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1. Effect of Surface Hydraulics and Salmon Redd Size on Redd‐Induced Hyporheic Exchange

   https://doi.org/10.1029/2022WR033977  

   Bhattarai, Bishal ; Hilliard, Brandon ; Reeder, William J. ; Budwig, Ralph ; Martin, Benjamin T. ; Xing, Tao ; Tonina, Daniele ( June 2023 , Water Resources Research)

   Salmonids create an egg nest, called a redd, in hyporheic streambed gravel to bury their eggs, characterized by a pit and a hump topography, resembling a dune. Embryos' survival depends on downwelling oxygen‐rich stream water fluxes, influenced by the redd shape, stream hydraulics, and the hydraulic conductivity of the redd sediment,K. We hypothesize that downwelling fluxes increase with stream discharge and redd aspect ratio (A_R = A/L,withA,the redd amplitude andL,its length), and they can be predicted using a set of dimensionless numbers, which include the stream flow Reynolds (Re) and Froude (Fr) numbers,A_R, and the redd relative submergence (A/Y₀, withY₀, the water depth). We address our goal by simulating the surface and subsurface flows with numerical hydraulic models linked through the near‐bed pressure distribution quantified with a two‐phase (air‐water) two‐dimensional surface water computational fluid dynamics model, validated with experiments. We apply the modeling approach to five redd sizes, which span the field observed range (from ∼1 to ∼4 m long), and by increasing discharge from shallow (0.1 m) and slow (0.15 m/s) to deep (8 m) and fast (3.3 m/s). Results confirm that downwelling fluxes increase with discharge and redd aspect ratio due to the increased near‐bed head gradient over the redd. Averaged downwelling fluxes are a function ofRe,Fr,A_R, and hydraulic conductivity of the redd and not of the undisturbed streambed material. The derived regression equation may help evaluate regulated and unregulated flow impacts on hyporheic flows during embryo incubation.

    

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2. Gelatinous Zooplankton‐Mediated Carbon Flows in the Global Oceans: A Data‐Driven Modeling Study

   https://doi.org/10.1029/2020GB006704  

   Luo, Jessica Y. ; Condon, Robert H. ; Stock, Charles A. ; Duarte, Carlos M. ; Lucas, Cathy H. ; Pitt, Kylie A. ; Cowen, Robert K. ( September 2020 , Global Biogeochemical Cycles)

   Among marine organisms, gelatinous zooplankton (GZ; cnidarians, ctenophores, and pelagic tunicates) are unique in their energetic efficiency, as the gelatinous body plan allows them to process and assimilate high proportions of oceanic carbon. Upon death, their body shape facilitates rapid sinking through the water column, resulting in carcass depositions on the seafloor (“jelly‐falls”). GZ are thought to be important components of the biological pump, but their overall contribution to global carbon fluxes remains unknown. Using a data‐driven, three‐dimensional, carbon cycle model resolved to a 1° global grid, with a Monte Carlo uncertainty analysis, we estimate that GZ consumed 7.9–13 Pg C y⁻¹in phytoplankton and zooplankton, resulting in a net production of 3.9–5.8 Pg C y⁻¹in the upper ocean (top 200 m), with the largest fluxes from pelagic tunicates. Non‐predation mortality (carcasses) comprised 25% of GZ production, and combined with the much greater fecal matter flux, total GZ particulate organic carbon (POC) export at 100 m was 1.6–5.2 Pg C y⁻¹, equivalent to 32–40% of the global POC export. The fast sinking GZ export resulted in a high transfer efficiency (T_eff) of 38–62% to 1,000 m and 25–40% to the seafloor. Finally, jelly‐falls at depths >50 m are likely unaccounted for in current POC flux estimates and could increase benthic POC flux by 8–35%. The significant magnitude of and distinct sinking properties of GZ fluxes support a critical yet underrecognized role of GZ carcasses and fecal matter to the biological pump and air‐sea carbon balance.

    

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3. Quadrilateral Mesh Generation III : Optimizing Singularity Configuration Based on Abel-Jacobi Theory

   Zheng, Xiaopeng ; Zhu, Yiming ; Chen, Wei ; Lei, Na ; Luo, Zhongxuan ; Gu, Xianfeng ( April 2022 , Computer methods in applied mechanics and engineering)

   null (Ed.)

