which are of great significance in the study of extreme events and hazards.
SURVEYS IN GEOPHYSICS
(2022)
Article
Environmental Sciences
Antonios Mamalakis, Amir AghaKouchak, James T. Randerson, Efi Foufoula-Georgiou
Summary: Precipitation prediction at seasonal timescales is important for water resources planning and management, as well as preparedness for hazards. This study introduces a probabilistic framework to assess predictability of winter precipitation in the contiguous United States, using sea surface temperature-derived indices as predictors. It identifies predictability hotspots and shows that extreme dry and wet conditions are more predictable than normal conditions.
WATER RESOURCES RESEARCH
(2022)
Article
Multidisciplinary Sciences
Yang Chen, Stijn Hantson, Niels Andela, Shane R. Coffield, Casey A. Graff, Douglas C. Morton, Lesley E. Ott, Efi Foufoula-Georgiou, Padhraic Smyth, Michael L. Goulden, James T. Randerson
Summary: This study develops a novel object-based system to track individual wildfires using satellite data, improving our understanding and quantification of wildfire spread, behavior, and impacts. The system successfully mapped the history of California wildfires from 2012 to 2020.
Article
Meteorology & Atmospheric Sciences
Clement Guilloteau, Efi Foufoula-Georgiou, Pierre Kirstetter, Jackson Tan, George J. Huffman
Summary: This study proposes a spectral error model for satellite precipitation estimation, which takes into account the multiscale dynamics of neighboring space-time. The empirical analysis shows that systematic filtering plays an important role in the error of IMERG product, highlighting the significance of considering filtering effects in high-resolution satellite precipitation products.
JOURNAL OF HYDROMETEOROLOGY
(2022)
Article
Geosciences, Multidisciplinary
L. Vulis, A. Tejedor, H. Ma, J. H. Nienhuis, C. M. Broaddus, J. Brown, D. A. Edmonds, J. C. Rowland, E. Foufoula-Georgiou
Summary: In this study, a novel multiscale characterization of shorelines is introduced, which explains the relative influence of fluvial, wave, and tidal processes on delta formation and evolution. The characterization method automatically divides deltas into morphologically similar classes, known as delta morphotypes, and predicts the dominant forcing of each class. The study also shows the consistency between the inferred dominant forcings from shoreline structure and the estimated sediment fluxes, while recognizing the deviations caused by spatiotemporal heterogeneity in sediment fluxes.
GEOPHYSICAL RESEARCH LETTERS
(2023)
Article
Geosciences, Multidisciplinary
Runze Li, Clement Guilloteau, Pierre-Emmanuel Kirstetter, Efi Foufoula-Georgiou
Summary: Understanding the nature and origin of errors in satellite precipitation products is important for applications and product improvement. A new error decomposition scheme is proposed to characterize satellite errors, attributing errors to the inaccuracies in event occurrence, timing, and intensity. The study applies the method to a test product and finds that the listed factors contribute differently to the total bias and errors are asymmetric in the temporal distribution throughout events. This error decomposition scheme provides insight into sources of error for improved retrievals.
GEOPHYSICAL RESEARCH LETTERS
(2023)
Article
Geosciences, Multidisciplinary
Sagar K. Tamang, Ardeshir Ebtehaj, Peter Jan van Leeuwen, Gilad Lerman, Efi Foufoula-Georgiou
Summary: This paper presents the results of ensemble Riemannian data assimilation for relatively high-dimensional nonlinear dynamical systems, focusing on the Lorenz-96 model and the quasi-geostrophic model. The method infers the analysis state from a joint distribution, which effectively handles systematic biases. Comparisons with classic implementations of particle filter and stochastic ensemble Kalman filter show that this method can improve the predictability of dynamical systems with the same ensemble size.
NONLINEAR PROCESSES IN GEOPHYSICS
(2022)
Article
Physics, Fluids & Plasmas
Yevgeniy Kovchegov, Ilya Zaliapin, Efi Foufoula-Georgiou
Summary: This study utilizes the theory of random self-similar trees to explain the hierarchical organization and self-similarity in river basins, elucidating the mathematical origin and relation of Horton's laws, Hack's laws, basin fractal dimensions, and power-law distributions of link attributes. The results contribute to a better understanding of landscape organization under different hydroclimatic forcings and extend scaling relationships useful for hydrologic prediction.