   This work proposes a rigorous and practical algorithm for quad-mesh generation based the Abel-Jacobi theory of algebraic \textcolor{red}{curves}. We prove sufficient and necessary conditions for a flat metric with cone singularities to be compatible with a quad-mesh, in terms of the deck-transformation, then develop an algorithm based on the theorem. The algorithm has two stages: first, a meromorphic quartic differential is generated to induce a T-mesh; second, the edge lengths of the T-mesh are adjusted by solving a linear system to satisfy the deck transformation condition, which produces a quad-mesh. In the first stage, the algorithm pipeline can be summarized as follows: calculate the homology group; compute the holomorphic differential group; construct the period matrix of the surface and Jacobi variety; calculate the Abel-Jacobi map for a given divisor; optimize the divisor to satisfy the Abel-Jacobi condition by integer programming; compute \textcolor{red}{a} flat Riemannian metric with cone singularities at the divisor by Ricci flow; \textcolor{red}{isometrically} immerse the surface punctured at the divisor onto the complex plane and pull back the canonical holomorphic differential to the surface to obtain the meromorphic quartic differential; construct a motorcycle graph to generate a T-Mesh. In the second stage, the deck transformation constraints are formulated as a linear equation system of the edge lengths of the T-mesh. The solution provides a flat metric with integral deck transformations, which leads to the final quad-mesh. The proposed method is rigorous and practical. The T-mesh and quad-mesh results can be applied for constructing Splines directly. The efficiency and efficacy of the proposed algorithm are demonstrated by experimental results on surfaces with complicated topologies and geometries. 

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4. Simplified model for unsteady air cavities under ship hulls

   https://doi.org/10.1177/1475090219862898  

   Matveev, Konstantin I ( February 2020 , Proceedings of the Institution of Mechanical Engineers, Part M: Journal of Engineering for the Maritime Environment)

   The drag reduction technique involving air cavities under ship hulls is a promising energy-saving technology. Understanding the air cavity dynamics in unsteady conditions and developing methods for the air cavity system optimization are critically important for practical implementation of this technology. In this study, a potential-flow theory is applied for modeling the air cavities under solid walls in water flow with fluctuating pressure. The present modeling approach incorporates detachment of macroscopic air pockets from the cavity tail. For specific configurations considered in this article, it is found that a change of the rate of air supply into the cavity can partly mitigate degradation of the overall power savings by the air cavity system in unsteady conditions. 

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5. Can Convection‐Permitting Modeling Provide Decent Precipitation for Offline High‐Resolution Snowpack Simulations Over Mountains?

   https://doi.org/10.1029/2019JD030823  

   He, Cenlin ; Chen, Fei ; Barlage, Michael ; Liu, Changhai ; Newman, Andrew ; Tang, Wenfu ; Ikeda, Kyoko ; Rasmussen, Roy ( December 2019 , Journal of Geophysical Research: Atmospheres)

   Accurate precipitation estimates are critical to simulating seasonal snowpack evolution. We conduct and evaluate high‐resolution (4‐km) snowpack simulations over the western United States (WUS) mountains in Water Year 2013 using the Noah with multi‐parameterization (Noah‐MP) land surface model driven by precipitation forcing from convection‐permitting (4‐km) Weather Research and Forecasting (WRF) modeling and four widely used high‐resolution datasets that are derived from statistical interpolation based on in situ measurements. Substantial differences in the precipitation amount among these five datasets, particularly over the western and northern portions of WUS mountains, significantly affect simulated snow water equivalent (SWE) and snow depth (SD) but have relatively limited effects on snow cover fraction (SCF) and surface albedo. WRF generally captures observed precipitation patterns and results in an overall best‐performed SWE and SD in the western and northern portions of WUS mountains, where the statistically interpolated datasets lead to underpredicted precipitation, SWE, and SD. Over the interior WUS mountains, all the datasets consistently underestimate precipitation, causing significant negative biases in SWE and SD, among which the results driven by the WRF precipitation show an average performance. Further analysis reveals systematic positive biases in SCF and surface albedo across the WUS mountains, with similar bias patterns and magnitudes for simulations driven by different precipitation datasets, suggesting an urgent need to improve the Noah‐MP snowpack physics. This study highlights that convection‐permitting modeling with proper configurations can have added values in providing decent precipitation for high‐resolution snowpack simulations over the WUS mountains in a typical ENSO‐neutral year, particularly over observation‐scarce regions.

    

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